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What Works in Conservation 2018

 | 
William J. Sutherland
, 
Lynn V. Dicks
, 
Nancy Ockendon
, 
et al.

3. Bird conservation

3.14 General responses to small/declining populations

Texte intégral

3.14.1 Inducing breeding, rehabilitation and egg removal

Unknown effectiveness (limited evidence)

● Rehabilitate injured birds

1Two studies of four studies from the UK and USA found that 25–40% of injured birds taken in by centres were rehabilitated and released. Three studies from the USA found that rehabilitated birds appeared to have high survival. One found that mortality rates were higher for owls than raptors. Assessment: unknown effectiveness — limited evidence (effectiveness 36%; certainty 30%; harms 0%).

2http://www.conservationevidence.com/​actions/​476

● Remove eggs from wild nests to increase reproductive output

3A study from Canada found that whooping crane reproductive success was higher for nests with one or two eggs removed than for controls. A study from the USA found that removing bald eagle eggs did not appear to affect the wild population and a replicated study from Mauritius found that removing entire Mauritius kestrel clutches appeared to increase productivity more than removing individual eggs as they were laid. Assessment: unknown effectiveness — limited evidence (effectiveness 24%; certainty 25%; harms 5%).

4http://www.conservationevidence.com/​actions/​477

● Use artificial visual and auditory stimuli to induce breeding in wild populations

5A small study from the British Virgin Islands found an increase in breeding behaviour after the introduction of visual and auditory stimulants. Assessment: unknown effectiveness — limited evidence (effectiveness 19%; certainty 11%; harms 0%).

6http://www.conservationevidence.com/​actions/​475

3.14.2 Provide artificial nesting sites

Beneficial

● Provide artificial nests (falcons)

7Four studies from the USA and Europe found that local populations of falcons increased following the installation of artificial nesting sites. However, a study from Canada found no increase in the local population of falcons following the erection of nest boxes. Eight studies from across the world found that the success and productivity of falcons in nest boxes was higher than or equal to those in natural nests. Four studies from across the world found that productivity in nest boxes was lower than in natural nests, or that some falcons were evicted from their nests by owls. Four studies from across the world found no differences in productivity between nest box designs or positions, whilst two from Spain and Israel found that productivity in boxes varied between designs and habitats. Twenty-one studies from across the world found nest boxes were used by falcons, with one in the UK finding that nest boxes were not used at all. Seven studies found that position or design affected use, whilst three found no differences between design or positioning. Assessment: beneficial (effectiveness 65%; certainty 65%; harms 0%).

8http://www.conservationevidence.com/​actions/​489

● Provide artificial nests (owls)

9Three studies from the UK appeared to show increases in local populations of owls following the installation of artificial nests. Another UK study found that providing nesting sites when renovating buildings maintained owl populations, whilst they declined at sites without nests. Four studies from the USA and the UK found high levels of breeding success in artificial nests. Two studies from the USA and Hungary found lower productivity or fledgling survival from breeding attempts in artificial nests, whilst a study from Finland found that artificial nests were only successful in the absence of larger owls. Four studies from the USA and Europe found that artificial nests were used as frequently as natural sites. Five studies from across the world found that owls used artificial nests. Seven studies found that nest position or design affected occupancy or productivity. However four studies found occupancy and/or productivity did not differ between different designs of nest box. Assessment: beneficial (effectiveness 65%; certainty 66%; harms 5%).

10http://www.conservationevidence.com/​actions/​490

● Provide artificial nests (songbirds)

11Only three out of 66 studies from across the world found low rates of nest box occupancy in songbirds. Low rates of use were seen in thrushes, crows, swallows and New World warblers. Thrushes, crows, finches, swallows, wrens, tits, Old World and tyrant flycatchers, New World blackbirds, sparrows, waxbills, starlings and ovenbirds all used nest boxes. Five studies from across the world found higher population densities or growth rates, and one study from the USA found higher species richness, in areas with nest boxes. Twelve studies from across the world found that productivity in nest boxes was higher than or similar to natural nests. One study found there were more nesting attempts in areas with more nest boxes, although a study from Canada found no differences in productivity between areas with different nest box densities. Two studies from Europe found lower predation of species using nest boxes but three studies from the USA found low production in nest boxes. Thirteen studies from across the world found that use, productivity or usurpation rate varied with nest box design, whilst seven found no difference in occupation rates or success between different designs. Similarly, fourteen studies found different occupation or success rates depending on the position of artificial nest sites but two studies found no such differences. Assessment: beneficial (effectiveness 67%; certainty 85%; harms 0%).

12http://www.conservationevidence.com/​actions/​498

● Provide artificial nests (wildfowl)

13Six studies from North America and Europe found that wildfowl populations increased with the provision of artificial nests, although one study from Finland found no increase in productivity in areas with nest boxes. Nine out of twelve studies from North America found that productivity was high in artificial nests. Two studies found that success for some species in nest boxes was lower than for natural nests. Nineteen studies from across the world found that occupancy rates varied from no use to 100% occupancy. Two studies found that occupancy rates were affected by design or positioning. Three studies from North America found that nest boxes could have other impacts on reproduction and behaviour. Assessment: beneficial (effectiveness 62%; certainty 76%; harms 0%).

14http://www.conservationevidence.com/​actions/​482

Likely to be beneficial

● Clean artificial nests to increase occupancy or reproductive success

15Five out of ten studies from North America and Europe found that songbirds preferentially nested in cleaned nest boxes or those sterilised using microwaves, compared to used nest boxes. One study found that the preference was not strong enough for birds to switch nest boxes after they were settled. One study found that birds avoided heavily-soiled nest boxes. Two studies birds had a preference for used nest boxes and one found no preference for cleaned or uncleaned boxes. None of the five studies that examined it found any effect of nest box cleanliness on nesting success or parasitism levels. Assessment: likely to be beneficial (effectiveness 40%; certainty 40%; harms 15%).

16http://www.conservationevidence.com/​actions/​499

● Provide artificial nests (burrow-nesting seabirds)

17Four studies from across the world found population increases or population establishment following the provision of nest boxes. In two cases this was combined with other interventions. Six studies from across the world found high occupancy rates for artificial burros by seabirds but three studies from across the world found very low occupancy rates for artificial burrows used by petrels. Eight studies from across the world found that the productivity of birds in artificial burrows was high although two studies from the USA and the Galapagos found low productivity in petrels. Assessment: likely to be beneficial (effectiveness 60%; certainty 71%; harms 5%).

18http://www.conservationevidence.com/​actions/​481

● Provide artificial nests (divers/loons)

19Three studies from the UK and the USA found increases in loon productivity on lakes provided with nesting rafts. A study in the UK found that usage of nesting rafts varied between sites. Assessment: likely to be beneficial (effectiveness 50%; certainty 50%; harms 0%).

20http://www.conservationevidence.com/​actions/​478

● Provide artificial nests (ground- and tree-nesting seabirds)

21Three studies from the UK and the Azores found increases in gull and tern populations following the provision of rafts/islands or nest boxes alongside other interventions. Five studies from Canada and Europe found that terns used artificial nesting sites. A study from the USA found that terns had higher nesting success on artificial rafts in some years and a study from Japan found increased nesting success after provision of nesting substrate. Design of nesting structure should be considered. Assessment: likely to be beneficial (effectiveness 60%; certainty 49%; harms 0%).

22http://www.conservationevidence.com/​actions/​480

● Provide artificial nests (oilbirds)

23A study in Trinidad and Tobago found an increase in the size of an oilbird colony after the creation of artificial nesting lodges. Assessment: likely to be beneficial (effectiveness 50%; certainty 45%; harms 0%).

24http://www.conservationevidence.com/​actions/​491

● Provide artificial nests (raptors)

25Nine studies from North America and Spain found that raptors used artificial nesting platforms. Two studies from the USA found increases in populations or densities following the installation of platforms. Three studies describe successful use of platforms but three found lower productivity or failed nesting attempts, although these studies only describe a single nesting attempt. Assessment: likely to be beneficial (effectiveness 55%; certainty 55%; harms 0%).

26http://www.conservationevidence.com/​actions/​488

● Provide artificial nests (wildfowl — artificial/floating islands)

27Two studies from North America found that wildfowl used artificial islands and floating rafts and had high nesting success. A study in the UK found that wildfowl preferentially nested on vegetated rather than bare islands. Assessment: likely to be beneficial (effectiveness 45%; certainty 45%; harms 0%).

28http://www.conservationevidence.com/​actions/​483

Unknown effectiveness (limited evidence)

● Artificially incubate eggs or warm nests

29One of two studies found that no kakapo chicks or eggs died of cold when they were artificially warmed when females left the nest. A study from the UK found that great tits were less likely to interrupt their laying sequence if their nest boxes were warmed, but there was no effect on egg or clutch size. Assessment: unknown effectiveness — limited evidence (effectiveness 26%; certainty 16%; harms 0%).

30http://www.conservationevidence.com/​actions/​503

● Guard nests

31We captured four studies describing the effects of guarding nests. One, from Costa Rica, found an increase in scarlet macaw population after nest monitoring and several other interventions. Two studies from Puerto Rico and New Zealand found that nest success was higher, or mortality lower, when nests were monitored. A study from New Zealand found that nest success was high overall when nests were monitored. Assessment: unknown effectiveness — limited evidence (effectiveness 41%; certainty 24%; harms 0%).

32http://www.conservationevidence.com/​actions/​506

● Provide artificial nests (gamebirds)

33A study in China found that approximately 40% of the local population of Cabot’s tragopans used nesting platforms. Assessment: unknown effectiveness — limited evidence (effectiveness 40%; certainty 13%; harms 0%).

34http://www.conservationevidence.com/​actions/​484

● Provide artificial nests (grebes)

35A study from the UK found that grebes used nesting rafts in some areas but not others. Assessment: unknown effectiveness — limited evidence (effectiveness 10%; certainty 9%; harms 0%).

36http://www.conservationevidence.com/​actions/​479

● Provide artificial nests (ibises and flamingos)

37A study from Turkey found that ibises moved to a site with artificial breeding ledges. A study from Spain and France found that large numbers of flamingos used artificial nesting islands. Assessment: unknown effectiveness — limited evidence (effectiveness 42%; certainty 31%; harms 0%).

38http://www.conservationevidence.com/​actions/​487

● Provide artificial nests (parrots)

39A study from Costa Rica found that the local population of scarlet macaws increased following the installation of nest boxes along with several other interventions. Five studies from South and Central America and Mauritius found that nest boxes were used by several species of parrots. One study from Peru found that blue-and-yellow macaws only used modified palms, not ‘boxes’, whilst another study found that scarlet macaws used both PVC and wooden boxes. Four studies from Venezuela and Columbia found that several species rarely, if ever, used nest boxes. Six studies from Central and South America found that parrots nested successfully in nest boxes, with two species showing higher levels of recruitment into the population following nest box erection and another finding that success rates for artificial nests were similar to natural nests. Three studies from South America found that artificial nests had low success rates, in two cases due to poaching. Assessment: unknown effectiveness — limited evidence (effectiveness 25%; certainty 38%; harms 11%).

40http://www.conservationevidence.com/​actions/​497

● Provide artificial nests (pigeons)

41Two studies from the USA and the Netherlands found high use rates and high nesting success of pigeons and doves using artificial nests. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 16%; harms 0%).

42http://www.conservationevidence.com/​actions/​492

● Provide artificial nests (rails)

43A study from the UK found that common moorhens and common coot readily used artificial nesting islands. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 11%; harms 0%).

44http://www.conservationevidence.com/​actions/​485

● Provide artificial nests (rollers)

45A study from Spain found that the use of nest boxes by rollers increased over time and varied between habitats. Another study from Spain found no difference in success rates between new and old nest boxes. Assessment: unknown effectiveness — limited evidence (effectiveness 20%; certainty 20%; harms 0%).

46http://www.conservationevidence.com/​actions/​494

● Provide artificial nests (swifts)

47A study from the USA found that Vaux’s swifts successfully used nest boxes provided. Assessment: unknown effectiveness — limited evidence (effectiveness 25%; certainty 16%; harms 0%).

48http://www.conservationevidence.com/​actions/​495

● Provide artificial nests (trogons)

49A small study from Guatemala found that at least one resplendent quetzal nested in nest boxes provided. Assessment: unknown effectiveness — limited evidence (effectiveness 19%; certainty 11%; harms 0%).

50http://www.conservationevidence.com/​actions/​493

● Provide artificial nests (waders)

51Two studies from the USA and the UK found that waders used artificial islands and nesting sites. Assessment: unknown effectiveness — limited evidence (effectiveness 25%; certainty 20%; harms 0%).

52http://www.conservationevidence.com/​actions/​486

● Provide artificial nests (woodpeckers)

53Four studies from the USA found local increases in red-cockaded woodpecker populations or the successful colonisation of new areas following the installation of ‘cavity inserts’. One study also found that the productivity of birds using the inserts was higher than the regional average. Two studies from the USA found that red-cockaded woodpeckers used cavity inserts, in one case more frequently than making their own holes or using natural cavities. One study from the USA found that woodpeckers roosted, but did not nest, in nest boxes. Five studies from the USA found that some woodpeckers excavated holes in artificial snags but only roosted in excavated holes or nest boxes. Assessment: unknown effectiveness — limited evidence (effectiveness 35%; certainty 39%; harms 0%).

54http://www.conservationevidence.com/​actions/​496

● Provide nesting habitat for birds that is safe from extreme weather

55Two of three studies found that nesting success of waders and terns was no higher on raised areas of nesting substrate, with one finding that similar numbers were lost to flooding. The third study found that Chatham Island oystercatchers used raised nest platforms, but did not report on nesting success. Assessment: unknown effectiveness — limited evidence (effectiveness 28%; certainty 23%; harms 0%).

56http://www.conservationevidence.com/​actions/​504

● Provide nesting material for wild birds

57One of two studies found that wild birds took nesting material provided; the other found only very low rates of use. Assessment: unknown effectiveness — limited evidence (effectiveness 11%; certainty 9%; harms 0%).

58http://www.conservationevidence.com/​actions/​501

● Remove vegetation to create nesting areas

59Two out of six studies found increases in population sizes at seabird and wader colonies after vegetation was cleared and a third found that an entire colony moved to a new site that was cleared of vegetation. Two of these studies found that several interventions were used at once. Two studies found that gulls and terns used plots cleared of vegetation, one of these found that nesting densities were higher on partially-cleared plots than totally cleared, or uncleared, plots. One study found that tern nesting success was higher on plots after they were cleared of vegetation and other interventions were used. Assessment: unknown effectiveness — limited evidence (effectiveness 45%; certainty 28%; harms 10%).

60http://www.conservationevidence.com/​actions/​505

● Repair/support nests to support breeding

61A study from Puerto Rico found that no chicks died from chilling after nine nests were repaired to prevent water getting in. Assessment: unknown effectiveness — limited evidence (effectiveness 20%; certainty 10%; harms 0%).

62http://www.conservationevidence.com/​actions/​502

● Use differently-coloured artificial nests

63A study from the USA found that two bird species (a thrush and a pigeon) both showed colour preferences for artificial nests, but that these preferences differed between species. In each case, clutches in the preferred colour nest were less successful than those in the other colour. Assessment: unknown effectiveness — limited evidence (effectiveness 3%; certainty 9%; harms 0%).

64http://www.conservationevidence.com/​actions/​500

3.14.3 Foster chicks in the wild

Likely to be beneficial

● Foster eggs or chicks with wild conspecifics (raptors)

65Ten out of 11 studies from across the world found that fostering raptor chicks to wild conspecifics had high success rates. A single study from the USA found that only one of six eggs fostered to wild eagle nests hatched and was raised. A study from Spain found that Spanish imperial eagle chicks were no more likely to survive to fledging if they were transferred to foster nests from three chick broods (at high risk from siblicide). A study from Spain found that young (15–20 day old) Montagu’s harrier chicks were successfully adopted, but three older (27–29 day old) chicks were rejected. Assessment: likely to be beneficial (effectiveness 70%; certainty 60%; harms 10%).

66http://www.conservationevidence.com/​actions/​510

● Foster eggs or chicks with wild non-conspecifics (cross-fostering) (songbirds)

67A study from the USA found that the survival of cross-fostered yellow warbler chicks was lower than previously-published rates for the species. A study from Norway found that the success of cross-fostering small songbirds varied depending on the species of chick and foster birds but recruitment was the same or higher than control chicks. The pairing success of cross-fostered chicks varied depending on species of chick and foster birds. Assessment: likely to be beneficial (effectiveness 45%; certainty 45%; harms 10%).

68http://www.conservationevidence.com/​actions/​520

Unknown effectiveness (limited evidence)

● Foster eggs or chicks with wild conspecifics (bustards)

69A small study in Saudi Arabia found that a captive-bred egg was successfully fostered to a female in the wild. Assessment: unknown effectiveness — limited evidence (effectiveness 20%; certainty 5%; harms 0%).

70http://www.conservationevidence.com/​actions/​513

● Foster eggs or chicks with wild conspecifics (cranes)

71A small study in Canada found high rates of fledging for whooping crane eggs fostered to first time breeders. Assessment: unknown effectiveness — limited evidence (effectiveness 26%; certainty 11%; harms 0%).

72http://www.conservationevidence.com/​actions/​512

● Foster eggs or chicks with wild conspecifics (gannets and boobies)

73A small study in Australia found that gannet chicks were lighter, and hatching and fledging success lower in nests which had an extra egg or chick added. However, overall productivity was non-significantly higher in experimental nests. Assessment: unknown effectiveness — limited evidence (effectiveness 9%; certainty 11%; harms 0%).

74http://www.conservationevidence.com/​actions/​507

● Foster eggs or chicks with wild conspecifics (owls)

75A study in the USA found high fledging rates for barn owl chicks fostered to wild pairs. A study from Canada found that captive-reared burrowing owl chicks fostered to wild nests did not have lower survival or growth rates than wild chicks. Assessment: unknown effectiveness — limited evidence (effectiveness 35%; certainty 21%; harms 0%).

76http://www.conservationevidence.com/​actions/​511

● Foster eggs or chicks with wild conspecifics (parrots)

77A study from Venezuela found that yellow-shouldered Amazon chicks had high fledging rates when fostered to conspecific nests in the wild. A second study from Venezuela found lower poaching rates of yellow-shouldered Amazons when chicks were moved to foster nests closer to a field base. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 14%; harms 0%).

78http://www.conservationevidence.com/​actions/​515

● Foster eggs or chicks with wild conspecifics (vultures)

79Two small studies in Italy and the USA found that single chicks were successfully adopted by foster conspecifics, although in one case this led to the death of one of the foster parents’ chicks. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 15%; harms 41%).

80http://www.conservationevidence.com/​actions/​509

● Foster eggs or chicks with wild conspecifics (waders)

81Two small trials in North America found that piping plovers accepted chicks introduced into their broods, although in one case the chick died. A study from New Zealand found that survival of fostered black stilts was higher for birds fostered to conspecifics rather than a closely related species. Assessment: unknown effectiveness — limited evidence (effectiveness 29%; certainty 9%; harms 0%).

82http://www.conservationevidence.com/​actions/​508

● Foster eggs or chicks with wild conspecifics (woodpeckers)

83Three studies from the USA found that red-cockaded woodpecker chicks fostered to conspecifics had high fledging rates. One small study found that fostered chicks survived better than chicks translocated with their parents. Assessment: unknown effectiveness — limited evidence (effectiveness 41%; certainty 29%; harms 0%).

84http://www.conservationevidence.com/​actions/​514

● Foster eggs or chicks with wild non-conspecifics (cross-fostering) (cranes)

85Two studies from the USA found low fledging success for cranes fostered to non-conspecifics’ nests. Assessment: unknown effectiveness — limited evidence (effectiveness 14%; certainty 35%; harms 10%).

86http://www.conservationevidence.com/​actions/​519

● Foster eggs or chicks with wild non-conspecifics (cross fostering) (ibises)

87A 2007 literature review describes attempting to foster northern bald ibis chicks with cattle egrets as unsuccessful. Assessment: unknown effectiveness—limited evidence (effectiveness 0%; certainty 10%; harms 0%).

88http://www.conservationevidence.com/​actions/​518

● Foster eggs or chicks with wild non-conspecifics (cross-fostering) (petrels and shearwaters)

89A study from Hawaii found that Newell’s shearwater eggs fostered to wedge-tailed shearwater nests had high fledging rates. Assessment: unknown effectiveness—limited evidence (effectiveness 45%; certainty 6%; harms 0%).

90http://www.conservationevidence.com/​actions/​516

● Foster eggs or chicks with wild non-conspecifics (cross-fostering) (waders)

91A study from the USA found that killdeer eggs incubated and raised by spotted sandpipers had similar fledging rates to parent-reared birds. A study from New Zealand found that cross-fostering black stilt chicks to black-winged stilt nests increased nest success, but cross-fostered chicks had lower success than chicks fostered to conspecifics’ nests. Assessment: unknown effectiveness — limited evidence (effectiveness 35%; certainty 30%; harms 0%).

92http://www.conservationevidence.com/​actions/​517

3.14.4 Provide supplementary food

Beneficial

● Provide supplementary food to increase adult survival (songbirds)

93Seven studies from Europe and the USA found higher densities or larger populations of songbird species in areas close to supplementary food. Six studies from Europe, Canada and Japan found that population trends or densities were no different between fed and unfed areas. Four studies from around the world found that birds had higher survival when supplied with supplementary food. However, in two studies this was only apparent in some individuals or species and one study from the USA found that birds with feeding stations in their territories had lower survival. Six studies from Europe and the USA found that birds supplied with supplementary food were in better physical condition than unfed birds. However, in four studies this was only true for some individuals, species or seasons. Two studies investigated the effect of feeding on behaviours: one in the USA found that male birds spent more time singing when supplied with food and one in Sweden found no behavioural differences between fed and unfed birds. Thirteen studies from the UK, Canada and the USA investigated use of feeders. Four studies from the USA and the UK found high use of supplementary food, with up to 21% of birds’ daily energy needs coming from feeders. However, another UK study found very low use of food. The timing of peak feeder use varied. Two trials from the UK found that the use of feeders increased with distance to houses and decreased with distance to cover. Two studies in Canada and the UK, found that preferences for feeder locations and positions varies between species. Assessment: beneficial (effectiveness 65%; certainty 75%; harms 0%).

94http://www.conservationevidence.com/​actions/​552

Likely to be beneficial

● Place feeders close to windows to reduce collisions

95A randomised, replicated and controlled study in the USA found that fewer birds hit windows, and fewer were killed, when feeders were placed close to windows, compared to when they were placed further away. Assessment: likely to be beneficial (effectiveness 44%; certainty 43%; harms 0%).

96http://www.conservationevidence.com/​actions/​557

● Provide calcium supplements to increase survival or reproductive success

97Eight of 13 studies (including a literature review) from across the world found some positive effects of calcium provisioning on birds’ productivites (six studies) or health (two studies). Six studies (including the review) found no evidence for positive effects on some of the species studied. One study from Europe found that birds at polluted sites took more calcium supplement than those at cleaner sites. Assessment: likely to be beneficial (effectiveness 55%; certainty 50%; harms 0%).

98http://www.conservationevidence.com/​actions/​559

● Provide supplementary food to increase adult survival (cranes)

99A study from Japan and a global literature review found that local crane populations increased after the provision of supplementary food. Assessment: likely to be beneficial (effectiveness 40%; certainty 40%; harms 15%).

100http://www.conservationevidence.com/​actions/​547

● Provide supplementary food to increase reproductive success (gulls, terns and skuas)

101Four studies of three experiments from Europe and Alaska found that providing supplementary food increased fledging success or chick survival in two gull species, although a study from the UK found that this was only true for one of two islands. One study from the Antarctic found no effect of feeding parent skuas on productivity. One study from Alaska found increased chick growth when parents were fed but a study from the Antarctic found no such increase. Assessment: likely to be beneficial (effectiveness 42%; certainty 41%; harms 0%).

102http://www.conservationevidence.com/​actions/​525

● Provide supplementary food to increase reproductive success (owls)

103Two replicated, controlled trials from Europe and the USA found that owls supplied with supplementary food had higher hatching and fledging rates. The European study, but not the American, also found that fed pairs laid earlier and had larger clutches. The study in the USA also found that owls were no more likely to colonise nest boxes provided with supplementary food. Assessment: likely to be beneficial (effectiveness 50%; certainty 42%; harms 0%).

104http://www.conservationevidence.com/​actions/​533

● Provide supplementary food to increase reproductive success (raptors)

105A small study in Italy described a small increase in local kite populations following the installation of a feeding station. Four European studies found that kestrels and Eurasian sparrowhawks laid earlier than control birds when supplied with supplementary food. Three studies from the USA and Europe found higher chick survival or condition when parents were supplied with food, whilst three from Europe found fed birds laid larger clutches and another found that fed male hen harriers bred with more females than control birds. Four studies from across the world found no evidence that feeding increased breeding frequency, clutch size, laying date, eggs size or hatching or fledging success. A study from Mauritius found uncertain effects of feeding on Mauritius kestrel reproduction. There was some evidence that the impact of feeding was lower in years with peak numbers of prey species. Assessment: likely to be beneficial (effectiveness 55%; certainty 52%; harms 0%).

106http://www.conservationevidence.com/​actions/​532

● Provide supplementary food to increase reproductive success (songbirds)

107Two studies from the USA found evidence for higher population densities of magpies and American blackbirds in areas provided with supplementary food, whilst two studies from the UK and Canada found that population densities were not affected by feeding. Twelve studies from across the world found that productivity was higher for fed birds than controls. Eleven studies from Europe and the USA found that fed birds had the same, or even lower, productivity or chick survival than control birds. Nine studies from Europe and North America found that the eggs of fed birds were larger or heavier, or that the chicks of fed birds were in better physical condition. However, eight studies from across the world found no evidence for better condition or increased size in the eggs or chicks of fed birds. Six studies from across the world found that food-supplemented pairs laid larger clutches, whilst 14 studies from Europe and North America found that fed birds did not lay larger clutches. Fifteen studies from across the world found that birds supplied with supplementary food began nesting earlier than controls, although in two cases only certain individuals, or those in particular habitats, laid earlier. One study found that fed birds had shorter incubations than controls whilst another found that fed birds re-nested quicker and had shorter second incubations. Four studies from the USA and Europe found that fed birds did not lay any earlier than controls. Seven studies from across the world found that fed parent birds showed positive behavioural responses to feeding. However, three studies from across the world found neutral or negative responses to feeding. Assessment: likely to be beneficial (effectiveness 51%; certainty 85%; harms 6%).

108http://www.conservationevidence.com/​actions/​537

Unknown effectiveness (limited evidence)

● Provide perches to improve foraging success

109One of four studies, from Sweden, found that raptors used clearcuts provided with perches more than clearcuts without perches. Two studies found that birds used perches provided, but a controlled study from the USA found that shrikes did not alter foraging behaviour when perches were present. Assessment: unknown effectiveness — limited evidence (effectiveness 45%; certainty 30%; harms 0%).

110http://www.conservationevidence.com/​actions/​556

● Provide supplementary food through the establishment of food populations

111One of four studies that established prey populations found that wildfowl fed on specially-planted rye grass. Two studies found that cranes in the USA and owls in Canada did not respond to established prey populations. A study from Sweden found that attempts to increase macroinvertebrate numbers for wildfowl did not succeed. Assessment: unknown effectiveness — limited evidence (effectiveness 9%; certainty 26%; harms 0%).

112http://www.conservationevidence.com/​actions/​555

● Provide supplementary food to allow the rescue of a second chick

113A study from Spain found that second chicks from lammergeier nests survived longer if nests were provided with food, in one case allowing a chick to be rescued. Assessment: unknown effectiveness — limited evidence (effectiveness 15%; certainty 14%; harms 0%).

114http://www.conservationevidence.com/​actions/​541

● Provide supplementary food to increase adult survival (gamebirds)

115Two European studies found increased numbers of birds in fed areas, compared to unfed areas. There was only an increase in the overall population in the study area in one of these studies. Of four studies in the USA on northern bobwhites, one found that birds had higher overwinter survival in fed areas, one found lower survival, one found fed birds had higher body fat percentages and a literature review found no overall effect of feeding. Assessment: unknown effectiveness — limited evidence (effectiveness 49%; certainty 38%; harms 0%).

116http://www.conservationevidence.com/​actions/​544

● Provide supplementary food to increase adult survival (gulls, terns and skuas)

117A study in the Antarctic found that fed female south polar skuas lost more weight whilst feeding two chicks than unfed birds. There was no difference for birds with single chicks, or male birds. Assessment: unknown effectiveness — limited evidence (effectiveness 0%; certainty 20%; harms 10%).

118http://www.conservationevidence.com/​actions/​548

● Provide supplementary food to increase adult survival (hummingbirds)

119Four studies from the USA found that three species of hummingbird preferred higher concentrations of sucrose, consuming more and visiting feeders more frequently. A study from the USA found that hummingbirds preferentially fed on sugar solutions over artificial sweeteners, and that the viscosity of these solutions did not affect their consumption. Two studies from Mexico and Argentina found that four species showed preferences for sucrose over fructose or glucose and sucrose over a sucrose-glucose mix, but no preference for sucrose over a glucose-fructose mix. A study from the USA found that birds showed a preference for red-dyed sugar solutions over five other colours. A study from the USA found that rufous hummingbirds preferentially fed on feeders that were placed higher. Assessment: unknown effectiveness — limited evidence (effectiveness 10%; certainty 24%; harms 0%).

120http://www.conservationevidence.com/​actions/​550

● Provide supplementary food to increase adult survival (nectar-feeding songbirds)

121Two studies from Australia and New Zealand found that ten species of honeyeaters and stitchbirds readily used feeders supplying sugar solutions, with seasonal variations varying between species. A series of ex situ trials using southern African birds found that most species preferred sucrose solutions over glucose or fructose. One study found that sunbirds and sugarbirds only showed such a preference at low concentrations. Two studies found that two species showed preferences for sucrose when comparing 20% solutions, although a third species did not show this preference. All species rejected solutions with xylose added. A final study found that sucrose preferences were only apparent at equicalorific concentrations high enough for birds to subsist on. Assessment: unknown effectiveness — limited evidence (effectiveness 10%; certainty 23%; harms 0%).

122http://www.conservationevidence.com/​actions/​553

● Provide supplementary food to increase adult survival (pigeons)

123The first of two studies of a recently-released pink pigeon population on Mauritius found that fewer than half the birds took supplementary food. However, the later study found that almost all birds used supplementary feeders. Assessment: unknown effectiveness — limited evidence (effectiveness 10%; certainty 19%; harms 0%).

124http://www.conservationevidence.com/​actions/​549

● Provide supplementary food to increase adult survival (raptors)

125Two studies in the USA found that nesting northern goshawks were significantly heavier in territories supplied with supplementary food, compared with those from unfed territories. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 23%; harms 0%).

126http://www.conservationevidence.com/​actions/​546

● Provide supplementary food to increase adult survival (vultures)

127A study from Spain found a large increase in griffon vulture population in the study area following multiple interventions including supplementary feeding. Two studies from the USA and Israel found that vultures fed on the carcasses provided for them. In the study in Israel vultures were sometimes dominated by larger species at a feeding station supplied twice a month, but not at one supplied every day. Assessment: unknown effectiveness — limited evidence (effectiveness 18%; certainty 18%; harms 0%).

128http://www.conservationevidence.com/​actions/​545

● Provide supplementary food to increase adult survival (waders)

129A study in Northern Ireland found that waders fed on millet seed when provided, but were dominated by other ducks when larger seeds were provided. Assessment: unknown effectiveness — limited evidence (effectiveness 22%; certainty 9%; harms 0%).

130http://www.conservationevidence.com/​actions/​543

● Provide supplementary food to increase adult survival (wildfowl)

131Two studies from Canada and Northern Ireland found that five species of wildfowl readily consumed supplementary grains and seeds. The Canadian study found that fed birds were heavier and had larger hearts or flight muscles or more body fat than controls. Assessment: unknown effectiveness — limited evidence (effectiveness 14%; certainty 15%; harms 0%).

132http://www.conservationevidence.com/​actions/​542

● Provide supplementary food to increase adult survival (woodpeckers)

133One replicated, controlled study from the USA found that 12 downy woodpeckers supplied with supplementary food had higher nutritional statuses than unfed birds. However, two analyses of a replicated, controlled study of 378 downy woodpeckers from the USA found that they did not have higher survival rates or nutritional statuses than unfed birds. Assessment: unknown effectiveness — limited evidence (effectiveness 10%; certainty 30%; harms 0%).

134http://www.conservationevidence.com/​actions/​551

● Provide supplementary food to increase reproductive success (auks)

135Two replicated studies from the UK found that Atlantic puffin chicks provided with supplementary food were significantly heavier than control chicks, but fed chicks fledged at the same time as controls. A randomised, replicated and controlled study from Canada found that tufted puffin chicks supplied with supplementary food fledged later than controls and that fed chicks had faster growth by some, but not all, metrics. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 38%; harms 0%).

136http://www.conservationevidence.com/​actions/​524

● Provide supplementary food to increase reproductive success (gamebirds)

137A controlled study in Tibet found that Tibetan eared pheasants fed supplementary food laid significantly larger eggs and clutches than control birds. Nesting success and laying dates were not affected. Assessment: unknown effectiveness — limited evidence (effectiveness 23%; certainty 10%; harms 0%).

138http://www.conservationevidence.com/​actions/​527

● Provide supplementary food to increase reproductive success (gannets and boobies)

139A small controlled study in Australia found that Australasian gannet chicks were significantly heavier if they were supplied with supplementary food, but only in one of two years. Fledging success of fed nests was also higher, but not significantly so. A randomised replicated and controlled study in the Galapagos Islands found that fed female Nazca boobies were more likely to produce two-egg clutches, and that second eggs were significantly heavier. Assessment: unknown effectiveness — limited evidence (effectiveness 33%; certainty 25%; harms 0%).

140http://www.conservationevidence.com/​actions/​523

● Provide supplementary food to increase reproductive success (ibises)

141A study from China found that breeding success of crested ibis was correlated with the amount of supplementary food provided, although no comparison was made with unfed nests. Assessment: unknown effectiveness — limited evidence (effectiveness 25%; certainty 11%; harms 0%).

142http://www.conservationevidence.com/​actions/​530

● Provide supplementary food to increase reproductive success (kingfishers)

143A controlled study in the USA found that belted kingfishers supplied with food had heavier nestlings and were more likely to renest. There was mixed evidence for the effect of feeding on laying date. Assessment: unknown effectiveness — limited evidence (effectiveness 33%; certainty 13%; harms 0%).

144http://www.conservationevidence.com/​actions/​534

● Provide supplementary food to increase reproductive success (parrots)

145Two studies from New Zealand found evidence that providing supplementary food for kakapos increased the number of breeding attempts made, whilst a third study found that birds provided with specially-formulated pellets appeared to have larger clutches than those fed on nuts. One study found no evidence that providing food increased the number of nesting attempts. Assessment: unknown effectiveness — limited evidence (effectiveness 33%; certainty 11%; harms 0%).

146http://www.conservationevidence.com/​actions/​536

● Provide supplementary food to increase reproductive success (petrels)

147A replicated controlled study in Australia found that Gould’s petrel chicks provided with supplementary food had similar fledging rates to both control and hand-reared birds, but were significantly heavier than other birds. Assessment: unknown effectiveness — limited evidence (effectiveness 19%; certainty 14%; harms 0%).

148http://www.conservationevidence.com/​actions/​522

● Provide supplementary food to increase reproductive success (pigeons)

149A study in the UK found no differences in reproductive parameters of European turtle doves between years when food was supplied and those when it was not. Assessment: unknown effectiveness — limited evidence (effectiveness 0%; certainty 21%; harms 0%).

150http://www.conservationevidence.com/​actions/​535

● Provide supplementary food to increase reproductive success (rails and coots)

151A small trial in the USA found that fed American coots laid heavier eggs, but not larger clutches, than controls. However, a randomised, replicated and controlled study in Canada found that clutch size, but not egg size, was larger in fed American coot territories. The Canadian study also found that coots laid earlier when fed, whilst a replicated trial from the UK found there was a shorter interval between common moorhens clutches in fed territories, but that fed birds were no more likely to produce second broods. Assessment: unknown effectiveness — limited evidence (effectiveness 33%; certainty 26%; harms 0%).

152http://www.conservationevidence.com/​actions/​528

● Provide supplementary food to increase reproductive success (vultures)

153Two studies from the USA and Greece found that there were local increases in two vulture populations following the provision of food in the area. A study from Israel found that a small, regularly supplied feeding station could provide sufficient food for breeding Egyptian vultures. A study from Italy found that a small population of Egyptian vultures declined following the provision of food, and only a single vulture was seen at the feeding station. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 24%; harms 0%).

154http://www.conservationevidence.com/​actions/​531

● Provide supplementary food to increase reproductive success (waders)

155A small controlled trial from the Netherlands found that Eurasian oystercatchers did not produce larger replacement eggs if provided with supplementary food. Instead their eggs were smaller than the first clutch, whereas control females laid larger replacement eggs. Assessment: unknown effectiveness — limited evidence (effectiveness 0%; certainty 10%; harms 0%).

156http://www.conservationevidence.com/​actions/​529

● Provide supplementary food to increase reproductive success (wildfowl)

157A small randomised controlled ex situ study from Canada found faster growth and higher weights for fed greater snow goose chicks than unfed ones, but no differences in mortality rates. Assessment: unknown effectiveness — limited evidence (effectiveness 30%; certainty 10%; harms 0%).

158http://www.conservationevidence.com/​actions/​526

● Provide supplementary water to increase survival or reproductive success

159A controlled study from Morocco found that northern bald ibises provided with supplementary water had higher reproductive success than those a long way from water sources. Assessment: unknown effectiveness — limited evidence (effectiveness 43%; certainty 14%; harms 0%).

160http://www.conservationevidence.com/​actions/​558

3.14.5 Translocations

Beneficial

● Translocate birds to re-establish populations or increase genetic variation (birds in general)

161A review of 239 bird translocation programmes found 63–67% resulted in establishment of a self-sustaining population. Assessment: beneficial (effectiveness 64%; certainty 65%; harms 0%).

162http://www.conservationevidence.com/​actions/​566

● Translocate birds to re-establish populations or increase genetic variation (raptors)

163Six studies of three translocation programmes in the UK and the USA found that all successfully established populations of white-tailed eagles, red kites and ospreys. A study in Spain found high survival of translocated Montagu’s harrier fledglings. Assessment: beneficial (effectiveness 65%; certainty 66%; harms 0%).

164http://www.conservationevidence.com/​actions/​574

Likely to be beneficial

● Translocate birds to re-establish populations or increase genetic variation (parrots)

165Three studies of two translocation programmes from the Pacific and New Zealand found that populations of parrots successfully established on islands after translocation. Survival of translocated birds ranged from 41% to 98% globally. Despite high survival, translocated kakapos in New Zealand had very low reproductive output. Assessment: likely to be beneficial (effectiveness 50%; certainty 60%; harms 10%).

166http://www.conservationevidence.com/​actions/​578

● Translocate birds to re-establish populations or increase genetic variation (pelicans)

167Two reviews of a pelican translocation programme in the USA found high survival of translocated nestlings and rapid target population growth. Some growth may have been due to additional immigration from the source populations. Assessment: likely to be beneficial (effectiveness 55%; certainty 49%; harms 0%).

168http://www.conservationevidence.com/​actions/​569

● Translocate birds to re-establish populations or increase genetic variation (petrels and shearwaters)

169Three studies from Australia and New Zealand found that colonies of burrow-nesting petrels and shearwaters were successfully established following the translocation and hand-rearing of chicks. Assessment: likely to be beneficial (effectiveness 60%; certainty 50%; harms 0%).

170http://www.conservationevidence.com/​actions/​568

● Translocate birds to re-establish populations or increase genetic variation (rails)

171Three studies of two translocation programmes in the Seychelles and New Zealand found high survival rates among translocated rail. All three studies round that the birds bred successfully. Assessment: likely to be beneficial (effectiveness 54%; certainty 44%; harms 14%).

172http://www.conservationevidence.com/​actions/​573

● Translocate birds to re-establish populations or increase genetic variation (songbirds)

173Nine studies from across the world, including a review of 31 translocation attempts, found that translocations led to the establishment of songbird populations. Eight studies were on islands. Three studies reported on translocations that failed to establish populations. One study found nesting success decreased as the latitudinal difference between source area and release site increased. Assessment: likely to be beneficial (effectiveness 50%; certainty 68%; harms 0%).

174http://www.conservationevidence.com/​actions/​580

● Translocate birds to re-establish populations or increase genetic variation (wildfowl)

175Three studies of two duck translocation programmes in New Zealand and Hawaii found high survival, breeding and successful establishment of new populations. However a study in the USA found that no ducks stayed at the release site and there was high mortality after release. A study in the USA found wing-clipping prevented female ducks from abandoning their ducklings. Assessment: likely to be beneficial (effectiveness 42%; certainty 50%; harms 19%).

176http://www.conservationevidence.com/​actions/​571

● Translocate birds to re-establish populations or increase genetic variation (woodpeckers)

177Six studies of four programmes found that >50% translocated birds remained at their new sites, and two studies reported large population increases. Birds from four programmes were reported as forming pairs or breeding and one study round translocated nestlings fledged at similar rates to native chicks. All studies were of red-cockaded woodpeckers. Assessment: likely to be beneficial (effectiveness 51%; certainty 42%; harms 0%).

178http://www.conservationevidence.com/​actions/​577

● Use decoys to attract birds to new sites

179Ten studies found that birds nested in areas where decoys were placed or that more birds landed in areas with decoys than control areas. Six studies used multiple interventions at once. One study found that three-dimensional models appeared more effective than two-dimensional ones, and that plastic models were more effective than rag decoys. Assessment: likely to be beneficial (effectiveness 51%; certainty 45%; harms 0%).

180http://www.conservationevidence.com/​actions/​586

● Use techniques to increase the survival of species after capture

181A study from the USA found that providing dark, quiet environments with readily-available food and water increased the survival of small songbirds after capture and the probability that they would adapt to captivity. A study from the USA found that keeping birds warm during transit increased survival. Assessment: likely to be beneficial (effectiveness 49%; certainty 41%; harms 0%).

182http://www.conservationevidence.com/​actions/​581

● Use vocalisations to attract birds to new sites

183Seven out of ten studies from around the world found that seabirds were more likely to nest or land to areas where vocalisations were played, or moved to new nesting areas after vocalisations were played. Four of these studied multiple interventions at once. Three studies found that birds were no more likely to nest or land in areas where vocalisations were played. Assessment: likely to be beneficial (effectiveness 45%; certainty 50%; harms 0%).

184http://www.conservationevidence.com/​actions/​585

Trade-off between benefit and harms

● Translocate birds to re-establish populations or increase genetic variation (gamebirds)

185Three studies from the USA found that translocation of gamebirds led to population establishment or growth or an increase in lekking sites. Four studies from the USA found that translocated birds had high survival, but two found high mortality in translocated birds. Four studies from the USA found breeding rates among translocated birds were high or similar to resident birds. Assessment: trade-offs between benefits and harms (effectiveness 50%; certainty 47%; harms 35%).

186http://www.conservationevidence.com/​actions/​572

Unknown effectiveness (limited evidence)

● Alter habitats to encourage birds to leave

187A study from Canada found that an entire Caspian tern population moved after habitat was altered at the old colony site, alongside several other interventions. Assessment: unknown effectiveness — limited evidence (effectiveness 20%; certainty 10%; harms 0%).

188http://www.conservationevidence.com/​actions/​587

● Ensure translocated birds are familiar with each other before release

189Two studies from New Zealand found no evidence that ensuring birds were familiar with each other increased translocation success. Assessment: unknown effectiveness — limited evidence (effectiveness 0%; certainty 33%; harms 0%).

190http://www.conservationevidence.com/​actions/​582

● Translocate birds to re-establish populations or increase genetic variation (auks)

191A study in the USA and Canada found that 20% of translocated Atlantic puffins remained in or near the release site, with up to 7% breeding. Assessment: unknown effectiveness — limited evidence (effectiveness 36%; certainty 38%; harms 0%).

192http://www.conservationevidence.com/​actions/​570

● Translocate birds to re-establish populations or increase genetic variation (herons, storks and ibises)

193A study in the USA found that a colony of black-crowned night herons was successfully translocated and bred the year after translocation. Assessment: unknown effectiveness — limited evidence (effectiveness 44%; certainty 3%; harms 0%).

194http://www.conservationevidence.com/​actions/​575

● Translocate birds to re-establish populations or increase genetic variation (megapodes)

195A study from Indonesia found that up to 78% maleo eggs hatched after translocation. Assessment: unknown effectiveness — limited evidence (effectiveness 49%; certainty 29%; harms 0%).

196http://www.conservationevidence.com/​actions/​567

● Translocate birds to re-establish populations or increase genetic variation (owls)

197A small study from New Zealand found that translocating two male boobooks allowed the establishment of a population when they interbred with a Norfolk Island boobook. A study in the USA found high survival amongst burrowing owls translocated as juveniles, although birds were not seen after release. Assessment: unknown effectiveness — limited evidence (effectiveness 20%; certainty 19%; harms 0%).

198http://www.conservationevidence.com/​actions/​576

● Translocate nests to avoid disturbance

199All five studies captured found some success in relocating nests while they were in use, but one found that fewer than half of the burrowing owls studied were moved successfully; a study found that repeated disturbance caused American kestrels to abandon their nest and a study found that one barn swallow abandoned its nest after it was moved. Assessment: unknown effectiveness — limited evidence (effectiveness 24%; certainty 39%; harms 30%).

200http://www.conservationevidence.com/​actions/​584

No evidence found (no assessment)

201We have captured no evidence for the following interventions:

202• Ensure genetic variation to increase translocation success.

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