Action: Artificially incubate and hand-rear raptors in captivity
- Six studies from across the world found high success rates for artificial incubation and hand-rearing of raptors.
- A replicated and controlled study from France found that artificially incubated raptor eggs had significantly lower hatching success than parent-incubated eggs. This study found that fledging success for hand-reared chicks was similar to wild chicks, whilst a replicated and controlled study from Canada found that hand-reared chicks had slower growth and attained a lower weight than parent-reared birds.
- A replicated study from Mauritius found that hand-rearing of wild eggs had higher success than hand-rearing captive-bred chicks.
- Three studies that provided methodological comparisons found that American kestrel Falco sparverius eggs were more likely to hatch at 38.5oC, compared to 36oC or 40oC, that peregrine falcon F. peregrinus eggs should be incubated over 37oC and that falcon chicks gained far more weight when saline was added to their diet.
Artificial incubation involves removing eggs from incubating parents and using an incubator to hatch them. Techniques can be extremely complex, with precision humidity and temperature control and turning of the eggs to ensure correct development Hand-rearing can be used with chicks from artificially-incubated eggs or with chicks removed from parents after hatching and involves manually feeding chicks until independence. Both techniques can be used to encourage parents to produce more offspring, or when naturally-raised chicks and eggs have low survival.
Supporting evidence from individual studies
A replicated study in a breeding centre in New York, USA, in spring 1970 (Snelling 1972) found that artificially incubated American kestrels Falco sparverius eggs were more likely to hatch when incubated at 38.5oC (100% of 11 eggs hatching), than at 36oC (34% of 13) or 40oC (25% of 12). Whether the eggs were cooled to 21oC twice daily or not did not affect hatching success (61% of 18 cooled eggs hatching vs. 44% of 18 non-cooled eggs). Sixteen of the 19 hatched chicks were raised to fledging on a diet of minced meat. Eggs had been naturally incubated for 2-26 days before being taken from the wild.
A replicated study in a breeding centre in Maryland, USA, in 1978-80 (Wiemeyer 1981) found that, of 16 bald eagle Haliaeetus leucocephalus eggs removed from captive breeding pairs (in a total of 11 clutches) and artificially incubated, 11 (69%) hatched. All 11 chicks were successfully raised until they were transferred to foster nests (see ‘Foster birds with wild conspecifics’). They were incubated at 56% humidity under one 37.6oC (‘dry’) bulb and one 30oC (‘wet’) bulb and turned every two hours. Once hatched, the chicks were fed on chopped meat and fish and provided with vitamin and calcium carbonate supplements. A further five eggs were removed from eagle nests with poor reproductive histories and artificially incubated. Three of these hatched and two of the eaglets survived hand-rearing to be fostered by more successful wild pairs. This programme is also discussed in ‘Use artificial insemination in captive breeding’, ‘Use captive breeding to increase or maintain populations’ and ‘Release captive-bred individuals’.
A replicated and controlled ex situ study in a research centre in Quebec, Canada (Bird & Clark 1983), found that 25 hand-reared American kestrels Falco sparverius grew more slowly than 19 parent-reared birds, also in captivity. Parent-reared birds also achieved greater body sizes than hand-reared birds (predicted weight of hand-reared birds of 119-130 g vs. 133-138 for parent-reared). Hand-reared birds were fed until sated four times a day, whilst parent birds were provided with food in excess. Survival and reproductive output were not measured in this study.
A replicated study in a breeding facility in Colorado, USA (Burnham 1983), found that for peregrine falcon Falco peregrinus, artificial incubation led to the hatching of 83% of approximately 300 captive-laid eggs and over 90% of 100 wild-obtained eggs incubated between 1978 and 1980. Eggs were incubated at between 37.2oC and 37.8oC and 60% humidity and were turned every 30 minutes. Eggs were ‘treated individually’, with weight loss being calculated and, if losing weight too rapidly, eggs were partially coated with paraffin. If losing weight slower than expected, shells were sanded very carefully above the air cell. Hatching success was approximately 20% higher if eggs received five days of natural incubation before being placed in incubators. Symptoms of low incubation temperatures (physical deformities and abnormalities) were found if eggs were incubated at below 37oC.
A small study in wetlands in the Doñana National Park, southern Spain, in summer 1984 (Gonzalez et al. 1986), found that an orphaned fledgling Spanish imperial eagle Aquila adalberti (91 days old) increased in weight by 1,250 g in nine days in captivity (growing from 2,300 g to 3,550 g). The chick was then successfully released and ‘adopted’ by a foster pair, discussed in ‘Foster eggs or chicks with wild conspecifics’.
A small study in a breeding centre in New York, USA, in 1977 and 1980 (Oliphant 1988) found that hand-reared chicks from five pairs of peregrine falcons Falco peregrinus and one pair of gyrfalcons F. rusticolus were twice as heavy at ten days old in 1980, when saline solution was added to their food, compared with 1977, when no saline was added. This was a significant difference, despite the small sample size. The authors note that food supply was not strictly controlled and no monitoring of chick health and survival was performed after day ten, therefore it is not certain whether the saline caused the increase in weight. Chicks were hand-raised on ground common quail Coturnix coturnix with or without 0.9% saline added. The amount of saline was not measured, but it increased the water content of the food to 73% from 68%.
A 1993 replicated study in Mauritius (Cade & Jones 1993) found that, of 265 Mauritius kestrel Falco punctatus eggs removed from wild nests and artificially incubated, 195 (74%) were fertile (higher than captive-bred eggs), 156 (80% of fertile eggs) hatched and 147 (94% of hatched eggs) were successfully hand-reared or fostered to other birds. This study is also discussed in ‘Use captive breeding to increase or maintain populations’, ‘Foster chicks or eggs with wild conspecifics’ and ‘Release captive-bred individuals’.
A 1995 update (8) of the same conservation programme studied in (Jones et al. 1995), found that hand-rearing young Mauritius kestrels Falco punctatus hatched from harvested eggs was significantly more successful than rearing eggs laid in captivity (96% and 80% hatching rate respectively). Of 292 fertile eggs, 83% were hatched artificially. Some chicks were retained for the captive breeding programme while the rest were released in areas outside the range of the original population (see ‘Release captive-bred individuals into the wild to restore or augment wild populations’).
A replicated controlled study in cereal fields in western France in 1995-6 (Amar et al. 2000) found that a programme to rescue Montagu’s harrier Circus pygargus eggs and chicks from nests in fields about to be harvested resulted in the release of 129 birds into the wild. The hatching success of 54 artificially incubated eggs was 62%: significantly lower than that of 322 naturally-incubated, wild eggs (hatching success not provided). However, fledging success of 33 hand-reared chicks was 64%, comparable to that of 313 wild chicks (wild fledging rates not provided). Among released birds, those that spent longer in captivity had shorter periods of dependence on the food provided and were in better condition. Captive-reared birds were re-observed more frequently following release (16-21% of 129 released birds re-observed vs. 8-9% of 181 naturally-fledged young), although the authors warn that this could be an artefact of lower dispersal in captive-reared birds. Eggs and chicks up to 15 days old were removed from at risk nests and released in groups of between one and eleven at two sites. Food (chicks and mice) was provided in excess during rearing and then at the release sites.
A replicated study in pine forests in Slovakia in summers between 1993 and 2000 (Kornan et al. 2003) found that golden eagle Aquila chrysaetos chicks removed from nests with two chicks, hand-reared or fostered in captivity and then fostered by wild conspecifics were successfully raised 74% of the time (of 35 fostering attempts). This study is discussed in detail in ‘Foster eggs or chicks with wild conspecifics’.
- Snelling J.C. (1972) Artificial Incubation of Sparrow Hawk Eggs. The Journal of Wildlife Management, 36, 1299-1304
- Wiemeyer S.N. (1981) Captive propagation of bald eagles at Patuxent Wildlife Research Center and introductions into the wild. Raptor Research, 15, 68-82
- Bird D.M. & Clark R.G. (1983) Growth of body components in parent-and hand-reared captive kestrels. Raptor Research, 17, 77-84
- Burnham W. (1983) Artificial incubation of falcon eggs. The Journal of Wildlife Management, 47, 158-168
- Gonzalez J.L., Heredia B., González L.M. & Alonso N. (1986) Adoption of a juvenile by breeding Spanish imperial eagles during the postfledging period. Raptor Research, 20, 77-78
- Oliphant L. (1988) Effect of saline added to food on weight gain of hand-raised falcons. Journal of Raptor Research, 22, 119-120
- Cade T.J. & Jones C.G. (1993) Progress in restoration of the Mauritius kestrel. Conservation Biology, 7, 169-175
- Jones C.G., Heck W., Lewis R.E., Mungroo Y. & Cade T.J. (1995) The restoration of the Mauritius kestrel Falco punctatus population. Ibis, 137, s173-s180
- Amar A., Arroyo B.E. & Bretagnolle V. (2000) Post-fledging dependence and dispersal in hacked and wild Montagu's harriers Circus pygargus. Ibis, 142, 21-28
- Kornan M., Majda M., Macek M. & Kornan J. (2003) An Unusual Case of Adoption of a Golden Eagle (Aquila chrysaetos) Chick in the Mala Fatra Mountains, Northwestern Slovakia. Journal of Raptor Research, 37, 259-260