Whitmore-Leary, Kathryn D. (Kate) – Developing hand-rearing techniques for the conservation of altricial passerines. 1996.
Conservation of endangered birds often involves hand-rearing nestlings after captive propagation or salvaging injured or abandoned chicks. Developing an easily-prepared, nutritionally-compete diet for altricial birds is a prerequisite for successful hand-rearing. I tested the effects on growth rate and survival of a variety of commercially-produced and custom-made diets. I also examined the effect of varying amounts of parental care (zero to 25 days) and compared the survival and growth of chicks in captivity to survival and growth of wild-reared chicks.
I used seven altricial bird species (common raven, Corvus corax; American crow, C. brachyrynchos; black-billed magpie, Pica pica; American robin, Turdus migratorius; red-winged blackbird, Agelaius phoeniceus; Brewers blackbird, Euphagus cyancephalius; and western kingbird, Tyrannus verticalis) that varied in size (29-1200 fledging weight) and degree of feeding specialization (generalist Corvids to specialist flycatchers). All chicks reared in captivity grew more slowly than wild-reared chicks, and hand-rearing extended nestling periods of most chicks. Survival of captive-reared corvid nestlings was similar or higher to that observed in the wild. Custom-prepared mixes of fruit, insects, hydrated dog food, and ground mice performed better than commercially-prepared diets. This is likely because they contained a high ratio of water to protein while maintaining a high level of protein (>28%), which is important for rearing omnivorous altricial nestlings. Commercial diets may be most useful as supplements to custom mixes because they contain known amounts of trace elements and minerals. Bringing chicks in 1/3 to 2/3 through their nesting period tends to result in the most successful hand-rearing after some parental care.
Captive propagation has become increasingly important in preventing extinction in many avian species, including the Hawaiian and Marian crows (Corvus hawaiiensis and C. kubaryi). I used three surrogate species, common raven (C. corax), American crow (C. brachyrynchos), and black-billed magpie (Pica pica), to compare the health, growth, and survival among nestlings hand-reared on one of 14 feeding regimes that differed in feeding rate and initial amount of food. Feeding rates for the chicks’ first two weeks after hatch varied from once every 30 min to once every two hours. From two weeks until near fledging age, feeding rates varied from once every hour to once every three hours. Initial amounts fed varied from unlimited (ad libitum) to a restricted amount (a total of 15, 25, or 40% of a chick’s body weight on day one). Combinations of frequent feeding and large amounts of food were most successful in rearing fast-growing, heavy birds who had few fault bars in their feathers. All hand-reared nestlings grew more slowly than wild-reared chicks. Initial amount of food offered to chicks affected growth and survival more than feeding rate in very large passerines (e.g., common ravens), while feeding rate affected growth and survival more than initial amount of food in small- and medium-sized passerines (e.g., black-billed magpies and American crows).