GROWTH OF HAND-REARED AMERICAN KESTRELS .2. BODY-COMPOSITION AND WINGLOADING OF FLEDGLINGS HAND-FED 2 DIFFERENT DIETS

The body composition of young American kestrels (Falco sparverius) han d-fed either a protein-rich diet (day-old cockerels Gallus domesticus) or a fat-rich diet (laboratory mice Mus musculus) was determined one day after fledging. Mouse-fed fledglings (n=16) had significantly grea ter fat deposits than cockerel-fed birds (n=15), while the crude prote in content of the carcass was unaffected by the diets. At fledging, mo use-fed birds showed a significantly greater wingloading than cockerel -fed birds. Larger fat reserves (as in mouse-fed birds) might be mobil ised in the event of a food shortage and thus these birds would be at an advantage in relation to fledglings with smaller reserves. On the o ther hand, large fat deposition, which alters wingloading, might impai r the flight performance of the fledglings.