Growth of hand-reared American kestrels I. The effect of two different diets and feeding frequency

Seventy captive-bred American kestrels (Falco sparverius) were hand-reared on diets of either day-old cockerels (Gallus domesticus) (n = 38) or laboratory mice (Mus musculus) (n = 32) at meal frequencies of 4 or 6 times per day. Ad libitum food was provided in all meals. A proximate analysis of the two diets was performed and showed that cockerels when compared to mice contained more crude protein (60.0% versus 42.7% dry matter) and less fat (28.1% versus 46.5% dry matter). Body mass of nestlings was recorded daily until fledging, while lengths of the antebrachium and 9th primary remex were measured at intervals of 2 to 5 days. Data were fitted to the Richards growth model. Cockerel-fed nestlings exhibited growth patterns similar to those found in free-ranging kestrels. Mouse-fed birds however, grew more slowly which could be related to inadequate protein intake. No effect of hand-feeding frequency (4 versus 6 times daily) on growth rates was noted under any of the two diets. Irrespective of the dietary group, female kestrels were significantly heavier at the end of the experiment, as expected from the reversed sexual size dimorphism present in adult American kestrels.