Da. Kirk et Ag. Gosler, BODY CONDITION VARIES WITH MIGRATION AND COMPETITION IN MIGRANT AND RESIDENT SOUTH-AMERICAN VULTURES, The Auk, 111(4), 1994, pp. 933-944
We investigated seasonal changes in the body condition of migrant and
resident Turkey Vultures (Cathartes aura meridionalis and C. a. rufico
llis), as well as Black Vultures (Coragyps atraius brasiliensis), in t
he Llanos of central Venezuela. Although the condition of adult migran
ts was below average in October and November following migration from
the breeding grounds, it increased through the dry season to reach a p
eak before northward migration in March and April. Juvenile (FY; first
-year) migrant Turkey Vultures followed a similar trend, but their con
dition improved more slowly than adults, perhaps due to intraspecific
competition. The condition and mass of Black Vultures also increased t
hrough the dry season. This suggested that abundant carrion was availa
ble for vultures in the Llanos during the dry season. However, the con
dition of resident Turkey Vultures was below average when sympatric wi
th migrants, whereas they were in above-average condition when migrant
s were absent. Unlike the linear relationship between condition and da
te in migrants, this relationship for residents was quadratic (second-
order polynomial). Strikingly, condition of resident Turkey Vultures w
as negatively correlated with the density of Cathartes vultures (almos
t entirely migrants) during the study period. Migrant Turkey Vultures
were significantly larger than resident Turkey Vultures in the majorit
y of body measurements, explaining why they were dominant to residents
in agonistic interactions at carcasses. These results may reflect the
detrimental consequences of competition between migrant and resident
Turkey Vultures on the condition of residents, and the physiological e
ffects of migration on the condition of migrant Turkey Vultures.