TERMINATION REPORT for U.S. Dept.
Agriculture, Hatch Project NYC-183429 (revised)
REPRODUCTIVE AND SOCIAL BEHAVIOR OF TWO
CROW SPECIES IN NEW YORK
PI: MCGOWAN, KEVIN J.
ECOLOGY & SYSTEMATICS, CORNELL UNIVERSITY
12 December 1997
Crows are migratory game birds and can be local crop pests.
This study provided much new information about the demography and
behavior of two crow species. 560 American Crow (Corvus
brachyrhynchos) nests were observed in Tompkins Co., NY from
1988 through 1997, and 651 young banded and marked for individual
identification. 22 Fish Crow (Corvus ossifragus) nests
were studied, and 17 young marked.
The primary findings are summarized below.
- American Crows are cooperative breeders. Offspring
remained with their parents for one to six years and
helped their parents raise young. Family size reached 15,
with young crows in five different years present at one
time. 80% of observed nests had helpers. Some individuals
left the parental group and helped a sibling who had a
- American Crows in New York hold territories throughout
the year. Crows left the territory to forage and roost,
especially in winter. Non-breeders left frequently, or
even migrated to Pennsylvania, then returned.
- Foraging flocks occurred in areas of large food supplies,
primarily outside the breeding season. All age and status
classes of crows joined these flocks. Flock membership
- American Crow nest success averaged 60%. Chief predators
were Great Horned Owls (Bubo virginianus),
Red-tailed Hawks (Buteo jamaicensis), and raccoons
(Procyon lotor). Fledgling production averaged 1.8
per nest, and 3.2 per successful nest. Nearly half the
eggs produced were lost via egg inviability and active
brood reduction and removal of nestlings.
- Approximately half of fledglings survived until the next
breeding season. Yearly survival was estimated at 75% for
helpers and 93% for breeders.
- Young crows delayed breeding from 2 to 6 years or more.
Average age of first breeding was 3.3 years for females
(n=19) and 4.9 for males (n=13). Dispersal to breeding
ranged from 0 to 60 km. Males were more likely to inherit
all or part of their natal territories, and tended to
disperse shorter distances (males = 1.1 km, n=17; females
= 6.2 km, n=19).
- Crows have only recently begun nesting in cities and
towns. Urban crows had nest success similar to rural
crows, but produced fewer, smaller young per nest. The
effect of a drought year on nestling production was more
pronounced on urban crows, indicating that food supply is
less dependable than in rural areas.
- Although Fish Crows are similar to American Crows in food
habits and appearance, they differed in many ways.
- Fish Crows defended small territories at the nest
site only during breeding season. When not
breeding, Fish Crows congregated at dependable
foraging areas. Fish Crows joined American Crows
in foraging flocks and nocturnal roosts.
- Fish Crows did not have helpers attending their
nests. No marked Fish Crow was ever seen
attending the nest of its parents. A third Fish
Crow was observed at several nests and they even
fed nestlings, but in all cases the parents
reacted aggressively toward the third individual.
It is likely that the extra individuals were
unpaired birds trying to interfere with the
nesting attempt rather than a contributing
- Nest success averaged 65.%, with 2.4 young
produced per successful nest. Factors affecting
nest success appeared the same as in American
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