juveniles (Lawton and Guindon 1981, Williams et al.
1994, D. Williams and M. Lawton, unpubl. data), which
suggests that helpers receive few direct fitness bene-
fits from the help they give.
Brown Jays probably receive some indirect benefit
from helping. Helping may serve as a way to form
social bonds with other group members and become
integrated into the group, thereby increasing the prob-
ability of obtaining a breeding position. From 1994
to 1996, 21 jays obtained breeding positions; 19 of
these had helped for at least one year in the group
where they attempted breeding. Dispersal rarely re-
sults in filling a breeding vacancy; only 13% of known
dispersers between 1994 and 1996 filled breeding
positions in the year they immigrated; the rest became
helpers. Helping in this population may provide prac-
tice in learning how to build nests and take care of
young, thereby increasing future potential to repro-
duce successfully.
Brown Jays apparently must wait a long time be-
fore obtaining a breeding position. Of eight individu-
als of known age that obtained breeding positions
between 1994 and 1996 (four females, four males),
seven were 5-8 years old and one was 3 years old.
Young females (1-2 years old) are frequently observed
sitting on their mother's nest for short periods of time,Figure 6.14. Increase and stabilization in the number of
Brown Jays and Brown Jay groups in the study area in
Monteverde.
but whether they are contributing eggs to the clutch
is unknown. Young helpers become more efficient
nest attendants over the course of a single breeding
season (Lawton and Guindon 1981). In 1977-78, there
was a strong positive correlation between the num-
ber of young fledged and number of experienced (>4
years old) jays in a flock. Groups that contained older,
more experienced breeders were also more efficient
at building nests and laying eggs (Lawton and Lawton
1985). In 1988-1996, however, these effects were not
apparent, possibly due to the increased conflict among
breeders, which is usually carried out by the older
individuals in a group (Williams et al. 1994).
As deforestation increases throughout Central
America, many bird species are threatened by loss
of primary forest and food resources. Some, like the
Brown Jay, have benefited from human activity. Only
with long-term data on marked, genetically sampled
individuals can we understand population dynamics
of tropical vertebrates and identify key life history
characteristics that allow such adaptable species to
track changes in habitat availability. Brown Jays re-
spond to a wide variety of social and breeding situa-
tions. This behavioral plasticity also typifies other
facets of their lives, such as an eclectic diet and the
ability to use a variety of human-altered habitats. For
a colonizing species such as the Brown Jay, group liv-
ing potentially lowers predation risks associated with
moving into a new area, gives an advantage in inter-
specific competition for food and nest sites, and al-
lows them to invade human-altered landscapes.Acknowledgments We thank Benito Guindon, with-
out whose help the study would not have survived, and
Laurie Williams, who helped in the field and put up
with the disruptions fieldwork brings to family life.
Amanda Hale provided invaluable help in the field and
laboratory. Norman Pastre provided essential help in
the field. Morgan Lewis, Hannah Lowther, Ricardo
Guindon, Tino Ramirez, Sue Trostle, and Minor Vargas
provided energetic field assistance. Thanks to land-
owners in Monteverde who gave us access to their
property. Kerry Rabenold, Peter Fauth, Carolina Yaber,
and Amanda Hale gave us useful comments on the
manuscript. Joey Haydock provided advice on DNA
fingerprinting and parentage analysis. Kerry Rabenold
shared useful discussions, productive ideas, and work
in the field. Funding came from the Frank M. Chapman
Fund (American Museum of Natural History), Ameri-
can Philosophical Society, Alabama Academy of Sci-
ences, The Ruth Hindman Foundation, a Sigma Xi
research grant, a Purdue Research Foundation fellow-
ship, and National Science Foundation Dissertation
Improvement Grant DEB 93-11491 to Kerry Rabenold
for D. Williams.213 Birds