BROWN JAYS: COMPLEX SOCIALITY IN A COLONIZING SPECIES
Dean A. Williams & Marcy R Lawtonrown Jays were one of the first birds for which
cooperative breeding was described (Skutch
1935), Cooperative breeding occurs when mem-
bers of a social group help raise offspring that are not
their own. This behavior occurs in 3% of the 9000 liv-
ing species of birds (Brown 1987, Stacey and Koenig
1990, Emlen 1991, Solomon and French 1996), In
Brown Jays, nonbreeding group members help build
nests; feed breeding females, nestlings, and fledglings;
and defend the nest and young from predators (Skutch
1935,1960, Lawton 1983, Lawton and Lawton 1985).
Studies of cooperatively breeding birds have ex-
plained these aid-giving behaviors using inclusive
fitness theory or "kin selection" (Hamilton 1964, May-
nard Smith 1964). Kin selection favors traits that posi-
tively affect the survival and reproduction of an indi-
vidual's kin. This means that an individual can gain
fitness benefits either directly (by reproducing) or
indirectly (by helping relatives reproduce). The New-
World jays are an important group for testing hypoth-
eses about environmental, demographic, and devel-
opmental determinants of sociality because they
inhabit a wide range of habitats and exhibit the full
spectrum of sociality (Brown 1974, Woolfenden and
Fitzpatrick 1984, Lawton and Lawton 1986).
The Brown Jay population in Monteverde provides
an example of how individuals in complex societies
pursue multiple pathways to fitness, and how the be-
haviors associated with these pathways can change in
response to increased population density. This study
was started in 1976 by Marcy and Robert Lawton. The
original study area covered about 4 km^2 and extended
from the Quebrada Maquina up to the MCFP and out
to the cliff edges. As the population grew (in 1990), the
main study area was reduced to one-half, including
most of Monteverde south of the Rio Guacimal and
Quebrada Cuecha. Starting in 1988, all nestlings within
this area and some surrounding areas were marked (n
= 431 by 1996) with a unique combination of colored
anodized aluminum bands. All nesting locations were
mapped, and data on clutch and brood size were re-
corded. As part of a genetic study of parentage, previ-
ously unmarked adults were captured and banded in
1994—1996 using baited traps and nets, and blood
samples have been taken from all captured adults and
nestlings (since 1992). By 1996, 157 jays had been
banded, of a total of 178 in 15 focal groups.
Brown Jays were absent from the Monteverde pla-
teau prior to the early 1960s (W. Guindon, pers.
comm.). After their initial colonization, the number
of Brown Jay individuals and social groups increased
and the population range expanded from the lower
Monteverde community into the MCFP (Williams
et al. 1994), Within the study area, the number of in-
dividuals and groups has begun to stabilize (Fig, 6.14).
Presently, the entire Monteverde plateau is occupied
by Brown Jays. This population expansion occurred
through a complex process of fissioning of large
groups, individual dispersal, and fusion among neigh-
boring groups. Most dispersal (97%, n = 36 individu-
als between 1994 and 1996) occurred between neigh-
boring groups, although some long-distance dispersal
also occurred. A banded jay was found dead in 1992
in La Cruz (~6 km), and banded jays have been re-
ported in San Rafael (~9 km) and La Tigra (>10 km),
which has recently been cleared of forest (C. Guindon,
pers, comm.).
Brown Jay breeding behavior has changed since- Most striking has been the marked increase in
reproductive competition among breeding females
residing in the same group (Williams et al. 1994).
Groups of Brown Jays in Monteverde may have a
single breeding female, a pair of females sharing a
single nest, or two or three females, each with her own
nest. In recent years, females building individual nests
in the same territory have been observed fighting each
other on the nest, chasing one another from the vicin-
ity of the nest, and destroying a rival's nest, eggs, and
nestlings. These behaviors occur more frequently in
large groups (>10 individuals) and when nests are
being built or when eggs are being laid. The overt
competition among females has not been observed
among males, even though more than one male can
breed in a group.
Behavioral and preliminary DNA fingerprinting
suggests that some females have mated with a single
male whereas others mate with multiple males within
or between groups. Males have been observed court-
ing several females within a group, At the current jay
density, resources critical to a female's reproductive
success (e.g., helpers) could be in short supply. When
one female disrupts another female's nesting attempt,
the female that lost her nest, and other group mem-
bers that were associated with her, switch and help
the "winning" female. This occurs even when a fe-
male witnesses the other female destroying her eggs.
There is no relationship between the number of help-
ers and the production of young, or the survival of
212 BirdsB