The major issue addressed by the Brown Jay study
is cooperative breeding in the context of rapid popu-
lation expansion. Cooperative breeding is a social
system in which nonbreeding individuals associate
with breeders to form social groups that communally
occupy and defend a joint territory. In most cases, the
nonbreeders are previous offspring of the breeders,
but unrelated individuals also join groups. The degree
to which these nonbreeders act as helpers at the nest
and the root cause of cooperative breeding are con-
troversial (Woolfenden and Fitzpatrick 1984, Brown
1987). A leading hypothesis ("habitat saturation") is
that few vacant areas exist within suitable habitat, so
young birds have little opportunity to establish their
own territories at early ages. They may also benefit
from remaining in their natal territories, where they
receive help in locating food sources, receive in-
creased vigilance against predators, and increase their
inclusive fitness by helping to increase the survivor-
ship of relatives ("kin selection").
The situation of Brown Jays at Monteverde is un-
usual among cooperative breeders in that the popu-
lation has expanded rapidly during the past 30 years
(see Williams and Lawton, "Brown Jays," pp. 212-
213). This species inhabits second growth and disturbed
habitats and has spread throughout Central America as
a result of deforestation (Stiles and Skutch 1989). The
social system of extended family groups has not been
altered by widespread breeding vacancies, which chal-
lenges the habitat saturation hypothesis. Another un-
usual feature of the mating system is that unlike Florida
Scrub-Jays (Aphelocoma coerulescens), in which the
pair of behaviorally dominant "breeders" has absolute
genetic paternity (J. Quinn, unpubl. data; D. McDonald,
W. Potts, J. Fitzpatrick, and G. Woolfenden, unpubl.
data), Brown Jay nests often contain eggs of more than
one female. The social system more closely resembles
that of Acorn Woodpeckers (Melanerpes formicivorus',
Koenig and Mumme 1987), in which several females
also lay in the same nest, than that of other jays.
Long-tailed Manakins are one of approximately 40
species in the neotropical family Pipridae, most of
which are frugivorous and have a lek mating system,
in which males provide no resources for breeding
females (e.g., nest sites, feeding territories, or paren-
tal care). Rather, males rely on elaborate displays,
often in traditional areas ("lek arenas") to which they
attract females for mating. Males compete vigorously
for mates either by displaying or by direct male-male
combat. In Long-tailed Manakins, male-male coopera-
tion in displays is juxtaposed against fierce competi-
tion among males for mates (see McDonald, "Coop-
eration between Long-Tailed Manakins," pp. 204-
205). The most important factor influencing female
visits to individual perches is the number of "toledo"
vocalizations given by the male partners. The most
successful partnerships call at an average rate of 300
"toledos" per hour, much greater than less success-
ful partnerships (McDonald 1989b). The calling rate,
however, is not as closely correlated with copulatory
success as it is with visitation success. To succeed in
copulations, males engage in protracted portions of
the dual-male dance display, particularly the "butter-
fly" display (Fig. 6.1), in which the partners radiate
outward from the perch with labored flights that re-
semble the erratic flight of Blue Morpho butterflies
(Morpho peleides-, Slud 1957). Mate choice by females
is hierarchical. Females visit males that call at high
rates and, for copulations, choose among the males
they visit on the basis of dance displays.
The large difference in mating success between the
most successful and least successful males in Long-
tailed Manakins has had profound effects on all as-
pects of the life history of the species (McDonald
1993b). Males and females differ in many ways: bril-
liant plumage in males versus cryptic green plumage
in the females; intense sociality among males versus
an essentially solitary existence for females; one of the
most complex vocal repertoires known in male birds
(Trainer and McDonald 1993) versus one or two dis-
tinct calls given by females. Another dramatic dif-
ference between the sexes is in their demographic
profiles. Males (17 g) are similar to long-lived Yellow-
eyed Penguins (5000 g) and male Northern Elephant
Seals (Mirounga angustirostris', 3,700,000 g) in that
their fitness depends on surviving for a long time. Be-
cause females begin reproducing at age 1 or 2 years,
long-term survivorship is far less important (McDonald
1993b). The demographic divergence between the
sexes within this species is almost as great as that
between the extremes found throughout the entire
class Aves.
Long-tailed Manakins are unusual in that males
take 4 years to attain the definitive male plumage (the
full "uniform" of red, black, and blue), in contrast to
the 1-2 years it takes for most male passerines to reach
definitive plumage. For each of the first 4 years of life,
the males have a distinct, age-specific plumage. When
they leave the nest, both males and females are green.
One year after hatching, the crowns of males become
red. Two years after hatching, their faces become
black. Three years after hatching, the back begins to
show powder blue. Four years after hatching, all
traces of green are replaced by black. In an experimen-
tal study, males reacted more strongly to taxidermic
mounts of males in definitive plumage than they did
to males in the predefinitive plumage characteristic
of yearling males (McDonald 1993a). This experiment
provided evidence that the transitional, predefinitive
plumages act as a signal of lower status, which reduces189 Birds