INVESTIGADORES
MASSONI Viviana
artículos
Título:
Cost of brood parasitism and the lack of defenses on the yellow-winged blackbird-shiny cowbird system
Autor/es:
VIVIANA MASSONI; JUAN CARLOS REBOREDA
Revista:
BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY
Editorial:
Springer-Verlag
Referencias:
Lugar: Berlin/Heidelberg; Año: 1998 vol. 42 p. 273 - 280
ISSN:
0340-5443
Resumen:
The shiny cowbird (Molothrus bonariensis) is a
generalist brood parasite that lays either white-immac-
ulate or spotted egg morphs in eastern Argentina and
Uruguay. Some hosts accept both morphs, others accept
spotted eggs and reject the white morph, but no host has
been found to accept white eggs and reject spotted ones.
It has been suggested that the yellow-winged blackbird
(Agelaius thilius) may be that type of host. The ®nding of
a white acceptor-spotted rejector species would help to
explain the occurrence and maintenance of the parasite
egg polymorphism. We studied the incidence of shiny
cowbird parasitism on this host, its costs for their re-
productive success and the presence of antiparasitic
defenses in the yellow-winged blackbird - shiny cowbird
system. The parasite aected the reproductive success of
the host in two ways. Cowbirds punctured host eggs
causing a reduction in clutch size, and yellow-winged
blackbirds deserted their nests whenever they suered
high egg loss. In addition, parasitized nests suered
higher predation during the nestling stage, but not
during egg stages, indicating that the dierence found
was related to the presence of the cowbird chick, and not
to higher exposure of parasitized nests to both para-
sites and predators. Despite the costs imposed by the
parasite, yellow-winged blackbirds have not evolved
antiparasitic defenses. This host did not reject any egg
morph of the shiny cowbird nor desert parasitized nests
unless it had suered high egg loss. Current explanations
for the host lack of defenses, the ``time lag'' and the
``equilibrium'' hypothesis, are discussed.