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We studied the frequency of intraspecific brood parasitism and physical transfer of eggs between nests in colonially nesting Cave Swallows (Petrochelidon fulva) and Cliff Swallows (P. pyrrhonota) in south Texas in 2001. Although the eggs of the two species look similar, frequency of brood parasitism in each species was unaffected by presence of the other species, which suggests that the parasitism we observed was largely by conspecifics. We detected brood parasitism in 4.6-5.0% of Cave Swallow nests and in 10.7-11.9% of Cliff Swallow nests. Brood parasitism was not significantly related to colony size in either species, to eventual success of the host nest, or to overall colony nesting success (a measure of environmental risk). We detected evidence of physical transfer of eggs in 0.7-2.0% of nests of these species. Cliff Swallows parasitized nests more often than Cave Swallows, but the frequencies of brood parasitism and egg transfer in the two species in south Texas appeared broadly comparable to those reported for Cliff Swallows in Nebraska, despite geographic differences in habitat, seasonality, breeding phenology, and levels of sociality between the populations. Received 28 January 2003, accepted 12 May 2004.
RESUMEN. – Estudiamos la frecuencia de parasitismo de nidada intraespecifico y de transferencia fisica de huevos en las golondrinas Petrochelidon fulva y P. pyrrhonota en el sur de Texas en 2001. A pesar de que los huevos de ambas especies son similares, la frecuencia de parasitismo en cada especie no se vio afectada por la presencia de la otra especie, lo que sugiere que en gran medida el parasitismo observado fue ocasionado por individuos coespecificos. Detectamos parasitismo de nidada en un 4.6-5.0% de los nidos de P. fulva y en un 10.7-11.9% de los nidos de P. pyrrhonota. El parasitismo de nidada no se correlaciono con el tamaño de la colonia, con el éxito eventual del nido hospedero, ni con el éxito de nidificatión general de la colonia (una medida de riesgo ambiental) en ninguna de las dos especies. P. pyrrhonota parasitó nidos con mayor frecuencia que P. fulva, pero la frecuencia de parasitismo de nidada y de transferencia de huevos en las dos especies en el sur de Texas parecen ser comparables con las frecuencias reportadas para P. pyrrhonota en Nebraska, a pesar de las diferencias geográficas en el hábitat, en la estacionalidad, en la fenología de nidification y en los niveles de estructura social entre las poblaciones.AN ALTERNATIVE REPRODUCTIVE tactic in some animals is to lay eggs in nests of conspecifics and parasitize the parental effort of the hosts. Brood parasitism among conspecifics is now known for scores of bird species and some insects (Yom-Tov 1980, Andersson 1984, Rohwer and Freeman 1989, Rothstein and Robinson 1998) and, across taxa, appears to be associated especially with high fecundity (Arnold and Owens 2002). However, ecological conditions favoring parasitic laying have been investigated for only a few species, such as swallows (Brown 1984, M011er 1987, Brown and Brown 1989), bee-eaters (Emlen and Wrege 1986), coots and moorhens (Gibbons 1986, Lyon 1993, McRae 1998), starlings (Evans 1988, Romagnano et al. 1990), weavers (Jackson 1993, 1998), and waterfowl (Andersson and Eriksson 1982, Semel et al. 1988, Lank et al. 1989, Sorenson 1998, Andersson and Ahlund 2000). From those studies, it is clear that the frequency of parasitic laying varies among individuals both within and between populations of the same species.
One potential ecological determinant of conspecific brood parasitism is population density. When suitable hosts occur in high density and close proximity, such as in breeding colonies, parasitism may be a viable alternative reproductive strategy (Eadie and Fryxell 1992). Various workers have shown that in some species, conspecific brood parasitism increases with colony size or is more prevalent in larger colonies (Brown 1984, Møller 1987, Brown and Brown 1996, Lyon and Everding 1996, Hill et al. 1997), though in other species, colony size or coloniality per se has no effect (Hoogland and Sherman 1976, Lank et al. 1989, Rohwer and Freeman 1989, Davis 1998).
Colonial Cliff Swallows (Petrochdidon pyrrhonotn) show a relatively high incidence of conspecific brood parasitism (Brown and Brown 1989, 1996). In that species, brood parasitism increases with colony size and appears to be a successful reproductive strategy of high-quality individuals (Brown and Brown 1998) that involves accurate assessment of the best host nests to parasitize (Brown and Brown 1991). However, some Cliff Swallow populations have been reported to have a much lower incidence of brood parasitism (Smyth et al. 1993). Better understanding of the ecological conditions that do or do not promote brood parasitism requires comparative data, collected in similar ways, on other populations and closely related species.
The present study examines patterns of brood parasitism in a congener of the Cliff Swallow, the Cave Swallow (P. fulva), and also reports information on brood parasitism in Cliff Swallows from an area (south Texas) where that species has been little studied. We provide the first known reports of brood parasitism (including physical transfer of eggs between nests) in Cave Swallows, and we investigate how brood parasitism in both Petrochdidon swallows varies with colony size.
