Can nest predation explain the lack of defenses against cowbird brood parasitism in the Rufous-collared Sparrow (Zonotrichia capensis)?

Abstract

Abstract.-Although interspecific avian brood parasitism usually lowers host productivity, some species lack any defense against parasites. We analyzed the effect of parasite egg removal or nest desertion following a parasitism event on the breeding productivity of the Rufous-collared Sparrow (Zonotrichia capensis), a common host of the Shiny Cowbird (Molothrus bonariensis). The Rufouscollared Sparrow is an effective cowbird host that does not eject parasite eggs. We removed cowbird eggs from nests of Rufouscollared Sparrows to test for differences in hatching, fledging, and nesting success among naturally unparasitized, parasitized, and experimentally unparasitized nests from which we removed the cowbird eggs. We also used simulations to test whether parasite egg removal or nest desertion provide viable strategies to counter the effects of parasitism in this species. Naturally unparasitized nests produced more nestlings and fledglings than parasitized and experimentally unparasitized nests, but there were no differences between parasitized nests and those from which cowbird eggs were removed. Moreover, the overall nesting success was similar for all nest types. Simulation models confirmed these results but also showed that productivity may still increase through parasite egg ejection when the nest predation rate is relaxed only if no cost of parasite egg ejection is assumed. By contrast, nest desertion was not a viable strategy to reduce the effect of parasitism. We suggest that high nest predation could reduce the benefits of antiparasite defenses in the Rufouscollared Sparrow and may help explain the lack of such behavior in this species. Resúmen.-A pesar de que el parasitismo de cría interespecífico usualmente reduce la productividad de las especies hospedadoras, algunas de estas especies carecen de defensas contra los parásitos. En este trabajo analizamos el efecto que la remoción de huevos de los parásitos de cría y la deserción del nido siguiendo un evento de parasitismo podrían tener sobre la productividad de Zonotrichia capensis, una especie hospedadora común de Molothrus bonariensis. Esta especie es un hospedador efectivo de M. bonariensis y no rechaza los huevos del parásito de su nido. Realizamos la remoción de los huevos del parásito de nidos de Z. capensis, y comparamos el éxito de eclosión, de volantoneo y de nidificación de nidos naturalmente no parasitados, nidos parasitados y aquellos donde realizamos la remoción del huevo parásito. Además, utilizamos modelos de simulación para evaluar si la remoción de huevos del parásito y la deserción del nido podrían constituir estrategias viables para reducir los efectos del parasitismo de cría en esta especie. Los nidos naturalmente no parasitados produjeron más pichones y volantones que los nidos experimentales o los parasitados, pero no existieron diferencias entre estos dos últimos tipos de nidos. Además, el éxito de nidificación fue similar para los distintos tipos de nidos. A pesar de la falta de diferencias detectada en el experimento a campo, los mo...

APUNTES SOBRE LA ANIDACIÓN DEL PICOGRUESO DORADO Pheucticus chrysogaster (CARDINALIDAE) Y LA PARASITACIÓN POR PARTE DEL VAQUERO BRILLOSO Molothrus bonariensis (ICTERIDAE) AL SUROCCIDENTE DEL ECUADOR

“…Molothrus bonariensis puede tener preferencia por las formas de los nidos donde parasitó anteriormente con éxito (e.g., nido cerrado o en cavidad del Soterrey Criollo Troglodytes aedon; Mahler et al, 2007), por especies que no rechazan los huevos sin importar los patrones de coloración diferentes (e.g., T. aedon; de la Colina et al, 2011) o preferir especies que no poseen mecanismos de defensa contra su parasitismo (e.g., Z. capensis; Carro & Fernández, 2013). Este Molothrus puede puncionar (picar) todos los huevos del hospedador, pero no parasitar el nido porque la nidada está avanzada en el desarrollo del embrión y la madre sustituta no alcanzaría a incubar el huevo del ictérido a tiempo (Massoni & Reboreda, 1999).…”

Impact of brood parasitism and predation on nest survival of the fan‐tailed gerygone in New Caledonia

“…This should result in a higher selection pressure for improved anti‐predator mechanisms rather than refined anti‐parasitism defences at the nest stage (Attisano et al ). Therefore, it seems unlikely that the highly advanced cuckoo‐host system between the shining bronze‐cuckoo and the fan‐tailed gerygone with polymorphic mimicry would have evolved under the current ecological situation (Carro and Fernández ). The fan‐tailed gerygone diverged from the other gerygone species an estimated 2.5 million years ago (Marki et al ), so there might have been periods of different ecological conditions characterised by lower predation pressure by birds but higher parasitism rates by cuckoos.…”

The Shiny Cowbird, Molothrus bonariensis (Gmelin, 1789) (Aves: Icteridae), at 2,800 m asl in Quito, Ecuador

“…Costs associated with such parasitism promote the evolution of host antiparasitic defenses – such as responding aggressively towards cowbirds to prevent them from gaining access to the nest, burying or ejecting parasite eggs, or abandoning parasitized nests – and create a coevolutionary arms race between hosts and parasites ( Astie and Reboreda 2005 ). Nevertheless, a number of hosts, even commonly parasitized hosts like the Rufous-collared sparrow, have not evolved antiparasite defenses, despite the associated fitness costs, due probably to morphological or ecological constraints ( Carro and Fernández 2013 ). In addition, in the case of invasive parasites, native hosts may be naïve to the parasite and lack defenses or appropriate mechanisms to counteract its negative effects ( Taraschewski 2006 , Fassbinder-Orth et al 2013 ).…”