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Avian Brood Parasites (avian + brood_parasite)

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Life Sciences	100%

Selected Abstracts

Function of egg punctures by Shiny Cowbirds in parasitized and nonparasitized Creamy-bellied Thrush nests

JOURNAL OF FIELD ORNITHOLOGY, Issue 4 2009
Andrea A. Astie
ABSTRACT Avian brood parasites usually remove or puncture host eggs. Several hypotheses have been proposed to explain the function of these behaviors. Removing or puncturing host eggs may enhance the efficiency of incubation of cowbird eggs (incubation-efficiency hypothesis) or reduce competition for food between cowbird and host chicks in parasitized nests (competition-reduction hypothesis) and, in nonparasitized nests, may force hosts to renest and provide cowbirds with new opportunities for parasitism when nests are too advanced to be parasitized (nest-predation hypothesis). Puncturing eggs may also allow cowbirds to assess the development of host eggs and use this information to decide whether to parasitize a nest (test-incubation hypothesis). From 1999 to 2002, we tested these hypotheses using a population of Creamy-bellied Thrushes (Turdus amaurochalinus) in Argentina that was heavily parasitized by Shiny Cowbirds (Molothrus bonariensis). We found that 56 of 94 Creamy-bellied Thrush nests (60%) found during nest building or egg laying were parasitized by Shiny Cowbirds, and the mean number of cowbird eggs per parasitized nest was 1.6 ± 0.1 (N= 54 nests). At least one thrush egg was punctured in 71% (40/56) of parasitized nests, and 42% (16/38) of nonparasitized nests. We found that cowbird hatching success did not differ among nests where zero, one, or two thrush eggs were punctured and that the proportion of egg punctures associated with parasitism decreased as incubation progressed. Thus, our results do not support the incubation-efficiency, nest-predation, or test-incubation hypotheses. However, the survival of cowbird chicks in our study was negatively associated with the number of thrush chicks. Thus, our results support the competition-reduction hypothesis, with Shiny Cowbirds reducing competition between their young and host chicks by puncturing host eggs in parasitized nests. RESUMEN Las aves parásitas usualmente remueven o pican los huevos de sus hospedadores. Se han propuesto varias hipótesis para explicar la función de este comportamiento. El remover o picar los huevos del hospedador podría mejorar la eficiencia de la incubación de los huevos del parásito (hipótesis de la eficiencia de incubación) o reducir la competencia por comida entre los pichones del parásito y del hospedador (hipótesis de la reducción de la competencia). En nidos no parasitados en avanzado estado de incubación, podría forzar al duéo de éste a reanidar y de esta forma proveerle al tordo la oportunidad de parasitar nidos nuevos (hipótesis de depredación). La picadura de huevos podría también permitirle al tordo determinar el estado de desarrollo de los huevos del hospedador y utilizar esta información para decidir si parasita o no el nido (hipótesis de prueba del estado de incubación). Entre los áos 1999 y 2002 pusimos a prueba estas hipótesis utilizando una población de Zorzal chalchalero, Turdus amaurochalinus en Mendoza, Argentina, que estaba siendo altamente parasitada por el tordo renegrido (Molothrus bonariensis). Encontramos que 56 de 94 nidos (60%) fueron parasitados durante los estadios de construcción y puesta y que el número promedio de huevos de tordo resultó ser de 1.6 ± 0.1 (N= 54). Al menos un huevo del zorzal fue picado en 71% (40 de 56) de los nidos parasitados y en 42% (16/38) de los no-parasitados. Encontramos que el éxito de eclosión de los huevos de tordo no fue distinto en nidos donde fueron picados cero, uno o dos huevos de hospedador y que la proporción de huevos picados asociados al parasitismo disminuyó a medida que avanzó la incubación. Por lo tanto nuestros resultados no apoyan las hipótesis de eficiencia en la incubación, depredación de nidos o estado de desarrollo de los huevos. Sin embargo, la supervivencia de los pichones de tordo estuvo asociada negativamente al número de pichones de zorzal en los nidos. Por lo cual, nuestros resultados apoyan la hipótesis de reducción de la competencia, en donde los tordos pican los huevos de la especie hospedadora para reducir la competencia entre sus pichones y los del hospedador. [source]

Coevolution of daily activity timing in a host,parasite system

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2009
IRENE ORTOLANI
Coevolutionary theories applied in the study of host,parasite systems indicate that lineages exhibit progressive trends in response to reciprocal selective pressures. Avian brood parasites have generated intense interest as models for coevolutionary processes. Similar to avian cuckoos, Polistes wasp social parasites usurp a nest and exploit the parental care of a congeneric species to rear their own brood. In the present study, we show a coevolutionary arms race in the daily activity pattern in a Polistes host,parasite pair. We measured the daily activity rate, in constant laboratory conditions, of both host and parasite females during the period in which nest usurpations occur. The parasites showed a hyperkinesis in the middle of the day. As the field observations suggested, this mid-day activity is used to perform host nest usurpation attempts. Timing the usurpations allows the parasite to maximize its usurpation attempts during daytime when the host defence is lower. A field comparison of host presence on the nest in two populations with different parasitism rates showed that populations under strong parasitic pressure exhibit timing counteradaptations to optimize nest defence. This study provides the first example of a mutual coadaptation in timing activity in a parasite,host system. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 399,405. [source]

Experimentally Constrained Virulence is Costly for Common Cuckoo Chicks

ETHOLOGY, Issue 1 2009
Grim
Chicks of some avian brood parasites show high virulence by eliminating all host progeny in the nest whereas others develop in the presence of host nestmates. Common cuckoo (Cuculus canorus) chicks are typically highly virulent parasites as they attempt to evict all host eggs and chicks soon after hatching. However, several features of nest design, including steep walls and/or cavity nests, may effectively prevent cuckoo hatchlings from evicting nestmates. A previous observational study showed low success of cuckoo chicks in evicting progeny of a cavity nester host, the redstart (Phoenicurus phoenicurus) but cuckoo chicks showed low survival both when reared alone or in mixed broods with host nestmates. Whether poor cuckoo performance was caused by eviction costs and/or by the effect of presence of host chicks per se remains unclear. We experimentally cancelled any potential eviction costs by removing host eggs immediately after the cuckoo hatched and creating mixed broods 5 days later when the eviction instinct of the cuckoo already ceased. Cuckoos that were forced to compete with host nestlings experienced lower provisioning rates, poorer growth, and lower fledging success than control lone cuckoos. Cuckoos in mixed broods that survived until fledging fledged later, and at lower masses, than those in the sole cuckoo group. Thus, the cuckoo gens specializing on redstarts is similar to other cuckoo gentes, whose chicks are more successful in evicting host nestmates, and it does not benefit from the presence of host brood. Cohabitation with host nestlings then should be viewed as a maladaptive by-product of host cavity nest design. [source]

Host density predicts presence of cuckoo parasitism in reed warblers

OIKOS, Issue 6 2007
Bård G. Stokke
In some hosts of avian brood parasites, several populations apparently escape parasitism, while others are parasitized. Many migratory specialist brood parasites like common cuckoos, Cuculus canorus, experience a short breeding season, and in order to maintain local parasite populations host densities should be sufficiently high to allow efficient nest search. However, no studies have investigated the possible effect of host density on presence of cuckoo parasitism among populations of a single host species. Here, we investigated possible predictors of common cuckoo parasitism in 16 populations of reed warblers, Acrocephalus scirpaceus, across Europe. In more detail, we quantified the effect of host density, number of host breeding pairs, habitat type, mean distance to nearest cuckoo vantage point, predation rate and latitude on the presence of cuckoo parasitism while controlling for geographical distance among study populations. Host density was a powerful predictor of parasitism. We also found a less pronounced effect of habitat type on occurrence of parasitism, while the other variables did not explain why cuckoos utilize some reed warbler populations and not others. This is the first study focusing on patterns of common cuckoo-host interactions within a specific host species on a large geographic scale. The results indicate that if host density is below a specific threshold, cuckoo parasitism is absent regardless of the state of other potentially confounding variables. [source]