Egg Removal by Brown-Headed Cowbirds: A Field Test of the Host Incubation Efficiency Hypothesis

Wood, Douglas R.; Bollinger, Eric K.

doi:10.2307/1370134

Cited by 16 publications

(8 citation statements)

References 22 publications

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“…We found no difference in the hatching success of Shiny Cowbird eggs in nests with 1–3 host eggs (i.e., nests with 0–2 host eggs punctured). Our results agree with those of Wood and Bollinger (1997) and McMaster and Sealy (1997), but these studies involved hosts either similar in size or smaller than the brood parasite. In these species, the removal or puncture of host eggs would be less critical for the parasite because their larger eggs would still contact the host's brood patch (Peer and Bollinger 1997, 2000).…”

Section: Discussionsupporting

confidence: 91%

“…Consistent with this prediction, Peer and Bollinger (1997) found that eggs of Brown-headed Cowbirds translocated to nests of a host larger than the parasite (Common Grackle, Quiscalus quiscula) did not hatch when clutches contained four to six eggs, but hatched when clutches had three or fewer eggs. In contrast, studies of host species either similar in size or smaller than Brownheaded Cowbirds indicate that removal of host eggs did not increase hatching success of parasite eggs (Wood andBollinger 1997, McMaster andSealy 1997). Egg punctures could have the same effect as egg removal by a parasite if hosts remove punctured eggs as a result of nest sanitation (Kemal and Rothstein 1988).…”

Section: Resumen Función De La Picadura De Huevos Por Parte Del Tordmentioning

confidence: 99%

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

Astié

Reboreda

2009

Journal of Field Ornithology

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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.

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Section: Discussionsupporting

confidence: 91%

Section: Resumen Función De La Picadura De Huevos Por Parte Del Tordmentioning

confidence: 99%

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

Astié

Reboreda

2009

Journal of Field Ornithology

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“…The extra egg could decrease the incubation e¤ciency of the enlarged clutch (Davies & Brooke 1988). However, evidence in support of this hypothesis is not conclusive (Lerkelund et al 1993;McMaster & Sealy 1997;Wood & Bollinger 1997). In addition, a complete clutch would represent a competitive environment for the cowbird chick unless some of the host eggs were destroyed (Scott 1977;Blankespoor et al 1982).…”

Section: Discussionmentioning

confidence: 99%

Egg puncture allows shiny cowbirds to assess host egg development and suitability for parasitism

Massoni

Reboreda

1999

Proc. R. Soc. Lond. B

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Parasitic cowbirds and cuckoos generally reduce the clutch size of the hosts they parasitize by removing or destroying some of their eggs. Shiny cowbirds (Molothrus bonariensis) puncture their hosts' eggs both when parasitizing the nests and also when they do not parasitize them. We propose that, by puncturing the host's eggs, shiny cowbirds gain an informational bene¢t. They assess the degree of development of the host's embryos and so avoid laying in nests that would not provide enough incubation time for the parasitic eggs to hatch. Two predictions follow: (i) punctures should occur in advance or immediately before parasitic events, and (ii) the occurrence of parasitism should depend on the degree of development of the host's embryos when punctures occurred, i.e. on the stage of incubation. Both predictions are supported by our data of shiny cowbirds parasitizing yellow-winged blackbirds (Agelaius thilius). Egg punctures are not used to reset the host's nesting attempt when shiny cowbirds do not parasitize the nests. We discuss the potential mechanisms implicated in egg development assessment and propose a critical experiment to test this hypothesis.

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“…Cowbirds adversely affect the breeding success of their hosts through predation (McLaren and Sealy 2000), egg punctures (Massoni and Reboreda 2002), ejection of eggs and nestlings (Dearborn 1996, Wood and Bollinger 1997, Granfors et al 2001 and competition between nestlings (Dearborn 1998, Lichtenstein andSealy 1998). Parasitism rates in localities with high cowbird density can reach more than 90% (Payne 1997, Smith 1999, and severely reduce the reproductive output of host species.…”

Section: Introductionmentioning

confidence: 99%

Cowbird parasitism of Pale-headed Brush-finch Atlapetes pallidiceps: implications for conservation and management

Oppel

Schaefer

Schmidt

et al. 2004

Bird Conservation International

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SummaryPale-headed Brush-finch Atlapetes pallidiceps is a restricted-range species that is threatened with extinction due to habitat loss. The total population of 60-80 individuals achieved a reproductive output of only 0.74 young per breeding pair in 2002. Brood parasitism by Shiny Cowbird Molothrus bonariensis was a major factor reducing breeding success, affecting 38.5% of broods. Parasitism rates reached 50% in an ungrazed reserve, but only 14% on an adjacent grazed plot. The resulting difference in breeding success was not, however, attributable to vegetation parameters used to describe microhabitat use. Cowbird parasitism rates therefore seem to be influenced largely by factors operating at the landscape level. These may include grazing scheme, topography, humidity and host availability. It is suggested that lower species diversity and bird abundance rendered the grazed site less attractive to cowbirds. Current parasitism rates are of great conservation concern due to the low population size of Pale-headed Brush-finch, and the initiation of controlling measures is pressing. Management options described from intensive cowbird control programmes in North America are reviewed and evaluated for their applicability here. To combine the possibility of further data collection with commencement of immediate conservation action, we consider two alternative approaches. Nest monitoring and cowbird egg removal would enable the study of the distribution of parasitism in relation to landscape and vegetation variables, whereas cowbird shooting and nest monitoring might provide a larger short-term benefit to reproductive output. Habitat management, resumption of some grazing in the reserve and cowbird removal should be considered for the intermediate future.

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Egg Removal by Brown-Headed Cowbirds: A Field Test of the Host Incubation Efficiency Hypothesis

Cited by 16 publications

References 22 publications

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

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

Egg puncture allows shiny cowbirds to assess host egg development and suitability for parasitism

Cowbird parasitism of Pale-headed Brush-finch Atlapetes pallidiceps: implications for conservation and management

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