Brood parasitism increases provisioning rate, and reduces offspring recruitment and adult return rates, in a cowbird host. Oecologia

University of Florida, Gainesville, Florida, United States
Oecologia (Impact Factor: 3.09). 09/2006; 149(1):165-73. DOI: 10.1007/s00442-006-0424-1
Source: PubMed


Interspecific brood parasitism in birds presents a special problem for the host because the parasitic offspring exploit their foster parents, causing them to invest more energy in their current reproductive effort. Nestling brown-headed cowbirds (Molothrus ater) are a burden to relatively small hosts and may reduce fledgling quality and adult survival. We documented food-provisioning rates of one small host, the prothonotary warbler (Protonotaria citrea), at broods that were similar in age (containing nestlings 8-9 days old), but that varied in composition (number of warbler and cowbird nestlings) and mass, and measured the effect of brood parasitism on offspring recruitment and adult returns in the host. The rate of food provisioning increased with brood mass, and males and females contributed equally to feeding nestlings. Controlling for brood mass, the provisioning rate was higher for nests with cowbirds than those without. Recruitment of warbler fledglings from unparasitized nests was 1.6 and 3.7 times higher than that of fledglings from nests containing one or two cowbirds, respectively. Returns of double-brooded adult male and female warblers decreased with an increase in the number of cowbirds raised, but the decrease was more pronounced in males. Reduced returns of warbler adults and recruitment of warbler fledglings with increased cowbird parasitism was likely a result of reduced survival. Cowbird parasitism increased the warblers' investment in current reproductive effort, while exerting additional costs to current reproduction and residual reproductive value. Our study provides the strongest evidence to date for negative effects of cowbird parasitism on recruitment of host fledglings and survival of host adults.

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Available from: Matthew J. Reetz
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    • "Contrary to unsuccessful breeders that decided to change the breeding site, the significantly decreased return rate of females caring for the parasite was most probably driven by the costs in terms of increased time and energy expenditures (for similar results in hosts of non-evicting brood parasites, see Sedgwick 2004; Hoover and Reetz 2006; Molina-Morales et al. 2012, but see Payne and Payne 1998). Female investment to breeding is larger than those of (often polygynous) males (Trnka and Grim 2013; Požgayová et al. 2015), and hence, the prolonged care for a cuckoo chick could be much more demanding for host females than males. "
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    ABSTRACT: Returning to a breeding site and decision where to breed belong to the key life-history traits, especially in migratory birds. Yet, we still lack knowledge about the drivers of adult return rates and breeding dispersal distances in populations under pressure of brood parasitism. We explored these issues in a trans-Saharan migratory passerine, the great reed warbler (Acrocephalus arundinaceus), in a population parasitized by the common cuckoo (Cuculus canorus)—an evicting brood parasite. In 2008–2012, a total of 563 great reed warblers were colour-marked and 185 of them were re-encountered 303 times in a year following their breeding at a fishpond area in the Czech Republic. We tested how brood parasitism and host breeding parameters in 1 year affect host return rate and dispersal distances in a following year. Return rate was lower in females fledging a cuckoo and in both sexes that failed to produce any offspring than in birds that fledged own chicks in the preceding year. Individual brood parasitism had a negative effect on the probability of female returning, but this relationship disappeared when excluding females fledging cuckoos. Although return rates did not differ between females that rejected and those that accepted cuckoo eggs, rejecter females dispersed less than acceptors. We conclude that brood parasitism and fostering the parasite might be negatively related to host female survival. The other breeding conditions might rather be related to the decision where to breed in the future. Establishing new long-term studies monitoring parasitized populations might open up avenues for future research.
    Full-text · Article · Nov 2015 · Behavioral Ecology and Sociobiology
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    • "On average, female cowbirds remove a single prothonotary warbler egg from about 60% of nests that are parasitized in our study system and cowbird nestlings increase host offspring mortality, ultimately reducing the number of warblers fledging (Hoover 2003c). In prothonotary warbler nests, cowbird nestlings increase the rate of food provisioning by adult warblers (Hoover and Reetz 2006) and, weigh on average 2–3 times more than warbler nestlings (Hoover 2003c). Each year, approximately 1500 nest-boxes (1.9-L cardboard milk carton; 95 × 95 × 200 mm) were placed 40–50 m apart within appropriate habitat in approximately 20 study sites. "
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    ABSTRACT: Host manipulation by parasites is generally regarded as a classic example of the extended phenotype, where selection favors parasite genes that adaptively alter their host’s phenotype. However, selection would simultaneously favor both hosts that recoup some fitness lost to infection (i.e., compensation) and the parasites that enhance transmission by exploiting the host’s compensatory responses. Using a long-term study (19 years) of an avian brood parasite system, we demonstrate that female prothonotary warblers Protonotaria citrea compensate for partial fecundity reduction during their first brood by initiating a second breeding attempt (i.e., double-brooding). Similarly, in successful nests with naturally reduced fecundity as a result of brood parasitism, we show that being parasitized also stimulates a compensatory double-brooding response, where female warblers raising at least 1 brown-headed cowbird Molothrus ater offspring are more likely to initiate a second brood when compared with successful nonparasitized first broods. In support of the “exploitation of compensatory responses” hypothesis, parasitized females are often parasitized again in their second brood, thereby providing additional fitness benefits to cowbirds while enabling parasitized warblers that double-brood to recoup some fitness lost in the first brood. Experimentally parasitized female warblers exhibited a similar increase in double-brooding behavior, and the double-brooding frequency of parasitized female warblers was not attributable to reduced post-fledgling survival of cowbirds, thereby supplying further support for the role of parasite-induced fecundity reduction in the compensatory double-brooding behavior of a host.
    Full-text · Article · Jan 2015 · Behavioral Ecology
    • "Simulations also assumed that costs of parasitism were restricted to the reduction in host productivity. However, the presence of a parasite nestling could affect the host's nestling development and adult parental effort, reducing the host's offspring recruitment and adult survival (Dearborn et al. 1998, Hoover and Reetz 2006). Given these costs, cowbird-egg ejection could still constitute an adaptive strategy if it improved the host's offspring or adult survival. "
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    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. Received 3 September 2012, accepted 4 June 2013.
    No preview · Article · Jul 2013 · The Auk
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