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

Abstract

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.

Indirect estimates of breeding and natal philopatry in an obligate avian brood parasite

“…These published magnitudes of overall breeding versus natal philopatry estimated for Brown-head Cowbirds (hereafter: Cowbirds) are similar to those reported for several non-parasitic, migratory parental songbird species that are sympatric with Cowbirds throughout North America (*50% adults vs. 5% nestlings; Weatherhead and Forbes 1995;Winkler et al 2005;Hoover and Reetz 2006). Hence, alternative reproductive strategies (i.e.…”

“…Here, we argue that sampling individuals at sufficient distances to encompass the breeding ranges of several adult parasites is spatially more relevant and statistically more feasible for the analysis of parasite-specific patterns of natal philopatry, dispersal, and population structure (Winkler et al 2005;Hoover and Reetz 2006;Schlossberg 2009). Specifically, in our work, we analyzed genetic estimates of relatedness of avian brood parasite chicks across different scales of host-nest distances to study and test whether natal and breeding philopatry by Cowbirds resulted in spatially-scaled genetic population structure.…”

Intraclutch variation in egg appearance of Brown-headed Cowbird hosts

“…Similarly, higher provisioning rates have been reported for nests with parasite nestlings than for nests without parasites of the same species (Dearborn et al 1998, Hoover andReetz 2006). Thus, the presence of a cuckoo nestling in nests of L. amaurocephalus might represent a higher cost to host adults, but more data are needed to understand whether this increase in parental investment reduces future reproductive success by decreasing adult survival, decreasing energy available for investment in subsequent broods, or increasing the time until the next reproductive attempt (Dearborn et al 1998, Tewksbury et al 2002, Hoover and Reetz 2006.…”

“…The Pavonine Cuckoo's nestling period (24 days) was longer than those of other small brood-parasitic cuckoos (18-20 days;Payne 2005), including the closely related Striped Cuckoo (Tapera naevia, 18 days; Payne 2005). It was also 5 days longer than the nestling period of L. amaurocephalus (19 days), which represents an extra cost to the host that can decrease the capacity of the foster parents to invest in the next reproductive attempt (Hoover and Reetz 2006). The expulsion of feces when handled may represent an antipredator adaptation as it does in the Great Spotted Cuckoo (Canestrari et al 2014).…”

A game-theoretic model of interspecific brood parasitism with sequential decisions

“…For example, some parasites have evolved to the point where they are able to mimic the host egg to a good degree (Stokke et al(1999)); this can cause the host to eject the wrong egg. There is also the possibility that it could also damage its own nest in trying to eject the parasite (Hoover and Reetz(2006)). Thus the host must balance the costs of resisting this parasitism with the potential benefits of resistance, the cost-benefit equilibrium (Winfree(1999)).…”