Community-level patterns of population recruitment in a generalist avian brood parasite, the brown-headed cowbird

Abstract

The brown-headed cowbird (Molothrus ater) is a generalist brood parasite that typically parasitizes many host species in a single bird community. Population recruitment in a generalist parasite should be diverse with respect to host species; however, host-specific rates of cowbird recruitment have not been reported in any host community, and the determinants of host quality are poorly known. We studied the combined influence of parasitism level, nest abundance, and host quality on community-level patterns of cowbird recruitment in New Mexico, USA. Our objectives were to: (1) evaluate patterns of host use and quality; (2) compare cowbird egg investment and recruitment among host species; (3) identify host species of most importance to cowbird recruitment. Cowbirds parasitized 11 host species, with five "major" hosts experiencing high parasitism levels (>or=1 cowbird egg/nest) and six minor hosts experiencing low parasitism levels (<0.3 cowbird eggs/nest). Parasitism level was not correlated with host species abundance, host mass, host nestling period length, or host success at fledging cowbirds. However, tree-nesting hosts were parasitized more than ground-nesters, and foliage-gleaners more than sally-foragers and ground-foragers. Average estimated survival to fledging of cowbird eggs laid in active host nests was 0.19. Cowbird recruitment was diverse with respect to hosts but was less evenly distributed across the host community than was cowbird egg investment because western tanagers (Piranga ludovicianus) fledged cowbirds more successfully than other hosts. This success in western tanagers was due to high cowbird survivorship in tanager nests and may be associated with the larger body size of tanagers relative to other hosts.

A generalist brood parasite modifies use of a host in response to reproductive success

“…The brown-headed cowbird (Molothrus ater; cowbirds hereafter) is an extreme host generalist known to parasitize more than 220 species throughout its range [11,12]. The degree to which female cowbirds select hosts based on the variation in fitness potential is poorly known [13,14]. While hosts have been observed to modify their behaviour in response to past interactions with brood parasites [15][16][17][18], obligate interspecific parasites modifying their use of hosts in response to previous reproductive success has not been demonstrated.…”

Assessing the influence of geography, land cover and host species on the local abundance of a generalist brood parasite, the brown‐headed cowbird

“…Cowbirds co-evolved with a large number of passerine host species in the Great Plains. Cowbirds are known to recruit from the nests of different hosts at substantially different rates (Curson et al, 2010). Some hosts are rejecter species capable of removing cowbird eggs from nest or overlaying nesting material onto cowbird eggs, and the rate of this rejection behaviour may vary between species (Rothstein, 1975;Strausberger & Ashley, 1997;Robinson et al, 1999;Peer et al, 2000).…”

“…Therefore, although host species richness had the greatest influence on cowbird abundance for our collective group of 168 sites, at any one site in any one year, recruitment (successful fledging) of cowbirds likely depends on specific conditions such as total density and rejection (or acceptance) behaviour of particular host species. Cowbirds are known to recruit from the nests of different hosts at substantially different rates (Curson et al, 2010). In addition, the other fundamental agents of population regulation (e.g.…”

Breeding bird assemblage dynamics of a primaeval temperate mixed forest in the Western Carpathians (Slovakia): support for pluralistic community concept

“…This model can be generalized with certain specific local limitations to other communities. In addition, other factors such as predation (Martin 1993, Weso³owski & Tomia³ojae 2005, Weatherhead et al 2010, parasitism (Brown et al 1995, Dudaniec et al 2007, brood parasitism (Goguen & Mathews 1998, Powell & Steidl 2000, Curson et al 2010, multiple density dependent processes (Holmes 2011), environmental disturbance (Fuller 2000, Greenberg et al 2001, Hirao et al 2008, Russell et al 2009, heterospecific attraction (Mönkkönen et al 1990, Forsman et al 1998, Sebastian-Gonzalez et al 2010) and pollution (Flousek 1989, Rheindt 2003, Kempenaers et al 2010) may also affect structure, dynamics and functioning of bird assemblages.…”