Site fidelity in habitats with contrasting levels of nest predation and brood parasitism

The phenomenon of site fidelity (i.e. remaining faithful to sites where an individual has bred successfully in the past) has been documented for many taxa, especially birds. It has been suggested that individuals may use a simple rule of thumb: stay (or return) if breeding was successful, or switch to a new site if breeding was unsuccessful (win-stay/lose-switch; WSLS). Using simulations, I examined the evolutionary dynamics of the WSLS strategy in competition with two alternative strategies: stay-always (SA; total site fidelity) and two forms of an ideal-free settlement strategy (IFS; site indifferent). I considered two habitats identical in all respects except that one habitat (low quality) had a higher level of nest predation than the other. Between breeding seasons, females: (1) remained in a habitat if they successfully bred or otherwise dispersed to the alternative habitat (WSLS); (2) remained in the habitat regardless of their breeding success (SA); or (3) settled within habitats such that the quality of the highest ranking unoccupied territory was equalized, when possible, across habitats (IFS). The WSLS strategy invades and replaces either of the alternative strategies. I then examined the consequences of the WSLS strategy on population density and mean fecundity across two habitats that had contrasting levels of nest predation or brood parasitism. Unlike contrasting predation rates between habitats, higher levels of brood parasitism in the low-quality habitat rapidly drained away individuals from the better habitat. This result, however, depended both qualitatively and quantitatively on differences (or the lack thereof) in predation between the two habitats. A second invasibility analysis conducted on populations experiencing contrasting brood parasitism between habitats indicated that the WSLS resists invasion by the SA strategy but not the IFS strategy. The IFS strategy resists invasions by either alternative. Thus cowbird brood parasitism may rapidly drain individuals away from high-quality habitat because birds cannot discriminate between low- and high-quality habitats. Furthermore, parasitism alters the evolutionary dynamics of competing site fidelity strategies.