The roles of food and predation in shaping adaptive and maladaptive behaviors in postfire bird species

by Robertson, Bruce A.

Most animals live in rapidly changing environments, and within-individual phenotypic plasticity can allow populations to track sources of selection that often vary dramatically in time and space. However, if conditions change too rapidly, the cues animals use to track environmental changes may become uncoupled from the ultimately important factors with which they have been historically correlated. Animals relying upon proximal cues to guide their behaviors may, in novel environments, consistently make errors. When these errors occur within the context of choosing a habitat, the organism is said to be caught in an ‘ecological trap’. Herein, I develop a conceptual model to explain how an ecological trap might work, outline the specific criteria that are necessary for demonstrating the existence of an ecological trap, and provide tools for researchers to use in detecting ecological traps. I then review the existing literature and summarize the state of empirical evidence for the existence of traps. My conceptual model suggests that there are two basic kinds of ecological traps and three mechanisms by which traps may be created. To this point in time, there are still only a few solid empirical examples of ecological traps in the published literature, although those examples suggest that both types of traps and all three of the predicted mechanisms do exist in nature. Next I examine habitat selection behavior and nest success of Olive-sided Flycatchers (Contopus cooperi) in naturally occurring burned forest and in an anthropogenically created habitat type—a selectively harvested forest. I show that Olive-sided Flycatchers preferred to settle in the selectively harvested forest despite the fact that estimated nest success in that habitat was roughly half that found in naturally burned forest. These results are consistent with the hypothesis that selectively harvested forest can act as an “ecological trap” by attracting Olive-sided Flycatchers to a poor-quality habitat type. Natural disturbances, such as wildfire, are important ecological processes in that they alter habitat structure and resource availability. I used the dramatic temporal and spatial variation in microclimatic conditions generated by variation in wildlife severity to examine the microclimatic consequences of nest site preferences and the fitness costs to parents and offspring in the Dark-eyed Junco (Junco hyemalis). Adults preferred to select nest sites with the most moderate microclimates. Nestlings reared in colder nest sites gained mass more slowly and experienced retarded skeletal growth while parents suffered costs associated with hot microclimates; incubating females reduced their nest attentiveness and doubled their nestling provisioning rate at hot nest sites. Nest site preference in junco appear to be an adaptive consequence of the costs of hot nest sites to parents and the costs of overly cool climates to developing young. Resource levels have been widely recognized to change over time as organisms recover from fire damage or recolonize a site after a wildfire. I report on the importance iii of food limitation versus nest predation on the expression of plastic life-history traits in Dark-eyed Junco (Junco hyemalis). Junco clutch size was primarily determined by habitat-specific and seasonal changes in food availability, while nest predation risk shaped egg laying decisions when food was extremely limited. Conversely, nestling growth rates were primarily determined by habitat-specific, seasonal changes in nest predation risk, but were mediated by food availability. Results illustrate that food is more important than environmental risk of nest predation in shaping the expression of clutch size. Overall, results demonstrate the birds assess and respond to variation in nest predation risk and food availability at fine temporal and spatial scales, and that that both factors play an important role in the expression of avian reproductive strategies. iv