Novel questions about avian nesting ecology

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Predators put birds at extreme risk while at nests, whether as eggs, nestlings, or parents. For example, one major review reported that 23.1-87.0% of passerine nests produced fledglings, and that 20.2-85.3% of nest failures were due to predators. Thus, nest sites and behaviours that reduce predation risk can be of pivotal importance to a bird's reproductive strategy, particularly in species where many individuals do not survive beyond their first breeding season. Nest concealment is commonly assessed in studies of nest predation. However, concealment of nest odours has scarcely been considered. This is surprising given that the most common predators of passerine nests are reptiles and mammals that rely more on olfaction than vision to find nests. Similarly, little attention has been devoted to considering how predators use odours to find bird nests. These and many other overlooked questions complement my ongoing research program that is evaluating the importance of crypsis to reproductive success in tree swallows. To quantify their relative importance, I will collect data on visual, acoustic, and olfactory concealment of nests; I focus here on the latter. Odours produced by adults, nestlings, and nest materials have scarcely been quantified for any species. From nest-building through to post-fledging, I will quantify odours of tree swallow nest contents using state-of-the-art equipment: gas chromatography-mass spectrometry. A longer term goal is to collect data from numerous species to evaluate ecological (e.g., cavity- versus open-nesting, ground- vs. above-ground nesting) and phylogenetic (e.g., passerine versus non-passerine) signatures in nest odours. Once I identify single-molecule (odorant) contributors to nest odours, a next step will be to evaluate odorants to which predators respond. For example, candidate odorants will be piped into Y-tubes where model predators (e.g., deer mice) can choose to visit control versus known nest odorants. Subsequent work will evaluate combinations of odorants. Do different predator species (e.g., mice versus squirrels) prefer different odorants? At nests I monitor each year, are particular odorants associated with rates of nest predation? My research is highly collaborative; I work with swallow biologists (Golondrinas de las Americas) that have already published 8 papers investigating spatial variation in numerous aspects of swallow biology at an unprecedented spatial scale (i.e., from Tierra del Fuego to Alaska). My students and I will similarly be able to tap into this network to explore spatial variation in nest odours. I am excited about the diversity of questions within this novel research program, and the opportunities it presents to my students.