Weather and Land Cover Interact to Create Thermal Refuges for Wintering Birds Inhabiting Human-modified Landscapes PDF Download

Author: Christopher Edward Latimer
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Languages : en
Pages : 169

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Book Description
Changes to winter temperatures and variability of winter conditions are occurring at a faster rate than in other seasons. Over the past thirty years, researchers have documented poleward range shifts for many North American winter avifauna, but responses tend to be highly variable and idiosyncratic. Synergies between land-cover and regional climate can generate variable responses to climate change by altering species' exposure (e.g. creation of unique or altered microclimates) and/or sensitivity (e.g. physiological limits, behavior) to environmental change. My dissertation focuses on how landscape pattern interacts with weather to alter the relationships between exposure and sensitivity of wintering birds and their demographic consequences in human-modified landscapes. In Chapter 1, I used a network of temperature sensors to investigate the multi-scaled predictors of subcanopy microclimates (exposure) within a heterogeneous Midwestern landscape. Forests in fragmented landscapes further from urban centers experienced colder, more variable conditions that differed from gridded temperature estimates suggesting biophysical properties of landscapes should be considered when assessing species' vulnerabilities to future climate change. In Chapter 2, I measured the upper limit to heat production in a cold environment (MSUM) and used radiofrequency identification-enabled bird feeders to examine how MSUM influenced feeder use and survival of black-capped chickadees (Poecile atricapillus) across a forest fragmentation gradient. Birds with lower MSUM increased their use of feeders on colder days, and had lower apparent survival probabilities in highly fragmented forests. Chapter 3 examined whether microclimates and feeder use mediated the vulnerability of chickadees to extreme weather. Survivorship was higher during warmer periods, in more urban environments, and for birds with more frequent use of bird feeders throughout winter, but was unrelated to spatial microclimate heterogeneity. In Chapter 4, I used data from Project FeederWatch and dynamic occupancy models to examine how land cover moderates the effects of winter weather on population dynamics of resident bird species. Populations were more dynamic in more forested landscapes, presumably enabling them to better track resources. Together, these results suggest that habitat loss and fragmentation alter the relationships between environmental variability, behavior and physiology, and result in context-specific fitness consequences across landscapes.