Biology ETDs
Publication Date
7-28-2026
Abstract
Body size is a trait with profound consequences for physiology, ecology, and fitness. Evolutionary changes in bird body size in response to anthropogenic changes have been widely reported. A suite of recent studies suggests the body size of modern birds is declining, with rates of size reduction of up to 1.8% per decade. Understanding why modern bird body sizes are changing would benefit from examining ways birds have responded to past episodes of environmental upheaval. Observed declines have been widely attributed to warming, but if this were a general phenomenon, we should also see substantial body size reductions as temperatures rose by ~10°C since the end of the Pleistocene 12 Ka. The Late Pleistocene was also marked by extinctions of large-bodied species, a perturbation to the community that should favor generalist niches in surviving species, with variable effects on body size. I characterized body size changes across 24 bird species from southern California, USA, from the Late Pleistocene (~25–11 Ka) to today. Additionally, I examined morphological changes in functional traits: eagle toes and claws, to investigate consequences of bird community shifts following the Pleistocene megafaunal extinctions. I reviewed studies on recent, decadal-scale body size change in birds with a focus on methods of body size quantification, drivers, and mechanisms of size change. Most studies on recent body size change in birds have focused on small-bodied songbirds. Through a collaboration with the New Mexico Department of Game & Fish, we quantified body size change in two subspecies of migratory Sandhill Cranes from wintering grounds in New Mexico using a 40-year morphological dataset.
Language
English
Keywords
evolution, ecology, ornithology, paleontology, birds
Document Type
Dissertation
Degree Name
Biology
Level of Degree
Doctoral
Department Name
UNM Biology Department
First Committee Member (Chair)
Christopher Witt
Second Committee Member
Felisa Smith
Third Committee Member
Shane DuBay
Fourth Committee Member
David Steadman
Recommended Citation
Takano, Oona M.. "Drivers of Bird Body Size Evolution." (2026). https://digitalrepository.unm.edu/biol_etds/670