Why Do Birds Fatten Up for Migration? – Hobart and William Smith Colleges \
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Why Do Birds Fatten Up for Migration?

Birds develop ample energy reserves in preparation for and during migration but often store more fat than they need for the journey alone.

In a recent study in The Auk: Ornithological Advances, Professor of Biology Mark Deutschlander and his colleague Jennalee Holzschuh, who earned her master’s degree in the Department of Environmental Science and Biology at SUNY Brockport under the mentorship of Deutschlander, discovered that both male and female warblers put on the extra weight during spring migration to stay in good reproductive shape.

The article — “Do migratory warblers carry excess fuel reserves during migration for insurance or for breeding purposes?” — is the result of a multi-year analysis of data collected between 1999 and 2012 at the Braddock Bay Bird Observatory in Hilton, N.Y. To determine whether the excess fuel reserves served “as insurance against potentially poor environmental conditions in early spring” or to “offset the demands of breeding,” Deutschlander and Holzschuh examined banding data for 12 species of warblers during both fall and spring migration. This is the first of two manuscripts published from Holzschuh’s master’s thesis.

“I think this paper really illustrates the types of questions and analyses that can be addressed with archived banding data,” Deutschlander explains on The Auk blog. “There are lots of data being collected at bird observatories, and much of it is waiting for interested researchers and students to use that data to address questions about bird migration.”  Deutschlander currently serves on the Board of Directors for the Braddock Bay Bird Observatory (and served as a past president and vice president), and he chairs the Observatory’s research committee.

The study, which has been picked up by several news outlets nationally and internationally, ultimately concludes that the excess energy stores were most likely for reproductive efforts. As The Auk notes, “females arrived with more fat reserves than males, earlier birds arrived with less fat than later birds (rather than the other way around), and all birds carried more fat in spring than in fall.”  The fat helps the birds prepare for the stresses of reproduction, particularly females who must produce energetically-expensive eggs.

A peer-reviewed, international journal of ornithology, The Auk began in 1884 as the official publication of the American Ornithologists’ Union (AOU), the oldest and largest society for the study of ornithology in the Western Hemisphere. In 2009, the journal was honored as one of the 100 most influential journals of biology and medicine over the past 100 years. Deutschlander currently serves as one of the journal’s associate editors.

This most recent study has been covered by:



The Independent

Market Business News


Top Birding Tours

Over the past 20 years, Deutschlander’s research has focused on the sensory and physiological aspects of migration and navigation, particularly the use of the earth’s magnetic field and visual cues in animal orientation. His publications on navigation appear in a wide array of prestigious international and national journals, including NatureThe Journal of Experimental Biology, and Journal of Field Ornithology. This most recent paper in The Auk is Deutschlander’s first venture into other aspects of migration biology.  In 2009, he shared his expertise on bird migration on National Public Radio during a live broadcast of “Science Friday” from Cornell’s Bailey Hall. In 2013, he became an elective member of the AOU.

Deutschlander currently serves as first vice president for the Wilson Ornithological Society, the second oldest and second largest scientific ornithological society in North America. When that appointment concludes, he will serve two years as president. 

He earned his B.S. in biology summa cum laude from the State University of New York at Geneseo, and his Ph.D. in zoology from Indiana University, where he specialized in animal behavior and minored in neuroscience. He has taught previously at the Rochester Institute of Technology and was a postdoctoral fellow at University of Victoria in British Columbia, as well as a visiting scientist at the University of Technology in Sydney, Australia. He joined the HWS faculty in 2000 and has served as chair of Biology Department, the HWS Health Professions Program, and the Colleges’ Committee on Academic Affairs.

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