One Smart Egg: Birds Sense Day Length Before Hatching and Change How They Develop
July 10, 2012 – Fargo, N.D. – This is one smart egg. Talk about adjusting your internal clock. New research at North Dakota State University, Fargo, shows that some chicks can sense day length, even while they are still in the egg, which in turn, affects how they develop.
Dr. Mark E. Clark, associate professor, and Dr. Wendy Reed, head of biological sciences at NDSU, found in their study that embryos in eggs appear to sense external environments and adjust how they develop. The research is being published in Functional Ecology, a British Ecological Journal, available in early view online.
Franklin’s gull is a bird that migrates long distances and requires precise timing. It winters along the west coast of South America until returning to the prairie wetlands of North America, where it nests in large colonies come springtime. Clark, Reed and NDSU graduate and undergraduate students conducted field research at J. Clark Salyer National Wildlife Refuge and Lake Alice National Wildlife Refuge in north-central North Dakota along the Souris River.
The dark hood, gray wings and pink-tinted breast of Franklin’s gulls are a harbinger of spring to the people of the Northern Great Plains, who call it the prairie rose gull. Soon after large wetlands thaw, Franklin’s gulls arrive to build floating nests from wetland vegetation to hold three green-and-black speckled eggs.
Inside these dark eggs, the developing chicks also sense spring days. “The growing embryos integrate signals from the nutrients provided to eggs by mothers with the amount of daylight,” said Dr. Clark. “The signals let the chick know whether the egg was laid at the beginning, or at the end of the nesting period.”
Clark and Reed note that chicks from eggs produced at the beginning of nesting take longer to hatch, but are larger than chicks from eggs laid at the end of nesting. Contrast that with eggs laid at the end of the nesting period, which hatch in less time, but at a smaller size.
“Chicks hatching later in the season have less time to grow, less time to become independent, and less time for flying lessons before they must migrate to South America in the fall,” said Dr. Reed.
According to Dr. Clark, data indicate embryos in late season eggs appear to be sensing external environments and adjusting their development. These changes in development time and size may be important for chicks to successfully migrate.
Many birds, including Franklin’s gulls, are arriving earlier on their breeding grounds. “This research suggests that the impacts of changing seasonal signals have far reaching effects on bird biology, including chick development,” said Dr. Clark. Researchers collected early and late season eggs, separating some into component parts and incubating others for short or long photoperiods. Upon hatching, chicks were evaluated for size and yolk sac reserves.
As a student, NDSU graduate Nathaniel Cross from Maple Grove, Minn., worked with Franklin’s gulls in the J. Clark Salyer Wildlife Refuge in North Dakota. He monitored nests, recording hatch dates and banding chicks. “It was my first time working out in the field, so I had to learn all the ins and outs of data collection and management and the difficulties of conducting research in an uncontrolled situation. I also learned a lot about the behavior of Franklin’s gulls nesting and parenting strategies,” said Cross, who plans to pursue a master’s degree in wildlife biology.
Former NDSU graduate students who participated in the research include Shawn Weissenfluh and Emily Davenport-Berg. “I conducted nest checks and collected eggs during the breeding season,” said Weissenfluh of Princeton, Minn., who noted that birds that initiate nests later in the season are in poorer condition. Other NDSU students who assisted in the research include Peter Martin, Dan Larsen, Michelle Harviell and Andrew Nygaard, along with Petar Miljkovic of Grinnell College.
Results of the study show that hatchling size is sensitive both to egg contents provided by mothers and to photoperiod, and development time increases across the season. When cues of season from eggs are mismatched with cues from photoperiod, alternate phenotypes, which are an organism’s physical or biochemical characteristics, are created.
Clark and Reed also found that seasonal variation in egg size, yolk, albumen or shell content of the eggs does not account for the seasonal maternal egg effect on hatchling size. “We expect our results to initiate new studies on how vertebrate embryos integrate environmental cues with maternal effects and offspring responses to optimize the expression of offspring phenotype,” said Clark.
Research funding was provided by the National Science Foundation (IOS-0445848), the North Dakota Game and Fish Department and the U.S. Fish and Wildlife Service.
North Dakota State University, Fargo, is a student focused, land-grant, research university – an economic engine that educates students, conducts primary research, creates new knowledge and advances technology. NDSU is among the top 108 universities in the country with very high research activity, as determined by the Carnegie Commission on Higher Education.