A Pacific brant family on the Yukon-Kuskokwim Delta, Alaska. Photo: Jeff Wasley, courtesy U.S. Geological Survey
Warming Temperatures Affect Geese Migration
As Alaska’s climate has warmed over the last four decades, Pacific brant geese have drastically changed their winter migration, according to a recent study in the journal Arctic. Whereas 90 percent of the population recently wintered in Mexico, today about 30 percent of the population —roughly 40,000 birds—are spending their winters in Alaska, according to the U.S. Geological Survey-led study.
"This increase in wintering numbers of brant in Alaska coincides with a general warming of temperatures in the North Pacific and Bering Sea," said David Ward, the lead author of the study and a USGS researcher at the Alaska Science Center. "This suggests that environmental conditions have changed for one of the northernmost-wintering populations of geese."
The study found that the migration shift appears related to the changes in availability and abundance of eelgrass, the primary food in the non-breeding season. Release of the study garnered widespread news reports of the impacts a warming climate has on species migration. In Mother Jones, Julia Witty notes that warming temperatures have well-documented effects on the abundance and distribution of many marine species, including walleye Pollock, Pacific cod, northern fur seals, and thick billed murres.
A Polar Field Services Series: Changing Climate, Changing Patterns
The field notes team plans to report a series of stories and interviews with scientists on the real-time impacts climate change has on native populations—both human and animal. The recent article by Ward et al. details the changing patterns in brant outside of the breeding season. To learn more about how climate change is altering the birds during the summer breeding season, we asked Jim Sedinger, professor at the Department of Natural Resources and Environmental Science at the University of Nevada, about his long-term research on breeding strategies of Pacific brant in Alaska, funded by the NSF.
Interview With Jim Sedinger
Polar Field Services (PFS): What makes brant geese an interesting species to study for ornithologists, ecologists, and climate scientists?
Jim Sedinger: The colonial nesting nature of brant makes it possible to study demography (survival, reproductive effort, recruitment into the breeding population, etc.), which is difficult for many other species. Brant behavior in winter also allows following individuals in winter and spring. Brant come out of the water following high tide each day to preen and acquire grit. Investigators can read their uniquely engraved plastic leg bands during these periods. In some years during the 1990s David Ward’s crews read > 14,000 bands in Mexico during winter. Individual brant are also observed in large numbers in Humboldt Bay (Jeff Black and students) and the Strait of Georgia (Environment Canada).
Brant on the Pacific coast are dependent on eelgrass in bays and estuaries extending from Alaska to Baja, so they are excellent indicators of environmental conditions along the coast.
PFS: As you investigate reproductive strategies for the geese, how do you account for climate change in your interpretation of your data?
Jim Sedinger: We are very concerned about climate change. One MS Thesis (Jason Schamber, a former student of mine at the University of Alaska Fairbanks) showed that wintering location during the 1998 El Nino had an important effect on whether brant nested the next summer. Birds in more southern wintering areas were substantially less likely to nest. Sedinger et al. (2006. Ecology 87:151-159) showed that the 1998 el Nino reduced breeding the next summer by about 30%. By implication, increased sea surface temperature, associated with climate warming, will negatively affect brant populations.
PFS: Have you noticed any changes in summer distribution of the geese over the years of your study?
Jim Sedinger: Brant are extensively surveyed in Alaska and less so in the Canadian Arctic. No regular surveys exist for Russia. There have been no known major shifts in distribution. Some colonies on the Yukon –Kuskokwim Delta were described in the late 1800s and others date at least to the 1940s. There have been substantial declines in some colonies, including the Tutakoke River colony, where I work. These declines are associated with increased arctic fox predation since about 1980.
PFS: Have you documented shifts in when the brant leave for their fall migration?
Jim Sedinger: We are not in the field late enough to detect fall departure. I am not aware that staff at Izembek National Wildlife Refuge have detected a change in arrival there during fall.
PFS: Have you compared the trends you observe with temperature trends? If so, what have you seen?
Jim Sedinger: Brant arrived on the breeding colony at steadily earlier dates from the 1970s through the late 1990s. A shift to a cold cycle in the North Pacific has stopped the trend to increasingly early arrival dates since that time, although arrival dates have generally still been earlier than in the early 1980s.
PFS: The article in Arctic focuses on the availability and abundance of eelgrass, the primary food of brant in their nonbreeding season. What is their primary food during breeding season? Does that source appear to have been affected by warming temperatures?
Jim Sedinger: Brant are terrestrial grazers during the breeding season. They nest and raise young in terrestrial habitats that are a few inches above sea level and are flooded regularly during storm surges in fall. They feed on a few grasses and sedges and another species called arrowgrass, which is not really a grass. We have not detected major changes in vegetation, although Torre Jorgenson has detected melting of permafrost in more inland habitats. Grazing lawns required by brant goslings for growth are maintained by the grazing activities of the geese themselves. We have found that periods of low nest success, caused by predation, result in a reduction in the amount of grazing lawn, available to goslings. This, in turn, reduces growth rate and recruitment of young into the breeding population. A series of high predation years in the early 1980s required more than a decade before geese had restored grazing lawns to something approximating their earlier abundance. Consequently, predation reduces recruitment for a number of years after the predation event associated with these changes in food for goslings.
PFS: How might the results of the study on the winter distribution of Pacific brant impact your long-term study of the geese? Will you take up more (any?) winter field work?
Jim Sedinger: David Ward (and more recently Jeff Black at Humboldt State Univ.) have been primarily responsible for winter studies. We have collaborated closely and are pursuing funding to study in more detail migration and the relationship to reproductive success and population dynamics. For example, how does an individual’s decision about how much time to spend in Humboldt Bay affect its reproductive success that summer? By association, how important is Humboldt Bay to the overall Pacific brant population?