Copenhagen Post | 30-06 - 09:13
A study by U.S. biologists suggests the number of long-tailed ducks nesting in the Yukon-Kuskokwim Delta in southwest Alaska is likely continuing to decline
Aerial surveys of long-tailed duck populations that straddle the Yukon-Alaska border suggest that numbers have dropped by as much as 50% in the last 30 years.
But while the surveys provided estimates of population trends, they offered little information on factors influencing the decline.
Jason Schamber, a biologist with the U.S. Geological Survey in Anchorage, and several colleagues conducted ground surveys of long-tailed duck nesting sites between 1991 and 2004.
Their results, published in the June issue of the journal Arctic, predicted a rate of decline of as much as 19% per year. The researchers also examined possible demographic influences on the population trend of long-tailed ducks breeding on the delta based on a population model they developed that could help with bird management strategies.
The study focuses on long-tailed ducks in the Yukon-Kuskokwim Delta, where 30 percent of the Alaskan population breeds.
The remote region, approximately the size of Oregon, is also home to some 20,000 mostly Aboriginal people who have a lifestyle based heavily on subsistence hunting and fishing.
Schamber and his colleagues examined factors such as the number of nests, number of eggs, successful hatch rates, and survival rates of females and ducklings. One reason for the decline may be related to high mortality rates in adult females.
Schamber suspects that the ingestion of lead shot could be partially responsible for the high rate of death at the time of study.
‘But that’s difficult for us to pin down because there are no cause-specific estimates of mortality we can rely on to plug into our population model,’ said Schamber.
He cautions that the results of the study could be influenced by the low number of nests found by researchers. Studying sea ducks is always difficult. Long-tailed ducks, for example, typically spend 80% of the year on the ocean where they are hard to track.
When they return to land to breed, their nesting sites are very dispersed. This means researchers have a difficult time collecting enough data to strengthen confidence in study results. Schamber is quick to point out the study is based on a small sample of nests.
‘Our prediction of a 19% annual rate of decline is associated with a level of uncertainty that suggests the decline could be steeper or the population could be relatively stable. While this is some of the best data available for breeding long-tailed ducks in North America, small sample size results in some uncertainty in study results and our conclusions, ‘said Schamber.
Adding weight to Schamber’s study are two long-term aerial surveys of the area that indicate populations have been in decline for decades.
Despite the drop in numbers on the Yukon-Kuskokwim Delta, long- tailed ducks world-wide likely are not in trouble. In fact the species, which ranges around the circumpolar Arctic, is one of the most abundant sea-duck populations in the world. Nonetheless populations should continue to be monitored, especially in light of declining trends.
‘We need additional data to more precisely estimate the demographics of these populations; so little is known about this species.’
Effective management strategies are hindered by the lack of information about factors that are influencing population trends.