01 April 2009

Peak in Winter Population of Trumpeter Swans in the Sandhills

Map of the Sand Hills and general features. All images from the swan report issued by the Nebraska Game and Parks Commission.

Fifty years after the first Trumpeter Swans were reintroduced to the Nebraska sandhills, a survey of winter birds indicates the population is the greatest ever recorded.

There were 639 swans counted during a survey conducted by personnel of the Nebraska Game and Parks Commission, according to Mark P. Vrtiska, Ph.D, waterfowl program manager for the state agency. The survey was done using two high-winged aircraft, with additional details derived from ground counts.

According to details provided by a report issued in March:

"We counted 639 trumpeter swans in the High Plains flock during the 2008 winter survey compared to 593 in 2007. In 2008, most swans were observed on the North Loup River and on or near Merritt Reservoir. The North Loup, North Platte, and Calamus Rivers along with Birdwood and Blue Creeks also held significant numbers of swans. The 2008 winter count was a 7.8% increase in number from 2007 and represents the highest winter count recorded. There was about a 49% increase in the numbers of trumpeter swans counted between the fall 2008 (429 swans) and winter 2008 (639 swans) surveys. We observed no swans on Lacreek NWR during the 2008 winter survey. In addition to High Plains trumpeter swans, 30 other swans were observed during the 2008 winter survey on the Loup River. Given their more southeasterly occurrence, it is likely that these birds are from restoration efforts in other states (e.g., Iowa). However, their origin was not investigated or confirmed.

Number of trumpeter swans considered as part of the High Plains flock, observed during the 2008 and previous winter trumpeter swan surveys.

"During the week of the survey, there was little to open water at Lacreek NWR (approximately 110%) and most Sandhill Lakes. Weather conditions during the survey included winds at 0-8 kph and temperatures near 0o C. The month of December was colder than past years as there was a large ice/snow even occurring in November."

At Lacreek National Wildlife Refuge, near Martin, SD, where the Trumpeter Swan was reintroduced in 1960, there were 384 swans counted on November 8, 2008. This is the largest number of swans ever recorded at this locality.

Severe weather conditions occurred in the region just prior to the survey period. " Below average temperatures and ice on Sandhill lakes concentrated birds on open water and reservoirs more so than in years past and probably increased the accuracy of the counts," according to the survey report.

At Lacreek refuge, management of wetland pools will continue to have a focus on providing conditions suitable for the use by the swans:

"Water management in the developed wetland units will continue to emphasize arrowhead and other preferred submerged aquatic plant species preferred by waterfowl, and the units will be flooded to preferred foraging depths from October through March on approximately 25% of the units during fall 2009."

"A notable aspect of the winter count was a reduction in the relative percentage of cygnets," the report said. "The count continued to denote an increasing number of "white" Trumpeter Swans. Swans are classified as cygnets, or young swans, if they have a gray plumage, according to survey protocol.

"It appears that counts of white birds in both fall and winter surveys continue to increase, while the cygnet production rate (i.e., cygnets/white birds) appears to be steadily declining over time, although a slight increase occurs in 2008. The decline could be the result of the flock reaching the carrying capacity of the landscape, a reduction in the quality of habitats, an increased number of non-breeding pairs or subadults, or other factors. Continued monitoring of this flock and directed research is needed to better understand the ecology of these birds. Ensuring separate counts for adults and cygnets will assist in determining production in the future."

Surveys of the swans are "conducted annually to assess wintering-ground abundance and distribution." Personnel from Lacreek NWR had conducted the aerial surveys prior to 2005.

Trumpeter Swans are also common summer residents at large wetlands in the Sand Hills region of north-central Nebraska.

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