Annual whooping crane survey finds more endangered birds
The final numbers for the 2013-14 winter whooping crane survey show an increase in the endangered bird population.
An estimated 304 cranes from the Aransas-Wood Buffalo population wintered in the primary survey area of 154,000 acres on and around the Aransas National Wildlife Refuge, according to a U.S. Fish and Wildlife Service news release.
Last year's wintering survey estimated there were 257 birds, said Wade Harrell, U.S. Fish and Wildlife Service whooping crane recovery coordinator. The confidence interval, a population parameter that describes the reliability of the estimate, narrowed to less than 10 percent this year as a result of more experienced observers, he said.
"The observers in the plane, myself being one of them, are getting better with time," Harrell said.
Last year, the confidence interval was between 178 and 362 birds.
Because both last year and this year's estimates come with a confidence interval, it is difficult to say whether there has been a significant increase in the population, Harrell said.
But the raw survey data - the number of birds spotted on the ground before being put into a statistical model - indicate the population has increased, he said.
The wild whooping crane population also appeared to be closer to the coast this year, Harrell said. This is likely a result of a wetter year leading to lower salinity and more blue crabs, a primary part of the cranes' diet.
"Food seems to be relatively more abundant along the coast this year, and as you expect, the birds respond to that," he said.
The move toward the water put more birds in the survey area, which also may have contributed to the increase in the observed population size, Harrell said.
The 304-bird estimate includes 39 juveniles.
"This was a relatively good year for recruiting new juveniles into the population," Harrell said.
About 15 juveniles were observed per 100 adults, making it a slightly above-average year for recruitment, he said.
Wintering season is coming to an end and some whoopers have already started their migration back to Canada. Harrell said birds have been seen in Oklahoma and Kansas.
"We expect most of the population to have left the coast by mid-April," Harrell said.