In May 2007, the U.S. Fish and Wildlife Service published an estimate of the size of the bald eagle population in the lower 48 states and the District of Columbia in 2006. The agency’s estimate of 9,789 pairs is not a direct count of eagles in 2006; it is a summation of the most recent count from each state between the years 2004-2006. This method is necessary because not all states reported (or conducted) counts in 2006. Fifty-one percent of the agency’s data is from 2006, 39 percent from 2005, and 10 percent from 2004. This method is reasonable, but underestimates the true 2006 population size because 49 percent of its data is from previous years.
To estimate the 2007 eagle population size, we contacted state, federal and university biologists to obtain the most recent census data. Much of the data would not be available before mid-June 2007. Final or estimated 2007 counts were available for 63 percent of the states. The most recent survey for 24 percent of states was 2006, for 10 percent it was 2005, and for two percent it was 2004. Combining these counts yields 10,368 eagle pairs. This is less than the actual 2007 count because 37 percent of the data are from earlier years. We derived a better estimate by assuming the growth rate immediately preceding 2007 (i.e the three prior years) continued through 2007. This method yields 11,062 eagle pairs.
We are updating the data throughout the breeding season as new 2007 counts arrive. When first posted on June 22, 2007, the estimate was 11,040.
HISTORIC POPULATION TREND
By consulting databases, annual census reports, and biologists at state and federal agencies, we determine the annual number of eagle pairs in each of the 49 states going back as far the data allowed. The U.S. Fish and Wildlife Service announcement presented state-by-state data going back only to 1990. Our compilation is the most comprehensive, long-term, state-by-state dataset available.
1. U.S. Fish and Wildlife Service. 2007. Bald Eagle Population Size, Numbers Soaring! May 14, 2007 press release available at: http://www.fws.gov/midwest/eagle/population/index.html