Bald eagles in Arizona follow their own flight plan

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September 15th, 2008

Bald eagles in Arizona follow their own flight plan
Real-life population trends contradict model

As is often the case, real life does not always follow a predetermined plan, and such is the case with bald eagles in Arizona.

The Arizona Game and Fish Department’s real-life data shows that the bald eagle population in the state has been growing four percent annually. Paradoxically, a demographic model recently developed by the department predicted that the population at best would remain stable or would have declined at a rate of 3.6 to 5.5 percent (depending on the data input) during the same period.

In reality, bald eagle numbers over the past 30 years have grown more than 400 percent in Arizona, with the number of breeding pairs increasing in that time from only 11 pairs to 56 in 2008. The state also welcomed a record 53 fledglings to the skies this year, a 26 percent increase over 2007.

A test of the initial data has been completed, and the model, “Demographic Analysis of the Bald Eagle in Arizona,” is now available through the department.

“Modeling is a basic tool of science that is used to determine how different variables affect a population. In this case, the model does not fit our real data and it has no value as a management tool,” says Eric Gardner, nongame branch chief for the Arizona Game and Fish Department. “We were disappointed that the model produced results that were contrary to our real data, but models aren’t perfect and real data remains the best indicator of the health of a species’ population.”

The model uses data collected from 1991 through 2003. Since data was first entered into the model, additional data collected from 2004 through 2008 on the bald eagle population further demonstrates the upward trend of the species in the state.

“Bald eagles in Arizona are one of the most studied populations, and we have one of the most comprehensive data collections on bald eagles in the country,” says Gardner. “The effort to develop this model wasn’t wasted because it showed us where the current data set is lacking.”

To obtain a copy of the demographic analysis, contact the department at (623) 236-7575.

One Response to “Bald eagles in Arizona follow their own flight plan”

  1. Three bald eagle fledglings spotted at PVCC.

    Today at 10:00 AM I spotted 3 fledglings squawking and flying about in the retention basin just south of PVCC [32nd and Union Hills]. Wingspans were about 4 – 5 feet, white tailfeathers, bodies and heads dark feathered; beaks yellow. Not sure of their ages, but guess would be about 8 – 9 months.

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