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Nest Turnover Rates and List‐Frame Decay in Bald Eagles: Implications for the National Monitoring Plan
Author(s) -
WATTS BRYAN D.,
DUERR ADAM E.
Publication year - 2010
Publication title -
the journal of wildlife management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.94
H-Index - 111
eISSN - 1937-2817
pISSN - 0022-541X
DOI - 10.2193/2009-018
Subject(s) - frame (networking) , plan (archaeology) , computer science , bald eagle , sampling frame , wildlife , set (abstract data type) , statistics , geography , ecology , mathematics , telecommunications , demography , biology , population , programming language , archaeology , sociology
In accordance with federal regulations, the United States Fish and Wildlife Service developed a postdelisting monitoring plan for the bald eagle ( Haliaeetus leucocephalus ) designed to detect a change in the number of occupied nests on a national scale. The plan employs a dual‐frame approach to the survey design where a list frame (list of known nests) and an area frame (set of survey plots) are used in concert to estimate the number of occupied nests in 5‐year intervals over a 20‐year period. The plan offers no provisions for changes in list‐frame integrity, nor does it contemplate the impact of such changes on survey performance. We used a long‐term data set to quantify occupancy patterns for nests in Virginia, USA, and evaluated their influence on integrity of the list frame and performance of the proposed dual‐frame monitoring approach. The average annual turnover rate for nests was 0.261, resulting in a rapid decay of the list frame. Decay of the list frame leads to a functional collapse of the dual‐frame approach, down to the area‐frame survey alone, early within the monitoring time horizon. This early decay of the list frame implies that the area‐frame coverage needed to maintain the same statistical power as stated in the monitoring plan would have to be increased by a factor of 3 to 5 beyond that recommended in the current plan. Remedies for this deficiency undermine the cost benefit associated with inclusion of the list frame. We examined response of the dual‐frame survey to variation in nest turnover rates and population growth rates and defined a state space where time to collapse is beyond the proposed 20‐year time horizon. Because, under realistic estimates of turnover rates, the dual‐frame approach collapses to the area frame within the proposed monitoring window, we recommend that the costs of list‐frame maintenance be included in the procedure to optimize allocation of survey effort.