Estimated annual avian mortality from communication towers by Bird Conservation Region.

<p>High mortality estimates in Peninsular Florida and Southeastern Coastal Plain reflect the more numerous and taller communication towers in these regions.</p

Map of communication towers in the United States and Canada by height class.

<p>Data acquired from Federal Communications Commission, Towermaps.com, and NAV CANADA.</p

Number of communication towers ≥60 m by type and associated avian mortality estimates for Canada and the continental United States.

1<p>Tower attributes (guy wires, lighting type) for Canada are extrapolated from proportions in the United States because these attributes are not found in the NAV CANADA database.</p

Summary of factors used to develop the search and scavenging correction for bird mortality at communication towers.

<p>Summary of factors used to develop the search and scavenging correction for bird mortality at communication towers.</p

Regression and 95% confidence intervals of annual avian fatalities by tower height.

<p>Annual avian fatalities were adjusted for sampling effort, search efficiency, and scavenging and regressed by log-transformed tower height (Ln(Mean Annual Fatalities +1) = 3.4684 · Ln(Tower Height) – 12.86, <i>R</i>² = 0.84, p<0.0001).</p

Relationship of bird fatalities to free airspace at WCTV Tower, 1956–1967.

<p>Raw data from Crawford and Engstrom (2001) were used to plot daily bird fatalities against the mean free airspace between the top of the tower and the cloud ceiling each day. Days with maximum ceiling were excluded. Daily avian mortality increases significantly as free airspace decreases (Ln(Bird Fatalities +1) = 1.443928 – 0.0016667 · Mean Free Airspace (m), <i>R</i>² = 0.17, p<0.001).</p

Total estimated annual avian mortality at towers ≥60 m in the United States and Canada by Bird Conservation Region (BCR).

<p>Total estimated annual avian mortality at towers ≥60 m in the United States and Canada by Bird Conservation Region (BCR).</p

Assumed rates for search efficiency and scavenger removal by tower height and habitat type when not provided by investigator.

<p>Assumed rates for search efficiency and scavenger removal by tower height and habitat type when not provided by investigator.</p

Average search and scavenging rates taken from pesticide impact studies [42].

<p>Search and detection rates are based on daily averages weighted by the number of study plots. Search rates represent the proportion of carcasses found over the total number still present at the time of search. Scavenging rates represent daily measurements averaged over all plots without regard for the number of placed carcasses. Search rates are undoubtedly at the high end of that which is possible because the search procedures were optimized, always including trained lines of searchers spaced optimally for the habitat as well as the use of search dogs in some studies.</p

Distribution of residuals of tower height–mortality regression for 38 towers in the United States as adjusted for sampling effort, search efficiency, and scavenging.

<p>Contour lines indicate regions above and below the regression line. Although exhibiting a geographically variable pattern, the residuals are not significantly spatially autocorrelated.</p