An Estimate of Avian Mortality at Communication Towers in the United States and Canada

Avian mortality at communication towers in the continental United States and Canada is an issue of pressing conservation concern. Previous estimates of this mortality have been based on limited data and have not included Canada. We compiled a database of communication towers in the continental United States and Canada and estimated avian mortality by tower with a regression relating avian mortality to tower height. This equation was derived from 38 tower studies for which mortality data were available and corrected for sampling effort, search efficiency, and scavenging where appropriate. Although most studies document mortality at guyed towers with steady-burning lights, we accounted for lower mortality at towers without guy wires or steady-burning lights by adjusting estimates based on published studies. The resulting estimate of mortality at towers is 6.8 million birds per year in the United States and Canada. Bootstrapped subsampling indicated that the regression was robust to the choice of studies included and a comparison of multiple regression models showed that incorporating sampling, scavenging, and search efficiency adjustments improved model fit. Estimating total avian mortality is only a first step in developing an assessment of the biological significance of mortality at communication towers for individual species or groups of species. Nevertheless, our estimate can be used to evaluate this source of mortality, develop subsequent per-species mortality estimates, and motivate policy action

Tephrochronology

Tephrochronology is the use of primary, characterized tephras or cryptotephras as chronostratigraphic marker beds to connect and synchronize geological, paleoenvironmental, or archaeological sequences or events, or soils/paleosols, and, uniquely, to transfer relative or numerical ages or dates to them using stratigraphic and age information together with mineralogical and geochemical compositional data, especially from individual glass-shard analyses, obtained for the tephra/cryptotephra deposits. To function as an age-equivalent correlation and chronostratigraphic dating tool, tephrochronology may be undertaken in three steps: (i) mapping and describing tephras and determining their stratigraphic relationships, (ii) characterizing tephras or cryptotephras in the laboratory, and (iii) dating them using a wide range of geochronological methods. Tephrochronology is also an important tool in volcanology, informing studies on volcanic petrology, volcano eruption histories and hazards, and volcano-climate forcing. Although limitations and challenges remain, multidisciplinary applications of tephrochronology continue to grow markedly

Ecto- and Endoparasites of the Black Bear in Northern Wisconsin

Black bears (Ursus americanus) were live-trapped and examined for ectoparasites during the summers of 1974 and 1975 in northern Wisconsin. Nine bears were captured in 1974 and 104 bears (including 18 recaptures) were captured in 1975. Thirty-five (79.5%) of 44 captures from Clam Lake in 1975 carried the dog tick (Dermacentor variabilis Say, 1821), one (2.3%) the winter tick (Q. albipictus Packard, 1869), and one (2.3%) the black-legged tick (Ixodes scapularis Say, 1821) -- a new host and state record. Forty-five (75%) of 60 bears captured in Iron County in 1975 carried dog ticks. Dog ticks occurred on 76.9% of the 1975 captures and on 72.6% of all captures. Four (6.7%) of the bears captured in Iron County in 1975 had moderate to heavy infestations of a louse (Trichodectes pinguis euarctidos Hopkins, 1954). Mange was observed on five (5.8%) bears captured in 1975; two Demodex (Owen, 1843) mites were discovered in a scab sample. The black bear is a new recorded host for this mite. None of 70 tissue samples was positive for Demodex. A flea was collected in 1974 from an Iron County bear. Dental caries were present in nine (10.5%) bears captured in 1975. Periodontal disease was present in one (1.2%) Clam Lake bear. Twenty-eight viscera were obtained from hunter-killed bears during the 1974 and 1975 fall bear hunting seasons. Twenty-five (89.3%) intestinal tracts contained ascarid worms (Baylisascaris transfuga Rudolphi, 1819). Fifty-nine (64.1%) of 92 fecal samples examined from live-trapped bears had B. transfuga eggs; 11 (39.3%) of 28 samples examined from viscera were positive. An unidentified hookworm larva was recovered froa a bear captured in 1975. Adult filarial worms (Dirofilaria ursi Yamaguti, 1941) were found in two (7.1%) viscera. Seventeen (19.5%) of 87 blood smears contained microfilariae. The broad fish tapeworm (Diphyllobothrium latum Linnaeus, 1785), reportedly common in humans and black bears in the Lake Superior region earlier in this century, was absent from all viscera and fecal samples examined. The trichina worm (Trichinella spiralis Owen, 1835) was found in 6 (3.8%) of 163 Wisconsin bears in a study from 1970 to 1973; none was found in viscera or tissue samples examined from this study. Tooth sectioning revealed an age range from 0.5 to 15.5 years for bears captured in 1975. The average age for males and females was 4.5 and 6.02 years, respectively.Wisconsin Bear Hunters Associatio

An Estimate of Avian Mortality at Communication Towers in the United States and Canada

Avian mortality at communication towers in the continental United States and Canada is an issue of pressing conservation concern. Previous estimates of this mortality have been based on limited data and have not included Canada. We compiled a database of communication towers in the continental United States and Canada and estimated avian mortality by tower with a regression relating avian mortality to tower height. This equation was derived from 38 tower studies for which mortality data were available and corrected for sampling effort, search efficiency, and scavenging where appropriate. Although most studies document mortality at guyed towers with steady-burning lights, we accounted for lower mortality at towers without guy wires or steady-burning lights by adjusting estimates based on published studies. The resulting estimate of mortality at towers is 6.8 million birds per year in the United States and Canada. Bootstrapped subsampling indicated that the regression was robust to the choice of studies included and a comparison of multiple regression models showed that incorporating sampling, scavenging, and search efficiency adjustments improved model fit. Estimating total avian mortality is only a first step in developing an assessment of the biological significance of mortality at communication towers for individual species or groups of species. Nevertheless, our estimate can be used to evaluate this source of mortality, develop subsequent per-species mortality estimates, and motivate policy action

Avian mortality at communication towers in the United States and Canada: which species, how many, and where?

Birds migrating to and from breeding grounds in the United States and Canada are killed by the millions in collisions with lighted towers and their guy wires. Avian mortality at towers is highly variable across species, and the importance to each population depends on its size and trajectory. Building on our previous estimate of avian mortality at communication towers, we calculated mortality by species and by regions. To do this, we constructed a database of mortality by species at towers from available records and calculated the mean proportion of each species killed at towers within aggregated Bird Conservation Regions. These proportions were combined with mortality estimates that we previously calculated for those regions. We then compared our estimated bird mortality rates to the estimated populations of these species in the United States and Canada. Neotropical migrants suffer the greatest mortality; 97.4% of birds killed are passerines, mostly warblers (Parulidae, 58.4%), vireos (Vireonidae, 13.4%), thrushes (Turdidae, 7.7%), and sparrows (Emberizidae, 5.8%). Thirteen birds of conservation concern in the United States or Canada suffer annual mortality of 1–9% of their estimated total population. Of these, estimated annual mortality is \u3e2% for Yellow Rail (Coturnicops noveboracensis), Swainson’s Warbler (Limnothlypis swainsonii), Pied-billed Grebe (Podilymbus podiceps), Bay-breasted Warbler (Setophaga castanea), Golden-winged Warbler (Vermivora chrysoptera), Worm-eating Warbler (Helmitheros vermivorum), Prairie Warbler (Setophaga discolor), and Ovenbird (Seiurus aurocapilla). Avian mortality from anthropogenic sources is almost always reported in the aggregate (‘‘number of birds killed’’), which cannot detect the species-level effects necessary to make conservation assessments. Our approach to per species estimates could be undertaken for other sources of chronic anthropogenic mortality

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

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

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

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