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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.

a b s t r a c tBirds 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 >2% 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.

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We compared the minnow assemblages of Adirondack lakes with top piscivores with those of lakes having similar physiochemical and biotic characteristics but no top piscivores using a subset of data collected from 1984 to 87 by the Adirondack Lake Survey Corporation. Native minnow richness in lakes with top piscivores was about one third that of lakes without piscivores, with piscivore assemblages dominated by introduced species such as northern pike (Esox lucius), largemouth bass (Micropterus salmoides), and smallmouth bass (Micropterus dolomieu). There was strong evidence that at least four minnow species, including creek chub (Semotilus atromaculatus), northern redbelly dace (Phoxinus eos), blacknose dace (Rhinichthys atratulus), and common shiner (Luxilus cornutus), were less likely to occur in lakes with piscivores; for a fifth species (pearl dace (Margariscus margarita)), the evidence is suggestive but not as strong. Of 13 minnow species, only for two nonnative species (bluntnose minnow (Pimephales notatus) and golden shiner (Notemigonus crysoleucas)) was there strong evidence that their occurrence was unaffected by the presence of introduced piscivores. These results add to the growing body of evidence that the introduction of top piscivores to small temperate lakes puts native minnow communities at high extinction risk.Résumé : Nous avons comparé les assemblages de cyprinidés de lacs des Adirondacks renfermant des piscivores supé-rieurs à ceux de lacs ayant des caractéristiques physicochimiques et biotiques similaires mais dépourvus de piscivores supérieurs en utilisant un sous-ensemble de données recueillies de 1984 à 1987 par l'Adirondack Lake Survey Corporation. La diversité de cyprinidés indigènes dans les lacs renfermant des piscivores supérieurs était environ trois fois infé-rieure à celle observée dans les lacs dépourvus de piscivores supérieurs. Les assemblages de piscivores étaient dominés par des espèces introduites comme le grand brochet, l'achigan à grande bouche et l'achigan à petite bouche. Les données montrent assez clairement que la probabilité de présence dans les lacs avec piscivores est plus faible pour au moins quatre espèces de cyprinidés, soit le mulet à cornes, le ventre rouge du nord, le naseux noir et le méné à nageoires rouges; dans le cas d'une cinquième espèce, le mulet perlé, les données vont aussi dans ce sens mais sont moins concluantes. Parmi treize espèces de cyprinidés, seules deux espèces introduites (le ventre-pourri et la chatte de l'est) ne seraient vraisemblablement pas affectées par la présence de piscivores introduits. Ces résultats vont dans le sens des résultats de plus en plus nombreux qui tendent à montrer que l'introduction de piscivores supérieurs dans les petits lacs tempérés expose les assemblages indigènes de cyprinidés à un risque d'extinction élevé.[Traduit par la Rédaction] Findlay et al. 580

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ABSTRACT. Mechanical operations such as mowing, tilling, seeding, and harvesting are well-known sources of direct avian mortality in agricultural fields. However, there are currently no mortality rate estimates available for any species group or larger jurisdiction. Even reviews of sources of mortality in birds have failed to address mechanical disturbance in farm fields. To overcome this information gap we provide estimates of total mortality rates by mechanical operations for five selected species across Canada. In our step-by-step modeling approach we (i) quantified the amount of various types of agricultural land in each Bird Conservation Region (BCR) in Canada, (ii) estimated population densities by region and agricultural habitat type for each selected species, (iii) estimated the average timing of mechanical agricultural activities, egg laying, and fledging, (iv) and used these values and additional demographical parameters to derive estimates of total mortality by species within each BCR. Based on our calculations the total annual estimated incidental take of young ranged from ~138,000 for Horned Lark (Eremophila alpestris) to as much as ~941,000 for Savannah Sparrow (Passerculus sandwichensis). Net losses to the fall flight of birds, i.e., those birds that would have fledged successfully in the absence of mechanical disturbance, were, for example ~321,000 for Bobolink (Dolichonyx oryzivorus) and ~483,000 for Savannah Sparrow. Although our estimates are subject to an unknown degree of uncertainty, this assessment is a very important first step because it provides a broad estimate of incidental take for a set of species that may be particularly vulnerable to mechanical operations and a starting point for future refinements of model parameters if and when they become available.RÉSUMÉ. Les opérations mécanisées telles que le fauchage, le labourage, l'ensemencement et la récolte sont des sources bien connues de mortalité aviaire directe dans les champs agricoles. Toutefois, il n'existe actuellement aucune estimation du taux de mortalité pour tout groupe d'oiseaux ou grande région. Même les revues de littérature visant à dresser les sources de mortalité d'oiseaux n'ont pas examiné le dérangement attribué aux opérations mécanisées dans les champs agricoles. Pour pallier ce manque d'information, nous présentons des estimations du taux de mortalité totale par les opérations mécanisées chez cinq espèces dans l'ensemble du Canada. Notre approche de modélisation par étape nous a permis de : 1) quantifier la superficie de divers types de milieux agricoles dans chaque région de conservation des oiseaux (RCO) au Canada; 2) estimer les densités de population par RCO et type de milieux agricoles pour chacune des cinq espèces; 3) estimer la période moyenne des activités agricoles mécanisées, de la ponte et de l'envol de jeunes; et 4) utiliser ces valeurs et d'autres paramètres démographiques pour calculer des estimations de la mortalité totale par espèce dans chaque RCO. Selon nos calculs, la prise accessoire annuelle de...