Estimated Mortality of Selected Migratory Bird Species from Mowing and Other Mechanical Operations in Canadian Agriculture

Abstract

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...

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