Anna M. Calvert

Landscape Movements of Migratory Birds and Bats Reveal an Expanded Scale of Stopover

Many species of birds and bats undertake seasonal migrations between breeding and over-wintering sites. En-route, migrants alternate periods of flight with time spent at stopover – the time and space where individuals rest and refuel for subsequent flights. We assessed the spatial scale of movements made by migrants during stopover by using an array of automated telemetry receivers with multiple antennae to track the daily location of individuals over a geographic area ∼20×40 km. We tracked the movements of 322 individuals of seven migratory vertebrate species (5 passerines, 1 owl and 1 bat) during spring and fall migratory stopover on and adjacent to a large lake peninsula. Our results show that many individuals leaving their capture site relocate within the same landscape at some point during stopover, moving as much as 30 km distant from their site of initial capture. We show that many apparent nocturnal departures from stopover sites are not a resumption of migration in the strictest sense, but are instead relocations that represent continued stopover at a broader spatial scale.

A Synthesis of Human-related Avian Mortality in Canada

Many human activities in Canada kill wild birds, yet the relative magnitude of mortality from different sources and the consequent effects on bird populations have not been systematically evaluated. We synthesize recent estimates of avian mortality in Canada from a range of industrial and other human activities, to provide context for the estimates from individual sources presented in this special feature. We assessed the geographic, seasonal, and taxonomic variation in the magnitude of national-scale mortality and in population-level effects on species or groups across Canada, by combining these estimates into a stochastic model of stage-specific mortality. The range of estimates of avian mortality from each source covers several orders of magnitude, and, numerically, landbirds were the most affected group. In total, we estimate that approximately 269 million birds and 2 million nests are destroyed annually in Canada, the equivalent of over 186 million breeding individuals. Combined, cat predation and collisions with windows, vehicles, and transmission lines caused > 95% of all mortality; the highest industrial causes of mortality were the electrical power and agriculture sectors. Other mortality sources such as fisheries bycatch can have important local or species-specific impacts, but are relatively small at a national scale. Mortality rates differed across species and families within major bird groups, highlighting that mortality is not simply proportional to abundance. We also found that mortality is not evenly spread across the country; the largest mortality sources are coincident with human population distribution, while industrial sources are concentrated in southern Ontario, Alberta, and southwestern British Columbia. Many species are therefore likely to be vulnerable to cumulative effects of multiple human-related impacts. This assessment also confirms the high uncertainty in estimating human-related avian mortality in terms of species involved, potential for population-level effects, and the cumulative effects of mortality across the landscape. Effort is still required to improve these estimates, and to guide conservation efforts to minimize direct mortality caused by human activities on Canada’s wild bird populations. As avian mortality represents only a portion of the overall impact to avifauna, indirect effects such as habitat fragmentation and alteration, site avoidance, disturbance, and related issues must also be carefully considered.

Nonbreeding-Season Drivers of Population Dynamics in Seasonal Migrants: Conservation Parallels Across Taxa

For seasonal migrants, logistical constraints have often limited conservation efforts to improving survival and reproduction during the breeding season only. Yet, mounting empirical evidence suggests that events occurring throughout the migratory life cycle can critically alter the demography of many migrant species. Herein, we build upon recent syntheses of avian migration research to review the role of non-breeding seasons in determining the population dynamics and fitness of diverse migratory taxa, including salmonid fishes, marine mammals, ungulates, sea turtles, butterflies, and numerous bird groups. We discuss several similarities across these varied migrants: (i) non-breeding survivorship tends to be a strong driver of population growth; (ii) non-breeding events can affect fitness in subsequent seasons through seasonal interactions at individual- and population-levels; (iii) broad-scale climatic influences often alter non-breeding resources and migration timing, and may amplify population impacts through covariation among seasonal vital rates; and (iv) changes to both stationary and migratory non-breeding habitats can have important consequences for abundance and population trends. Finally, we draw on these patterns to recommend that future conservation research for seasonal migrants will benefit from: (1) more explicit recognition of the important parallels among taxonomically diverse migratory animals; (2) an expanded research perspective focused on quantification of all seasonal vital rates and their interactions; and (3) the development of detailed population projection models that account for complexity and uncertainty in migrant population dynamics.

Contrasting seasonal survivorship of two migratory songbirds wintering in threatened mangrove forests.

Long-distance migrants wintering in tropical regions face a number of critical conservation threats throughout their lives, but seasonal estimates of key demographic parameters such as winter survival are rare. Using mist-netting-based mark-recapture data collected in coastal Costa Rica over a six-year period, we examined variation in withinand between-winter survivorship of the Prothonotary Warbler (Protonotaria citrea; 753 young and 376 adults banded), a declining neotropical habitat specialist that depends on threatened mangrove forests during the nonbreeding season. We derived parallel seasonal survivorship estimates for the Northern Waterthrush (Seiurus noveboracensis; 564 young and 93 adults banded), a cohabitant mangrove specialist that has not shown the same population decline in North America, to assess whether contrasting survivorship might contribute to the observed differences in the species’ population trajectories. Although average annual survival probability was relatively similar between the two species for both young and adult birds, monthly estimates indicated that relative to Northern Waterthrush, Prothonotary Warblers exhibited: greater interannual variation in survivorship, especially within winters; greater variation in survivorship among the three study sites; lower average between-winter survivorship, particularly among females, and; a sharp decline in between-winter survivorship from 2003 to 2009 for both age groups and both sexes. Rather than identifying one seasonal vital rate as a causal factor of Prothonotary Warbler population declines, our species comparison suggests that the combination of variable within-winter survival with decreasing between-winter survival demands a multi-seasonal approach to the conservation of this and other tropicalwintering migrants. RESUME. Les migrateurs de longue distance qui hivernent dans les regions tropicales font face a d’importantes menaces tout au long de leur vie, et les estimations saisonnieres de parametres demographiques cles, comme la survie hivernale, sont rares. A partir de donnees de capture-recapture recoltees avec des filets japonais pendant 6 ans au Costa Rica, nous avons examine la variation de la survie intraet inter-hivernale de la Paruline orangee (Protonotaria citrea; 753 jeunes et 376 adultes bagues), migrateur neotropical en declin qui depend des mangroves menacees en dehors de la saison de reproduction. De la meme facon, nous avons estime la survie saisonniere de la Paruline des ruisseaux (Seiurus noveboracensis; 564 jeunes et 93 adultes bagues), espece specialiste de la mangrove qui cohabite avec la precedente, mais dont les populations n’ont pas montre le meme declin en Amerique du Nord. Ces donnees ont ete utilisees afin d’evaluer si les taux de survie differents des deux especes peuvent expliquer en partie les differences observees dans leurs trajectoires demographiques. Quoique la probabilite de survie annuelle moyenne etait relativement semblable chez les deux especes, tant pour les jeunes que pour les adultes, les estimations mensuelles ont indique que, comparativement a la Paruline des ruisseaux, la Paruline orangee montrait des variations interannuelles plus grandes de son taux de survie (particulierement durant un meme hiver), une plus grande variation de son taux de survie entre les trois sites d’etude, un taux de survie interhivernal moyen plus faible (particulierement Bird Studies Canada, Thunder Cape Bird Observatory Avian Conservation and Ecology Ecologie et conservation des oiseaux 5(1): 2 http://www.ace-eco.org/vol5/iss1/art2/ chez les femelles) et un declin prononce de son taux de survie interhivernal de 2003 a 2009 pour les deux groupes d’âges et les deux sexes. Etant donne les resultats differents obtenus pour nos deux especes cibles et la variabilite du taux de survie intrahivernal combinee a la diminution du taux de survie interhivernal observees chez la Paruline orangee, nous croyons que la conservation de cette espece et celle d’autres migrateurs neotropicaux doivent etre abordees selon une approche multi-saisonniere.

Measuring Conservation Trade-offs: Demographic Models Provide Critical Context to Empirical Studies

The decline of Piping Plover (Charadrius melodus) populations in North America (Haig et al. 2005) has triggered conservation concern throughout their range and active intervention at their breeding grounds. Protection of nests from both natural and human disturbance has been a particular focus of many regional conservation efforts, such as the predator exclusion methods applied in Prince Edward Island National Park (PEINP) as described in Barber et al. (2010). We applaud Barber et al.’s direct quantifications of the effect of specific conservation actions, given that demographic data for endangered species are rare and often imprecise (Heppell et al. 2000). Our purpose here is to incorporate their data into a previously published population model for the species, to maximize the value of these data for Piping Plover conservation in the region.

Survival of Large Gulls Breeding in Eastern Newfoundland, Canada

Abstract. In response to human activity and ecosystem changes, large gulls in eastern North America have shown a variety of population trends over the last 100 years. Seven years of capture-mark-recapture data were analyzed for Herring (Larus argentatus) and Great Black-backed (L. marinus) gulls breeding in eastern Newfoundland, Canada to estimate apparent survival and survival rates. Estimated survival was 0.864 for Great Black-backed Gulls and 0.837 for Herring Gulls. For both species, the survival rate calculated using live and dead encounters was higher than the apparent survival rate calculated from resighting data only and added almost an additional year of expected life. While these values are in the range of survival rates reported from other studies along the eastern coast of North America, the values for Herring Gulls were lower than survival rates reported elsewhere in North America and Europe. The lower survival rates seen in eastern North American Herring Gulls may be attributable to characteristics of the migration and wintering habitat, including poorer habitat quality (i.e., highly developed and industrialized east coast) and possibly gull (Laridae) control programs.