Junior A. Tremblay

Estimating updraft velocity components over large spatial scales: contrasting migration strategies of golden eagles and turkey vultures

Soaring birds migrate in massive numbers worldwide. These migrations are complex and dynamic phenomena, strongly influenced by meteorological conditions that produce thermal and orographic uplift as the birds traverse the landscape. Herein we report on how methods were developed to estimate the strength of thermal and orographic uplift using publicly available digital weather and topography datasets at continental scale. We apply these methods to contrast flight strategies of two morphologically similar but behaviourally different species: golden eagle, Aquila chrysaetos, and turkey vulture, Cathartes aura, during autumn migration across eastern North America tracked using GPS tags. We show that turkey vultures nearly exclusively used thermal lift, whereas golden eagles primarily use orographic lift during migration. It has not been shown previously that migration tracks are affected by species-specific specialisation to a particular uplift mode. The methods introduced herein to estimate uplift components and test for differences in weather use can be applied to study movement of any soaring species.

Testing an Emerging Paradigm in Migration Ecology Shows Surprising Differences in Efficiency between Flight Modes

To maximize fitness, flying animals should maximize flight speed while minimizing energetic expenditure. Soaring speeds of large-bodied birds are determined by flight routes and tradeoffs between minimizing time and energetic costs. Large raptors migrating in eastern North America predominantly glide between thermals that provide lift or soar along slopes or ridgelines using orographic lift (slope soaring). It is usually assumed that slope soaring is faster than thermal gliding because forward progress is constant compared to interrupted progress when birds pause to regain altitude in thermals. We tested this slope-soaring hypothesis using high-frequency GPS-GSM telemetry devices to track golden eagles during northbound migration. In contrast to expectations, flight speed was slower when slope soaring and eagles also were diverted from their migratory path, incurring possible energetic costs and reducing speed of progress towards a migratory endpoint. When gliding between thermals, eagles stayed on track and fast gliding speeds compensated for lack of progress during thermal soaring. When thermals were not available, eagles minimized migration time, not energy, by choosing energetically expensive slope soaring instead of waiting for thermals to develop. Sites suited to slope soaring include ridges preferred for wind-energy generation, thus avian risk of collision with wind turbines is associated with evolutionary trade-offs required to maximize fitness of time-minimizing migratory raptors.

Flight responses by a migratory soaring raptor to changing meteorological conditions.

Soaring birds that undertake long-distance migration should develop strategies to minimize the energetic costs of endurance flight. This is relevant because condition upon completion of migration has direct consequences for fecundity, fitness and thus, demography. Therefore, strong evolutionary pressures are expected for energy minimization tactics linked to weather and topography. Importantly, the minute-by-minute mechanisms birds use to subsidize migration in variable weather are largely unknown, in large part because of the technological limitations in studying detailed long-distance bird flight. Here, we show golden eagle (Aquila chrysaetos) migratory response to changing meteorological conditions as monitored by high-resolution telemetry. In contrast to expectations, responses to meteorological variability were stereotyped across the 10 individuals studied. Eagles reacted to increased wind speed by using more orographic lift and less thermal lift. Concomitantly, as use of thermals decreased, variation in flight speed and altitude also decreased. These results demonstrate how soaring migrant birds can minimize energetic expenditures, they show the context for avian decisions and choices of specific instantaneous flight mechanisms and they have important implications for design of bird-friendly wind energy.

Assessing risk to birds from industrial wind energy development via paired resource selection models.

When wildlife habitat overlaps with industrial development animals may be harmed. Because wildlife and people select resources to maximize biological fitness and economic return, respectively, we estimated risk, the probability of eagles encountering and being affected by turbines, by overlaying models of resource selection for each entity. This conceptual framework can be applied across multiple spatial scales to understand and mitigate impacts of industry on wildlife. We estimated risk to Golden Eagles (Aquila chrysaetos) from wind energy development in 3 topographically distinct regions of the central Appalachian Mountains of Pennsylvania (United States) based on models of resource selection of wind facilities (n = 43) and of northbound migrating eagles (n = 30). Risk to eagles from wind energy was greatest in the Ridge and Valley region; all 24 eagles that passed through that region used the highest risk landscapes at least once during low altitude flight. In contrast, only half of the birds that entered the Allegheny Plateau region used highest risk landscapes and none did in the Allegheny Mountains. Likewise, in the Allegheny Mountains, the majority of wind turbines (56%) were situated in poor eagle habitat; thus, risk to eagles is lower there than in the Ridge and Valley, where only 1% of turbines are in poor eagle habitat. Risk within individual facilities was extremely variable; on average, facilities had 11% (SD 23; range = 0-100%) of turbines in highest risk landscapes and 26% (SD 30; range = 0-85%) of turbines in the lowest risk landscapes. Our results provide a mechanism for relocating high-risk turbines, and they show the feasibility of this novel and highly adaptable framework for managing risk of harm to wildlife from industrial development.

Status, Biology, and Conservation Priorities for North America's Eastern Golden Eagle (Aquila chrysaetos) Population

TODD KATZNER,1,2,26 BRIAN W. SMITH,3 TRICIA A. MILLER,4,5 DAVID BRANDES,6 JEFF COOPER,7 MICHAEL LANZONE,5,8 DANIEL BRAUNING,9 CHRISTOPHER FARMER,10 SERGIO HARDING,11 DAVID E. KRAMAR,12 CRAIG KOPPIE,13 CHARLES MAISONNEUVE,14 MARK MARTELL,15 ELIZABETH K. MOJICA,16 CHARLIE TODD,17 JUNIOR A. TREMBLAY,18 MARIA WHEELER,19 DAVID F. BRINKER,20 TONY E. CHUBBS,21 ROLF GUBLER,22 KIERAN O’MALLEY,23 SCOTT MEHUS,24 BRADY PORTER,19 ROBERT P. BROOKS,4 BRYAN D. WATTS,16 AND KEITH L. BILDSTEIN25

Flight response of slope-soaring birds to seasonal variation in thermal generation

Animals respond to a variety of environmental cues, including weather conditions, when migrating. Understanding the relationship between weather and migration behaviour is vital to assessing time- and energy limitations of soaring birds. Different soaring modes have different efficiencies, are dependent upon different types of subsidized lift and are weather dependent. We collected GPS locations from 47 known-age golden eagles that moved along 83 migration tracks. We paired each location with weather to determine meteorological correlates of migration during spring and fall as birds crossed three distinct ecoregions in north-east North America. Golden eagle migration was associated with weather conditions that promoted thermal development, regardless of season, ecoregion or age. Eagle migration showed age- and season-specific responses to weather conditions that promoted orographic lift.

Habitat Requirements of Breeding Black-Backed Woodpeckers ( Picoides arcticus ) in Managed, Unburned Boreal Forest

We investigated home-range characteristics and habitat selection by Black-backed Woodpeckers (Picoides arcticus) in an unburned, boreal forest landscape managed by mosaic harvesting in Quebec, Canada. Habitat selection by this species was specifically examined to determine home-range establishment and foraging activities. We hypothesized that Black-backed Woodpeckers would respond to harvesting by adjusting their home-range size as a function of the amount of dead wood available. Twenty-two birds were tracked using radiotelemetry, and reliable estimates of home-range size were obtained for seven breeding individuals (six males and one female). The average home-range size was 151.5 +/- 18.8 ha (range: 100.4-256.4 ha). Our results indicate that this species establishes home ranges in areas where both open and forested habitats are available. However, during foraging activities, individuals preferentially selected areas dominated by old coniferous stands. The study also showed that the spatial distribution of preferred foraging habitat patches influenced space use, with home-range area increasing with the median distance between old coniferous habitat patches available within the landscape. Finally, these data show that Black-backed Woodpeckers may successfully breed in an unburned forest with at least 35m3 • ha-1 of dead wood, of which 42% (15m3• ha-1) is represented by dead wood at the early decay stage. Nous avons etudie les caracteristiques du domaine vital et la selection de l’habitat chez le Pic a dos noir (Picoides arcticus) en foret boreale non brulee et amenagee par coupes en mosaique, au Quebec (Canada). La selection de l’habitat a ete tout particulierement examinee afin de determiner le domaine vital et les activites liees a l’alimentation chez cette espece. Nous avons emis l’hypothese selon laquelle le Pic a dos noir reagirait a la recolte de bois en modifiant la taille de son domaine vital selon la quantite de bois mort accessible. Vingt-deux oiseaux ont ete suivis a l’aide de la telemetrie et des estimations fiables de la taille du domaine vital ont ete obtenues pour sept individus nicheurs (six mâles et une femelle). La taille moyenne du domaine vital a ete evaluee a 151,5 ± 18,8 ha (etendue : 100,4–256,4 ha). Nos resultats indiquent que cette espece etablit son domaine vital la ou des milieux ouverts et des milieux forestiers sont accessibles. Toutefois, au moment de s’alimenter, les individus selectionnent preferablement les endroits ou dominent les peuplements de vieux coniferes. Les travaux ont egalement montre que la repartition spatiale des ilots d’habitat preferes pour l’alimentation du pic influence l’utilisation de l’espace : la taille du domaine vital augmente en fonction de la distance mediane entre les ilots de vieux coniferes accessibles dans le paysage. Enfin, les resultats indiquent que le Pic a dos noir peut nicher avec succes en foret non brulee s’il y a un volume de bois mort d’au moins 35 m3 • ha-1, dont 42 % (15 m3 • ha-1) est en debut de decomposition.

Known Breeding Distribution and Abundance of Golden Eagles in Eastern North America

Abstract Aquila chrysaetos (Golden Eagle) breeds in both eastern and western North America. However, the former population has received much less attention than the latter. The purpose of this paper is to document the known distribution and abundance of eastern Golden Eagles within their breeding range and to identify gaps in knowledge for future studies. Eastern Golden Eagles breed in Labrador, Québec, and Ontario, Canada. The species has been extirpated as a breeder from the eastern US. In 2013, 187 Golden Eagle territorial pairs were documented in eastern Canada. Most territorial pairs occur in Québec (65.8%) and Labrador (26.7%). However, probably less than 16% of the total area of these regions has been surveyed. Based on the number of pairs observed and the proportion of area surveyed, we estimate that the total number of territorial pairs of eastern Golden Eagles to be ∼1236. The large area of unsurveyed landscapes and the corresponding lack of precision of the estimate highlight an important next step for future research.

Breeding Status and Population Trends of Golden Eagles in Northeastern Québec, Canada

In North America, it is hypothesized that the Golden Eagle’s (Aquila chrysaetos) eastern population declined during the period 1946-1973 because of organochlorine pesticides and other anthropogenic causes of mortality. Since 1970, upward trends for the species have been observed at most eastern hawkwatches. To determine whether such positive trends can be observed on breeding grounds, Golden Eagle counts were performed to monitor nesting territory occupancy between 1994 and 2007 in the Moisie and Sainte-Marguerite River valleys, northeastern Quebec. Aerial surveys were conducted during seven of the 14 years. During this period, the number of known nesting territories in the study area increased from 10 to 20, while the number of pairs rose from six to 14. The increase is attributed mostly to investigators’ improved experience in finding nests and to their greater familiarity with the study area, and possibly to the growth of the regional population. Occupancy of nesting territories by pairs was very stable over the years. Annual mean % of laying pairs (or laying rate) was 48.0 (SD = 19.9), and productivity (mean number of fledglings per pair) was 0.49 (SD = 0.35). RESUME. En Amerique du Nord, on a souleve l’hypothese voulant que les pesticides organochlores et d’autres causes de mortalite d’origine anthropique aient ete responsables de la diminution de la population de l’Est de l’Aigle royal (Aquila chrysaetos) au cours de la periode de 1946 a 1973. Depuis 1970, des tendances a la hausse ont ete observees chez cette espece a la plupart des observatoires d’oiseaux de proie dans l’Est. Afin de determiner si ces tendances a la hausse se refletaient sur les lieux de reproduction, des denombrements d’Aigles royaux ont ete realises pour suivre l’occupation des territoires de nidification de 1994 a 2007 dans les vallees des rivieres Moisie et Sainte-Marguerite, dans le nord-est du Quebec. Des denombrements aeriens ont ete effectues au cours de 7 des 14 annees du suivi. Durant cette periode, le nombre de territoires de nidification connus dans l’aire d’etude a augmente de 10 a 20, tandis que le nombre de couples est passe de 6 a 14. La hausse s’explique principalement par l’experience accrue des observateurs a decouvrir les nids et leur plus grande familiarite avec l’aire d’etude, et peut-etre par la croissance de la population regionale. L’occupation des territoires de nidification par des couples a ete tres stable au cours des annees. Le pourcentage annuel moyen de couples pondeurs (ou taux de ponte) s’elevait a 48,0 (ecart type = 19,9) et la productivite (nombre moyen de jeunes a l’envol par couple) etait de 0,49 (ecart type = 0,35).

Influence of Old Coniferous Habitat on Nestling Growth of Black-Backed Woodpeckers Picoides arcticus

Abstract. Nest success is often used to evaluate the impact of environmental stressors on species, but nestling growth may also be indicative of subtle consequences on individual fitness. We monitored Black-backed Woodpecker Picoides arcticus nestling growth in unburned boreal forests under the influence of commercial logging. The objectives of our exploratory study were to estimate growth rate constants of weight and three morphometric measures (culmen length, tarsal length and wing length) in nestling Black-backed Woodpeckers and to determine how the amount of old coniferous habitat in home ranges may affect these rates. The amount of old coniferous habitat positively influenced weight gain in Black-backed Woodpecker nestlings but did not influence the three morphometric measures of growth rate. Our results suggest that Black-backed Woodpecker fitness may be affected by the reduction of old coniferous habitat in managed forest landscapes. We encourage further studies on the relationship between habitat quality and nestling growth as a potentially useful indicator of how habitat loss might influence individual fitness in these species.