Jean‐François Therrien

• Ph.D.
• Senior Researcher at Hawk Mountain Sanctuary

Measuring survival in a declining species provides the foundation for continued research, demographic modeling, and informed conservation strategies. Although American Kestrel (Falco sparverius) populations have continued to decline since the 1970s, little is known about their survival throughout the full annual cycle, making it difficult to identi...

The global population and status of Snowy Owls Bubo scandiacus are particularly challenging to assess because individuals are irruptive and nomadic, and the breeding range is restricted to the remote circumpolar Arctic tundra. The International Union for Conservation of Nature (IUCN) uplisted the Snowy Owl to “Vulnerable” in 2017 because the sugges...

Bird populations within the same species may follow different migratory strategies and phenology depending on their breeding location and latitude, and migratory strategies may be influenced by important stopover sites. Understanding these strategies and identifying important stopover sites is crucial for the conservation of species with regionally...

Context In a conservation context, identifying key habitats suitable for reproduction, foraging, or survival is a useful tool, yet challenging for species with large geographic distributions and/or living in remote regions. Objectives The objective of this study is to identify selected habitats at multiple levels and scales of the threatened easte...

Urbanization increasingly causes alterations in prey diversity and abundance, land cover, and human disturbance, subsequently impacting populations of even the most adaptable species. American Kestrels are currently considered urban adapters, which may be veiling the influence of urbanization on their continental population decline. We quantified o...

Migratory raptors can fuel their journeys by feeding along the way. To maximize migration success, raptors are suspected to time their movements with the availability of their prey. Feeding rates can vary among species depending on migration distance (long vs. short distance), flight strategies (flapping vs. soaring), and within species according t...

The demography of, and factors that influence these metrics, are largely unknown for most vultures in the Americas. Survivorship of Turkey Vultures (Cathartes aura) may be influenced by landscape heterogeneity and human disturbance. We quantified the effects of landscape composition (Shannon's diversity index) and configuration (contagion, edge den...

Ongoing climate change can affect migration phenology in a variety of species. We assessed autumn migration phenology of Northern Saw-whet Owls (Aegolius acadicus) using 25 years of banding data from 7 sites throughout eastern North America. Using a linear mixed model, we found a significant trend toward a later passage for the median passage date....

The American Kestrel (Falco sparverius) has been steadily declining throughout most of its eastern North American range, and the cause of this decline is still relatively unknown. As a cavity nesting species, the American Kestrel often competes with other cavity nesters such as the invasive and abundant European Starling (Sturnus vulgaris) over nes...

Reproduction of long-distance migrants can be affected by local conditions on the breeding grounds as well as those encountered during the nonbreeding season through carry-over effects. We show that this is true in Long-tailed Jaegers (Stercorarius longicaudus) because individuals that spent less time flying at sea during winter had a high breeding...

Gut microbiota are increasingly recognized as important drivers of host health and fitness across vertebrate taxa. Given that gut microbial composition is directly influenced by the environment, gut microbiota may also serve as an eco‐physiological mechanism connecting host ecology, such as diet, and physiology. Although gut microbiota have been we...

Diet is an important component of life history that can vary with, and ultimately determine, individual variation in phenotypically plastic traits. American Kestrels (Falco sparverius) generally have low post-fledging survival rates, which suggests a need to better understand what ecological factors, such as diet, influence nestling maturity. The g...

Genetic analysis can provide valuable information for conservation programs by unraveling the demographic trajectory of populations, by estimating effective population size, or by inferring genetic differentiation between populations. Here, we investigated the genetic differentiation within the Snowy Owl (Bubo scandiacus) in North America, a specie...

Feet and talons are the most specialized predatory attributes of raptor morphology. As such, the hindlimb morphology of owls should reflect their dietary specialization. Owls' diet varies widely between species with only a subset of owl species preying predominantly on small mammals. We hypothesize that different owl species have varied hindlimb mo...

Seasonal migrants transport energy, nutrients, contaminants, parasites and diseases, while also connecting distant food webs between communities and ecosystems, which contributes to structuring meta-communities and meta-ecosystems. However, we currently lack a framework to characterize the structure of the spatial connections maintained by all migr...

The demography of, and factors that influence these metrics, are largely unknown for most vultures in the Americas. Survivorship of Turkey Vultures (Cathartes aura) may be influenced by landscape heterogeneity and human disturbance. We quantified the effects of landscape composition (Shannon's diversity index) and configuration (contagion, edge den...

In long‐lived seabirds, social monogamy and mate and site fidelity are common due to the cost entailed by site change and divorce such as delayed laying or reduced reproductive success. We used thirteen years of monitoring data from marked Long‐tailed Jaegers Stercorarius longicaudus in the Canadian High Arctic to quantify the degree of mate and si...

Raptors are of global conservation concern and thus country-level assessments of their status are needed. We review studies and conservation databases to determine priorities for raptor conservation within the USA and Canada. We specifically examine databases compiled by the International Union for the Conservation of Nature (IUCN), BirdLife Intern...

Interannual consistency (an indicator of the strength of adjustments) in migration phenology of Golden Eagles (Aquila chrysaetos) in North America is most strongly associated with breeding region, the season and with late season temperature on breeding and wintering grounds. Consistency was greatest in boreal spring migration and the breeding regio...

Genetic analysis can provide valuable information for conservation programs by unraveling the demographic trajectory of populations, by estimating effective population size, or by inferring genetic differentiation between populations. Here, we investigated the genetic differentiation within the Snowy Owl ( Bubo scandiacus ), a species identified as...

Human‐dominated environments often include ecological traps for wildlife, such as airports that may be perceived as suitable habitat by grassland birds but reduce fitness because of collisions with aircraft. Birds of prey are often attracted to airports where collisions with aircraft (i.e., bird strikes) are usually fatal for the birds and are a si...

Winter irruption refers to an unpredictable increase in the number of individuals usually dominated by one age class, either juvenile or adult, into a given area as a response to fluctuations in the food supply. Irruptions are well documented for avian predators breeding in the Arctic and Subarctic regions whereby individuals irrupt into irregular...

Highly mobile predators can show strong numerical responses to pulsed resources, sometimes resulting in irruptions where large numbers of young invade landscapes at a continental scale. High production of young in irruption years may have a strong influence on the population dynamics unless immature survival is reduced compared to non-irruption yea...

The examination of raptor pellets can be used to evaluate Arctic biodiversity. We found the remains of Meadow Vole (Microtus pennsylvanicus) and Ungava Collared Lemming (Dicrostonyx hudsonius) in pellets from Snowy Owl (Bubo scandiacus) nesting in the northern part of the Ungava Peninsula. We differentiated the two species by visual identification...

Long-distance migratory seabirds need to adjust their migration strategy according to internal (breeding, molting) and external factors (seasonality, resource availability). Time-minimizing strategies are common during spring migration to arrive at the optimal time to breed. We studied the annual movements and migration strategy of the long-tailed...

Most raptor populations are declining and nearly a fifth are threatened with extinction; thus there is a need to increase collaboration to ensure efficient and effective research, management, and conservation. Here, we introduce the Global Raptor Impact Network (GRIN; www.globalraptors.org), a tool to enhance collaboration and conservation impact o...

Flying over the open sea is energetically costly for terrestrial birds. Despite this, over-water journeys of many birds, sometimes hundreds of kilometres long, are uncovered by bio-logging technology. To understand how these birds afford their flights over the open sea, we investigated the role of atmospheric conditions, specifically wind and uplif...

The current and rapid anthropogenic environmental changes could disproportionately impact ecosystems, particularly when they affect species with critical roles in ecosystem integrity. As top predators, raptors provide critical top-down ecosystem services and structure food webs. Yet, many avian predators are currently experiencing global population...

Due to the low detectability of Northern Saw-whet Owls (Aegolius acadicus; hereafter, NSWO) throughout their annual cycle, standardized monitoring during migration allows for population assessments over time. We assessed age-class population trends in NSWO throughout eastern North America using banding data from 7 sites over a 25 year period. Using...

Identifying population genetic structure is useful for inferring evolutionary process and comparing the resulting structure with subspecies boundaries can aid in species management. The American Kestrel (Falco sparverius) is a widespread and highly diverse species with 17 total subspecies, only 2 of which are found north of U.S./Mexico border (F. s...

Migrating animals occur along a continuum from species that spend the nonbreeding season at a fixed location to species that are nomadic during the nonbreeding season, essentially continuously moving. Such variation is likely driven by the economics of territoriality or heterogeneity in the environment. The Snowy Owl (Bubo scandiacus) is known for...

Whereas most migratory animals, such as many birds of prey, return to the same breeding area each summer, nomadic breeders search over large distances to locate breeding areas that vary greatly in location from year to year. Nomadic breeders are assumed to extensively sample patch quality before selecting a summer settlement site (e.g. breeding sit...

Demographic differences between stable and declining populations can lend insight into drivers of population decline. The American Kestrel (Falco sparverius) is a widespread and often‐studied falcon, yet its demography is poorly understood and causes of observed population declines across much of North America remain unknown. Using integrated popul...

Although many studies have documented the developmental trajectory of somatic traits in birds, few measure physiological traits, and even fewer document individual variation in developmental trajectory across ecological context. Hematological traits underlying aerobic capacity can be predictive of nestling survival, fledgling flight ability, and ul...

The Arctic is entering a new ecological state, with alarming consequences for humanity. Animal-borne sensors offer a window into these changes. Although substantial animal tracking data from the Arctic and subarctic exist, most are difficult to discover and access. Here, we present the new Arctic Animal Movement Archive (AAMA), a growing collection...

Ecological “big data” Human activities are rapidly altering the natural world. Nowhere is this more evident, perhaps, than in the Arctic, yet this region remains one of the most remote and difficult to study. Researchers have increasingly relied on animal tracking data in these regions to understand individual species' responses, but if we want to...

Coupling isotope values of feathers and satellite tracking of individuals have the potential to reveal multi-season linkages between wintering habitat, diet and carry-over effects on reproductive parameters in migrating birds. Snowy owls Bubo scandiacus have multiple wintering tactics as they can use both terrestrial and marine resources during the...

Interspecific competition can play a key role in structuring ecological communities. The Arctic tundra is a low productivity ecosystem supporting simple food webs, but several predators often feed on the same prey species, lemmings, known for their large‐amplitude population fluctuations. We examined mechanisms involved in reducing intra‐guild comp...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The open sea is considered an ecological barrier to terrestrial bird movement. However, over-water journeys of many terrestrial birds, sometimes hundreds of kilometers long, are being uncovered by bio-logging technology. To understand how these birds afford their flights over the open sea, we investigated the role of atmospheric conditions in subsi...

Background Animals need adaptive strategies to cope with seasonal changes in prey availability to survive and reproduce, which can include migrating, prey-switching, or reducing metabolic needs. Human settlements can disrupt spatiotemporal patterning in resource availability, which can affect animals’ foraging success, particularly for juveniles wh...

Migratory species display a range of migration patterns between irruptive (facultative) to regular (obligate), as a response to different predictability of resources. In the Arctic, snow directly influences resource availability. The causes and consequences of different migration patterns of migratory species as a response to the snow conditions re...

Predator–prey interactions can control population fluctuations of several terrestrial vertebrates and energy fluxes in food webs. Quantifying these interactions typically requires the number of prey consumed by predators to be known, but prey size is often ignored. We hypothesized that rodent mandibles, which are routinely found in predatory bird p...

This study aimed to establish a reliable method based on morphometrics to sex Long-tailed Jaeger (Stercorarius longicaudus), a species with slight differences in body size between sexes but no plumage differences. The presence of assortative mating based on size was also examined to determine if within-pair differences in size could improve sexing....

Migration is used in birds as a strategy to maximize survival and fitness by avoiding seasonal depletion of resources. Migration behaviour can be very plastic among season and populations, calibrating schedule and routes to various environmental changes in order to reduce trade-off between survival and reproduction. Yet quantifying such plasticity...

Annual movements have been widely described for birds migrating across the Americas and between Eurasia and Africa, yet relatively little information exists for intra-African migrants. Identifying the areas used throughout a species annual cycle by understanding migratory patterns and settlement areas during breeding and non-breeding seasons is ess...

Summary of annual movement data obtained from the 13 adult Black Harriers marked with GPS-GSM or PTT tracker devices and followed in south-western South Africa during the 2008–2016 period. (DOCX)

More detailed summary data for the identified breeding and non-breeding settlement areas used by the 13 adult Black Harriers marked with GPS-GSM or PTT tracker devices followed in south-western South Africa during the 2008–2016 period. (DOCX)

Animal movement varies according to individual and environmental factors, creating variation among seasons and years. Changes in the environment represent a global test of how individuals can alter their movement patterns. In partial migrants, some populations are considered resident (i.e., overwintering on their breeding ground) or migratory (i.e....

Patterns of winter irruptions in several owl species apparently follow the “lack of food” hypothesis, which predicts that individuals leave their breeding grounds in search of food when prey populations do not allow breeding and are too low to ensure survival. Recent analyses however suggest an alternative mechanism dubbed the “breeding success” hy...

Many American kestrel (Falco sparverius) populations are declining across North America. Potential causes include mortality from reduction in food availability, a changing climate, habitat degradation, an increase in avian predators, disease, and toxins. We analyzed American kestrel count and banding data from seven raptor migration sites throughou...

Migratory species can exploit many habitats over vast geographic areas and adopt various patterns of space and habitat use throughout their annual cycle. In nomadic species, determinants of habitat use during the non-breeding season are poorly known due to the unpredictability of their movement patterns. Here, we analysed variability in wintering s...

Winter irruptions, defined as irregular massive movement of individuals over large distances, have been linked to food supply. Two hypotheses have been put forward: the “lack-of-food” suggests that a shortage of food forces individuals to leave their regular winter range and the “breeding output” suggests that unusually large food supplies during t...

Populations of “urban” raptors are increasing globally. Trained falcons are now being flown in city golf courses to scare off geese in hopes of reducing accumulated droppings along the fairways. In both the Old World and New, tens of thousands of vultures rummage through urban garbage dumps in search of humans’ leftovers. In Spain, lesser kestrels...

The Snowy Owl (Bubo scandiacus) is a circumpolar raptor that nests in Arctic tundra. Satellite tracking of nesting Snowy Owls in Alaska and eastern Canada has allowed researchers to document the widely nomadic movements of these owls between summer and winter ranges. This study expands that knowledge for Snowy Owls in the western Canadian Arctic. B...

Climate change can affect the distribution, abundance, and phenology of organisms globally. Variations in the timing of passage during autumn and spring migration can have consequences at individual and population levels. We assessed whether global climatic indexes and increasing air temperature over a 28 yr period were concurrent with shifts in th...

Global change can affect several aspects of bird biology, including population size and migration timing. We used count data collected during 25 years (1990-2014) at Hawk Mountain Sanctuary, a raptor migration watch-site in eastern Pennsylvania, to investigate population changes in Ruby-throated Hummingbirds (Archilochus colubris) and the timing of...

Increase in temperature and precipitation associated with climate change may enhance the risk of destruction by geomorphological processes of nests or dens used by Arctic wildlife. We assessed nest vulnerability to mass movements and identified environmental factors associated with the persistence of nesting structures of rough-legged hawks (Buteo...

Bubo scandiacus (Snowy Owl) is an irregular winter visitor in the northeastern US and southeastern Canada, where winter irruptions occur roughly every 4 years with varying intensity. The consecutive winters of 2013-2014 and 2014-2015 saw unusually large irruptions of Snowy Owls across eastern North American states and provinces and the Great Lakes...

The snowy owl is an elusive arctic predator known for its nomadic behaviour. Satellite tracking has revealed that some adult snowy owls could make an extensive use of the marine environment during the non-breeding season. However, the relative contribution of marine resources to their diet is unknown. Stable isotope analyses can be useful to docume...

Migratory raptors play a key role in the tundra ecosystem and contribute to the regulation of small mammal populations. Changes in their abundance or distribution could have important consequences on the tundra food web but the monitoring of these species is often hindered because of their low density and long-distance movements. Technological adva...

Both wing size and wing shape affect the flight abilities of birds. Intra and inter-specific studies have revealed a pattern where high aspect ratio and low wing loading favour migratory behaviour. This, however, have not been studied in soaring migrants. We assessed the relationship between the wing size and shape and the characteristics of the mi...

Physical characteristics of nest sites are thought to influence their use by birds and the outcome of breeding attempts. The presence of preexisting nesting structures can also be an important factor influencing reuse patterns and reproductive success. We examined the relationships between nest-site physical characteristics, patterns of nest reuse,...

Irruptive migration is mostly observed in species specialized on pulsed resources and is thought to be a response to unpredictable changes in food supply. We assessed two alternative hypotheses to explain the periodic winter irruptions of snowy owls Bubo scandiacus every 3-5 years in temperate North America: (a) the lack-of-food hypothesis, which s...

Tracking individual animals using satellite telemetry has improved our understanding of animal movements considerably. Nonetheless, thorough statistical treatment of Argos datasets is often jeopardized by their coarse temporal resolution. State-space modelling can circumvent some of the inherent limitations of Argos datasets, such as the limited te...

Under varying prey abundance, generalist consumers should be less affected than specialists due to their more diverse diet. Nonetheless, when prey availability declines, interspecific competition among consumers should increase and could lead to increased intraguild predation. We examined these potential effects in a generalist predator of the tund...

Nous avons étudié l’écologie estivale du harfang des neiges à l’île Bylot, au Nunavut, pendant plus de 20 ans. Nous avons examiné l’influence de la phénologie de la fonte de la neige au printemps et de la densité de lemmings sur le nombre de nids, la date et la taille moyenne de ponte ainsi que le succès de nidification des harfangs. Nous avons éga...

Permafrost thawing and increase in precipitation due to climate warming may augment the vulnerability of nesting structures to slope processes related hazards resulting in habitat loss for arctic-breeding birds. It is therefore important to better understand how environmental factors influence nesting structures stability as well as nest use and re...

Carry-over effects, which occur when events or processes in one season influence the success of an individual in the following seasons, could strongly influence arctic wildlife. However, those effects are not easy to quantify, especially in migratory birds, because it is difficult to follow them during the non-breeding season. Among arctic-nesting...

Mobility and irruptive movements have been proposed as mechanisms that could allow some diet specialists to inhabit and breed in environments with highly unpredictable resources, like the arctic tundra. The snowy owl, one of the main avian predators of the tundra, is known to specialize on lemmings during the breeding season. These small mammals ar...

Predation has been suggested to be especially important in simple food webs and less productive ecosystems such as the arctic tundra, but very few data are available to evaluate this hypothesis. We examined the hypothesis that avian predators could drive the population dynamics of two cyclic lemming species in the Canadian Arctic. A dense and diver...

Allochthonous input of resources (i.e., originating from a place other than where they are found) can have a significant impact on food availability for consumers. We assessed the impact of an allochthonous source of food (the sewage outfall stream of a military base) on an avian predator breeding in a low-productivity, high-arctic site (Alert, 83°...

A dense and diverse suite of predatory birds such as Long-tailed Jaegers inhabits the Arctic tundra and preys on lemmings during the snow-free period. We evaluated the predation pressure exerted by these predators by combining their numerical and functional responses to variations in lemming densities over a seven-year period. We showed that predat...

Satellite telemetry can provide valuable information on spatial ecology of animals, especially in species inhabiting remote areas such as the Arctic. However, caution is always needed when selecting transmitter size and attachment methods because of the potential negative impact of the device itself on individuals. We determined survival and reprod...

In most northern temperate regions diurnal birds of prey, or raptors, migrate seasonally between their breeding and wintering grounds. Although their populations can be logistically difficult to survey and monitor because the birds are largely secretive and wide-ranging, most raptors are obligate or facultative soaring migrants that congregate alon...

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem...

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem...

It is increasingly recognized that ecosystems are not closed systems and that exchanges of resources across ecosystem boundaries can have repercussions on food webs, especially in low productivity systems such as the terrestrial Arctic. However, because these exchanges can take multiple forms, assessing their significance in the functioning of the...