THE PUZZLE OF PARTIAL MIGRATION
Migration, including the seasonal movements of wildebeest around the Serengeti or the long-distance migration of swallows between Europe and Africa, has fascinated ecologists for centuries. However, it is increasingly apparent that many populations of mammals, birds, amphibians, fish, and even insects are composed of both migratory and sedentary individuals. Few studies have addressed the problem of how migratory and sedentary individuals persist in a single population; a problem first posed by David Lack in 1944. Theoretical models show that partial migration can evolve and be maintained if the two phenotypes are a product of a genetic polymorphism with equivalent fitness returns or are conditional strategies where the optimum outcome for an individual is dependent on their state. Our long-term study on American dippers provides compelling evidence for the latter. However, the primary drivers of individual variation in migratory tendency remain contentious and little is known about how anthropogenic change will influence migratory strategies and the population dynamics of partially migratory species over large geographical areas. Our current work on Black Oystercatchers in Alaska and BC uses a combination of satellite telemetry, stable isotope analysis, monitoring data and a range of modelling approaches to address this knowledge gap.
SELECTED PUBLICATIONS
Gillis EA, Green DJ, Middleton HA, and Morrissey CA. (2008). Life history correlates of alternative migratory strategies in American dippers. Ecology 89: 1687-1695.
Green DJ, Whitehorne IBJ, Middleton HA, Morrissey CA. (2015). Do American dippers obtain a survival benefit from altitudinal migration? PLoS ONE 10(4): e0125734.
Mackas RH, Green DJ, Whitehorne IBJ, Fairhurst EN, Middleton HA and Morrissey CA. (2010). Altitudinal migration in American dippers: do migrants produce higher quality offspring? Canadian Journal of Zoology 88:148-160.
FULL ANNUAL CYCLE APPROACHES TO THE STUDY OF MIGRATORY BIRDS
Populations of neotropical migrants are often argued to be limited by conditions on the wintering grounds that have direct effects on survival or carryover and influence performance later in the annual life-cycle. We have investigated how factors at every stage of the annual cycle influence the demography of yellow warblers and yellow-breasted chats that migrate between western Canada and Mexico. Our work challenges the prevalent view that carryover effects from the wintering grounds play an important role in the population dynamics of neotropical migrants. Instead, our work highlights the importance of conditions on the Pacific flyway during spring migration. Our current work on yellow warblers uses physiological assays to investigate the mechanistic basis for carryover effects from migration on reproduction, and spatially explicit survival models to estimate mortality rates at each stage of the annual cycle.
SELECTED PUBLICATIONS
Drake A, Rock CA, Quinlan SP, Martin M, Green DJ. (2014). Wind speed during migration influences the survival, timing of breeding, and productivity of a neotropical migrant, Setophaga petechia. PLoS ONE9: e97152.
Drake A, Rock C, Quinlan SP and Green DJ. (2013). Carry-over effects of winter habitat vary with age and sex in yellow warblers, Setophaga petechia. Journal of Avian Biology 44: 321-330.
Huang AC, Bishop CA, McKibbin R, Drake A and Green DJ. (2017). Wind conditions on migration influences the survival of a neotropical migrant, the western yellow-breasted chat (Icteria sirens auricles). BMC Ecology 17: 29.
Valdez-Juarez SO, Krebs EA, Drake AE and Green DJ. (2019). Assessing the effect of seasonal agriculture on the condition and winter survival of a migratory songbird in Mexico. Conservation Science and Practice 1: e19
DECLINING POPULATIONS – TESTING HYPOTHESES AND IDENTIFYING MANAGEMENT OPTIONS
The State of Canada’s Birds 2019 Report describes the changing health of Canada’s birds, highlighting the population declines of shorebirds, grassland bird and aerial insectivores and conservation concern for Canada’s seabirds. COSEWIC has assessed over 50 bird species or sub-species as being endangered, threatened or of conservation concern. In collaboration with Environment and Climate Change Canada, Ontario Ministry of Natural Resources and others, we have worked to evaluate hypotheses for population declines, assess the impact of habitat loss, conversion and fragmentation, and evaluate management options for a range of species at risk. We have found evidence that long-term changes in insect availability play a role in the population declines of an endangered nightjar (the eastern whip-poor-will), and demonstrated the importance of considering both directand indirect effects of predators when evaluating conservation strategies for an endangered seabird (Scripp’s murrelet). More recent work with UNAM Estación de Biología Chamela shows howthe conversion of forest to agriculture can have contrasting positive effects on the migratory bird community and negative effects on the resident bird community. We continue to conduct research that fills identified knowledge gaps for species at risk (including work with FLNROD, BC on northern goshawk), and investigate the role of land use change and species interactions as drivers of songbird community structure in the dry forests of Mexico.
SELECTED PUBLICATIONS
English PA, JJ Nocera, BA Pond and DJ Green. (2016). Habitat and food supply across multiple spatial scales influence the distribution and abundance of a nocturnal aerial insectivore. Landscape Ecology 32: 343-359.
Hindmarch S, Krebs EA, Elliott J and Green DJ. (2012). Land use predicts the persistence and distribution of barn owls in a rapidly changing agricultural landscape. Landscape and Urban Planning 107: 255-262.
Knight EC, Mahony NA and Green DJ. (2016). Effects of agricultural fragmentation on the bird community in sagebrush shrubsteppe. Agriculture, Ecosystems and the Environment 223: 278-288.
Thomsen SK and Green DJ. (2019). Predator-mediated effects of severe drought associated with poor reproductive success in a nocturnal seabird in a cross-ecosystem cascade. Global Change Biology 15: 1642-52.
TRACKING THE MOVEMENT OF BIRDS AT MULTIPLE SPATIAL SCALES
Advances in tracking technology have helped identify the migratory routes and wintering locations of long-distance migrants essential to understanding what factors drive population trends, collect fine-scale data on habitat use critical to delineating conservation areas, and monitor the survival of individuals during critical life history stages. We use a range of tracking devices and indirect methods to study the movement, habitat selection and survival of birds. Light sensitive geolocators were deployed to investigate the migratory strategies of whip-poor-will from four regions in Canada, gps satellite tags to assess whether the foraging habitat used by Cassin’s auklet fall within the boundaries of the Scott Islands Marine Wildlife Area, and miniature radiotelemetry tags were used to examine how reservoir operations influence juvenile survival of yellow warblers. We are currently tracking the seasonal movement and fine-scale habitat selection of black oystercatchers an important indicator of rocky intertidal community health in BC and Alaska.
SELECTED PUBLICATIONS
Domalik AD, Hipfner JM, Studholme KR, Crossin GT and Green DJ. (2018). At-sea distribution and fine-scale habitat use patterns of zooplanktivorous Cassin’s auklets during the chick-rearing period. Marine Biology 165: 177-191.
Hepp M, Ware LI, van Oort H, Beauchesne S, Cooper H and Green DJ. (2018). Postfledging survival and local recruitment of a riparian songbird in habitat influenced by reservoir operations. Avian Conservation and Ecology 13: 1
English PA, Mills AM, Cadman MD, Heagy AE, Rand GJ and Green DJ. (2018). Tracking the migration of a nocturnal aerial insectivore in the Americas. BMC Zoology 2: 5
