Greg W. Mitchell

Timing of breeding carries over to influence migratory departure in a songbird: an automated radiotracking study.

1. Determining how events interact across stages of the annual cycle is critical for understanding the factors that affect individual fitness. However, there is currently little information detailing how breeding events influence migratory behaviour. 2. Using an automated digital telemetry array and an isolated island-breeding population of Savannah sparrows Passerculus sandwichensis, we provide the first direct evidence that the timing of breeding events carries over to influence the timing of migration in a songbird and assess for the first time how weather conditions on the breeding grounds also affect departure dates. 3. Date of migratory departure between September and October was strongly influenced by date of breeding completion in adults and fledging date in juveniles from June to July. 4. With respect to weather, adults departed during the first half of high-pressure systems, while juveniles departed throughout the entirety of high-pressure systems (including rainy evenings on the western edge of systems). 5. By combining both ecological and weather data, we could explain almost all variation in departure date for adults (95%), but weather conditions were not a good predictor of departure date for juveniles. 6. Our results provide strong evidence that the timing of breeding events is an important driver of migration timing and that exact departure dates are fine-tuned according to local weather conditions in adults, but not in juveniles.

The Motus Wildlife Tracking System: a collaborative research network to enhance the understanding of wildlife movement

We describe a new collaborative network, the Motus Wildlife Tracking System (Motus; https://motus.org), which is an international network of researchers using coordinated automated radio-telemetry arrays to study movements of small flying organisms including birds, bats, and insects, at local, regional, and hemispheric scales. Radio-telemetry has been a cornerstone of tracking studies for over 50 years, and because of current limitations of geographic positioning systems (GPS) and satellite transmitters, has remained the primary means to track movements of small animals with high temporal and spatial precision. Automated receivers, along with recent miniaturization and digital coding of tags, have further improved the utility of radio-telemetry by allowing many individuals to be tracked continuously and simultaneously across broad landscapes. Motus is novel among automated arrays in that collaborators employ a single radio frequency across receiving stations over a broad geographic scale, allowing individuals to be detected at sites maintained by others. Motus also coordinates, disseminates, and archives detections and associated metadata in a central repository. Combined with the ability to track many individuals simultaneously, Motus has expanded the scope and spatial scale of research questions that can be addressed using radio-telemetry from local to regional and even hemispheric scales. Since its inception in 2012, more than 9000 individuals of over 87 species of birds, bats, and insects have been tracked, resulting in more than 250 million detections. This rich and comprehensive dataset includes detections of individuals during all phases of the annual cycle (breeding, migration, and nonbreeding), and at a variety of spatial scales, resulting in novel insights into the movement behavior of small flying animals. The value of the Motus network will grow as spatial coverage of stations and number of partners and collaborators increases. With continued expansion and support, Motus can provide a framework for global collaboration, and a coordinated approach to solving some of the most complex problems in movement biology and ecology.

Early life events carry over to influence pre-migratory condition in a free-living songbird.

Conditions experienced during development can have long-term consequences for individual success. In migratory songbirds, the proximate mechanisms linking early life events and survival are not well understood because tracking individuals across stages of the annual cycle can be extremely challenging. In this paper, we first use a 13 year dataset to demonstrate a positive relationship between 1st year survival and nestling mass in migratory Savannah sparrows (Passerculus sandwichensis). We also use a brood manipulation experiment to show that nestlings from smaller broods have higher mass in the nest relative to individuals from larger broods. Having established these relationships, we then use three years of field data involving multiple captures of individuals throughout the pre-migratory period and a multi-level path model to examine the hypothesis that conditions during development limit survival during migration by affecting an individuals ability to accumulate sufficient lean tissue and fat mass prior to migration. We found a positive relationship between fat mass during the pre-migratory period (Sept–Oct) and nestling mass and a negative indirect relationship between pre-migratory fat mass and fledging date. Our results provide the first evidence that conditions during development limit survival during migration through their effect on fat stores. These results are particularly important given recent evidence showing that body condition of songbirds at fledging is affected by climate change and anthropogenic changes to landscape structure.

Multiscale Postfledging Habitat Associations of Juvenile Songbirds in a Managed Landscape

ABSTRACT. Habitat selection is a hierarchical process that proceeds from broad to fine spatial scales. Failure to account for spatial scale in studies of habitat selection may result in an incomplete understanding of key habitat characteristics. For juvenile songbirds, postfledging habitat may be important for migratory preparation and survival; however, there is currently little information regarding habitat associations during this period. We used radiotelemetry to investigate habitat associations at fine and broad spatial scales in juvenile Yellow-rumped Warblers (Dendroica coronata) and Blackpoll Warblers (D. striata) in a managed boreal forest in northwestern Newfoundland. At the local scale, both species were associated with locations characterized by dense vegetative cover, and Blackpoll Warblers were also associated with locations characterized by high amounts of coarse woody debris. At broader extents, Yellow-rumped Warblers were associated with patches situated downslope of their previous location, as well as patches surrounded by low amounts of clearcut land cover at the 115-m scale and patches with high foliage density during 2006. Unlike Yellow-rumped Warblers, Blackpoll Warblers were more likely to be observed in patches surrounded by high amounts of clearcut land cover at the 115-m scale and were sensitive to clearcut land cover at the 1,250-m scale. Our results demonstrate the importance of spatial scale in studies of habitat association; given interspecific differences in response to clearcut land cover, they also suggest that a general management strategy for songbirds with respect to clearcut land cover in the boreal forest may remain elusive.

Movement of Juvenile Songbirds in Harvested Boreal Forest: Assessing Residency Time and Landscape Connectivity

Little is known about juvenile songbird movement in response to timber harvest, particularly in the boreal forest. If clearcut land cover facilitates movement, the availability of resources may increase. However, if clearcut land cover impedes movement, important post-fledging resources may be rendered inaccessible. Using radio telemetry, we tested the hypothesis that regenerating clearcut land cover would affect the movement of recently independent Yellow-rumped Myrtle Warblers (Dendroica coronata coronata) and Blackpoll Warblers (Dendroica striata) differently than forested land cover owing to intrinsic differences in each land-cover type or in how they are perceived. We found that both species moved extensively before migration. We also found that Blackpoll Warblers were quick to exit local areas composed of clearcut land cover and that both species were quick to exit neighborhoods composed of large proportions of clearcut land cover. However, if individuals encountered clearcut land cover when exiting the neighborhood, movement rate was slowed. Effectively, residency time decreased in clearcut neighborhoods and landscape connectivity was impeded by clearcut land cover. Our results suggest that clearcut land cover may represent low-quality habitat for both species during the post-fledging period. Further research is needed to determine if changes in movement behavior associated with landscape structure affect individual condition and higher-level ecological processes. RESUME. On connait peu de choses en ce qui concerne le deplacement des jeunes passereaux suite a la recolte forestiere, particulierement en foret boreale. Dans le cas ou un parterre de coupe a blanc favorise les deplacements, l’accessibilite aux ressources peut augmenter. Toutefois, si le parterre de coupe a blanc nuit aux deplacements, des ressources importantes apres l’envol pourraient devenir inaccessibles. A l’aide de la radio-telemetrie, nous avons teste l’hypothese selon laquelle l’effet d’un parterre de coupe a blanc en regeneration est different de celui d’un couvert forestier sur le deplacement de Parulines a croupion jaune (Dendroica coronata coronata) et de Parulines rayees (Dendroica striata) ayant tout juste acquis leur independance, a cause des differences intrinseques relatives a chaque type de couvert ou de la perception qu’en ont les oiseaux. Nous avons trouve que les deux especes de paruline se deplacent considerablement avant la migration. Nous avons egalement constate que la Paruline rayee quittait rapidement les secteurs locaux constitues de parterres de coupe a blanc et que les deux especes quittaient rapidement les secteurs voisins qui comportaient une grande proportion de parterre de coupe a blanc. Cependant, si un individu atteignait un parterre de coupe a blanc au moment de quitter le voisinage, son taux de deplacement etait ralenti. Dans les faits, le temps de passage diminuait dans le voisinage des parterres de coupe a blanc et ces derniers reduisaient la connectivite du paysage. Nos resultats donnent a penser que les parterres de coupe a blanc representent des milieux de faible qualite pour les deux especes de paruline durant la periode qui suit l’envol. De plus amples recherches sont necessaires afin de determiner si les changements au plan du comportement en deplacement selon la structure du paysage ont un effet sur la condition de l’individu et sur les processus ecologiques generaux.

Experienced migratory songbirds do not display goal-ward orientation after release following a cross-continental displacement: an automated telemetry study

The ability to navigate implies that animals have the capability to compensate for geographical displacement and return to their initial goal or target. Although some species are capable of adjusting their direction after displacement, the environmental cues used to achieve this remain elusive. Two possible cues are geomagnetic parameters (magnetic map hypothesis) or atmospheric odour-forming gradients (olfactory map hypothesis). In this study, we examined both of these hypotheses by surgically deactivating either the magnetic or olfactory sensory systems in experienced white-throated sparrows (Zonotrichia albicollis) captured in southern Ontario, Canada, during spring migration. Treated, sham-treated, and intact birds were then displaced 2,200 km west to Saskatchewan, Canada. Tracking their initial post-displacement migration using an array of automated VHF receiving towers, we found no evidence in any of the groups for compensatory directional response towards their expected breeding grounds. Our results suggest that white-throated sparrows may fall back to a simple constant-vector orientation strategy instead of performing true navigation after they have been geographically displaced to an unfamiliar area during spring migration. Such a basic strategy may be more common than currently thought in experienced migratory birds and its occurrence could be determined by habitat preferences or range size.

Prevalence of Disjunct Roosting in Nesting Bank Swallows (Riparia riparia)

ABSTRACT Bank Swallows (Riparia riparia) congregate in large nocturnal roosts during the non-breeding season. Scant evidence suggests that Bank Swallows may also congregate regularly in nocturnal roosts during the breeding period. To help clarify the issue, we used automated radio-telemetry to document the roosting behavior of 11 males and 11 females that were tending nests with young at two nesting colonies. Nineteen of the 22 birds (86%) spent at least one night roosting away from the colony, and 13 of the 22 birds (59%) spent at least one night roosting likely within a large marsh located ~30 km away from the colonies. Females tended to roost overnight at the colony more than males. The proportion of nights birds spent roosting away from the colony was highly variable between individuals. Minimum flight speeds to an evening roost site (~30 km distant) were significantly greater than return flights back to the colony in the morning. Our study confirms that breeding Bank Swallows do in fact regularly roo...