All routes are not created equal: An ungulate's choice of migration route can influence its survival

Abstract

1. Our knowledge of migration ecology has progressed quickly in concert with technological advances that collect fine-scale movement data through time. We now know that migration plays a critical role in the annual nutritional cycle of large herbivores and that sustaining functional migratory routes is key to long-term conservation. Yet, we lack basic information on whether one migratory route may function better than another, or more specifically, if choosing one route over another has fitness consequences -knowledge that could help inform conservation and restoration efforts.2. Here, we examined how a suite of migratory parameters influenced the survival of mule deer Odocoileus hemionus that shared a common winter range in New Mexico, USA, but migrated to various summer ranges in Colorado, USA. We used a Cox proportional hazard model and longitudinal global positioning system data collected over a 7-year period to investigate whether the mortality risk of 66 deer was affected by choice of migratory route, summer range, migration distance, speed or the number of administrative boundaries each route crossed.3. We found mule deer survival was not influenced by migratory distance, speed or number of administrative boundaries, but was strongly affected by the choice of migratory route and summer range. The magnitude of these effects was surprisingly large, doubling or tripling mortality risk. Cumulative survival rates showed that regardless of summer range, individuals migrating along high-use exterior routes had cumulative survival rates approximately 30% lower than individuals migrating along high-use interior routes. To our knowledge, this is the first direct evidence that a mammal's choice of migration route can influence its probability of survival. Synthesis and applications.Our finding that large herbivores may experience up to three times higher mortality risk by using a different migratory route reveals a novel link between migration and demography. Importantly, our results also suggest that spatially explicit model parameters and predictions could help in the conservation and restoration of migratory populations by identifying specific migratory routes or seasonal ranges that reduce survival.

Migrating curlews on schedule: departure and arrival patterns of a long-distance migrant depend on time and breeding location rather than on wind conditions

“…Migration is an essential part of the life cycle of a wide range of species, with potentially important consequences for their fitness [1][2][3][4][5]. Birds show the most extensive and far-ranging migrations [6][7][8].…”

“…[36]). (4) We hypothesized that birds breeding further from their wintering site at higher latitudes and more easterly longitudes would depart later to time their arrival at their Arctic and sub-Arctic breeding grounds according to snowmelt and the underlying availability of food resources [13][14][15]. In this context, we expected males to arrive at the wintering sites later than females, because, as for other shorebird species, females are known to desert their chicks earlier than males [37].…”

Releases of Asian houbara must respect genetic and geographic origin to preserve inherited migration behaviour: evidence from a translocation experiment

“…However, if newly expressed migration routes achieve lower survival [26] or productivity (e.g. through carry-over effects [27]) relative to established strategies, this may reduce population viability [28] and potentially result in catastrophic population losses [29]. Conservation and welfare considerations combine to require that experimental evidence in an adaptive management approach is sought to avoid the potential negative consequences of translocations.…”

Migrating Curlews on Schedule: Departure and Arrival Patterns of a Long-Distance Migrant Depend on Time Rather than on Wind Conditions

“…Migration is an essential part of the life cycle of a wide range of species, with potentially important consequences for their tness [1][2][3][4][5]. Birds show the most extensive and far-ranging migrations [6][7][8].…”

“…3We expected ight heights (as recorded by GPS tags) to increase during non-tailwind conditions to allow the birds to reach air layers with improved wind conditions [25][26]. (4) We hypothesized that birds breeding further from their wintering site would depart earlier because they needed more time for travelling. In this context, we expected males to arrive at the wintering sites later than female curlews, because, as for other shorebird species, females are known to desert their chicks earlier than males [27].…”