Many routes lead to Rome: potential causes for the multi‐route migration system of Red Knots, Calidris canutus islandica

Abstract

Abstract. Migrants, such as birds or representatives of other taxa, usually make use of several stopover sites to cover the distance between their site of origin and destination. Potentially, multiple routes exist, but often little is known about the causes and consequences of alternative migration routes. Apart from their geographical distribution, the suitability of potential sites might play an important role in the animals' decisions for a particular itinerary.We used an optimal-migration model to test three nonmutually exclusive hypotheses leading to variations in the spring migration routes of a subspecies of Red Knot, Calidris canutus islandica, which migrates from wintering grounds in Western Europe to breeding grounds in Greenland and the Canadian Arctic: the breeding location hypothesis, the energy budget hypothesis, and the predation risk hypothesis. Varying only breeding location, the model predicted that birds breeding in the Canadian Arctic and on West Greenland stop over on Iceland, whereas birds breeding in East and Northeast Greenland migrate via northern Norway, a prediction that is supported by empirical findings. Energy budgets on stopover sites had a strong influence on the choice of route and staging times. Varying foraging-intensity and mass-dependent predation risk prompted the birds to use less risky sites, if possible. The effect of simultaneous changes in the energy budget and predation risk strongly depended on the site where these occurred.Our findings provide potential explanations for the observations that C. canutus islandica uses a diverse array of migration routes. Scrutinizing the three alternative driving forces for the choice of migratory routes awaits further, specific data collection in rapidly developing fields of research (e.g., predation risk assessment, GPS tracking). Generally, the type of modeling presented here may not only highlight alternative explanations, but also direct follow-up empirical research.

Differential Annual Movement Patterns in a Migratory Species: Effects of Experience and Sexual Maturation

“…Evidence from other species has suggested the existence of distinct patterns of movement in terms of timing of migration [32], in the direction of the migratory movement [33], [34] or in the itinerary [35]. Although the presence of movement differences between juveniles and adults has been hypothesized [14], [15], [33], no clear evidence has so far been presented, and the results of the current study are therefore significant in demonstrating these differences in migratory behavior for the first time, using data from living individuals.…”

Migration of two calidrid sandpiper species on the predator landscape: how stopover time and hence migration speed vary with geographical proximity to danger

“…Most early work focused on time and energy aspects (Lindström and Alerstam 1992, Hedenström and Alerstam 1997). More recently, the influence of predation danger has attracted theoretical and empirical attention (Dierschke 1998, Dierschke 2003, Lank et al 2003, Ydenberg et al 2004, 2007 Schmaljohann and Dierschke 2005, Lind and Cresswell 2006, Pomeroy 2006, Ydenberg et al 2007, Bauer et al 2010). Here we explore how minimizing the probability of mortality affects decisions made by migrants in the course of passage at a single stopover site.…”

“…They do not explicitly consider seasonal changes in predation danger. Tactics that could be employed to reduce mortality include: migrating at times or along routes with reduced predator presence, even if the rate of migration is slowed; avoiding habitats or stopover sites with higher predation danger; increasing vigilance; and reducing the fuel load to decrease wing‐loading, thereby increasing escape performance (Alerstam and Lindström 1990, Burns and Ydenberg 2002, Ydenberg et al 2002, 2004, Lank et al 2003, Pomeroy 2006, Pomeroy et al 2006, Sansom et al 2009, Bauer et al 2010).…”

Food availability and flight routes for migratory birds: a GIS approach

“…We propose a new method to link non-spatial data about plant phenology with spatial open maps of vegetation and 3D visibility analysis as a starting point to deepen the knowledge of the bonds between migration and environment. The literature examination shows that the topic is extremely hot but very few studies have explored a complex approach like the one we followed in this work (Berthold, 2001;Bauer et al, 2010;Bairlein, 2008;Chevallier et al, 2010). We used open source tools for all the research process, from data analysis to editing (GRASS GIS (GRASS Development Team, 2008) The main goals of this study are:…”

“…Even if migration is increasingly studied, many factors that influence migratory flows and routes still remain unknown or poorly understood (Bairlein, 2003(Bairlein, , 2008. Different works studied migration paths and birds features taking into account various parameters (Chevallier et al, 2010;Vilkov, 2013;Bauer et al, 2010). The relation between migration paths and trophic availability en route is particularly difficult to study, since it is not so easy to model food availability on the terrain (Drent et al, 2006;Ma et al, 2005;Moore and Woodrey, 1999;Gyimóthy et al, 2011).…”