Arctic avian predators synchronise their spring migration with the northern progression of snowmelt

Abstract

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 remains however unexplored. Birds migrating to the Arctic are expected to follow the spring snowmelt to optimise their arrival time and select for snow-free areas to maximise prey encounter en-route. Based on large-scale movement data, we compared the migration patterns of three top predator species of the tundra in relation to the spatio-temporal dynamics of snow cover. The snowy owl, an irruptive migrant, the rough-legged buzzard, with an intermediary migration pattern, and the peregrine falcon as a regular migrant, all followed, as expected, the spring snowmelt during their migrations. However, the owl stayed ahead, the buzzard stayed on, and the falcon stayed behind the spatio-temporal peak in snowmelt. Although none of the species avoided snow-covered areas, they presumably used snow presence as a cue to time their arrival at their breeding grounds. We show the importance of environmental cues for species with different migration patterns.

Nomadic breeders Snowy Owls (Bubo scandiacus) do not use stopovers to sample the summer environment

“…Stopovers on waterbodies that were still frozen may provide good visibility when scanning for prey and good camouflage against the still-white ice. Recent work showed that Snowy Owls closely followed the receding snow line (Curk et al 2020) and we suggest the presence of ice on lakes and oceans may be an attractive feature correlated with the timing of snowmelt that may persist on the landscape a few weeks after snow cover has disappeared.…”

“…Such tactics, however, may not apply to species such as Snowy Owls Bubo scandiacus, which do not have a fixed breeding site that is their destination. After reaching the breeding range, Snowy Owls must prospect, apparently nomadically, as they seek out appropriate areas with high food abundance on which to settle (Therrien et al 2014, Curk et al 2020. Hence, movements within the breeding range may be used primarily to prospect for lemming peaks, as Snowy Owls will only settle to breed in areas of high lemming abundance (Gauthier et al 2013, Therrien et al 2014, Robillard et al 2016.…”

“…The limited empirical data suggest that Snowy Owls do not migrate in groups, but many individuals seem to use similar migratory paths, following coastlines, river valleys and mountain ridgelines as they move from non-breeding areas to breeding areas (Holt et al 2020). Owls time their spring migration with the retreating snow line, moving on average just north of the snow line (Curk et al 2020). Therrien et al (2015) equipped nine breeding adult female Snowy Owls with satellite transmitters and found that stopovers during prebreeding movements in the breeding range occurred where snow depth was shallow.…”

Certainty and integration of options in animal movement

“…The spatiotemporal variation in the availability and depletion of energy has consequences resulting in, for example, the mass-movement tracking of resources [41,58,59] and thus animal migration (i.e., following a resource wave). As we begin to understand the value of energy as a single currency and its variation, social sampling should facilitate gradient-tracking across landscapes, including regional and seasonal gradient-tracking, that gives rise to a concerted energy wavenamely balancing and synchronising the tracking of good conditions for movement (such as winds, currents or substrates) with good conditions for foraging (such as green-up [60] or snow melt [61]) and safe conditions of refuge (away from predator activity), simultaneously.…”

Long-term population decline of a genetically homogenous continental-wide top Arctic predator

“…2018). Snowy Owls from the central regions of North America appear to follow similar and constant migration routes from breeding to winter areas (Curk et al 2020; K. L. Wiebe personal communication), and other studies concluded there was some site fidelity to wintering areas by Snowy Owls (Therrien et al . 2011, Robillard et al .…”