Sex-Specific Spatiotemporal Variation and Carry-Over Effects in a Migratory Alpine Songbird

Abstract

For migratory animals, events at one stage of the annual cycle can produce constraints or benefits that carry over to subsequent stages. Differing life-history strategies among individuals can influence the expression of these carry-over effects, leading to pronounced within-population variation in migration. For example, reproductive roles can drive spatiotemporal segregation during the non-breeding season and promote sex-specific carry-over effects, such as reproductive effort affecting autumn migration behavior. For an alpine breeding population of horned larks Eremophila alpestris in northern British Columbia, Canada, we addressed sex-specific variation in migration behavior and carry-over effects during both autumn and spring migration using light-level geolocators. Males spent more time farther north and arrived an average of 6 days earlier at the breeding site in spring. Females delayed autumn departure following greater reproductive effort, in turn demonstrating flexible migration behavior by increasing migration speed and decreasing stopover use. Males maintained autumn migration behavior regardless of reproductive effort or departure date. Finally, both sexes used staging areas in spring (average stopover = 41 days), with consequences for breeding success. Individuals that used staging areas during spring migration exhibited greater nest success and produced 1.8 more fledglings on average than those that migrated directly from their winter site. Consistent use of staging areas may allow individuals to monitor environmental conditions and optimize their breeding arrival date to acquire high-quality territories while avoiding the cost of arriving too early in a harsh alpine habitat. Overall, our results indicate: (1) sex-specific flexibility in migration strategies that carry-over to and from the reproductive period, and (2) spring staging areas may be a critical component of the annual life-cycle for alpine breeding larks. These behaviors may be particularly important for alpine and arctic birds because the stochastic nature of their breeding habitat likely selects for flexible responses to prevailing conditions.

Reduced Breeding Success Suggests Trophic Mismatch Despite Timely Arrival in an Alpine Songbird

“…It has been suggested that these longer stopovers after the Sahara crossing are used to assess the environmental conditions in Europe and could therefore be used to buffer interannual variation in the timing of spring. Similar patterns were found in migratory Horned larks (Eremophila alpestris) that performed long stopovers before reaching their high elevation breeding grounds 20 . In addition to a general adjustment in the arrival time, wheatears can adjust the arrival-breeding interval according to their arrival dates and spring progression 34 , strongly suggesting that, to some extent, wheatears are able to match their migration and breeding activities with local conditions and seasonally limited resources 37 .…”

“…3.500 km). However, the high-elevation breeding sites are, to some extent, comparable with those of the more northerly breeding populations; alpine breeding grounds are characterised by strong seasonal climate and food resources, and the duration of snow cover and the short season limits the reproductive period and requires accurate timing of life-history events 19,20 . The similarity is also re ected in life-history traits, such as a single clutch per year, of the wheatear subpopulations (leucorhoa) and the southern Alpine populations 13,16 .…”

“…The generally shorter migratory distances of Alpine breeding birds and the higher potential to adjust the timing in synchrony with lower trophic levels may reduce the risk of trophic mismatches. Alpine breeding individuals may have always arrived in advance or stayed at nearby stopovers to monitor environmental conditions and occupy their breeding sites as soon as conditions permit 20 , thereby buffering effects of recent earlier springs in the Alps.…”

Complex Seasonal and Day-to-day Movements of an Alpine Passerine May Act as an Insurance Against Environmental Variability

“…Indeed, ring ouzels migrate much faster in the spring than in the autumn, a pattern commonly observed in migratory species in Europe 38 . However, this contrasts with the migration strategy of other mountain or arctic bird species, that make prolonged pre-breeding stopovers at lower elevations or latitudes not far from their reproductive grounds, waiting there for the snowmelt at their nearby breeding sites and/or building fat reserves 39,40 . With their daily transhumance, ring ouzels have thus found an innovative solution to cope with the highly seasonal and unpredictable breeding environment that prevails at high elevation.…”

Complex Day-to-day Movements of an Alpine Passerine May Act as an Insurance Against Environmental Variability

“…Indeed, ring ouzels migrate much faster in the spring than in the autumn, a pattern commonly observed across various migration yways and species (Nilsson et al 2013;Schmaljohann 2018). However, this contrasts with the migration strategy of other mountain or arctic bird species, that make prolonged pre-breeding stopovers at lower elevations or latitudes not far from their reproductive grounds, waiting there for the snowmelt at their nearby breeding sites and/or building fat reserves (de Zwaan et al 2019;Kölzsch et al 2016). With their daily elevational movements, ring ouzels have thus found an innovative solution to cope with the highly seasonal and unpredictable breeding environment that prevails at high elevation.…”