Abstract
Migratory birds often follow detours when confronted with ecological barriers, and understanding the extent and the underlying drivers of such detours can provide important insights into the associated cost to the annual energy budget and the migration strategies. The Qinghai-Tibetan Plateau is the most daunting geographical barrier for migratory birds because the partial pressure of oxygen is dramatically reduced and flight costs greatly increase. We analyzed the repeated migration detours and habitat associations of four Pallas’s Gulls Larus ichthyaetus across the Qinghai-Tibetan Plateau over 22 migration seasons. Gulls exhibited notable detours, with the maximum distance being more than double that of the expected shortest route, that extended rather than reduced the passage across the plateau. The extent of longitudinal detours significantly increased with latitude, and detours were longer in autumn than in spring. Compared with the expected shortest routes, proximity to water bodies increased along autumn migration routes, but detour-habitat associations were weak along spring migration routes. Thus, habitat availability was likely one, but not the only, factor shaping the extent of detours, and migration routes were determined by different mechanisms between seasons. Significant between-individual variation but high individual consistency in migration timing and routes were revealed in both seasons, indicating a stronger influence of endogenous schedules than local environmental conditions. Gulls may benefit from repeated use of familiar routes and stopover sites, which may be particularly significant in the challenging environment of the Qinghai-Tibetan Plateau.
Highlights
Migratory birds often follow detours, which are spatial deviations from the most direct route, to minimize energy expenditure or travel time and arrive at their destinations safely and optimally (Alerstam, 2001; Alerstam, 2011)
Previous studies have primarily focused on migration detours across ecological barriers such as deserts, oceans and bad weather fronts (Mellone et al, 2011; Hawkes et al, 2013; Smolinsky et al, 2013; Hahn et al, 2014; Vansteelant et al, 2017), but the performance of migrants confronted with the challenging environment of high plateaus remains poorly explored, this type of migration has been documented in a few species (Zhang et al, 2011b; Zhang et al, 2014; Liu et al, 2012; Hawkes et al, 2013)
Our dataset was relatively small, this study provides important insights into the cost of migratory detours in terms of the annual energy budget of an individual as well as the factors underlying these detours across a high plateau
Summary
Migratory birds often follow detours, which are spatial deviations from the most direct route, to minimize energy expenditure or travel time and arrive at their destinations safely and optimally (Alerstam, 2001; Alerstam, 2011). Previous studies have primarily focused on migration detours across ecological barriers such as deserts, oceans and bad weather fronts (Mellone et al, 2011; Hawkes et al, 2013; Smolinsky et al, 2013; Hahn et al, 2014; Vansteelant et al, 2017), but the performance of migrants confronted with the challenging environment of high plateaus remains poorly explored, this type of migration has been documented in a few species (Zhang et al, 2011b; Zhang et al, 2014; Liu et al, 2012; Hawkes et al, 2013). Birds can make stopovers on plateaus when necessary, and take advantage of the predictable daily slope winds to climb high plateaus (Hawkes et al, 2011) This may result in different detour patterns among migratory birds encountering high plateaus
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