Long-distance migratory shorebirds travel faster towards their breeding grounds, but fly faster post-breeding

Abstract

Long-distance migrants are assumed to be more time-limited during the pre-breeding season compared to the post-breeding season. Although breeding-related time constraints may be absent post-breeding, additional factors such as predation risk could lead to time constraints that were previously underestimated. By using an automated radio telemetry system, we compared pre- and post-breeding movements of long-distance migrant shorebirds on a continent-wide scale. From 2014 to 2016, we deployed radio transmitters on 1,937 individuals of 4 shorebird species at 13 sites distributed across North America. Following theoretical predictions, all species migrated faster during the pre-breeding season, compared to the post-breeding season. These differences in migration speed between seasons were attributable primarily to longer stopover durations in the post-breeding season. In contrast, and counter to our expectations, all species had higher airspeeds during the post-breeding season, even after accounting for seasonal differences in wind. Arriving at the breeding grounds in good body condition is beneficial for survival and reproductive success and this energetic constraint might explain why airspeeds are not maximised in the pre-breeding season. We show that the higher airspeeds in the post-breeding season precede a wave of avian predators, which could suggest that migrant shorebirds show predation-minimizing behaviour during the post-breeding season. Our results reaffirm the important role of time constraints during northward migration and suggest that both energy and predation-risk constrain migratory behaviour during the post-breeding season.

Danger management and the seasonal adjustment of migratory speed by sandpipers

“…Better measures of migratory speed are becoming possible (Duijns et al 2019) as tracking devices improve; this will enable descriptions of intra-seasonal patterns to be compiled -though interpretation of 'migration speed' (Lindström et al 2019) remains an issue. Better measures of migratory speed are becoming possible (Duijns et al 2019) as tracking devices improve; this will enable descriptions of intra-seasonal patterns to be compiled -though interpretation of 'migration speed' (Lindström et al 2019) remains an issue.…”

“…Several features of the theory developed here lend themselves to empirical testing. Better measures of migratory speed are becoming possible (Duijns et al 2019) as tracking devices improve; this will enable descriptions of intra-seasonal patterns to be compiled -though interpretation of 'migration speed' (Lindström et al 2019) remains an issue. In addition to direct measures of migratory speed, measures of behavior supporting foraging intensity (for shorebirds including vigilance, site choice, foraging rate, flock size, feeding distance from cover, escape distance) should show similar patterns.…”

Migrant Semipalmated Sandpipers (Calidris pusilla) Have Over Four Decades Steadily Shifted Towards Safer Stopover Locations

“…Semipalmated sandpipers display many of the attributes expected of mortality-minimizing migrants (Hope et al, 2011;Duijns et al, 2019), and hence we expect that safety is important to their stopover decisions. Small shorebirds show a diverse range of behavioral tactics in response to predation danger (e.g., Hilton et al, 1999;Ydenberg et al, 2004;Pomeroy et al, 2008;Sprague et al, 2008;Beauchamp, 2010;Fernández and Lank, 2010;van den Hout et al, 2010van den Hout et al, , 2017Cresswell and Quinn, 2013;Martins et al, 2016, and references therein).…”

Bio‐energetic data show weak spatial but strong seasonal differences in wetland quality for waders in a Mediterranean migration bottleneck

“…In spring, they rush to occupy breeding territories. Competition, predation risk, and prey depletion are generally expected to play a more important role during post‐ than pre‐breeding migration (Duijns et al., 2019; Schneider & Harrington, 1981). The extent to which this seasonal asymmetry is present in the local quality of different stopover sites (i.e.…”