Migration Distance and Body Condition Influence Shorebird Migration Strategies and Stopover Decisions During Southbound Migration

Alexandra M Anderson,Christian Friis,Erica Nol,Paul A Smith,Sjoerd Duijns

doi:10.3389/fevo.2019.00251

Alexandra M Anderson, Christian Friis + Show 3 more

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https://doi.org/10.3389/fevo.2019.00251

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Abstract

Technological constraints have limited our ability to compare and determine the proximate and ultimate drivers of migratory behaviour in small-bodied birds. Small VHF transmitters ( 9,000 km; pectoral sandpiper, Calidris melanotos, and white-rumped sandpiper, Calidris fuscicollis) would be more likely to migrate with characteristics of a time-minimizing migration strategy compared to species migrating intermediate distances (5,000-7,500 km; semipalmated sandpiper, Calidris pusilla; and lesser yellowlegs, Tringa flavipes) or shorter distances (~5,000 km; least sandpiper, Calidris minutilla; semipalmated plover, Charadrius semipalmatus), which would migrate with more characteristics of an energy-minimizing strategy. Our results indicate that migration and stopover behaviours for adults matched this prediction; longer distance migrants had longer stopover lengths, departed with higher relative fuel loads, flew with faster ground and airspeeds, and had a lower probability of stopover in North America after departing the subarctic. The predicted relationship between migration distance and migratory strategy was not as clear for juveniles. Despite our prediction that longer distance migrants would be less wind selective at departure and fly into headwinds en route, all species and age classes departed and migrated with supportive winds. Birds with higher estimated fuel loads at departure were less likely to stop in North America after departing the subarctic, indicating that some birds attempted non-stop flights from the subarctic to the Caribbean or South America. Additionally, within species, adults with higher relative fuel loads at departure had a higher detection probability after departing the subarctic, which we interpret as evidence of higher survival compared to juveniles. This study shows that migratory behaviour of shorebirds has predictable patterns based on migration distance that are moderated by body condition of individuals, with potential implications for fitness.

Highlights

Many animals migrate to exploit spatial and temporal increases in prey abundance (Alerstam et al, 2003; Teitelbaum et al, 2015) while reducing predation risk (Hebblewhite and Merrill, 2007; McKinnon et al, 2010)
Optimal migration theory provides clear predictions about migratory strategies for individuals under different energy, time, and predation constraints (Alerstam and Lindström, 1990; Hedenström and Alerstam, 1997; Alerstam, 2011), but the theory is less clear about how total migration distance influences migratory behavior and the currency individuals use to maximize fitness
We examine the relationship between migration distance and stopover length, departure fuel loads, wind selectivity, ground speeds and airspeeds, and subsequent stopover probability and determine if these patterns match previously observed patterns of time-minimizing migration in longer-distance migrants (e.g., Nilsson et al, 2014)

Summary

Introduction

Many animals migrate to exploit spatial and temporal increases in prey abundance (Alerstam et al, 2003; Teitelbaum et al, 2015) while reducing predation risk (Hebblewhite and Merrill, 2007; McKinnon et al, 2010). Migration distances vary across species, and this variation may influence migratory behaviors and strategies. Long-distance migrants must rely on local conditions, circannual clocks, and photoperiod to make migratory decisions (Gwinner, 1996) about far-away destinations. This may, in part, explain more consistent and less plastic timing of migration for long-distance migrants compared to short-distance migrants (Rubolini et al, 2007; Miller-Rushing et al, 2008). Long-distance migrants must balance high energetic demands of migration with predation risk and time constraints to complete farther migrations (Alerstam et al, 2003). A recent study found support for the hypothesis that long-distance migrants are more time-constrained than short-distance migrants because of farther travel distance (Nilsson et al, 2014)

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