Automated VHF Radiotelemetry Revealed Site-Specific Differences in Fall Migration Strategies of Semipalmated Sandpipers on Stopover in the Gulf of Maine

Rebecca L Holberton,Lindsay M Tudor,Glen H Mittelhauser,Ana Breit,Kathleen M O'Brien,Philip D Taylor

doi:10.3389/fevo.2019.00327

Abstract

The Gulf of Maine has long been recognized as a major stopover area for shorebirds in fall. Knowing how birds move within and beyond the region will be paramount to protecting threatened shorebird habitat. To determine stopover behavior during fall migration (2013-2017) in Maine, 180 (104 AHY, 76 HY) Semipalmated Sandpipers, Calidris pusilla, were tracked using VHF radiotelemetry and an extensive array of automated receivers (Motus Wildlife Tracking System). Birds tagged at three locations along the Maine coastline showed no effect of age class or stopover site on body condition (body mass, estimated fat mass) or stopover length (post capture detection period). However, movement after departure varied greatly among sites. Few birds captured at the northern-most site (“Downeast”, n=71), which had the greatest amount of mudflats and offshore roost sites and the least amount of human disturbance, were detected beyond the initial tagging location, suggesting that they, like birds in the Bay of Fundy just to the north, initiated trans-oceanic flights from that location. At the Downeast site, leaner birds remained significantly longer than fatter birds, suggesting that time of departure there depended on energy reserves, which would be critical for making extensive flights. In contrast, over half of the birds tagged further south (Popham Beach, n= 59; Rachel Carson NWR, n = 50) were later detected at coastal locations to the north (few) or to the south (most). Stopover period at these sites was independent of fat, suggesting that other factors (e.g. feeding/roosting site availability, human activity) influenced departure decisions. In Maine, Semipalmated sandpipers, regardless of age, may move north (Downeast) or south (e.g. Cape Cod, Rhode Island, Long Island Sound) where the local topography, habitat characteristics (feeding/roosting sites), and/or lower human activity, may best enable them to initiate trans-oceanic flights to the wintering grounds. Future study should determine if variation in stopover behavior is population-specific and if population-segregation occurs in Maine. Use of automated VHF radiotelemetry has lead to a greater understanding of stopover behavior and the degree of connectivity among stopover sites, which should be taken into account for conserving migratory bird habitat across broad spatial scales.

Highlights

Many Arctic-breeding shorebird populations have declined rapidly over the past few decades, with some populations decreasing by as much as 60%
Semipalmated Sandpipers, Calidris pusilla, breed across the North American Arctic, different breeding populations show a high degree of geographic segregation in their respective wintering areas and migration routes (Andres et al, 2012; Gratto-Trevor et al, 2012a; Brown et al, 2017)
We found no effect of age [F(1, 143) = 0.04, p = 0.8] on post-capture detection period (PCDP), but evidence for a significant interaction between site and EFM [F(2,143) = 5.1, p = 0.007) on PCDP

Summary

Introduction

Many Arctic-breeding shorebird populations have declined rapidly over the past few decades, with some populations decreasing by as much as 60% (for review, see 2012 North American Bird Conservation Initiative Report; U.S Shorebird Conservation Plan Partnership, U.S Shorebirds of Conservation Concern, 2015). Western and central breeding populations appear to be stable or slightly increasing over the past few decades, but eastern Semipalmated Sandpiper populations have shown little to no increase, with some indications that they continue to decline (Andres et al, 2012; Gratto-Trevor et al, 2012b; Morrison et al, 2012; Smith et al, 2012; Brown et al, 2017) This pattern prompted Andres et al (2012) to propose that eastern breeding populations of this species be considered “of high conservation concern.”. This pattern prompted Andres et al (2012) to propose that eastern breeding populations of this species be considered “of high conservation concern.” Understanding the behavior and ecology of different Semipalmated Sandpiper populations throughout the annual cycle will be key to determining how each breeding population is regulated and, how to manage resources to support them

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