Fall migratory departure decisions and routes of blackpoll warblers Setophaga striata and red‐eyed vireos Vireo olivaceus at a coastal barrier in the Gulf of Maine

Abstract

Each year, millions of songbirds concentrate in coastal areas during fall migration. The choices birds make at the coast about stopover habitat use and migratory route can influence both the success of their migratory journey and fitness in subsequent life stages. We made use of a regional‐scale automated radio telemetry array to study stopover and migratory flights and migratory routes of blackpoll warblers Setophaga striata and red‐eyed vireos Vireo olivaceus during fall migration in the Gulf of Maine, USA. We focused on differences between species, sexes, age groups, breeding origins, and time of year. Both species made within‐stopover relocations (i.e. ‘stopover flights’) from the coastal capture site. Stopover flights were primarily oriented inland, and were more frequent for blackpolls (87%) than vireos (44%). By studying migratory behavior at a broad spatial scale, we demonstrated that most blackpolls and vireos took coastal and offshore routes through the Gulf of Maine, despite initially relocating inland from the capture site. Though we captured blackpolls and vireos from a broad breeding range, more than 70% of migratory flights from the capture site were oriented for coastal or offshore travel for both species, suggesting that birds actively chose coastal and offshore routes, and were not simply displaced by wind drift. Later vireos oriented offshore more frequently during migratory flights from the coast, indicating that they may be more inclined towards time‐minimizing overwater flight routes and thus more exposed to coastal and offshore collision hazards than earlier conspecifics.

Prolonged stopover and consequences of migratory strategy on local-scale movements within a regional songbird staging area

“…Indeed, later conspecifics of these vireos also departed from the capture site in an overwater trajectory more frequently, indicating a time-minimizing tendency for more direct travel (Smetzer et al 2017). That later vireos exhibited greater flight distances per stop is consistent with previous findings that later blackpolls also made fewer tortuous landscape-scale flights than earlier conspecifics (Brown and Taylor 2017).…”

“…We chose 6 km because it is half the detection range for a bird aloft, and we used the bearing of the antenna with the greatest signal strength because the power received by our directional antennas is maximized along the beam (Friis 1946, Shaw 2013. Finally, we calculated the ground speed for every segment of every bird's movement track and used these movement rates to classify track segments as either ''sustained migratory flights'' or ''slow movements'' (Smetzer et al 2017). There was a clear threshold at 1 m s À1 for ground speed, indicating a behavioral difference below this rate.…”

Age-Specific Differences in Fat Reserves and Migratory Passage ofSetophaga striata(Blackpoll Warbler)

“…From north to south, we caught >50% of Blackpoll Warblers at each respective site over ~18 d, covering 2.65° latitude. These data concur with Cooke's (1904) and Murray's (1965) work indicating that this species travels SSW down the northern Atlantic Coast, although individual birds may not follow a coastal-specific migratory path (Smetzer et al 2017). Blackpoll Warbler abundance peaked earlier at the most northern latitude and later at the most southern latitude.…”

“…While eBird observations consisted of all Blackpoll Warblers seen or heard in particular counties throughout the months of September and October, the banding effort only included the birds caught 2 days each week between 0630 and 0930 in September and October. Finally, differences between banding and eBird data could reflect birds congregating at coastal and inland sites at different latitudes (e.g., Smetzer et al 2017). Regardless of differences in peak arrival between the 2 datasets, our results were consistent with our hypothesis that peak Blackpoll Warbler passage would occur earlier at higher latitudes.…”

The fall migratory movements of Bank Swallows, Riparia riparia: fly-and-forage migration?

“…As in Smetzer et al (2017), we considered the date of the last detection of an individual at the colony to be the departure date.…”