Trans-Gulf of Mexico loop migration of tree swallows revealed by solar geolocation

Abstract

One of the greatest feats of avian migration is the non-stop crossing of extensive areas of inhospitable habitat such as deserts and seas. Differences in spring and autumn migration routes have been reported in species that cross such barriers, and are thought to have evolved in response to seasonal variation in prevailing wind direction. We tested the hypothesis that migration routes vary seasonally with respect to the Gulf of Mexico in the tree swallow Tachycineta bicolor using solar geolocators attached and retrieved at 4 breeding sites in central North America. We found that 100 % of birds (n = 10) made a trans-Gulf flight of >850 km from Louisiana south to their wintering grounds in the Yucatan Peninsula in 12–36 hours, achieving minimum ground speeds as high as 32 m/s. Although most days during autumn migration were characterized by unfavorable headwinds blowing to the northwest, migration over the Gulf mostly occurred on days with strong winds blowing to the south. In contrast, in 8 of 9 (88 %) birds on spring migration returned from the wintering grounds towards Louisiana following a clockwise loop pat tern flying over land to the west around the Gulf. During this spring period there were few days with prevailing winds from the south to assist northward migration. Results suggest that, despite being up to three times further (ca. 2,700 km), a coastal cir- cum-Gulf spring migration represents the less risky route when wind conditions are not favorable. These findings also help to re solve a long-standing dispute in the literature concerning migration patterns between the US Gulf coast and Mexico, and provide insight into the factors shaping migration strategies of small songbirds migrating across large bodies of water.

Global aerial flyways allow efficient travelling

“…North America, southbound migrations are more eastern than the northbound migrations, a pattern also observed in both individual trajectories around the Gulf of Mexico (Bradley et al 2014) as well as average migrations (La Sorte et al 2013). In Asia, we find prominent migration routes through the Philippines and Malaysian peninsula much like the existing flyways (Newton 2007).…”

“…Similarly, in North America, southbound migrations are more eastern than the northbound migrations, a pattern also observed in both individual trajectories around the Gulf of Mexico (Bradley et al . ) as well as average migrations (La Sorte et al . ).…”

Wind and rain are the primary climate factors driving changing phenology of an aerial insectivore

“…Climate change is a global phenomenon with well-documented effects, including increasing temperatures as well as changes in precipitation, humidity, snow pack depth and duration, storm frequency, and wind speed [1][2][3][4]. There is substantial evidence that climate change is causing or will cause range and phenology shifts in individual species and will alter the structure and composition of entire communities [5][6][7][8][9][10][11][12][13][14]. Determining what aspects of climate are driving these changes is challenging because of annual climate variation and the correlated shifts in multiple aspects of climate.…”

“…Determining what aspects of climate are driving these changes is challenging because of annual climate variation and the correlated shifts in multiple aspects of climate. To date, most analyses in terrestrial systems have implicitly or explicitly assumed that temperature is the major driver of ecological effects ( [1,[5][6][7][8][9]11,13,[15][16][17][18][19][20][21][22][23][24][25][26][27][28], but see [10,12,29]) Better understanding and prediction of climate effects relies on testing this assumption, as populations, species, communities, and ecosystems are likely to be differentially buffered against changes in the many aspects of the physical environment. Indeed, paleo-ecological data emphasize the non-congruent responses of different species to climate change, potentially a result of differential sensitivity to different aspects of climate [30,31].…”

Constructing and evaluating a continent‐wide migratory songbird network across the annual cycle

“…), and East Mexico (Bradley et al. ); however, the major stopover sites we identified above were not previously recognized as important sites. Individuals from 5 of the 12 populations moved through the Midwest stopover node, coming from breeding regions with some of the highest indices of abundance, and moving to non‐breeding nodes from East Mexico to South Florida.…”