Stopover behavior of Red-eyed Vireos (Vireo olivaceus) during fall migration on the coast of the Yucatan Peninsula

Background For migrating birds, stopover requires spending time and energy that otherwise could be allocated to flying. Thus, birds optimally refuel their subsequent migratory flight by reducing stopover duration or foraging activity in food-rich environments. In coastal habitats, birds may forego refueling and take short stopovers irrespective of local food availability. Given the paucity of studies exploring how migrants adjust stopover behavior in response to temporal variation in food availability, especially in the Neotropics, we fixed radio tags to 51 Red-eyed Vireos (Vireo olivaceous) over two years at two sites on the coast of Mexico’s Yucatan Peninsula. Methods We applied VHF radio tags during the fall of 2016 and 2017, and tracked birds using automatic and manual receiving units. We estimated stopover duration and activity levels (one site only) for between six and fifteen birds, depending on site and year. We measured fruit availability weekly along the net lanes where we captured birds. We used a generalized linear model to estimate the relationships between stopover duration/activity level and fruit density, bird body mass and year. We interpreted relationships for the model with the lowest AICc value. Results We found that approximately half of the birds departed on the same day they were captured. For the birds that stayed longer, we could not discern whether they did so because they were light, or fruit density was high. On the other hand, lighter birds were more active than heavier birds but only in one of the two years. Conclusions Given our results, it is unlikely that Red-eyed Vireos refuel along the Yucatan coast. However, they still likely need to recuperate from crossing the Gulf of Mexico, which may necessitate foraging more often if in poor body condition. If the birds then move inland then stopover should be thought of as a large-scale phenomenon, where habitats with different functions may be spread out over a broad landscape.

The Iowa Bird That Inspired Antonín Dvořák's American String Quartet in 1893: Controversy over the Species’ Identity and Why It Matters

Antonín Dvořák composed the String Quartet in F major (op. 96, the ‘American’) in June 1893 while visiting the town of Spillville, Iowa, USA. Based on accounts from Dvořák's secretary Josef Kovařík, portions of the quartet's Scherzo movement were inspired by birdsong Dvořák heard in Spillville. Kovařík's account included both Dvořák's visual description of the bird that inspired him and a transcribed fragment of the birdsong Dvořák reportedly used. In 1954, Clapham identified the bird as a scarlet tanager (Piranga olivacea), based mainly on the visual description. This widely accepted identification was questionable because of the poor match of the tanager's song to musical material in the Scherzo. In 2016, Floyd proposed the red-eyed vireo (Vireo olivaceus) as Dvořák's inspiration, based on song rather than appearance. The vireo's song is clearly identifiable in the Scherzo as well in the birdsong fragment recorded by Kovařík. The mismatch between the visual description and the transcribed song fragment could have occurred when Dvořák heard and recorded the persistent singing of a cryptic red-eyed vireo, but misidentified the song's source when he caught sight of a brightly coloured tanager. Correct identification of the birdsong changes the interpretation of the movement. Previously, birdsong has been considered the source of a short secondary motif. But red-eyed vireo songs are highly variable, and a slight variation of Kovařík's song fragment could be the basis of the main theme of the Scherzo. Therefore, Dvořák may have used American birdsong in the movement considerably more than previously appreciated.

Intrinsic Markers Reveal Breeding Origin and Geographically-Structured Migration Timing of Two Songbird Species at a Coastal Stopover Site

We used stable hydrogen isotope markers to identify geographic provenance of Blackpoll Warblers (Setophaga striata) and Red-eyed Vireos (Vireo olivaceus) passing through a coastal stopover area in the Gulf of Maine on fall migration, and supplemented δ2 H signatures from feathers with wing length data as an additional proxy for migration origin, since geographic size variation has been documented for this species. We captured migrant blackpolls with putative origins from as close as the Adirondacks, New Brunswick, and northwestern Maine, and potentially as far as Alaska. We captured vireos with putative origins from as close as Maine and Nova Scotia, and potentially as far as British Columbia and Alberta. We found a significant relationship between blackpoll wing length and capture date indicating that birds with longer wings– and thus likely from more western and northern breeding regions – passed through the capture site earlier in the season than more local breeders. In contrast, vireos from more distant breeding latitudes passed through the capture site later in the season. These results demonstrate that mid-coast Maine serves as a catchment area for both Blackpoll Warblers, and Red-eyed Vireos, and provides some evidence that connectivity between breeding areas and stopover sites may be strong for blackpolls; however, additional study linking breeding and stopover sites across the migratory range of both species is necessary to understand more fully how strong connectivity is between breeding and stopover areas for these species.