“Dietary flexibility promotes a more flexible migration strategy,” says La Sorte. That is, these birds enjoy the omnivore’s advantage of waiting for just the right nights for flight. They are a very successful group of birds.
Their syrinx (vocal organ) is able to produce varied and beautiful singing. There are about 4000 species of songbird. They are the suborder Passeri, sometimes called 'oscines' ( Latin for songbird). La Sorte’s research, using eBird data and weather radar images of massive flocks of birds, provided the first documented evidence that these insectivores-turned-omnivores migrate on the omnivore’s later schedule, with a migration window that extends into November. Songbirds are the main group of birds in the order Passeriformes. Insectivores-that-become-omnivores: Then there’s a third group of species-including Hermit Thrush, Eastern Phoebe, Yellow-rumped Warbler, and Red-eyed Vireo-that possess the physiological adaptation in their digestive systems to switch from a diet of insects to fruits and seeds in fall. For omnivorous birds, the fall migration window can stretch well into November. So they have the luxury of waiting for optimal travel conditions (fair skies and a favorable tailwind), which can make for a less dangerous migration than insectivorous birds often encounter. Omnivores: Birds that eat a balanced diet of insects, fruits, and seeds-such as sparrows-aren’t forced out of their northern breeding grounds because the food supply of bugs runs out. But when insect abundance fades in late summer, these insectivorous birds leave on migration-typically from late August to mid-September. After all, eating insects was an evolutionary reason their ancestors started flying long distances from the tropics to cash in on the protein pulse of the insect hatch in North America. And it makes sense that diet drives their population movements. Insectivores: Most species of warblers, vireos, and flycatchers primarily eat insects. Put simply, what some birds eat seems to determine when they fly south for the winter. New research published by Cornell Lab scientist Frank La Sorte delves into diet as a factor in migration timing. Studies have shown decreasing daylight to be a cue for many species.
Scientists still don’t know all the drivers of fall migration.
Others thought migratory birds flew all the way to the moon! In centuries past, people thought songbirds hitched a ride on the backs of storks. According to this theory, vocal convergence might be adaptive in species that overlap broadly in resource use, as it leads to better distinction of territory boundaries between the species and thus reduces the level of interspecific competition.Fall bird migration has fascinated humans for ages. Our results are consistent with the concept of convergent agonistic character displacement. We suggest that this similar level of interspecific and conspecific aggression in the thrush nightingale results from mixed singing of this species in sympatry, as males may not distinguish conspecifics from heterospecifics by song alone. Interestingly, while the common nightingale reacted significantly more aggressively to the conspecific than the heterospecific stimulus, the thrush nightingale showed similarly strong responses to both stimuli. The species did not differ in aggressive responses to a heterospecific stimulus, suggesting that competitive dominance is not associated with higher interspecific aggressiveness in nightingales. Using playback experiments, we evaluated the strength of nonvocal aggressive responses of both species to conspecific and heterospecific stimuli. In the secondary contact zone most thrush nightingales incorporate common nightingale song types in their repertoires. However, the thrush nightingale is slightly larger and several lines of evidence indicate its competitive dominance. These species are morphologically and ecologically very similar. Luscinia megarhynchos, and the thrush nightingale, Luscinia luscinia, might be an adaptive response to interspecific interference competition. Here we tested the hypothesis that song convergence observed in a secondary contact zone of two songbird species, the common nightingale. The intensity of interspecific aggression and the outcomes of interference competition between closely related species might be substantially modified by copying of vocal signals used in territory defence. In animals, interspecific interference competition is often associated with their aggressive behaviour.