"This could potentially lead individual thrushes to attempt breeding elsewhere." He speculates that birds might assess the available food supplies each spring before deciding where – and whether – to nest and reproduce. ![]() "They may be finding less good-quality food and having to work harder to find it," Hames says. At the same time, acidic conditions could also increase the amounts of toxic aluminum and heavy metals (such as lead, cadmium and mercury) that the wood thrush ingests. Fallen, decaying leaves and other natural litter on the forest floor could decompose more slowly under acidic conditions. However, low levels of soil calcium might also affect a wide range of prey, such as earthworms, millipedes and centipedes, pillbugs and other insects that adult birds need to nourish themselves and feed their young. ![]() In particular, shortages of calcium-rich foods, such as snails and snail shells, might be critical at egg-laying time, when calcium demand is highest for female birds, or during the nesting period, when calcium supplements are often provided to growing young. Previous studies by other investigators had shown that calcium-depletion can affect breeding birds in a number of ways, Hames notes. European studies of heavy acid-rain regions similarly have linked declining bird populations to acid-rain-induced depletion of soil calcium. Although the exact mechanism leading to the declines is still unknown, it may well be related to the leaching of calcium from the soil by acid rain, according to Hames. ![]() High elevations, such as the Adirondack, Appalachian and Great Smokey mountains as well as the Allegheny Plateau, where the amount of acid deposited in precipitation could be highest, show long-term declines of up to nearly 5 percent annually in wood thrush populations. In the United States, about two-thirds of all SO2 and one-fourth of all NOx come from electric-power generation that relies on burning fossil fuels, such as coal. Sulfur dioxide (SO2) and oxides of nitrogen (NOx) are the primary causes of acid rain. Dhondt.Īcid rain is the broad term used to describe several ways that a weak solution of inorganic acids, such as nitric and sulfuric acid, falls out of the atmosphere as rain, snow, mist and fog. Hames, a postdoctoral associate at the Cornell Lab of Ornithology who conducted the research with colleagues Kenneth V. The finding is reported in the current Proceedings of the National Academy of Sciences (PNAS Vol.99 No. Using data collected by thousands of volunteer citizen-scientists in the Birds in Forested Landscapes project, scientists at the Cornell Lab of Ornithology showed that the wood thrush is less likely to attempt to breed in regions that receive high levels of acid rain. Calcium depletion affecting the birds' food is a possible cause, Cornell University ecologists say. These results show how a brain region important to reproduction in both birds and mammals enables holistic courtship displays in male zebra finches, which include learning songs, calls, and other non-vocal behaviors.A large-scale study has for the first time shown a clear link in North America between acid rain and widespread declines across the breeding range of a songbird, the wood thrush. Lastly, imaging calcium-related activity in A11 terminals in HVC showed that during courtship, A11 signals HVC about female-directed calls and during female-directed singing, about the transition from simpler introductory notes to the acoustically more complex syllables that depend intimately on HVC for their production. ![]() However, males with either type of lesion still produced songs when in social isolation. In contrast, lesioning A11 cell bodies strongly reduced and often abolished all female-directed courtship behaviors. Notably, lesioning A11 terminals in HVC blocked female-directed singing but did not interfere with female-directed calling, orientation, or pursuit. Anatomical mapping reveals that A11 is at the center of a complex network including the song premotor nucleus HVC as well as brainstem regions crucial to calling and locomotion. Here, we identify a midbrain cell group (A11) that enables male zebra finches to produce their learned songs in concert with various other behaviors, including female-directed orientation, pursuit, and calling. The neural circuits that enable the concerted production of the component behaviors of a courtship display are not well understood. Courtship displays often involve the concerted production of several distinct courtship behaviors.
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