Research Highlights from the Martin Lab

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Rapid Evolution of Colour Patterns in High Latitude Birds Rates of evolution in birds are believed to vary with latitude, but not in the way that you might expect. We provide evidence that the rates of evolution of distinct colour patterns of birds are accelerated at higher latitudes compared to the tropics, opposite the global patterns of species richness where the tropics are most diverse. The cause of this rapid evolution at higher latitudes? Rapid shifting of ranges through glacial cycles that allow closely-related species that were once isolated to overlap each other's ranges. Once closely-related species coexist with each other, they either (i) hybridize, reducing the number of weakly-differentiated birds at higher latitudes, or (ii) persist together with a strong potential for interaction with each other, accelerating each other's rates of evolution. These simple consequences of rapid range shifting at high latitudes can create some of the striking colour patterns we see in high latitude birds, such as the Chestnut-sided Warbler and White-headed Woodpecker. (Evolution, 2010) Links: pdf

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Population Densities of Golden-winged Warblers Global populations of Golden-winged Warblers are in decline. The decline has sparked a great deal of research on this species by Raleigh Robertson at the Queen's University Biological Station (QUBS) over the past 10 years. This past year, we collaborated with Raleigh and Rachel Vallender (Cornell University) to provide the first ever estimated densities of Golden-winged Warblers, Blue-winged Warblers, and their hybrids on the three main tracts of land at QUBS. We estimated populations in the area at about 200 breeding pairs, and banded and mapped 30 male Golden-winged Warblers, one male Blue-winged Warbler, and 3 male hybrids (all "Brewster's") on our intensive study plots. We will revisit these same plots in 5-10 years to measure changes in population sizes and proportion of hybrids. This work was led by two Queen's undergraduate students, Laura King and Virginia Emery. (Ontario Birds, 2009)  Links: pdf

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Blood Parasites in Andean Birds Blood parasites, like the disease malaria, are found across many species of birds, but we know very little about their prevalence in the tropics. We examined blood samples from a number of species of birds occurring in the Ecuadorian Andes, documenting some of the first blood parasite infections for a number of species. We also found blood parasites in young nestlings. Infections take time to develop, and these results suggest that some blood parasites may be transferred from mother to offspring through the egg itself! We will conduct further work to confirm if this is indeed a mode of disease transmission. This work was led by Queen's undergraduate student Hannah Munro. (Ornitologia Neotropical, 2009)  Links: pdf

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Sap-well Use and Maintenance in a Tanager We described the first record of sap-well use and maintenance in a tanager, based on observations of a Glossy Flowerpiercer on the east slope of the Andes in Ecuador. Sap-well use is well known in the sapsuckers and in some other woodpeckers, but is otherwise rare in birds. Only three non-woodpeckers have been observed to maintain sap-wells: a strange New Zealand parrot (the Kaka), a species of Hawaiian Honeycreeper (the Akiapolaau), and now, the Glossy Flowerpiercer. Flowerpiercers usually steal nectar from flowers by piercing the base of the flower using their hooked upper mandible to hold the flower, their sharp lower mandible to pierce it, and their paint-brush-like tongues to lick the nectar. Like many flowerpiercers, Glossy Flowerpiercers steal nectar and eat fruit, but are unique in using their specialized bill and tongue for sap. (Wilson Journal of Ornithology, 2009)   Links: pdf video

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Begging Kids and Stress Hormone Levels Stress hormones (corticosteroids) are secreted in response to environmental challenges or stressful conditions. When a bird or other vertebrate encounters a severe storm, drought, predation attempt, or disease, they secrete stress hormones that promote a diversity of responses in the organism. In our work on Tree Swallows (led by Dr. Frances Bonier), we showed that stress hormones are also secreted in response to the peak demands of nestlings in the nest. Thus, hungry nestlings elicit the same kind of physiological response as bad weather or other challenges facing the swallows, prompting them to reallocate their resources towards provisioning their brood. (General and Comparative Physiology, 2009)   Links: pdf

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The Breeding Biology of Antpittas We summarize the breeding biology for two genera of Neotropical antpittas – understory birds that are notoriously shy and secretive. One species is so secretive that it went undescribed by scientists until 1999, despite occurring at a birding lodge with a history of ornithological work! Nests for over half of the 39 species are still unknown. This work was led by Harold Greeney at the Yanayacu Biological Station in Cosanga, Ecuador. (Journal of Field Ornithology, 2008)   Links: pdf

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New Nests of Tropical Andean Birds We described the first nests known to science for two Andean species: the Agile Tit-Tyrant (Uromyias agilis), a small, uncommon flycatcher with a fondness for bamboo, and the Spectacled Whitestart (Myioborus melanocephalus), a stunning wood warbler that flashes its white outer tail feathers to scare insects from leaves in montane forests. (Ornitologia Neotropical, 2008)   Links: Uromyias pdf Myioborus pdf

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Mother Birds Manipulate the Sex of Their Offspring Mother birds can manipulate the sex of their offspring using changes in corticosterone – a hormone secreted in response to stressful conditions. Higher corticosterone levels lead to more daughters, which are a safer investment because all females breed each year. In contrast, poor quality males often remain unpaired and may not breed – quite a gamble when environmental conditions are stressful. This work was led by Dr. Frances Bonier. (Behavioral Ecology, 2007)   Links: pdf

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Coping with Life in the City Urbanization dramatically changes the composition and diversity of animal and plant communities. The characteristics distinguishing species that persist in urban environments, however, are poorly understood. In this study, we found that  species of bird able to cope with urban environments have broader environmental tolerances compared with closely-related species. This pattern is consistent across Europe, Asia, Africa, Australia, and North and South Americas. Our results suggest that broad environmental tolerance may predispose some birds to thrive in urban habitats. This work was led by Dr. Frances Bonier. (Biology Letters, 2007)   Links: pdf Sciencentral News Feature (video)

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Narrow Thermal Tolerance of Tropical Insects The impact of climate change on terrestrial organisms is often predicted to be greatest in regions that are warming the fastest - typically regions occurring at higher latitudes. Yet the impact of rising temperatures also depends on the sensitivity of organisms to temperature change. In this study, we review evidence that tropical insects and "cold-blooded" vertebrates (such as lizards and turtles) show very little tolerance to warming temperatures. The narrow thermal tolerances of these tropical organisms may amplify the impacts of climate warming on tropical species, potentially placing the majority of the earth's biodiversity at risk. This work was led by Curtis Deutsch and Josh Tewksbury. (Proceedings of the National Academy of Sciences USA, 2008) Links: pdf BBC World News article

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Subspecies Diversification in Birds Patterns of evolution are believed to vary with latitude, but our understanding of this variation remains limited. In this work, we found that subspecies of birds occur more frequently at lower latitudes within the distributions of species in almost all regions on earth. Subspecies represent the early stages of species formation, and thus these results suggest that more species are currently being formed at tropical latitudes within species. (Evolution, 2008)   Links: pdf

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Mechanistic Causes of Latitudinal Variation in Diversity Biodiversity increases dramatically from the poles to the equator. From a mechanistic perspective, abiotic factors produce the gradient in diversity by creating latitudinal variation in rates of formation of new taxa, extinction, immigration and/or emigration, the latter two processes resulting from range expansion, contraction and shifting. In this study, we tested the contributions of all four possible mechanisms underlying a present day latitudinal gradient in the diversity of orders of marine invertebrates with good fossil histories. In these orders, high tropical biodiversity was caused by higher rates of formation of new taxa in the tropics, followed by the expansion of these new taxa into other tropical regions. Extinction rates were highest in the tropics, and thus extinction reduced tropical diversity relative to higher latitudes. (Journal of Evolutionary Biology, 2007) (photo: The Natural History Museum, London) Links: pdf

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Costs, Constraints, and Trade-offs in Young Arctic Birds  Many young arctic birds are confronted by a challenging task: they must change their feathers (moult) and accumulate fat stores for the autumn migration before climatic conditions deteriorate. We used field studies from northern Alaska coupled with controlled aviary experiments to show significant costs to moulting body feathers. These costs of moulting feathers result in an allocational tradeoff between moult and fat accumulation, caused by a fundamental limitation of food for juvenile arctic sparrows. (Ecology, 2007)   Links: pdf

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