Urbanization favors sedentary males

Urbanization changes landscapes and local environments, which can alter the life histories and traits of the creatures living in and around these areas. Studying European blackbirds (Turdus merula), Jesko Partecke and Eberhard Gwinner (Max Planck Institute for Ornithology) discovered certain adaptive traits, that in the long run, could lead to more offspring. The study, "Increased sedentariness in European Blackbirds following urbanization: a consequence of local adaptation?," appears in the April issue of Ecology.

Earlier field studies revealed a greater tendency for birds to over-winter in urban populations of migratory species such as the European Blackbird and the European Robin, especially when compared with populations of the same species living in nearby forest and rural habitats.

"The decision to migrate is probably influenced by both genetics and environment," say the authors in the study. "In this study, we wanted to determine if changing migratory habits were due to changes in genetic composition in urban populations, or were environmental-induced."

To test the effects of environment and genetics on migration habits, the scientists set up an experiment where they raised birds from both the city and forest environments. They monitored their movements at night and during the day and measured body fat, an indicator that the bird is preparing for migration. The researchers also looked at sexual maturity, to see if migratory disposition had an impact on the seasonal timing of reproduction.

Partecke and Gwinner found that the birds exhibited migratory traits - fat buildup and more nocturnal activity, during periods in the spring and fall. While they found little difference between forest and urban females, urban males were less likely to show a desire to migrate (migratory disposition). Furthermore, those individuals with a lower migratory disposition were more likely to develop gonads earlier in the season than their forest counterparts with higher migratory propensity.

"We suggest the migratory drives for urban and forest blackbirds are genetically driven and consider it likely that they are the result of microevolutionary changes following urbanization," say the researchers.

So why the males and not the females? The authors suggest that selection in urban habitats operates differently on the migratory habits of male and female European blackbirds. In partially migratory species, sedentary individuals are not only able to establish territories and to begin pair formation earlier than migratory birds, but also may have a longer reproductive season. The earlier onset of favorable conditions for breeding in urban areas should, thus, favor selection for sedentariness. The advantage of both sedentariness and earlier onset of territory establishment in terms of reproductive success for males seems to outweigh that of the females.

Source: Ecological Society of America

Related stories:

Researchers explain how birds navigate
It has long been known that birds and many other animals including turtles, salamanders and lobsters, use the Earth’s magnetic field to navigate, but the nature of their global positioning systems (GPS) has not been completely understood.
Flying off course: Why migratory birds from Asia land in Europe
Migratory birds make mistakes in terms of direction, but not distance. These are the findings of a team of ornithologists and ecologists from the University of Marburg, the Ornithological Society in Bavaria and the Helmholtz Centre for Environmental Research (UFZ), writing in the Journal of Ornithology.
Some migratory birds can't find success in urban areas, study finds
New research finds fresh evidence that urbanization in the United States threatens the populations of some species of migratory birds. But the six-year study also refutes one of the most widely accepted explanations of why urban areas are so hostile to some kinds of birds.
Feathered friends favor fruity flavonoids
Fruit-eating birds actively select fruit with the highest concentrations of antioxidants – compounds that help them maintain a healthy immune system – ecologists have found. This is the first time that a group of antioxidants known as flavonoids have been found to boost the immune system in studies on living animals, as opposed to test-tube studies. The results are published online in the British Ecological Society’s Functional Ecology.
Woodburn, Ore.: a microcosm of immigrant shifts in America
Travelers on I-5 know that Woodburn, Ore., is home to the region's largest tax-free outlet center. A University of Oregon researcher, however, turns away from the mall to study the heart of town, which, she says, provides insight on how new immigrant settlement patterns are transforming place and identity in small- to medium-sized U.S. cities.
National Zoo scimitar-horned oryx going into the wild
A male scimitar-horned oryx from the Smithsonian’s National Zoo’s Conservation and Research Center in Front Royal, Va., is playing an important role in ensuring the species does not vanish from the planet.
Mapping the English language – from cockney to Orkney
If they were Scousers they’d be “made up”; from the Black Country they’d be “bostin”. But researchers from the University of Leeds are naturally “well chuffed” to receive a £460,000 grant to examine and catalogue the dialects and diversities of the English language.

Cancer is a stem cell issue
There is an urgent reason to study stem cells: stem cells are at the heart of some, if not all, cancers. Mounting evidence implicates a clutch of rogue stem cells brandishing ‘epigenetic’ marks as the main culprits in cancer. Wiping out tumours for good, some biologists believe, depends on uprooting these wayward stem cells.

News discussion:

General Science news