Why Birds Need Native Trees
The Carolina chickadee is giving scientists a model to study the impact of nonnative trees on food available for breeding birds.
With six hungry hatchlings begging for food, a Carolina chickadee needed to find some nourishment fast. The bird flew from her cavity nest to forage in the treetops for caterpillars and other insects. Surprisingly, she bypassed nearly a dozen leafy gingko and crape myrtle trees located a few hundred yards from her nest. Instead, the bird made a beeline to a willow oak on a busy street half a city block away.
Apparently, she knew what she was doing. “Native trees such as oak produce more insect prey than do non-native species such as crape myrtle and gingko,” biologist Jasmine Rajbhandary told me as we raced behind the tiny bird. An intern for the Smithsonian Migratory Bird Center (SMBC), Rajbhandary works with Desiree Narango, a doctoral student with the University of Delaware and SMBC who is conducting a three-year study to learn how nonnative, or exotic, trees in cities and suburbs affect the availability of food birds need during the breeding season.
“We’re focusing on the chickadee because it’s a common backyard species that, like most birds, feeds insects to its young,” Narango says. Because chickadees are c Last March, Narango installed one of these houses in a backyard in Washington, D.C.
The team discovered that “chickadees indeed prefer to forage on native rather than nonnative trees—overwhelmingly so,” Narango says. The aerial map below shows the amount of time the birds spent foraging in different tree species in and around one residential yard. Ignoring nonnatives close to the nest, chickadees preferred to fly farther to natives such as American elm, black cherry and several oak species.
To read the rest of this interesting article, click the following link: http://www.nwf.org/News-and-Magazines/National-Wildlife/Birds/Archives/2015/Chickadees-And-Native-Trees.aspx
For a related article, check out the following: http://www.esajournals.org/doi/abs/10.1890/14-0171.1
Characterizing Bird Survival Along a Rural to Urban Gradient
Many avian species persist in human-dominated landscapes; however, little is known about the demographic consequences of urbanization in these populations. Given that urban habitats introduce novel benefits and pressures, conflicting mechanisms have been hypothesized to drive the dynamics of urban bird populations. Top-down processes such as predation predict reduced survivorship in suburban and urban habitats, whereas bottom-up processes, such as increased resource availability, predict peak survival in suburban habitats.
In this study, we use mark-recapture data of seven species encountered between 2000 and 2012 to test hypotheses about the processes that regulate avian survival along an urbanization gradient in greater Washington, DC. American Robin, Gray Catbird, Northern Cardinal, and Song Sparrow, exhibited peak survival at intermediate and upper portions of the rural-to-urban gradient and this pattern supports the hypothesis that bottom-up processes including resource availability can drive patterns of avian survival in some species.
In contrast, Carolina Chickadee showed no response and Carolina and House Wren showed a slightly negative response to urban land cover. These contrasting results underscore the need for comparative studies that document the mechanisms that drive demography and how those factors differentially affect urban adapted and urban avoiding species.