Mike Newhouse, a Towson University graduate student, studied house wrens to examine patterns of reproductive success and parental care in selected backyards of Neighborhood Nestwatch participants along the urban to wildlands gradient.
House wrens are 1 of the 8 Neighborhood Nestwatch focal species. Like Carolina chickadees, they are a cavity-nester and frequently breed in nest boxes. Unlike chickadees, which stay put for the winter, house wrens migrate, traveling as far south as Central America to spend the winter.
Their cavity-nesting behavior makes it relatively easy to study their reproductive biology because nest boxes can be placed in strategic locations that give scientists easy access and unobstructed views of parental activity during the nesting period.
For birds breeding in natural habitats, the quality of nesting habitat is determined by a variety of factors including food availability. Once babies hatch, adults maximize the rate at which they bring food to nestlings. This intense period of parental care is an important determinant of whether a nest fails or succeeds.
Growth rates of nestlings often mirror patterns of parental care as well as local food abundance. With this in mind, Mike placed an equal number of nest boxes in suburban and rural backyards and measured nestling growth rates.
In total, he compared parental care and nestling growth rates of 26 suburban and 26 rural house wren pairs. That's a lot of driving!
Although preliminary, the results are starting to reveal some intriguing patterns. House wren parents made significantly more feeding trips per hour in suburban backyards compared to rural backyards.
Yet rural nestlings grew at a faster rate than their suburban counterparts.
In addition, suburban parents spent less time brooding (sitting on the nest) compared to rural parents.
Such results suggest that suburban backyard habitats offer house wrens food for nestlings that is inferior in either quality or quantity to what rural habitats offer. Food items may, for example, be smaller in suburban habitats, and force adults to make more trips to the box.
Another interesting finding is that females spend significantly more time feeding nestlings than males so, although male parental effort does increase as nestlings age.
This article summarizes the information in this publication:
Reproductive Success of House Wrens in Suburban and Rural Land-Use Areas. 2008. Newhouse, M., Marra, Peter P. and Johnson, L. S. The Wilson Journal of Ornithology, 120(1): 99-104.
We investigated the impacts of urbanization on reproductive success of House Wrens (Troglodytes aedon). We compared reproductive effort and success for 33 nesting attempts in suburban sites (2.5–10 buildings/ha) and 43 nesting attempts in rural sites (<2.5 buildings/ha) in and around the Washington, D.C.– Baltimore, Maryland, metropolitan area. There were no differences in clutch initiation dates or clutch sizes between suburban and rural nests. However, nestlings at suburban nests weighed less and had smaller body size prior to fledging compared to nestlings at rural nests. Parental feeding rates differed between suburban and rural nests during the “early nestling stage” (day 3 to day 6), but not in the “late nestling stage” (day 8 to day 12) suggesting average quality of prey for nestlings may be lower at suburban sites. Overall, suburban nests fledged more young than rural nests largely because of higher rates of nest predation on rural nests. Further research on how food availability and predation affects nesting success of House Wrens and other birds along urbanization gradients may provide important insights into impacts of urbanization on birds.
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