New research suggests fear is responsible for underweight chicks – ScienceDaily


A team of researchers based at the University of Massachusetts at Amherst recently discovered that fear plays an important and unrecognized role in the underdevelopment and increased vulnerability of backyard songbirds.

Scientists have long known that urban songbirds face a myriad of increased challenges, ranging from habitat loss to altered food sources and a larger population of predators, such as skunks, rats, squirrels and, in particular, domestic cats, compared to their rural cousins. In particular, urban chicks weigh significantly less than those born in the countryside and are therefore less likely to survive to adulthood. New research, published in the journal Ecosphere, helps to understand exactly why.

Part of the difficulty in understanding why urban chicks struggle is due to what biologists call the “predation paradox”: Although there are an increased number of predators in urban areas, there is actually a lower per capita predation rate. “The key,” says Aaron Grade, the lead author of the article who completed this research as a graduate student in the Organism and Evolutionary Biology program at UMass Amherst, “s’ is hidden in plain sight. We haven’t paid enough attention to the fear itself. “

To come to this conclusion, Grade, with his coauthors Susannah B. Lerman, research ecologist at the USDA Forest Service Northern Research Station; and Paige S. Warren, professor in the Department of Environmental Conservation at UMass Amherst; built 38 nesting boxes for house troglodytes and placed them in participants’ backyards. Participants lived in a variety of landscapes, all in Massachusetts’ Connecticut River Valley, from urban (Springfield, with a population density of 4,775 people per square mile), to low-density suburbs (Amherst, 1,445 people per square mile) to rural (Whately, 72 people per square mile).

Grade and his colleagues then played the cries of Cooper’s owls and hawks, both of which feed on house wren in Massachusetts, from loudspeakers installed in each participant’s yard. “The participants were wonderful,” says Grade. “They put up with this noise in their garden and were very invested in the experience.” The chicks in each box were then weighed every three days until they left the nest.

The authors found that due to a variety of “urban effects,” including food availability, habitat loss, and predation, urban chicks all weighed about 10% less than rural chicks – an expected conclusion that is consistent with previous studies showing the effects of urban development on wildlife. But the authors also found that all the chicks, both rural and urban, subjected to the calls of the owl and the hawk also saw their weight decrease by 10%.

“This is a largely unexplored component of the human / wildlife interaction,” explains Grade. “Birds are very aware of what’s going on, and if they see, or in this case hear, a predator, they will change their behavior.” For example, parent birds might spend less time finding food for their young to avoid predation. “These scary landscapes,” Grade explains, “may have a greater effect on behavior and survival than the predator itself.”

In general, birders should avoid using predator records, as they can cause unintended reactions and undue stress in birds, as Grade’s research shows. These experiments were conducted with the approval of the UMass Institutional Animal Care and Use Committee and followed best practices for reading experiments to reduce any potential harm.

This research was funded by the University of Massachusetts Amherst Graduate School; the Manomet Center for Conservation Sciences; the Blodget Fund for Ornithological Studies; the Animal Behavior Society; the American Ornithological Society; and the National Science Foundation.


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