Cranberry Lake Biological Station

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When forest birds feel threatened by the presence of a potential predator, they may respond with an anti-predator strategy called mobbing. Mobbing is a set of behaviors intended to harass and drive a predator away. In order to observe the response of forest birds to native and non-native owl calls, 3 separate species’ calls were played 4 times a day for 4 days at 8 different locations (n=31, 1 point was discarded due to severe weather). Four calls were broadcasted: the Black-Capped Chickadee (Poecile atricapillus) as the control, the Barred Owl (Strix varia) as the native predator, and the Spotted Owl (Strix occidentalis) and Eurasian Tawny Owl (Strix aluco) as non-native predators. During and after the broadcasted calls, the number of forest birds that flew in and the strength of the alarm calls (based on a scale), both characteristics of mobbing behavior, were recorded. Using an ANOVA and Tukey Test, it was concluded that the number of birds that flew into the area in response to the native Barred Owl was statistically different than the Black-Capped Chickadee, Spotted Owl and Eurasian Tawny Owl. However, the response to the Black-Capped Chickadee, Spotted Owl, and Eurasian Tawny Owl was statistically similar. Based on the Chi-Squared test, the difference between the strength of alarm calls in response to the different species of owls was found to be statistically significant. It was found that the forest birds at Cranberry Lake Biological Station tended to exhibit mobbing behavior more often in response to the native Barred Owl than to the non-native Spotted Owl and Eurasian Tawny Owl.


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