Date of Award

2014

Document Type

Honors Thesis (Open Access)

Department

Colby College. Biology Dept.

Advisor(s)

Herb Wilson

Second Advisor

Catherine Bevier

Third Advisor

Andrea Tilden

Abstract

Mobbing calls are produced by a variety of bird species in response to predator sightings. These mobbing calls often function in intraspecific recruitment, but have recently been shown to have an interspecific response component as well. The mobbing calls produced by the Black-capped Chickadee (Poecile atricapillus) are distinct and encode information about the threat level of the predator. Conservation biologists often use playbacks of chickadee mobbing calls to detect species of birds and numbers of individuals in an area with higher accuracy than counts conducted without the use of playbacks. In this study, the factors that could potentially influence intra- and interspecific response to chickadee mobbing calls were investigated, including: threat level encoded in the mobbing call (low or high), time of day, season, type and amount of tree cover, and weather conditions. The species and number of birds responding to playbacks of mobbing calls were compared to baseline levels of birds in the area, as well as to the response to territorial chickadee songs, an intraspecific signal. Playbacks took place at sites in the Perkins Arboretum at Colby College, from November 2013 to April 2014. More species and a greater number of total birds responded to low dee playbacks in the morning than they did at midday or afternoon. A greater number of total birds responded to low dee calls in conditions without wind when compared to windy conditions. More species and a greater number of birds responded to low dee calls in the rain when compared to conditions with snow or without precipitation. Chickadees also produced significantly more dee notes in response to tapes with mobbing calls, when compared to tapes with songs, though there was no significant difference in calls as a response to high dee or low dee tapes. These results suggest that the most accurate estimate of bird populations in an area can be assessed via low dee playbacks on mornings with no wind.

Keywords

avian mobbing, interspecific eavesdropping, conservation assessment, Perkins Arboretum, playbacks

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