Winona State University
BIOL 406/506 - ORNITHOLOGY
Lab Exercise

EASTERN SCREECH-OWL PELLET ANALYSIS

OBJECTIVE

During the winter months, Eastern Screech-owls in Winona occupy nest boxes placed in wetland areas for use by Wood Ducks. Since owls regularly regurgitate pellets containing bones and other prey remains, pellets collected from nest boxes in late winter can be used to assess the types of prey consumed by owls during the winter. This exercise will examine owl pellets collected from nest boxes bordering Lake Winona and Boller Lake to determine the diet of an "urban" owl population.


HYPOTHESIS

Eastern Screech-owls consume a variety of prey types in equal proportions during the winter months.


METHODOLOGY

As many owl pellets as possible will be collected by the instructor during late-February or early-March. No attempt will be made to keep pellets collected from one nest box separate from those collected from other boxes. In the laboratory, pellets will be dissected individually under a dissecting microscope, and prey identity will be determined based on skulls, jaw bones, teeth, beaks, feathers, or other materials present within the pellets. The total numbers of different types of prey consumed will be tabulated. See the Powerpoint for help in identifying prey.


ANALYSIS

After data are collected, display the types and numbers of prey eaten by screech-owls in table form. The following are genus names of potential prey types:
deer mice/white-footed mice - Peromyscus
house mice - Mus
meadow jumping mice - Zapus
voles - Microtus
shrews - Sorex
various birds - consult field guide

Do not include prey types whose remains we expected to find, but did not detect. Determine whether prey types were consumed in equal proportions by comparing observed distributions among prey types versus expected distributions (Chi-square goodness of fit test, Ecology lab manual).


EQUIPMENT

Step ladder (for the instructor to play with during Spring Break!)
Dissecting tools
Dissecting microscopes
Mammal skull key
Bird field guide
Ecology lab manual

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