Micro-site Climatic Conditions Associated with Urban Thermal Refugia used by Canada Geese during Winter

In the past several decades temperate-breeding Canada geese (Branta canadensis) have increased throughout the midwestern United States and appear to concentrate in more urban environments opposed to migrating to southern latitudes during winter to aid in thermoregulation. We investigated Canada geese wintering in the Greater Chicago Metropolitan Area (GCMA) and identified winter roost sites to measure micro-site thermal benefits of selected thermal refugia. Our objectives were to determine thermal regulatory benefits of selected habitats during winter; identify the temperature gradient when geese transition from one roost site to another; and determine how thermal refugia can be manipulated so thermoregulatory benefits are no longer available and birds are forced to move into new locations. Use sites were determined by attaching solar-powered global positioning system (GPS) CTT 1040a transmitters (Cellular Tracking Technologies, Somerset, PA) to waterfowl neck collars on nine Canada geese and monitoring movements. Of the nine geese tracked, seven were deemed temperate-breeding and two deemed subarctic-breeding based on morphological measurements. At unique sites, we deployed iButton temperature loggers (Maxim Integrated, San Jose, CA) in January and February 2015 to determine differences in ambient temperature and these data were compared to local weather station data. Even after birds shifted from one site to another, iButtons were left deployed at each site for the remainder of the field season to identify at what temperatures sites were used. Four main roost locations where identified including two rooftops, a waste water treatment plant and a park along Lake Michigan. Areas that were previously used had temperatures in close proximity to data gathered from a local weather station, but the waste water treatment plant and rooftops had temperatures exceeding local temperatures by 21.6°C and 9.6°C at certain points throughout the day, respectively. Canada geese showed a preference for black color rooftops when compared to white and gray colored rooftops of adjacent buildings. Each black rooftop had as many as 350 individuals occupying them at one time. Of the geese using the rooftops as many as one third of the birds had been neck-collared during the year from areas all throughout the GCMA. Geese also had a tendency to congregate on the northeast corners and around heat vents of each building. During the winter of 2015‒2016 we will deploy temperature recorders along with anemometers to record micro-site specific data for use in an operative temperature model. Identifying thermal benefits will help understand why current sites are selected by wintering geese and how local businesses and wildlife managers can manage these areas to decrease conflicts with humans."