Urban Takeover: Canada Geese Shifting from City Parks to Industrial Rooftops

In the past several decades, temperate-breeding Canada geese (Branta canadensis) have increased throughout the midwestern United States. Moreover, subarctic-breeding populations of Canada geese appear to be shifting their wintering range northward from the south and central portions of the Mississippi Flyway to more northern latitudes. We investigated Canada geese wintering in the Greater Chicago Metropolitan Area (GCMA), including determining genetic composition of birds using locations nearby Midway International Airport, home range sizes, spatial and temporal use of thermal refugia, and response to harassment. During summers 2014–2015, we captured 690 Canada geese within the GCMA during their annual molt. We obtained morphological measurements (i.e., culmen length, skull length, tarsus length, mass) and DNA samples to determine a baseline for temperate-breeding Canada geese. We also affixed an aluminum leg band and a plastic waterfowl neck collar with unique alpha/numeric codes on all birds for use in re-sighting efforts. During the autumn and winters of 2014–2016, we captured 152 Canada geese using a combination of rocket nets, net guns, and cast nets within the urban area. We attached solar-powered global positioning system (GPS) CTT-1040a transmitters (Cellular Tracking Technologies, Somerset, PA) to neck collars of 39 geese spread throughout the two winter field seasons to collect detailed information on their movements and habitat use. DNA analysis from the first field season shows that the population of captured birds consisted of ~58% from subarctic-breeding populations and ~42% from the temperate-breeding population. The transmitters acquire a GPS location once per hour and relay data through global system for mobile communication (GSM) towers, also used by cell phones. By using GSM technology, we are able to receive data in near real time and have the ability to change transmission rates for finer scale resolution when needed. Multiple thermal refugia within close proximity to food sources were used by geese staying within the GCMA. During extreme cold periods, geese moved from parks and cemeteries to rooftops and warm water discharge areas along the canal to aid in thermal regulation. Geese sought thermal refuge on black rooftops, with as many as 450 individuals occupying a rooftop at one time. Temperature recorders and anemometers were deployed in these thermal refugia locations to compare weather variables between sites used during harsh weather and sites used during warmer periods of the winter to identify shifts in spatial use in relation to climactic variables. Operative temperature models were created for areas with and without roosting geese in order to determine if the thermal environment differs, and if so whether there is a "threshold" thermal environment needed for Canada geese to winter in the GCMA. We then took the weather data collected from each sight used and created an agent-based model to identify future goose movements in response to shifts in weather variables and assessed those movements with our transmitter data. The data gathered from this research will help evaluate current management practices and help design future management practices of Canada geese that winter in the GCMA area.