Greater White-fronted Goose (Anser albifrons) Nest Characteristics and Nesting Behavior Classifications from Time-lapse Photographs and Nest Visit Data; Point Lonely, Alaska, 2013-2014

For a subset of nests located within the disturbed and control sites, we placed digital time lapse cameras (Wingscapes, Moultrie, Lafayette, LA, USA) at ground level, approximately 5–10 m from the nest bowl, at the time of discovery. To provide concealment and minimize the attraction of predators, cameras were positioned within depressions in the ground or adjacent to microtopography so that they did not extend higher than the local terrain. Date and time were synchronized on all cameras and they were programmed to capture photographs on 1-minute intervals, with an expected battery life of 7 days. We revisited camera and non-camera nests every 5–7 days to record nest fate, clutch size, incubation stage, and to replace camera batteries; eggs were covered with nesting material upon completion of each nest visit. Within each site, we re-visited all nests on the same day and re-searched the site for additional nests; nest visits occurred primarily between 1400 and 2100 hours. Cameras from nests that failed were moved to active nests in close proximity. The ultimate fate (i.e., success or failure) of all nests was determined via visits independent of the camera data to allow for comparison of techniques. Nests were considered successful on a visit if at least one gosling or detached shell membrane was observed in the nest bowl.

Photographs from each nest were examined individually on a computer screen. For each nest photograph, we categorized the status of a female as: 1) incubating, 2) present, or 3) absent and these categories were entered into a spreadsheet for each nest and image. A female was considered to be ‘incubating’ when she was directly covering the eggs, ‘present’ when she was visible in the photograph and within the vicinity (~10 m) of the nest (i.e., not incubating, but available to defend against predators), and ‘absent’ when she was not visible in the photograph (i.e., possibly unavailable to defend against predators). For each photograph, Wwe also recorded the presence of investigators, documented predator observations and the behavioral response of geese to predators, and noted whether or not a predator was successful in depredating at least one egg. These data were also entered into the spreadsheet. When the success of a predator could not be determined from photographs, we used clutch size information recorded during nest visits to attribute depredation events to observed predators. Photographs in which the status of a female could not be determined (e.g., due to fog or camera misalignment) were categorized as uninterpretable and censored from analyses. Nests were considered successful when goslings were first visible in a photograph, and they were considered to have failed when the source of nest failure (i.e., predator or observer) was first present in a photograph. For instances in which a nest was depredated before the female returned following an observer visit, we attributed the source of failure to the observer. Nest abandonment in which a female did not return to incubate following a visit was also attributed to the observer.