Background and purpose: As Canada goose populations have recovered from near extirpation to approximately 113,000 individuals in Indiana over the past 60 years, urban densities have created persistent human-wildlife conflicts and novel behavioral adaptations. Canada geese typically nest on the ground or slightly elevated natural sites like muskrat lodges near water bodies. However, the effects of urbanization on nesting site selection in this species have been understudied. This article documented observations of Canada geese nesting on rooftops 2.6–12.2 meters above ground level in central Indiana to understand how urban environments are influencing nesting behavior in this adaptable waterfowl species.

Methods: Researchers conducted routine nest surveys across three study areas in the Indianapolis Metropolitan Area from March to July 2021. Five rooftop nests were discovered and monitored on a weekly basis. Data collection included capturing band information from adult geese, counting eggs, recording nest materials, and tracking nest success through observations of egg membranes and goslings. Nest characteristics such as height above ground, distance to nearest water body, clutch size, and construction materials were documented. Hatching success was compared between elevated nests and ground-level nests in the same study areas.

Results: Rooftop-nesting Canada geese showed distinct differences from traditional ground nesters. Elevated nests had significantly smaller clutch sizes (average 4.00 eggs) compared to ground nests (5.01 eggs), but achieved 100% hatching success versus only 59.9% for ground-level nests. This suggests that while elevated nesting may reduce reproductive output, it significantly improves nest survival. Nest construction materials differed substantially, with rooftop nests using atypical materials like automotive belts, plastic sheets, and loose gravel with minimal traditional down and body feathers. All five rooftop nests successfully hatched, though goslings from two nests required human rescue due to barriers preventing natural departure. The researchers hypothesize that geese are selecting these elevated sites to avoid ground predators including mammals and human disturbance.

Criticisms: This study provides valuable documentation of an emerging urban adaptation, but several limitations affect the strength of conclusions. The sample size of only five nests is quite small for making broad generalizations about population-level behavioral changes. The study lacks systematic methodology for nest discovery, so it’s unclear whether these represent rare occurrences or a more common behavior that’s simply underreported. I would be interested to know if the researchers were actively searching for rooftop nests or if they just happened upon them during other surveys. Additionally, the research provides no data on long-term gosling survival rates after hatching, which is crucial for determining whether this apparent nesting advantage translates to reproductive success. While hatching success was high, the fact that goslings from two nests required rescue suggests potential survival challenges that could offset the benefits. 

The study also lacks environmental controls such as temperature measurements comparing rooftop versus ground conditions, which could help explain the higher hatching success. I am curious whether this behavior is spreading to other regions or if it represents a local adaptation specific to central Indiana’s urban landscape. Future research would benefit from larger sample sizes across multiple urban areas and longitudinal tracking of gosling survival rates to determine the true fitness consequences of this behavior.

Reference:

Shearer, D. J., Carter, T. C., & O’Neal, B. J. (2022). Canada geese (Branta canadensis) nesting on elevated structures in urban Indiana, USA. Ecology and Evolution, 12(3), e8735. https://doi.org/10.1002/ece3.8735