Songbird Protection Coalition
Eastern Population Sandhill Crane Genetic Diversity
Michigan should not add hunting mortality to the significant threats that this species already faces
The crisis of the Eastern Population (EP) sandhill cranes (Grus Canadensis) has been well-documented since the 1800s. By the 1930s, sandhill crane numbers were reduced to approximately 50 breeding pairs in small, isolated populations in Michigan, Minnesota, and Wisconsin (Henika 1936, Walkinshaw 1949).
Human subsistence and recreational hunting, combined with the conversion of wetland habitat for agricultural use, caused the population to bottleneck by the early 1900s (Walkinshaw 1949).
While genetic diversity has been permanently lost in the EP sandhill crane population, its few surviving members have also suffered from a significant demographic isolation-by-distance. Sandhill cranes are philopatric, which means that offspring tend to return to their "natal site of origin," or place of birth. Site fidelity and territorial loyalty by biological design is key to the reproductive success of breeding pairs. Because of this strong natal philopatry and infrequent long-distance dispersal, the surviving individuals were heavily fragmented, making isolated population genetic clusters - therefore preserving some of the diverse genetic makeup of the once greater population.
Recent genetic research confirms that even sandhill cranes within even 60 miles of each other can be genetically unique from each other, creating geographically stratified breeding areas that are genetically important in the EP. Because of this, genetic researchers warn that a recreational hunting season in the northern breeding states, such as Michigan, could easily wipe out these unique breeding populations and eliminate the surviving genetic variation through yet another bottleneck crisis (Source: University of Wisconsin, US Fish and Wildlife Service, et al.).
This matters; because the more genetic diversity within a species, the more adaptable to change and the survival as a species to overcome deadly diseases and environmental changes. For example; diseases like West Nile virus and Avian Influenza can spread quickly, but bird populations with diverse genes are more resistant to those ailments and more likely to survive as a species. Another example given by researchers; the climate is changing, and how sandhill cranes fare is dependent on their genetic diversity and their capability to adapt to those changes as they occur now and in the future (Source: University of Wisconsin, US Fish and Wildlife Service, et al.).
Biologists affirm that much is still unknown, because of a lack of research and inconsistencies of reliable or long-term population studies of sandhill crane in the EP flyway. Researchers warn that numbers alone don’t predict a population’s biological stability - especially when a susceptible population has passed through a population bottleneck that has likely affected the fitness of their genetic structure.
In addition to these genetic challenges, sandhill cranes face ongoing threats to survival from disease, hailstorms, lightening, poisoning by the ingestion of lead ammunition and tackle and other toxins, predation, avian tuberculosis, and collisions with power lines. Adding trophy hunting mortality could even further imperil the continued recovery of EP sandhill cranes.
Sources, including but not limited to: US Fish and Wildlife Service, University of Wisconsin, Michigan DNR, Wisconsin DNR, Ohio DNR, Ad Hoc Eastern Population Sandhill Crane Committee, The Journal of Wildlife Management, Great Lakes Echo, The Birds of Michigan Atlas.