Birds Beneath Our Feet?

The Mississippi Valley Field Naturalists’ (MVFN) 2012-2013 public lecture series, Nature Beneath Our Feet, continues March 21 with the sixth presentation, “The changing face of predation on Arctic nesting birds: polar bears, foxes and eagles.” You do not need to be an expert to enjoy the presentations, just possess a curiosity or appreciation for wild nature. Cottagers, hunters, fishermen, canoeists, hikers, campers, artists and seasoned field naturalists alike will find something to interest them as we explore nature. Refreshments are offered at each lecture.

MVFN’s March speaker is Dr. Ken Abraham who is the wetlands and waterfowl scientist of the Wildlife Research Team of the Ministry of Natural Resources in Peterborough and an adjunct professor at Trent University in the Environmental and Life Sciences graduate program. His presentation will focus on ground-nesting birds—primarily geese, ducks and shorebirds—in the Arctic and how predation affects their survival. From predation by polar bears on geese and shorebirds, to the role of foxes and alternative prey in predation on common eiders, to unusual events like eagles taking adult ducks, Dr. Abraham will provide a variety of examples to illustrate predator-prey relations among ground-nesting birds.

Nesting on the ground seems inherently dangerous. While falling out of the nest may not be an issue, you would think ground-nesters and their eggs would be easy prey and easily trampled. In habitats where there are no trees, such as grasslands and the Arctic, the ground is it. What strategies might ground-nesters employ to enhance their chances of producing offspring in such areas? Perhaps they are experts at camouflaging nests or eggs. Laying many eggs in a nest, having more than one clutch of eggs, doing predator distracting displays, or behaving aggressively toward intruders also might help. Can you think of other deterrents?

Some ground-nesting birds select areas where ground predators are less abundant. For example, Dr. Abraham and his colleagues conducted a study of predation and ground-nesting Arctic shorebirds. They put out over 1,500 artificial nests with eggs along a north-south gradient covering almost 30 degrees of latitude (3,350 km). After two summers of investigation, they found that nests at the northern extreme (Alert Island, 82oN) experienced 66% less predation than nests at the southern end of the gradient (Akimiski Island, 53oN, southern-most tip of Nunavut). No wonder Arctic-nesting birds have some of the most impressive migratory strategies, such as flying from wintering areas at the southern tip of South America, southern Africa, and Oceania to their breeding grounds in the Arctic—the reward is fewer predators!

Another strategy ground-nesting birds may use for reducing the risk of predation is to enlist other species to provide some protection. The ‘protector species’ would show aggressive behaviour toward predators or provide early warning signals of predator approach, or both. This strategy was examined by Dr. Abraham in a study that compared nest survival of semipalmated plovers in areas with and without nesting arctic terns. He found that plover nests benefited substantially from protection against predators (<10% of all nests lost) through aggressive behaviour of the terns.

And the story about eagles taking adult ducks? For that you will need to come to Dr. Abraham’s presentation, “The changing face of predation on Arctic nesting birds: polar bears, foxes and eagles,” which will be held at 7:30 pm on Thursday March 21, 2013, Almonte United Church, 106 Elgin St., Almonte. All are welcome ($5 fee for non-members). For further information please contact MVFN’s Program Chair Cathy Keddy at 613-257-3089.


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