Sizing Up Territories
by Lea Craig-Moore, Wildlife Techncian, CWS
Whooping Cranes defend a territory in both summer and winter—on breeding grounds as well as on winter feeding grounds.
The breeding grounds will soon be a buzz of Whooping Crane activity as wetlands thaw and pairs select which wetland on which to build their nest. Happy to be back on their breeding territory in Canada, this crane pair dances. How do they pick and defend their territory? Keep reading and you'll see!
Same Territory: No Trespassing!
The first birds that arrive are the ones that have nested here before. Pairs arriving on the breeding grounds in and around Wood Buffalo National Park, Northwest Territories and Alberta will return to the same nesting territory of years past. We know from birds that were colour banded between 1977-1988 that some nesting territories have been occupied for nearly 20 years!
New pairs nesting for the first time must search for a territory with:
- wetlands of suitable vegetation, such as bulrush, and
- adequate water depth for nesting (average of 23 centimeters or about 10.5 inches) and
- enough food to support themselves and future young.
Another consideration for these new pairs is how well they can manage defending their territory against neighbouring whoopers.
The size of territories really depends on how close nesting neighbours are, which likely depends on available resources. Some marshes have 20 or more nests while other marshes, similar in size, may have only five nests. The size of a pair's territory ranges about 1.3 to 47.1 square kilometers (0.8 to 29 square miles) but averages 4.1 square km (2.5 square mi).
Pairs defend their territories upon arrival and throughout the summer in two ways. They use unison calls, which are territorial calls that both males and females take part in. And, of course, they chase other whoopers away!
Biologists Appreciate Territories
Thanks to the territorial nature of pairs, we can more easily count nests. Each year we fly aerial surveys over the entire nesting grounds. We start our search each year by returning to the location of the previous year's nests. Without this crane behaviour of territoriality, it would be much more difficult to monitor the population because we would have to search huge expanses of marsh habitat suitable for nesting.
Journal or Discussion:
- What are the advantages of territorial behaviors?
- How is having and keeping a good territory connected to crane survival?