SWAINSON'S HAWK NESTING ECOLOGY PROJECT
Each year, Swainson’s hawks undertake one of the longest migrations of any of Montana’s breeding raptors. They regularly travel roughly 7,000 miles to wintering grounds as far south as Argentina then return to western North America in April to breed. Theirs is truly an incredible migratory undertaking and one that requires an enormous investment of time and energy.
In mid April we were happy to see our first color-banded males showing up on territories from previous seasons. However, habitat is changing fast in this region. Where less than year ago there were open fields for Swainson’s hawks to hunt and suitable trees for nesting, there now are only paved roads and subdivisions. Indeed, the development and growth of the Missoula Valley seems to be catching up with them.
To give you an idea of the change, in 2006, we accounted for 10 occupied nesting territories. Six of the 10 pairs successfully fledged young, with an average of 2.8 young per nest and a total of 17. The 2007 season was far less productive. We observed seven active territories, and only two of those were successful in fledging, with just one chick each.
The poor breeding success of occupied territories may also be attributable to low rodent numbers, possibly a result of the drought-like conditions of this summer. Denver Holt, of the Owl Research Institute, reported that vole numbers crashed according to data from the institute’s Mission Valley small mammal surveys. Similarly, Denver reported low long-eared owl breeding success in Missoula Valley.
To date we have identified 14 Swainson’s hawks nesting territories in the Missoula Valley, banded more than 20 individual birds, and marked 17 with uniquely color-coded bands. We will continue to monitor the known territories and search for new ones as we learn more about Swainson’s hawks in the Missoula Valley.
We are investigating:
- nest site selection;
- home range size;
- nesting frequencies;
- nest site fidelity;
- possible inter-relatedness with neighboring birds through DNA analysis;
- mate fidelity; and
- effects of human encroachment and development on established territories.
We would like to extend a hearty thanks to our professional arborist friends: Rob Dylan, owner of Dylan Tree Service & Landscape in Missoula, and Tim Nesmith, owner of Salmon Logging in Seeley Lake. Both these gentlemen donated their time and climbing expertise in the past to access nests, and we hope to call on them again next spring.
Also, thanks to our friend Denver Holt, who remarkably and courageously climbed to the very top of a huge ponderosa pine this summer to access a Swainson’s hawk nest. Awesome, Denver!
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