News Article: Long-distance travellers - migratory birds defy the odds
Tuesday, April 28th 2009 3:08:43pm
By: Gregor Beck
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Biologists, like scientists and statisticians of any stripe, spend much of their time looking for averages to provide compelling information and irrefutable proof about what's going on in the environment around us. We gather piles of data and base our conclusions on what we've interpreted from it. But the early return of long-distance migrant purple martins, members of the swallow family, this spring provided a good reminder that it's important not to lose sight of the stories individual birds (or other wildlife) can tell as well.
On a balmy Sunday afternoon in early April, an adult male purple martin returned from its Latin American wintering grounds to the martin house we installed two years ago. Even though our Long Point area home on the Lake Erie shore is part of Ontario's "South Coast" and is relatively mild for Canada, this date is particularly early for the return of these handsome insect eaters.
After a few quick circles overhead, the purposeful martin made a beeline for the 16-hole martin house. Based on its behaviour, we're certain it is from one of the half dozen pairs of martins which nested here last year. It may even be one of the initial pair that nested in 2007. Within hours, a second advance guard arrived - a sub-adult male likely hatched at the site last summer.
No rest for the travel weary, though, as the two purple martins were forced to fend off several European starlings which were showing interest in the martin house also. Starlings are not native to North America and often compete with native species for nest cavities. Interestingly, these purple martins were illustrating the potential benefits of risking an early return - securing and defending nesting sites and breeding territory in advance of the returning females.
The rigorous defence of the nest site is particularly impressive given the magnitude of the migration the birds had just completed. Purple martins winter in South America and their one-way trip north may have exceeded 6,000km.
The potential down-side of returning early was illustrated when a harsh April snow storm and cold snap threatened their survival. In subzero temperatures and with a bitter wind blowing, the birds hunkered down inside the martin house. Perhaps they ventured out occasionally in search of flying insects. Survival in times like this is tenuous since martins rely on insects for nourishment, and after such a long migration individuals' energy stores would be greatly diminished.
Two days later, as temperatures started to climb back above the freezing mark, it appeared that these martins had survived not only their long migration and fended off aggressive nest-site competitors, but also weathered several days of abysmally-poor feeding conditions. Surprisingly, two more males arrived during this wintry period having flown through the late storm to reach prime breeding habitat in southern Canada.
"The trials and tribulations of these individual martins reveal broader environmental concerns," observed Caroline Schultz, executive director of Ontario Nature. "Recent publications, such as the Atlas of the Breeding Bird of Ontario, clearly indicate that birds that eat flying insects are in big trouble. Populations and breeding ranges of swallows, nighthawks and chimney swifts are all in sharp decline in Ontario."
The reasons for the declines are not clearly understood and the issue is now a hot research topic. Among the possible explanations for the decline of these "aerial forager" species are habitat loss on wintering and/or breeding grounds, environmental contaminants, and possibly direct or indirect effects of climate change. In the latter case, it is possible that more erratic weather patterns are affecting the timing of some species' return to breeding grounds and making them more susceptible to poor weather conditions on their return, or their breeding cycles may no longer be timed to coincide with peak insect hatches.
"Purple martins, like all wildlife, need stable food supplies and quality habitat," noted Peter Carson, president of the Long Point Basin Land Trust. "While martins and other swallows are declining significantly from inland and more northerly parts of Ontario, the Lake Erie shoreline remains a relative stronghold. It is possible that our area's productive coastal wetlands provide more reliable food resources and a more moderated climate."
Resources like the bird atlas and other surveys which show large-scale trends and scientific averages are tremendously helpful in providing an overview of the status of wildlife. But, sometimes it takes stories like this to really bring home the point that survival in nature comes down to strength, endurance and, often, luck of individuals. In the weeks to come, we hope that our early-bird martins are joined by dozens more and that they can buck the widespread and, sadly, downward trend of insect-eating birds in Ontario.
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Gregor Beck is a wildlife biologist, co-editor of the Atlas of the Breeding Birds of Ontario (www.birdsontario.org), and conservation science consultant to the Long Point Basin Land Trust.
Long Point Basin Land Trust protects important natural habitats in the central Carolinian Region in southern Ontario. It promotes conservation through outreach, research, habitat restoration, and species-at-risk recovery projects. For more information about this charitable organization, visit: www.longpointlandtrust.ca.
Ontario Nature is a not-for-profit organization that protects wild species and wild spaces through conservation, education and public engagement. It connects thousands of individuals and communities with nature through various conservation groups across the province (charitable registration # 10737 8952 RR0001). For more information, visit www.ontarionature.org.