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Loons are becoming tamer overall, according to a survey of loons on 200 Wisconsin lakes that began a quarter of a century ago.
Individual birds do not become more comfortable around humans over time, biologist Walter Piper has found. But humans are still the cause of the change.
Piper, from Chapman University in California, has been studying the behaviour of loons of northern Wisconsin since 1993.
While he and his students are out banding and observing loons, they have measured and recorded how tame each bird is, like this:
“An observer measures his/her distance to a resting bird with a rangefinder and then paddles slowly in the bird’s direction, taking distance readings every few strokes,” he writes in his blog. “The final distance reading — just before the loon dives to avoid us — is our measure of tameness.”
They find the distance ranges from less than two metres to more than 50 metres. “In fact, some of our marked birds … find our approach so innocuous that they simply veer slowly out of our path, instead of diving.”
Over the years Piper’s group has found that tame loons are more likely to live and reproduce near humans.
And while he doesn’t know the reasons, he has found “a strongly and statistically significant relationship” in which tame parents have tame chicks.
The study is still in its early stages, but Piper says the evidence so far suggests that tame birds do well on lakes with humans living nearby. The “skittish” loons are driven to lakes farther from towns and cottages, which are often smaller and less able to give the birds all the food they need. This is turn appears to result in poorer chances at raising chicks for the skittish loons.
The result: the population appears to be tilting toward loons that tolerate human presence.
If this holds up, Piper writes, “tame loons will produce a large proportion of all offspring in the northern Wisconsin population, and tameness should increase in frequency in coming decades to the point where skittish loons are hard to find at all.
“This vast behavioral shift might go unnoticed by most observers, since there will still be loons on the lakes. But to an ecologist, it is exciting to think that we might be on the brink of learning the precise mechanism by which a population of an important animal can become tame.”
Piper is chasing a second theory as well. He has noticed over the years that solitary loons, which are always on the lookout for a chance to attack another bird and take over its territory, appear to target birds that raised chicks successfully the previous year. The theory is that the attacking bird realizes that successful parents are occupying good breeding grounds.
“The effect is dramatic; the intrusion rate (i.e. the rate of attempts to grab territory) increases by 70 per cent following a year with chicks,” he writes.
For successful parent birds, “raising a chick is like painting a great big target on their backs. Those little brown fuzzballs look cute in the moment, but their presence portends many battles with floaters the following year. No wonder parents take steps to hide their chicks, when they can.”
Loons will return to our lakes in early May.
By Tom Spears
Copyright Postmedia Network Inc., 2019