Two Reasons to Scream

As living animals, we often face the task of sorting out meaningful patterns from the vast ocean of natural occurrences we encounter each day. Since we are human and reside in a protective bubble, this task is not as vital for us as for squirrels or deer or loons, of course. If we detect what we think is a natural pattern, act on it, and are wrong, we are unlikely to face lethal consequences. Suppose, for example, that you notice that fewer people do their grocery shopping at 3pm and change your shopping schedule to mid-afternoon so that you can avoid the rush. If you are mistaken, it will cost you time, but probably not your life. In contrast, a squirrel that concludes, based on limited experience, that predators are scarce from 3 to 4pm and decides to begin using that daily period for foraging might pay a dear price if she is wrong.

Despite the low stakes we face, humans have an irresistible and very rational inclination to take note of and try to discern meaning from natural events, especially when those events occur in quick succession. So it was the last few days with loons, bald eagles, a great blue heron, and me. The first incident happened on Squash Lake yesterday. I was watching a loon pair swimming along peacefully with their three-week-old chick. As a great blue heron passed harmlessly over the trio, the chick panicked and dove. Neither parent showed any other behavior in response to either heron or chick; they merely issued reassuring hoots when their youngster surfaced several seconds later, as if to say, “That’s okay; we are all young once!”

The Squash chick’s peculiar response to the heron flying overhead was a beautifully diagnostic act. Since all adult loons know their predators precisely and only flee or give alarm calls to those that are dangerous, I could instantly see from the Squash chick’s behavior that loons must learn their predators. To an animal behaviorist, this is not big news, I am afraid. While some fearfulness towards predators is innate (not learned), many — perhaps most — birds must learn which of the other species of animals they encounter in nature are truly dangerous. Thus, young birds commonly depend upon their parents to teach them.

Though I had witnessed a few other cases of loon chicks responding inappropriately to harmless animals in their vicinity, the striking confirmation yesterday on Squash that loon chicks are clueless when it comes to telling friend from foe was still firmly in my mind when I ventured to Hilts Lake today. There, the loons had to deal with the unpleasant presence of an adult bald eagle and its recent fledgling, which flew incessantly from one side of the lake to the other during my hourlong visit. We try to record every vocalization that the loons make during our routine visits; needless to say, I quickly began to curse the eagles almost as loudly as the loons were for the writer’s cramp they were causing me. I documented about 60 wails by the loon pair during my visit.

Now eagles are dangerous to loons, as I have emphasized recently. It is altogether appropriate that loons should call to eagles as a way of alerting other loons — and the eagles themselves — that their presence has been noted. But 60 wails is a lot of wails — far more than a pair of adult loons would normally produce, even when eagles made themselves so obvious as the parent and fledgling did today on Hilts. Why would a loon pair wail 60 times when 15 or 20 calls would have been ample to alert the eagles that an attack was likely to be fruitless?

Having seen the Squash chick’s response to the heron just a day before the Hilts pair’s overzealous calling to the eagles allowed me to put two and two together into a hypothesis. Part of the reason why loon pairs with chicks are so vocal when dangerous animals are nearby, I now presume, is that they are not merely protecting their chicks from those dangerous animals. They are also pointing out those animals to the chicks so that they will learn what predators are to be feared and respond appropriately once they are on their own.