June 19, 2022
This season has certainly shown us that there is intense competition between loons for the best breeding habitat. It seems to be a daily occurrence that our pair has to deal with intruders, sometimes as many as four or five at a time. A territorial pair must be constantly alert and know what’s happening within and beyond their territory. Exactly how they do it, how well they do it, and which senses they depend on for monitoring their territory have received very little study or discussion. Perhaps starting with the little bit we know about loons and throwing in some anecdotal evidence will shed some light.
It has been established that loons have high visual and auditory acuity. These are the two senses that are certainly most useful. Because loons are aquatic, they also benefit from the fact that water transmits sound five times better than air does, so they can increase their hearing by submerging their head. Loons also have a functioning olfactory bulb, above average in size compared to 107 other sampled bird species. So we can’t rule out the possibility that loons can smell each other, but it has yet to be positively demonstrated. Even if it were true, it wouldn’t be of much use other than at very close range, when the loon could already see and hear the intruder.
So, if they are using their hearing and vision, at what distance can they sense an intruding loon or other threat? I can recount two experiences that can shed some light on the question. On the first, I was monitoring a female with two chicks when the male showed up. The pair were exchanging pleasantries when suddenly the male turned toward the far end of the bay in a head up alert posture, gave a tremolo and then dove and swam in that direction. The female immediately stashed the chicks in a safe location and swam off to join him. I scanned the far end of the bay with my binoculars and could just barely make out a black dot floating in the water. Within a minute two more black dots appeared and a heated physical exchange ensued. The distance between the intruder and where the male was when he first sensed it was at least a half mile. That means that out in the open water, a loon might be able to sense another loon anywhere in a 500 acre circle.
The second instance started in a similar manner but this time the male didn’t swim off. He stayed within a hundred feet of the female and chicks, stared in one direction and let loose with some tremolos. At first I and the other biologist with me couldn’t figure what got the male all riled up. But, by the time the male switched to yodels and the female took over the tremolo, we recognized a paddleboarder headed in our direction. The loons didn’t take kindly to this newfangled sport. They gave him a royal tongue lashing as he passed. Again, the threat was perceived when it was still a half mile away. Although in this case a human standing on water is much more prominent than a loon. I think the take-away is that in many cases the loons know exactly what is going on in their entire territory. And then some.