Two days ago we learned that the male on Hilts Lake and the female on the East Central territory on Nokomis Lake have become the latest angling casualties in our study area. The Hilts male swallowed a lure or bait and is dragging line from his bill; the Nokomis-East Central female has line wrapped around her left leg, which she now carried behind her. We are dismayed for the two loons involved, of course. The male on Hilts is among our tamest; since 2007, he and his mate have permitted us to approach them closely without alarm so that we can record an hour of their lives every week or so during the breeding season. Each of us looks forward to visits to Hilts because of the relaxed pair we encounter there. The Nokomis-East Central female too permits us to view her and her mate and young from close by. She contrasts markedly with her mate, who forces us to view from a distance of 50 meters or so to avoid getting an earful of alarm calls. When we spy a lone adult and chick from a distance on Nokomis-East Central, we keep fingers crossed that it is the docile, approachable female, not the male, who happens to be guarding and feeding the chick. (Good news: Seth reports that the Nokomis-EC female leg appeared to be dragging no fishing line yesterday, so perhaps she is out of danger.)
The list of loons ensnared in fishing tackle is longer each year. Observations and reports of this kind have become an unrelenting and disheartening drumbeat. In the early 2000s, close encounters between loons and fishing tackle were anomalies that I wondered about almost dispassionately. Each angling casualty brought sadness and frustration, of course, since one becomes attached to the loons. But such events were so uncommon that I shrugged the losses off as the inevitable consequence of habitat overlap between loons and humans. The steady increase in entanglements in recent years has sensitized me. These days I brace myself for the several – perhaps I should change that to “many” – that will occur during the season and wonder how we can assemble a team to rescue victims without compromising the behavioral and ecological goals of the research. In fact, I have begun to prod Project LoonWatch in hopes of encouraging them to put together a loon rescue squad – a group of 3-5 folks that can remain “on-call” during summers to assist birds injured by human activity.
And I have begun to worry about the loon population. Loons are clearly getting caught on fishing lines more often than before. This makes sense, as fishing activity continues to increase in northern Wisconsin. (It might also be the case that the proportion of inexperienced anglers – those likely to lose lures and fishing line in the water and not make efforts to retrieve and discard tackle that they lose – has increased.) Loons did not evolve in an environment with monofilament line, live bait and lures that mimic small aquatic creatures. Hence, they have developed no system for avoiding these hazards. If the number of loons swallowing and blundering into fishing tackle continues to increase, will so many adults die that the population cannot sustain itself?
A quirk of fishing entanglements makes the situation a bit more severe than it might first appear. As the cases of the Hilts male and Nokomis female illustrate, males and female loons are differentially affected by fishing. For reasons that we do not understand, males appear much more likely than females to ingest lures and baits, as the Hilts male did. We do not understand this difference, although one might speculate that males, having larger bodies to sustain, are less picky in chasing and consuming underwater creatures than are females. In any event, both sexes seem to be equally prone to getting monofilament wrapped around their wings or legs, but males are more threatened by lead-based tackle (sinkers and jigs) — which poisons them and kills them quickly – and by hooks that damage their throats and prevent them from opening their bills and feeding themselves. In short, males are more apt than females to fall victim to fishing tackle and in a way that is likely to kill them.
Why should we care if adult male loons are more vulnerable to anglers? Because, weirdly, males choose the nest site where eggs are to be laid and cleverly reuse nestsites where they have hatched eggs successfully in years past. So males are a reservoir of information about how breeding pairs can best use the nesting habitat within their territories to produce young. When an established, experienced male from a productive territory is replaced by new male (because of death or eviction), the new male does not know where to place the nest and must learn by trial and error. In constrast, when a female is replaced, efficient reproduction can continue uninterrupted, because the identity of the female has no impact on nest placement.
Thus, I grieve for the Hilts male not only because he is a sweet bird who permits us to watch him without complaint but because his demise will cause a new, ignorant male to settle, who must blunder from one failed nestsite to another before he discovers a good one that he will use year after year. And his years of inept breeding will subtract many offspring from the population.