In my recent post, The Last Heron,* I linked the departure of many pond birds to the mass die-off of small, Bluegill sunfish in March 2012. A reader questioned this linkage, and even the disappearance of the birds themselves. What follows is not only a rebuttal, but also an opportunity for me to take a fresh look at these issues, and explore further their significance.
I readily acknowledge there may be other explanations for the missing birds — but missing they are, at least as I judge from my window. I’d been used to looking out and seeing a pond teeming with bird life, including two or three Great Blue Herons standing vigil on the rocks off Smith Point, gracefully taking flight when their patience runs out; a small flock of Double-crested Cormorants with infinite patience occupying the archipelago of rocks in mid-pond (top photo); and scores of gulls of various species sunning themselves on the water or soaring on the currents above, their plaintive cries reminding us of their presence.
More rarely have I seen a few Green Herons on those same rocks off Smith Point. More rarely, still, have I spotted the reclusive, Black-crowned Night Heron (photo left), with its fine white plume, at dusk in the same shallow, rocky water
Now these many, varied birds are all but gone. A sole, black cormorant daily stands vigil on the rocks in mid-pond, along with a few gulls. A large Great Blue Heron shows up off Smith Point at odd times, when the boats are gone. The waterfowl are all still here, of course, none fish-eaters: the innumerable Canada Geese, a dozen or so resident Mallard Ducks, and a tenaciously territorial pair of brilliant, white Mute Swans.
Many days, I look out on a vast, vacant waterscape. It reminds me of a book I read many years ago, Rachel Carson’s Silent Spring. When it first dawned on me that the birds had gone, the obvious questions sprung to mind. What do these different species have in common — the gulls, the cormorants and the various herons? Of course, they all depend more or less on small fish (see below). When did they begin to leave? Not surprisingly, soon after the small Bluegill sunfish died off by the thousands in March 2012.
The simultaneous departure of so many, varied birds, shortly after that traumatic event, could hardly be coincidental. It’s possible, of course, that whatever killed the fish scared off the birds as well, and thus remains a mystery. More likely, this is just another case, so often observed in nature, of wildlife populations adjusting to the food supply. When the acorns are scarce in a given year, the squirrels will be fewer too. There’s no mystery there!
Well…there was a mystery of sorts: many of the departing birds returned several weeks later, staying a few more months – some for almost a year – before leaving for good. What brought them back, and what prompted their second and final departure? Perhaps they had discovered a few surviving Bluegills, and remained until the prized prey were all but depleted.