Ecosystem. 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.
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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.

On the question of what these birds eat, there’s a wealth of documentary evidence. Here’s the Great Blue’s diet as described by Wikipedia (bold added):

The primary food for Great Blue Heron is small fish, though it is also known to opportunistically feed on a wide range of shrimp, crabs, aquatic insects, rodents and other small mammals, amphibians, reptiles, and small birds.

Indeed, I would occasionally see a Great Blue catch a small fish off Smith Point (photo above), then climb onto dry land (in case it drops the fish), reposition it in its bill, and swallow it whole. I don’t know if the Great Blues forage in the adjacent marsh, but I have to wonder what opportunities it can offer them now that it’s choked with Purple Loosestrife. Limited, I suspect.

Double-crested Cormorants enjoy a similar diet, described by Wikipedia as follows (emphasis added):

Food [for cormorants] can be found in the sea, freshwater lakes, and rivers. Like all cormorants, the double-crested dives to find its prey. It mainly eats fish, but will sometimes also eat amphibians and crustaceans. Fish are caught by diving under water. Smaller fish may be eaten while the bird is still beneath the surface but bigger prey is often brought to the surface before it is eaten.

I’ve never seen a cormorant bring a fish to the surface, so I have to assume that here, at least, they take smaller fish like Bluegill, or juvenile Largemouth Bass, which they can swallow while still under water. Nothing I’ve read suggests that they forage in swamps and marshes. To the contrary, all sources state categorically that they hunt fish by diving under water.

Gulls take a wide range of prey, I readily acknowledge, but above all, they prize small fish. I say this from direct observation. Only last year, visiting mergansers drove some Bluegills into shallow water before diving to bring them up one by one. Among the ever-alert gulls, it set off a feeding frenzy, marked by plunge-diving, snatching, and jostling, as these photos record. To watch the gulls agressively taking Bluegills is fully to understand what keeps these resouceful birds on the pond.

In March 2012, when the Bluegills died off, I was preoccupied with health issues. Four months later, I roused myself and called the Mass. Dept. of Ecological Protection (DEP) and the Dept. of Fish and Game (DFG). Among the people I talked to were two field workers who both made the same case — emphatically — that “natural” hypoxia never occurs in spring, but only in winter during prolonged ice cover, and in summer when water temperatures rise. If fish die in spring, whether by hypoxia or some other cause, it’s not a natural event, but one in which humans have played a role. One of them added that never in 30 years of field work has he seen a “natural” die-off in spring.

So there’s reason to believe that we humans were implicated, somehow, in the Bluegill die-off. Again, we may never know the exact “how,” but we certainly can air our suspicions. In my previous post on the subject, I pointed to the silted discharge channel as a possible culprit. I suggested that it may slow the natural flushing of the pond’s water, in turn hastening the build-up of either 1) toxins, or 2) decaying organic matter that depletes oxygen. Either scenario could explain the die-off. Both are related to human activity — or in this case a lack of it, a failure to clean the outlet channel. Think of a bathtub with a partially clogged drain: it never quite empties, so new water is added on top of the old, and the bathwater is never quite clean.

I don’t believe the pond is facing an existential crisis, at least, not yet. The Bluegills will come back, eventually, and so will the birds. Several recent events offer encouragement. Late last summer, schools of juvenile Bluegills were spotted (by an angler) in the shallows just north of Smith Point. Most days, a second cormorant now joins the vigil on the rocks in mid-pond. And the gulls are slowly recovering their numbers, at least at this end of the pond.

The birds’ departure reminds us — if reminding is needed — that everything in nature is connected, that we can never be too zealous in protecting the pond’s fragile ecosystem, or a day may come when the heron we see is the last we’ll see on the pond. Sadly, the Black-crowned Night Heron shown above — shy and reclusive under the best of circumstances — may be the last of its kind, at least here off Smith Point. Since the opening of a new, concrete boat ramp, small boats have preempted the warm spring and summer evenings, a time when the little night heron usually made its appearance.

Update, December 2013. I’ve stopped and restarted writing this post several times over the last four months, as other demands have intervened. The gull numbers have grown steadily, with several dozen congregating on the water most days before the pond froze over. Hooded and Common Mergansers have both passed through, along with migrating Ruddy Ducks and Buffleheads. None appeared in as large numbers as in years past. All were busy diving — whether for fish or something smaller, I couldn’t tell — with the gulls hovering restlessly overhead in the hope of scraps.

Flooding. If there’s one environmental issue that’s not complicated, it’s flooding. We know what causes it, and what steps are needed to prevent, or at least mitigate, this ever-present danger. We also know its occurrence is more likely and less predictable in this new era of climate change.

The silted channel stirs memories of the two great floods of March 2010, when a blocked culvert caused the pond to overflow its banks (photo left). Widespread property damage was just avoided – miraculously. Another time, and we may not be so lucky. Is that a risk we want to take, possibly to see pond families lose their homes, when it’s well within our power to prevent such a wrenching disaster?

The discharge channel, already burdened by years of neglect, was further silted by those two floods. Cleaning it out has been recommended by two flood-control studies (pdf) eight years apart. Water quality concerns aside, that should be reason enough to proceed with urgency. Sadly, the issue is an orphan. If residents and elected officials would pull together, the channel could be restored. But other issues and agendas seemingly take precedence. No one wants to spend precious political capital on a project so easily ignored. It is out of sight and out of mind.

Update, March 2014. The tragic mudslide in Washington state, so much in the news lately, should serve as a cautionary tale. Having been warned for years by scientists that the hill was unstable, and despite smaller, premonitory mudslides, an amnesic public continued to build homes there, while public officials pledged to protect their safety looked the other way.

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Related: The Last Heron*, Testing the Water*, Great Blue Fishing, Purple Loosestrife, Mono Lake*, Dead Fish*, Snatching Gulls*, The Great Flood.

 

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