A visit to a Common Tern colony is an uncommon experience. It is also a complete sensory experience which includes pain as one of the tour features. Needless to say, the birds do not want you there and do everything in their power to make you feel unwelcome. Terns are small birds but have knife-like beaks and lightning quick flying abilities which they employ to dive bomb and peck any intruder. All birds utter a loud raspy call when attacking. Add a shower of feces and multiply this by dozens of birds and you have a feathered onslaught – a pecking, pooping, and profanity laced barrage. In other words, it is a wonderful thing!
I recently had the opportunity to accompany U.S. Fish & Wildlife Service volunteer Natalie Ray as she made her semi-daily rounds of the tern colony located under the Grosse Ile Free Bridge (see above and here). These birds have taken advantage of the main pier beneath the central portion of the historic structure (a swing bridge built in 1932) which crosses the channel from Trenton to the big island in the Detroit River. Natalie is charged with changing the memory cards on the night-vision trail cameras set up at various locations around the small colony (see below). Nocturnal predators such as raccoons, mink, and black-crowned night herons occasionally raid the place and these cameras are placed to monitor these depredations.
Common Terns are a severely depleted species (down from over 5,000 local breeding pairs to a little over a few hundred), so they need all the help they can get. A single Night Heron could potentially wipe out this bridge colony in a matter of a few nights if left un-checked. Let’s just say that habitual interlopers are swiftly “taken care of” by U.S.F.W.S. staff. Oddly enough, the parent terns leave the colony undefended at night and are not available to employ their “triple P” defense on nest predators. The chicks are on their own once darkness falls.
A daytime visitor – regardless of intent -is accorded the full un-welcome ceremony, however. Before I could don my hard hat, one pugnacious bird landed a direct hit on the top of my head. I hate to be a wimp about it, but dog-gone it that really hurt. It drew blood as a matter of fact. Once hard-hatted, we received regular noggin bops about every minute or so throughout our time inspecting the place. A fine spray of droppings accompanied nearly every close approach. The noise can only be imagined. The combined rumble of overhead traffic on the bridge and the constant cackling of the terns was deafening. I said deafeni…oh, sorry… I needn’t shout any more. Take a look at this video and you should get a sense of what I am talking about. It looks and sounds like an Alfred Hitchcock movie trailer.
From the perspective of the elevated boardwalk that encircled the colony, I could see several nests and eggs. Each nest was a mere scrape in the soil framed with a few sticks. The speckled eggs numbered anywhere from 1 to 3, which is the average for this species (see below). A few of the females stuck to their incubation duties during our visit and peered cautiously over the scant vegetation in order to monitor our progress (see below).
Some of the chicks had already hatched and were scurrying around for cover (they are semi-precocial, which is a fancy way of saying they can partially fend for themselves). They are born, after a 23 day incubation period, with open eyes and a full covering of feathers but still require parental feeding for the next few weeks. One chick, spying my approach, tucked himself under a plant and instinctively froze. It became virtually invisible. Another, still hanging about the meager nest, also froze in place but her speckle pattern didn’t work nearly as well against the twiggy background (see below). Had she of been only a few feet over, she would have been better served (see wider angle shot below close up).
We made our visit short so as to not overly distress the birds. Even so, most of the birds went back to their nest duties even before we departed. One female, though located only a few feet away, wattled to her clutch and gingerly settled down on her charges (see below). She maintained a fierce cackle and directed a firm stink eye in my general direction as if you say “Ya’ll don’t come back now, ya’hear!” Actually I think she said “Please do not re-tern,” but that would be a shameless pun on my part. On a final note, please note my extreme restraint in this regard – a feat nearly as painful for me as my initial whack on the head.