DOLPHIN FLEET BIRDWATCHING NOTES: 1 to 16 AUGUST, 2008
John C. Conlon
The mid-August days are noticeably shorter than those days of June. Time cycles onward! So do bird concentrations. I often talk of pelagic birds in our area and much of the discussion revolves around those species that we would never expect to see onshore locally. These are the birds that many birders regard as spectacularly unusual in one way or another. But what about those other birds that we almost always take as a given? We acknowledge their presence and then look quickly beyond. In particular, I refer to the gulls and terns that are overshadowed by the other “pelagic” birds. I want to focus here on the terns but while speaking of gulls there is a slowly growing number of black-legged kittiwakes mingling with the ever growing flocks of laughing gulls that feed offshore.
We talk of pelagic birds that do not come ashore here. Many of them visit during a migration cycle and we tend to think of them as on the move. Meanwhile, we think of this as a place where they pass through and spend time foraging. These birds nest on remote islands in far off parts of the Atlantic. But what about those species that do come ashore here? Their nesting season is during our summer. Terns are massing offshore in feeding flocks.The chicks are fledging and needing more and more food as the terns begin preparation for their long migrations.
We often talk of the reasons that “pelagic” birds nest on remote islands in far off places. Indeed the most often stated reasons are: 1) Adaptations to life in marine environments, such as long wings for gliding and webbed feet that are far back along the body for swimming, make moving on land and avoiding land-based predators difficult. 2) This vulnerability to terrestrial predators makes remote islands that are relatively free of these predators an ideal location. 3) Remote islands surrounded by water offer greater foraging areas capable of supporting large seabird populations. 4) The nesting area is not within the foraging area and given the ephemeral tendencies of schooling fish and krill there is no real foraging area that would be defendable. 5) Breeding in huge and densely packed colonies reduces the risks of avian predation at least for the individual egg or chick. The greater shearwaters from Tristan da Cunha or the Cory’s from Madiera that I’ve talked about recently certainly fit this description of visitors from far away.
But what about the terns? They seem so terrestrially based here that we subconsciously think of them very differently. The terns we see here really are seabirds. Yet they spend so much time on land that we often hold them in a different light. They’ve become the most visiblesymbol of the Cape Cod National Seashore. Cape Cod is a piece of land not a region of ocean, but even Cape Cod itself is a product of water. First, water, frozen in the from of advancing glaciers, pushing and piling sand and soil ahead. And second, the erosiveeffects and subsequent reshaping of Cape Cod by melting glaciers and rising sea level. But the Cape does none the less have long stretches of sandy beaches.
Cape Cod does not seem so remote to many of us. We are so familiar with it. It is not a remote island though it does offer great habitat in close proximity to rich foraging areas: Cape Cod’s adjacent beach slopes and the slopes of Stellwagen Bank. It is not free, however, of terrestrial predators. Red fox, coyotes and raccoons are three examples. There are also the predatory black-backed and herring gulls, and even great-horned owls.
Cape Cod is a summer resort area easily accessible to one of the most densely populated regions of the USA. This human population loves the coastal / beach environment that is so important as nesting, roosting and staging grounds for terns. Conflicts are ever-present. Human encroachment in the form of behavioral disturbance and even habitat destruction, not to mention the occasional domestic dog, wreaks havoc on tern colonies. The terns’ mobbing and aerial dives at an intruders head, while unnerving, are their own best efforts to mitigate that disturbance.
The adult terns that were earlier feeding offshore are now joined by the juveniles and the mate that was guarding the nest while the first was foraging a month ago. The increase in size of the mixed feeding flocks of terns is growing with each day. These numbers will soon be joined by other terns migrating southward from farther north and the flocks will become even larger.
Look into these flocks. Certainly the most numerous are the common terns. There are roseate terns and least terns as well. The northwest Atlantic population of roseates is considered endangered. All three species nest here as do arctic terns though these are at the southern end of their breeding range and the numbers are decreasing. The least terns are easy to spot given their noticeably smaller size. The other three species present a bewildering array of confusion to many birders. The easiest way to find the roseates is to listen for the sharp two syllable “chivik chivik” and then look for the clean white belly. The commons and the arctics both havegray on the belly but the arctic’s bill is relatively short compared to that of the common. If those differences are not subtle and / or difficult enough to distinguish, have fun with the juveniles!
For those birders with experience go for the challenge! For those new to birding or even new to the pelagic terns perhaps start by simply enjoying the time spent in the excitement of the feeding frenzy. Watch the terns dive and rather than trying to identify terns to species simply make note of the fact that there are noticeable differences even among individuals of the same species. Catch a glimpse of the tern flying overhead with a sand lance in its bill. Or maybe even see the distant jaeger swooping up from below and looking to pirate a tern’s meal.
Watch for the rare but easy to recognize black terns off Wood End. We’ve even had a couple sightings of royal terns over these two weeks. At 21 inches in length and 41 inches across the wings they are much larger than the other terns. The royals have a fairly thick and bright orange-red bill. Between the bulk and the bill if you do see a royal it will stick out of the crowd with little effort!