- Research & Education
- Cape Cod
John C. Conlon
Labor Day weekend is behind us. Several days of northeast wind have given a cool hint that autumn is approaching. Days are bright and clear and that is good for spotting seabirds and whales. The clarity is especially good because while seabird diversity has remained high the numbers have dropped dramatically in many cases as these two weeks have progressed. Shearwater sightings in particular are decreasing. Meanwhile it has been two weeks of atypical bird sightings during our “whale watching” trips.
First, a couple of big numbers. On August 20th we had mixed feeding flocks of some 3500 to 4000 shearwaters, gulls and terns at Peaked Hill. They were spread in a narrow band over a mile and a half and were feeding with fin and humpback whales. The long feeding line extended east from the eastern end of the Peaked Hill sand bars. We watched these flocks for a couple of evenings in a row.
Migrating phalaropes in flocks of as few as 6 to as many as 20 are now seen more regularly. Look for the flocks flying low over the water or listen for their chirping while they’re set on the water’s surface. Red-necked phalaropes are somewhat more common. On August 28th we had one late-molting red-necked phalarope flying circles close around the Portuguese Princess and offering great looks at its striking plumage. It looped around the boat twice, flew off a bit of a distance, and returned to repeat the sequence two more times. It was a cautionary tactic of approach and retreat that many birds use in their curiosity investigations of new objects.
Second, the smaller unexpected sights. On August 28th we also had a momentary though close look at an American bittern. At a quick glance some folks thought immature black-crowned night heron. (We do see black-crowned night-herons in the intertidal zone of the breakwater off the pier’s end.) This bittern has a broader based neck that tapers toward the head and a more slender bill that is often angled upward from the outstretched neck. They are noticeably more light brown than the grayish immature night–herons. The bittern perched on the gangway rail leading down to the float. Then it flew eastward toward the Pilgrim Lake marshes.
On August 18th we had a quick look at a great skua. This was an exceptionally unexpected surprise. Mid-August is the earliest we might see one of these and any sighting during our whale watching season would be rare. Indeed, even wintertime sightings are only occasional. Great skuas are a noticeably larger relative of the jaegers that we find here. They measure some 23 inches in length, 55 inches across the wings, and weigh some 3.25 pounds. The skua’s broader body and wings with highly conspicuous white patches on the primaries make great skuas easy to distinguish. The red-brown tint helped distinguish this bird from the jaegers and the even less likely to be seen south polar skua.
Another unexpected surprise was a female goldfinch. Far offshore she circled the boat and made several attempts to land on railings but never settled down. We remind passengers not to disturb land-birds if they try to set down on the boat while over open water. They are unable to set down on water. Their wings become water-logged and they drown. That drowning assumes the land-birds are not first pecked and killed by gulls.
I often compare similarities and differences between seabirds and whales. The amazingly rapid growth of first year individuals is worth mention at this time of year. I’ve said many times that whales have the fastest natal growth rate of any mammals including primates. And we see that in the growth of finback and humpback calves. When you look into the mixed flocks of terns, notice that the young are now almost similar in size to the adults. And certainly a good part of this size is fat reserves. Remember the terns only hatched earlier this summer. Indeed northern gannets are noticeably larger than adults and young shearwaters may be as much as twice the weight of adults. This growth occurs early in life largely due to the adults provisioning nestlings with food before nestlings fledge. Fat reserves help fledglings through the first year when foraging skills have yet to develop fully. Look at the size of some of the immature greater shearwaters. It is not your imagination that they are sometimes still bigger.
For migrating birds and migrating whales fat is an important energy reserve, insulator, and aero- (hydro-) dynamic aid. Energy release during fat metabolism is approximately twice that released from protein or carbohydrates. Water release during fat metabolism is also about twice that of protein or carbohydrates. Having sufficient energy reserves and avoiding dehydration are major evolutionary concerns for any long-range migrating species as well as the individuals making those annual migrations. Fat stored in cavities spread over the body just beneath the skin also gives birds additional insulation though this would be supplementary to the insulative qualities of the feathers. As fat quantity differs over different body regions that fat makes for more aerodynamic shaping thus having significant impact on energy efficiency over long-range migration.
Common terns migrating to southeastern South America are one example of locally breeding seabirds needing the energy gained from dense schools of sand lance found outside the Peaked Hill bars of Provincetown and the Race Point Channel. Don’t forget your binoculars. Look for the young birds in the flocks!