DOLPHIN FLEET BIRDWATCHING NOTES: 16 to 31 JULY, 2008
John C. Conlon
These last two weeks of July have produced an exciting array of seabirds and their movements. As always, the pattern changes in both numbers and concentrationas as centers of food concentration shift. The relative numbers of each bird species also shift as each species follows different migration routes both spacially and temporally.
Over these two weeks the sooty, greater, and Cory’s shearwaters have remained in high numbers while manx shearwaters have remained in very low numbers. The manx are now, however, finally being seen in steady numbers of 5-10 during many trips. Early migrating phalaropes are also spotted. They typically are singles or pairs. Look close to the water’s surface for phalaropes. Listen for their chirping as well. Red-necked phalaropes generally show up first, and we have been seeing a few here and there. Red phalaropes follow close behind beginning in early August. Parasitic jaegers are now more regularly sighted than are pomarines. Oh, and some fifteen Canada geese graced Provincetowns inner harbor several days ago.
In just the last few days we are seeing rapidly increasing numbers of terns along the Herring Cove area. Actually they are along the slope outside Herring Cove. Terns, in increasing numbers, are also joining the offshore feeding aggregations of gulls and shearwaters. Watch for terns carrying freshly caught sand lance. As we pass time in the Race Point to Peaked Hill area least terns are particularly noteworthy. They are never really seen in large flocks, but because of their relatively small size (9 inch length and 20 inch wingspan) they are easy to spot in mixed avian feeding groups.
As feeding fin and humpback whales push fish toward the surface, laughing gulls are often the most noteworthy gull. They are a medium sized gull just over 16 inches in length, 40 inches across the wings, and weighing in at about .75 pounds. Laughing gulls are strikingly beautiful in adult breeding plumage. Their underside is a clean white plumage with lighter grey wings. The back side by comparison has a white tail and deep slate grey wings with black wing tips. The entire head is deep black and they have a brilliant crimson bill. We wait patiently. Laughing gulls with their keen vision spot rising fish-filled bubble clouds before we trained whalewatchers see those clouds. I tell people to watch the birds and the birds will tell us where the whales are surfacing. Listen for the nasal laughing as these gulls flock toward the rising fish and swarm down to surround the whales’ heads in the green swirling water.
All of these birds are migratory species and in previous Birdwatching Notes I have discussed some of their respective annual routes. Bird migrations are after all predictable over the seasons and from one year to the next. The costs of travelling great distances between nesting / breeding sites and non-nesting / foraging sites must be worth their efforts otherwise these migrations would not occur. This is especially true when we consider that many of these migrations will cover hundreds if not thousands of miles. The aforementioned laughing gulls that join us en masse around Cape Cod at this time of year are largely absent between the end of November and late March. These gulls can be found anywhere from North Carolina as far as eastern Brazil, across the Caribbean, across Central America, and on to down to western Peru during these colder months. Our common terns will make it to the far end of South America.
How exactly these phalaropes, gulls, terns, jaegers, shearwaters and storm petrels orient and navigate through these distances is a rather intense mystery. The flight part is easy. To be simplistic the flying itself is accomplished using those long, taperred, drag-reducing wings that are so common to seabirds. These birds also certainly take advantage of wind patterns; using advantageous wind directions when available and staying low in order to avoid disadvantageous wind directions.
First in the line of mystery is orientation. Which way is which? Orientation may be accomplished by several methods. Sun compassing and star compassing are two possibilities. Perhaps there is an avian understanding of the sun rising to the east and setting to the west. Night-time marks include the North Star. Polarized light may help migrating birds with their north to south orientation during the day-time. Periods of rain and heavy cloud cover can present problems with these visual cues. Magnetic compassing using Earths magnetic field is a third possibility. (Fin whale movements have been correlated to magnetic intensity while pilot whale movements have been correlated to magnetic anomalies.) Magnetic compassing becomes problematic near the Equator, during magnetic storms (from solar flares) and in areas of magnetic anomalies.
Navigation, the ability to recognize where one is and then orient toward where one wants to be, is the second big mystery. Land marks and sound (surf breaking along the shoreline) might work. Birds have much greater light sensitivity than humans and while their hearing is comparable to humans anybody living near the shore knows the sound of endlessly crashing waves along the shore carries great distances. Temperature and salinity are also possibilities of navigation aids. And while birds are generally considered to not have the keenest sense of smell, tubenoses, especially the storm-petrels, have a well developed olfactory system. Perhaps the heavy, sweet smell of plankton blooms that we seabird and whale watchers experience attract some of these migrants.
Ornithologists are quick to say these ideas are speculative. No single method has proven universal among bird species or even within a single species. Indeed for any given species the most effective orientation and navigation is likely done using some combination of these tools. Prevailing winds help greater shearwaters along their migration to the USA. And perhaps they have learned the shape of the eastern USA seaboard from following along in the crowd of older and previously migrated greaters.
The emphasis is on the “perhaps”! Perhaps they recognize the northesastern USA or eastern Canada and stop to gorge on sand lance before moving toward western Europe. Perhaps the laughing gulls recoginze Cape Cod and thus know they are in the area of the steep Stellwagen slopes and rich upwellings. The “perhaps” is a human question. They know! Keen gull eyes spot rising green bubble clouds. We hear them laugh while winging toward a very specific spot that to us looks little, if at all, different than any of the surrounding sea.
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