I try to make at least one whale-watching trip every summer. I enjoy seeing these great, mysterious mammals in their element. But there is also a bonus for us who are interested in birds: where there are whales, there are also seabirds. In fact, the presence of birds often alerts tour boat captains to the presence of whales.

The Gulf of Maine is large, and whales range over its vastness. However, there are areas that contain what biologists call upwellings: swirling currents that bring deeper water rich in nitrates and phosphates to the nutrient-poor surface layers.

This causes spectacular blooms of plankton and zooplankton, which in turn attract fish, marine mammals and birds.

Birds, of course, are more readily visible than whales, especially from far off. A cloud of birds swirling over the water is a sure sign that they’ve located a food-rich (and therefore a whale-rich) area.

But there are more subtle signs of the ocean’s bounty. As the boat enters an area of high productivity, birds begin gradually to appear, skimming along the surface of the sea ahead, alongside, and behind the boat. I’ve made it a game to note what species I see first, and this year’s was a new one for me: a Manx shearwater.

I was used to seeing the more common greater shearwaters as they skimmed over the sea, almost touching the water with the tips of their wings. Their flight patterns were distinct: several flaps followed by glides, during which they skillfully used the wind traveling over the surface of the ocean for lift and momentum.

The Manx shearwater, however, is a smaller bird and uses powered flight much more, with less gliding. It also has a faster wing beat, and these characteristics helped distinguish it from the greater shearwaters.

Shearwaters, along with petrels and albatrosses, belong to a family of birds known as “tubenoses.” This nickname arose from raised “tubes” that sit at the base of the bill, encasing the nostrils. Ornithologists think these structures serve to enhance these birds’ sense of smell, which they use in detecting prey and also to identify one another (this is unusual in birds; most are thought to have no sense of smell).

Another function of the tubes, and one just as vital, is the direction of salt away from the birds’ eyes. Glands above the bird’s bill secrete salt that builds up in its body – a consequence of a life spent almost entirely on the open ocean. This enables the bird to actually drink salt water without dire consequences; in fact, the bird will not drink fresh water even when it has an opportunity to do so.

The Manx shearwater breeds farther north than any other shearwater, and is known for its far-reaching migrations. It was one of the first subjects of homing studies done with birds, and became famous when one tagged individual flew a distance of 3,200 miles from Boston, to its Welsh nesting colony in 121/2 days.

Shearwaters and others of this family nest on islands in burrows that they will sometimes dig themselves. They return to their nest only at night (here’s where their sense of smell comes in handy) to reduce the risk of being preyed upon by gulls (some species of which have become much more numerous because of human activities). Still, predation by human-introduced species such as feral cats and rats has proved disastrous for some populations.

Chris Corio, a volunteer at Fields Pond Nature Center in Holden, can be reached at fieldspond@juno.com