Greater yellowlegs
Greater yellowlegs
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Typically when carnivorous animals are mentioned, we visualize a charging grizzly bear or prowling lion — by definition these are definitely animals that feed on flesh. Assortments of other species, including most humans, match this category to some extent. If we chronicle carnivorous birds, bald eagles and great horned owls are obviously high on the list. How about an American robin? Are those sedate little “savages” possible contenders for a carnivore’s who’s who list? They certainly are, since the bulk of the robin’s summer diet consists of plump, meaty earthworms. Wintering robins eventually become obligate vegetarians, feeding on waste fruits and berries once the ground freezes.

Carnivorous birds can be classified into several categories, depending on the specifics of their diets. Let’s review the categories. Insectivores — these are flycatchers, warblers, swallows that consume mostly flying and crawling insects. Avivores — these are bird-eating raptors like the sharp-shinned hawks that patrol our bird feeders and swift, open-sky aerialists like peregrine falcons. Molluscivores are mollusk-eating birds with specialized physical traits. Sea ducks, skimmers, certain sandpipers and American oystercatchers must all deal with processing a shellfish diet. Relying on their strong muscular gizzards to grind up the shells, sea ducks swallow blue mussels whole. Oystercatchers pry apart hardened mollusk shells with their stout bill, fashioned in the shape of a customized shucking tool.

And we shouldn’t ignore the piscivores, those birds that rely primarily on fish for sustenance. This group has specialized bill structures and includes puffins, loons, cormorants, herons, egrets and ospreys. Slippery fish are either speared directly by a sharp-pointed bill or corralled into bills equipped with ridged edges like the iconic Atlantic puffin. Some species have sensitized bills containing fine nerve endings that detect the slightest brush of a fish even if the prey is not seen directly.

Fish eaters have other anatomical adaptations, such as scaly feet and strong talons for gripping, to elevate hunting success. Long, thin legs of wading egrets and herons allow them to stealth their way through watery hunting habitats. Counter-shaded plumage on the great blue heron also provides camouflage while hunting in water. Feet set farther back on the body (puffins, loons and cormorants) provide extra propulsion for sustained, efficient underwater maneuvering. Tapered flipper-like wings enable species such as long-tailed ducks to pursue prey in rapid twisting “flight” while under water. Depending on the bird species and the size of its prey, the fish may be swallowed whole or ripped into pieces for easier eating.

Ospreys and northern gannets employ spectacular headlong diving techniques to snatch fish from beneath the water surface. The skulls of both species have built-in protective air sacs to minimize cranial shocks of striking water surfaces at 30 mph. On a lesser scale, I’ve watched a belted kingfisher pair at Weskeag Marsh hovering and plunge-diving into swirling schools of small fish in the shallow pools. At other times, the pair waited patiently atop roadside perches to assess the fish stocks and spot potential prey.

It may be a stretch to label any sparrow as a fish eater, but I once witnessed an event involving Nelson’s sharp-tail sparrows at Weskeag that speaks otherwise. During a summer high tide cycle, schools of tiny fish had filtered beyond the grassy margins of the overflowing salt pannes. The grasses were literally brimming with fish and a few of them had grounded themselves. Soon a begging juvenile sparrow rushed along the wet ground, where it was joined by an adult with a wriggling fish in its bill. The adult promptly crammed the fish down the chick’s gullet. A tight fit, but a nourishing meal.