Ocean Of Birds

Sea Birds: Designed For Fishing

Sea birds have developed a remarkable range of fishing methods in order to carve up amongst themselves the various dishes on offer. Some specialise in picking off tiny plankton items at their leisure, some chase high-speed fish, some are scavengers, some are general-purpose opportunists and some are thieves, taking food from other birds. Outside the breeding season, when they are released from the responsibility of taking a catch back to the nest ashore, they tend to be nomadic, sometimes travelling great distances in search of food.

sea bird catches fish prey

Few land birds have developed their sense of smell, for they don’t need it. But at sea it can have real value when, for instance, a floating whale corpse may be surrounded by hundreds of miles of featureless ocean. Tube-nosed birds are able to sniff it out from a great distance and flock to the feast. Giant Petrels, especially, excel at this useful task which tidies the ocean.

Sea birds; Fishing Structures.

In albatrosses and fulmars, for example, the nostrils extend as tubes along the bill, and the nasal chambers house a complex organ which includes valvular structures which may act as anemometers so that the bird is able to measure air pressure, a useful facility in dynamic soaring. But the nose is also an organ of smell, a particularly useful sense for scavengers. The tube-noses represent a highly successful sea-going group of birds, including albatrosses, shearwaters, petrels and storm-petrels. (Wilson’s Storm- Petrel may be the world’s most abundant bird.) Ocean-going mariners, in both blue and green water, they spend their entire lives at sea except for the enforced breeding period at some remote island.

All have webbed feet, with no hind toe, and they carry with them a powerful musky odour caused by the stomach oil which they will so freely spout at you if alarmed. Most of them breed in the Southern Hemisphere, some migrate north to ‘winter’ in the northern summer. And, likewise, those which breed in that northern summer, like the Manx Shearwater, fly south to ‘winter’ in the southern summer, thus making maximum use of the different seasons of plenty.

sea bird's well structure flight. wings giving it support to fly

Those which breed in tropical and sub-tropical latitudes tend to be more sedentary, because seasonal differences in those latitudes are less marked. Many of them are confirmed ship-followers and they are keen on galley waste. They are most enthusiastic in pursuit of whaling and fishing vessels since these can provide a significant source of high-calorie offal. In much the same way as freely available garden bird-table food sustains many first-winter passerines through to their first summer, so many first-year seabirds must bless the wasteful habits of ships.

Seabirds live more or less but they have evolved an armoury matter, of method, from Zooplankton to fish, for hunting it. Albatrosses and shearwaters may duck under surface and peck, or pluck from the surface in flight. Diving-petrel whir along at zero feet and plunge into the waves after shrimps and small fish. Storm-petrels feed on the wing, feet dangling and ‘walking’ on the water, sucking oily food from the surface.

Sea birds: White Pelicans

White Pelicans fish co-operatively, line abreast (a form of pair. Trawling) advancing on a shoal with their great beaks scooping in the water. Brown Pelicans have a much more spectacular tech. Nique, diving from a height in active chase of individual fish. This ‘plunge-diving’ is characteristic of the widespread family group of gannets and boobies. Typically, they will be spread out over the sea at a distance from each other until one of the parties locates a shoal. In plunging into the sea, the tell-tale flash of white alerts those distant colleagues to the action and in no time that first bird is joined by many others.

They dive from varying heights, up to a hundred feet or more, folding their wings just before they splash through the surface like a stone. They do not penetrate deep, indeed their buoyant plumage would make it difficult for them to dive far down, but it is the speed of entry into the water which gives the required impetus for a brief underwater chase. With forward facing eyes giving binocular vision so that they can judge distances accurately, they capture herrings or mackerel or flying fish in the powerful dagger-shaped bill. They have large webbed feet, not so much for swimming as for skilled underwater manoeuvring in the chase. To absorb the shock of the impact, they have a system of air sacs under the skin, inflated from the lungs to form a spongy protective mattress at the breast. Their external nostrils are much reduced (altogether closed in gannets). They have a secondary nostril system, where a narrow slit at the angle of the beak is sheltered by a horny flap which serves to stop water forcing itself into the mouth on impact.

sea bird resting after hunting.

Although most gannets and boobies have a lot of white in their plumage, they have black tips to the wings, a trait typical of seabirds. The insoluble dark pigment granules of melanin have a strengthening effect giving extra resistance to wear and tear at lese vulnerable extremities.

Sea birds; Food Hunting

In tropical waters the main food of the abundant boobies is squid and flying fish, which are chased both in the sea and over it. Both tropicbirds and terns plunge for their food, too, but from a lesser height, and they hover like kestrels before they commit themselves to the descent. Mostly they pick or scoop small fish from the surface with their straight, sharply pointed bills without getting their feathers, or even their feet, wet. Since they do not submerge or have any impact with the water they have external nostrils.

They do not rest on the water, but will perch on a piece of convenient driftwood or the rail of a ship if it suits them, but equally they may stay in flight for months on end without difficulty. The sea terns (known as sea-swallows to sailors because of their long tail streamers) live enviably free lives, many of them breeding in one hemisphere and ‘wintering’ in another in order to enjoy a life of perpetual summer, always where the feeding is at its seasonal best.




















One Comment

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button