The main reason birds migrate is to ensure they have access to food all year round. For some bird species this may mean flying half way around the world, and their migration patterns are so predictable that birders arrange special events to welcome the weary travelers to their wintering ground, as well as to see them off when they depart. For centuries, farmers have looked to the departure and arrival of local birds as an indication of what the seasons hold, while mariners judged ocean currents and the nearness of land by the birds they encountered. Some migrating bird species are somewhat less predictable and these are referred to as irruptive migrants, with their migration habits being referred to as irruptive migration.
Some species may have a cycle of irruptive migration where they visit an area every two or four years and are therefore still predictable, while others are completely random. Reasons for irruptive migration are varied, but the most common cause is a lack of food in their normal wintering grounds. Birds that depend on birch, pine, spruce and maple seeds and catkins are known to irrupt when these trees produce poor crops. As their name suggests, crossbills have unique crossed bill-tips designed to pry conifer cones open and extract the seeds. They do not have the luxury of choosing an alternative food source and are obliged to find food they can access. As these seeds are also rodent food, if they fail to appear or produce an insufficient crop for demand, raptors may also leave the area in search of a more readily available food source.
Irrespective of what the motivating factors are for irrupting, it is virtually impossible to predict which species will irrupt in any given year and where they will migrate to, however the following species have been noted for regularly irrupting: pine siskins, bohemian waxwings, boreal chickadees, evening grosbeaks, purple finches, pine grosbeaks, common redpolls, red crossbills, white-winged crossbills, northern shrikes, hoary redpolls, red-breasted nuthatches, snowy owls, great grey owls and rough-legged hawks.
While birders generally welcome seeing unfamiliar birds at their backyard feeders, they should be aware that sometimes the unexpected visitors, particularly if they arrive in great numbers, can intimidate the locals in their quest for food. This can be overcome by setting out extra feeders and spacing them as far apart as possible. Also ensure that plenty of water is provided and water sources are cleaned regularly. Then sit back, relax, and enjoy the sight of feathered friends from far away.
Based on the oldest recorded pelican fossil found at Luberon in southeastern France belonging to the Early Oligocene era, it has been deduced that pelicans have existed virtually unchanged for at least thirty million years. Fossils of several birds from the Pelecanus species have been identified elsewhere in the world – South Australia; Siwalik Hills, India; Bavaria, Germany; Idaho, United States; Odessa, Ukraine; and North Carolina, United States – backing up this claim. Today there are eight living pelican species distributed around the world and some of which are considered ‘vulnerable’ or ‘threatened’ by the IUCN, and all of which use their amazingly elastic pouches to catch fish.
With the exception of the brown pelican, which dives for fish and snatches it up in its bill, pelicans usually form cooperative groups for their fishing expeditions. They either swim along in a line or U-shape formation, beating their wings on the surface of the water to drive the fish into a group in the shallows where the pelicans scoop them up in their pouches. Contrary to popular belief, pelicans do not store fish in their pouches, but swallow them almost immediately upon catching them. Baby pelicans feed by retrieving fish from the throats of their parents.
Pelicans are very social birds, traveling in flocks and breeding in colonies, either along the coastline or inland alongside rivers and lakes. The brown pelican (Pelecanus occidentalis) was at one time considered to be ‘vulnerable’ in North America – primarily due to poisoning by chemical pesticides such as the notorious DDT which devastated the populations of many seabirds – but recent reports indicate that significant recovery has taken place and the birds’ conservation status is now that of ‘least concern’.
The Dalmation pelican (Pelecanus crispus), found in South-eastern Europe through to India and China, has the IUCN conservation status of ‘vulnerable’, while the Peruvian pelican (Pelecanus thagus) found on the Pacific Coast of South America, and the spot-billed pelican (Pelecanus philippensis) found in Southern Asia, are both considered to be ‘near threatened’. The other pelican species – pink-backed pelican (Pelecanus rufescens) found in Africa, Seychelles and southwestern Arabia; the American white pelican (Pelecanus erythrorhynchos) found in North America; the great white pelican (Pelecanus onocrotalus) found in the eastern Mediterranean, Malay Peninsula and South Africa; and the Australian pelican (Pelecanus conspicillatus) found in Australia, New Guinea, New Zealand, Bismarck Archipelago, Fiji and Walacea are all listed as being of ‘least concern’ from a conservation standpoint.