BIRDS CONTROL OWN POPULATION
Brutal Survival instinct
Skuas (genus Stercorarius)— gull-like sea birds known as the pirates of the Polar Regions, have very unique and ruthless way of controlling their own population during the years when food is scarce. Usually they raise two chicks, but in the event of scarcity of food, either the first chick will kill the second or the parents will themselves perform this brutal act. Skuas usually pair for life and both the sexes share the parental duties.
Classified under Family Stercorariidae with six-seven species, these ground-nesting birds are found worldwide, breeding in northern parts of Asia, Europe, North America, southern S. America and sub-Antarctic islands. Medium to large, dark brown sea birds, they feed on mammals, insects, eggs, fish and carrion. Their medium-length beak is strong and hooked and legs are short with webbed feet. These aggressive birds can be seen chasing seagulls, terns and knock flying gannets off balance to make them regurgitate their prey, which they quickly pick out of the air and swallow. They are courageous birds and at nesting site, which is usually in loose colonies, they do not hesitate in attacking falcons, foxes and even human beings.
Large or Great egrets (Egretta alba)—Like skuas these birds too take recourse to homicide for controlling their own population. When food is in short supply large egret parents do not mind if their offspring fight even to kill. Whenever such situation arises the parents ensure that their strongest chick should at least survive for which they encourage it to bully and kill its brothers and sisters.
In egret family also, like that of other animals, it is common practice that whenever parents bring food at nests, young fight over share in the spoils. But, if its time of scarcity, it becomes a serious problem and fights are not simply squabble but they take the form of ‘survival of the fittest’ and the strongest and largest of the chicks kills its siblings to ensure food for itself. Though, it is cannibalistic, it is the law of the jungle kill and survive or get killed.
The above behavior, perhaps, also results from the incubation pattern of egrets. Usually other birds do not start incubation until all the eggs are laid and the clutch is full, ensuring that all young hatch, more or less, at the same time, but here, parents commence incubation as soon as the first egg is laid, giving the first hatchling a head start over the others.
Found worldwide, these long-necked and long-legged, white birds are medium to large in size. Nesting in trees, they feed mainly on insects and aquatic animals.
In breeding season, all these birds develop ornamental lacy plumes on their back, which were in great demand for making women’s hats in Europe and America during early 20th century – hence the term aigrette (a plume or tuft of feathers esp. the back plume of any of various herons, arranged as a head ornament). Due to the fashion the trade in feathers was so lucrative that these beautiful birds were killed in such a large numbers that they almost reached to the point of extinction in many parts of the world, especially in the European and American countries. Now with the awareness about nature conservation increasing, international embargo on traffic in almost all wildlife products imposed and various punitive laws framed by different countries, have saved egrets from complete extinction.
Intelligent family planning
Kookaburras (genus Dacelo) — These terrestrial tree kingfishers have interesting system of controlling their own population. They live in social groups of more than two birds, sometimes as many as five or six, in specific territories, but only two birds at the top of the hierarchy breed, while the others act as helpers. When egg-laying begins only the dominant pair takes part in the process while rest of the group or helpers (who themselves may be mature males or females) share in the nesting duties, helping in incubation of eggs (of the dominant pair), feeding chicks and protecting them when they become fledglings. These helpers carry out nesting duties as arduously as if the young ones were their own. Thus, by not breeding themselves, helpers help in reducing their own population.
Native to Australia and New Guinea these birds belong to the family of kingfishers, but are not closely associated with water like their other family members. Their name is a loanword from Wiradjuri guuguubarra, onomatopoeic of its call. The single member of the genus Clytoceyx is commonly referred to as the shovel-billed kookaburra.
The kookaburra’s loud call sounds like echoing human laughter. They are found in habitats ranging from humid forest to arid savanna, as well as in suburban areas with tall trees or near running water.
According to the American biologist, Veronica Parry, these helpers or auxiliaries may maintain their subordinate position for three or four years. If any dominant bird in the neighboring territory dies, an auxiliary may then move over to fill the new vacancy. This study was the first detailed scientific account of kookaburras.
According to Parry, occasionally, after being an auxiliary for some years, a mature kookaburra may leave its territory and become a vagrant. They wander from territory to territory, seeking a mate and a place to settle down. These vagrants become very aggressive in their search, and often try to usurp other’s territory, which results in violent clashes.
Four species of kookaburra can be found in Australia, New Guinea, and the Aru Islands. They eat bird seeds and other seed products. Kookaburras are known to eat the young of other birds, mice, snakes, insects and small reptiles. They have also been known to take goldfish from garden ponds.