BIRDS ARE VERY USEFUL
World’s more than 10,000 bird species are key “mobile links” in most major ecosystems, from tropical rainforests to the depths of the Antarctic Ocean. Birds provide crucial ecosystem services, including seed dispersal, pollination, predation, scavenging, nutrient deposition, and ecosystem engineering. Countless plant species depend on mutualistic relationships with birds for their survival. However, threats such as habitat loss, introduced species, and exploitation, exacerbated by the growing impact of climate change, are causing large population declines and extinctions among birds. Researchers have speculated that these losses could lead to declines in dependent plants. It has been found that the functional extinction of three kinds of pollinating birds on an island in New Zealand has reduced pollination, seed production, and plant density in a dependent shrub.
Bird pollination (ornithophily)
Study of mechanisms of pollination started in Europe, where pollinating birds are scarce; therefore their importance is often underrated. On the other hand in the tropics and the southern temperate zones, birds are as important as pollinators as insects are, perhaps more so. Approximately a third of the 300 families of flowering plants have at least some members with ornithophilous (“bird-loving”) flowers, which means flowers attractive to birds. Same way around 2,000 species of birds, belonging to 50 or more families, visit flowers more or less regularly to feed on nectar, pollen, and flower-inhabiting insects or spiders.
Like hummingbirds, which are the most familiar nectar-feeding birds in North America, there are similar kinds of species in other parts of the globe: lories and lorikeets, sunbirds, honeyeaters, flowerpiercers, flowerpeckers, honeycreepers and bananaquits. Among the nectar-feeders, hummingbirds are the oldest group, with the greatest degree of specialization on nectar. Flowers attractive to hummingbirds that can hover in front of the flower has to be large, tubular, red or orange in color, with a lot of dilute nectar, secreted during the day. Since birds in general do not have a strong response to scent, the flowers attractive to them tend to be odorless. Perching birds need a considerable landing space, so honeyeaters, sunbirds and the like are less associated with tubular flowers.
Several species of mistletoe are threatened with possible extinction due to the disappearance of birds that pollinated them, and turned their attention to New Zealand gloxinia (Rhabdothamnus solandri), a large (two-meter-high) native shrub found only in the forests of northern New Zealand. The shrub, known for its bright orange flowers, was pollinated by the bellbird, stitchbird and tui, which all have long tongues able to reach into the flowers, which are about 10 mm long.
On the North Island, the tui (Prosthemadera novaeseelandiae) now seems to feed higher in the forest canopy. The stitchbird (Notiomystis cincta) and bellbird (Anothornis melanura) have been wiped out by introduced predators such as ship rats, cats, possums and stoats brought by European settlers. These birds now exist only on a few islands off the North Island, where there is little human interference, or where feral predators have been exterminated.
The researchers examined the areas of North Island and three small islands close by to see how gloxinia was faring. They found that on the mainland where the stitchbird and bellbird have gone, the fruit is smaller with just 37 seeds on an average compared to 232 seeds in fruits on the islands. Only a quarter of the mainland flowers demonstrated evidence of birds’ visits, compared to approximately 80% of the flowers on the island. The population densities of adult plants were around the same but on the mainland there were 55 percent fewer young plants growing.
When the plants were encased on both mainland and islands in wire mesh they also produced fewer seeds, which demonstrates birds are required for pollination, with insects playing a smaller role, if any, most likely because the flowers are too long and narrow for insects to successfully pollinate them. When the researchers sowed seeds themselves and manually pollinated the plants, they soon boosted their numbers.
Protection from insects
Birds render many invaluable services to mankind, not all of which can be enumerated here. For instance, various kinds of pests harmful to plants and humans could multiply to dangerous proportions, only if the birds were not there to make meal of them. According to an estimate, in the absence of birds the number of insects will grow so much that they will destroy the entire vegetation in the world within 10 years!
Birds, specially their growing nestlings, have voracious appetites. To feed them, parents keep collecting insects in large numbers, indirectly helping the humans and the herbivores of the world in keeping down the pest population. The extent to which they are affective in this activity is evident from the fact that a tiny bird like tit and its family eats up about 12 million insects in a year, an American bird, scarlet tanger was observed to have consumed 630 gypsy moth caterpillars in just 18 minutes. A wren on average feeds its young 37 times in an hour. There is a remarkable case of a wren, which fed its young 1217 times in 15 hours and 45 minutes. The wheat crop has over 200 species of insects pest where as the maize has more than 400. Over 500 species of insects thrive on fruit tree and berries. It has been estimated that a fly catcher catches about 20000 insects to feed their young. A cuckoo can eat several hundred caterpillars a day. These are the few examples that are sufficient to understand the importance of avian presence around us. The stomach of insectivorous birds may contain over 5,000 small insects such as mosquitoes and ants or several hundred caterpillars – impressive quantity considering that birds can pass food through their digestive tracts in 40-95 minutes and such number represent only a fraction of an average day’s consumption.
Besides insectivorous other birds too play a great role. Birds of prey also play a very prominent role in keeping the population of rodents, insects and even birds under control. Zoologists have estimated that songsters, game and other birds constitute no more than 10 to 15 percent of predatory bird’s diet; harmful insects and rodents account for the rest.
Going by these standards buzzards are the best friends of farmers; they feed chiefly on voles, mice and other harmful rodents, as well as on insects. Detailed analysis of the stomach contents of buzzards has revealed that mice and voles comprise a full 96% of their diet. Rats and mice are prolific breeders. If we take it mathematically, a single pair of rat, which feeds primarily on grain, can multiply into 880 individuals in a year. This means an overall loss of about 10% in the total food production only due to rats. Like diurnal (active in day) buzzards, nocturnal (active during night) barn owl also plays very important role in keeping rodent population under control. On an average a barn owl pair consumes 3 rats in a night, which means 1095 in a year. If 50 % of the rats eaten are females, then barn owls will reduce the increase of rat population by 481800 individuals in a year. Above fact is sufficient to imagine the magnitude of the menace of rats without the owls who serve us for free.
Birds are not only helpful in keeping down the pest population they also provide high-grade manure. Guano, the droppings of fish-eating birds, is considered to be the finest nitrogenous fertilizer in the world. Found mainly on the coastal islands of Peru, Chile and the West Indies along with some other countries guano contains about 6 per cent phosphorus, 9 per cent nitrogen, 2 per cent potassium and moisture. It is found mixed with feathers and bones of creatures that the birds feed upon. The famous Guano Islands off the coast of Peru are a major economic asset of that country.
For eons, Australia’s Abrolhos Islands have been attractive nesting grounds for thousands of sea birds that come here even today to lay eggs and raise their young. The presence of these birds down the centuries has produced rich guano beds, which are being dug out intermittently since 1844. During World War II the islands provided 10,000 tonnes of guano, as fertilizer for local farmers.
Birds are even more valuable as indicators of unforeseen events, which later play disastrous role in human lives. It is a proven fact in numerous pollution related cases, especially where chemicals are involved, the deteriorating bird life in the area first alerted naturalists about the dangers that will keep haunting the local residents, man or animal, for long periods of time. The case of Silent Spring, a book by Rachel Carson published in 1962, is the classic example of alerting the world about the hazards of synthetic chemicals. The book deals with the toxic effects of the chemicals and how these toxins reach the body of different animals through the mechanism of food chain in nature.
The phenomenon has been highlighted by the example of western grebe, a species belonging to the family Podicipedidae, which was a regular winter visitor to the famous Clear Lake in the United States. This water body was the favorite place of anglers, but because of the annoyance caused by mosquitoes and gnats DDT was sprayed on the waters in the proportion of 1/50 part per million, which is a minute proportion if we take into account the amount of water in the lake. Later, the planktons in the lake were found to be containing as much as five parts per million of DDT, 25 times the concentration applied to the water. When plankton feeding fish were examined they were found containing an incredible 2,500 parts per million! Finally it was observed that fish-eating western grebes have also started succumbing to the chemical poisoning.
Deposition of chemical in the system of different animals in increasing order was the result of mechanism of food chain that operates in nature. The fatal effects were visible much earlier in birds than man because their metabolism is much faster than humans. Moral of the story is if we keep a close watch on the results of pollution on bird life we can easily have the forewarning about the events that are going to come by.
Clearance of waste materials, dead bodies of animals and other putrefying material depends entirely on kites, crows and vultures. They feed on carcasses and waste in garbage dumps. By doing this they play an invaluable role in keeping our environment clean and disease-free. Among the birds that scavenge vultures are the most notable.
Vulture is the name given to two groups of convergently evolved scavenging birds. While the New World Vultures include the well-known Californian and Andean Condors, the group of Old World Vultures comprises of birds which are seen scavenging on carcasses of dead animals on Asian and African plains. New World Vultures are found in North and South America, Old World Vultures in Asia, Africa and Europe. This means that Vultures are found on every continent except Australia and Antarctica.
Many vultures have typical characteristic of having bald head — without the normal feathers. This helps the bird to keep its head clean while feeding. Research has indicated that the bare skin may also play an important role in thermoregulation.
These birds seldom attack healthy animals, but may kill the wounded or sick. They are so intelligent that when a carcass has too thick a hide for vulture’s beak to open, they wait for larger scavengers, like hyenas or jackals, to eat first. These birds are of great value as scavengers, especially in hot regions. The bird’s stomach acid is exceptionally corrosive, allowing them to safely digest putrid carcasses infected with anthrax bacteria, Botulinum toxin, hog cholera, etc. that would be lethal to other scavengers. New World vultures use their corrosive vomit as a defensive projectile when threatened. New World vultures also urinate straight down their legs; the uric acid kills bacteria accumulated from walking through carcasses, and also acts as evaporative cooling.