A limerick by Dixon Lanier Merritt.
This limerick has some truth; the pelicans’ pouch can hold up to three times more food than its stomach can, although they don’t hold food in their pouch for more than a few seconds.
‘A wonderful bird is the pelican,
His bill will hold more than his belican,
He can take in his beak,
Food enough for a week,
But I’m damned if I see how the helican.’
Ranging throughout the tropics to the temperate zone, pelicans are charismatic water birds that make up the family Pelecanidae, characterised by their long beak and throat pouch. Fossil evidence dating back 36 million years from Egypt shows a large bird with a close resemblance to the modern pelican, called the Tibiotarsus. Genetic studies have shown that pelicans are most closely related to the rather unusual, prehistoric looking bird the shoebill, although it was once thought they were close relatives of other sea birds like the frigatebirds, boobies and gannets. DNA sequencing also helped to organise the family tree of the living species around today. Traditionally, the eight species were divided into two groups, with one group containing ground nesting species and the other group containing those pelican species that preferentially nest in trees and rocks. But when scientists looked into their DNA, they found quite different relationships than those determined by similarities in behaviour and morphology. The New world pelicans form one lineage, consisting of the Brown Pelican (Pelecanus occidentalis), the Peruvian Pelican (Pelecanus thagus) and the American White Pelican (Pelecanus erythrorhynchos). The old world pelicans form the other lineage, consisting of the Australian (Pelecanus conspicillatus), Great white (Pelecanus onocrotalus), pink backed (Pelecanus rufescens), Spot billed (Pelecanus phillipensis) and Dalmatian pelican (Pelecanus crispus). DNA also decoded the history of the pelican lineage, with evidence that pelicans evolved in the old world and spread out into the Americas.
Pouches and Plunge Dives: Pelican behaviour and morphology
Pelicans are perhaps most famous for their throat pouch made up of stretchy skin that hangs from the lower jaw. They use this fleshy pouch like a built-in fishing net to scoop up fish, rich in collagen fibres so the pouch can flex. It is also rich in nerves, so the pelican can feel fish even at night or in murky water. Their tongue is especially small to ensure they don’t choke on it as they swallow down their lunch. The bones of the lower jaw are flexible, bowing outwards when the pelicans swipe up a mouthful of food. Under normal conditions, the distance between the mandibles of the jaw is around 5cm, but when the bones bend as the pelican scoops up a mouthful of water (as much as 2.5-3.5 gallons of water!), the distance can be as far as 15cm. Once they’ve caught a fish, the pelican will flex the pouch against its chest to expel the water and then with a quick toss of its head, the pelican swallows the fish whole.
As well as acting as a fishing net, the pouch of a pelican can also act like the ears of an elephant, helping to cool the pelican down in the heat of the day. The pouch is highly vascularised, and the pelican can use it like a bellows to cool itself, as heat escapes from the capillaries close to the surface of the thin skin. This is important for pelicans as they are larger birds and can easily overheat.
A soaring pelican is a common sight throughout the coastlines of the world, but how do such large birds look so effortless in flight? Pelicans have a thick layer of fibrous muscle in their chests, and these powerful muscles enable them to hold their wings rigid so they can soar on thermals as high as 3000 metres in the air. They can also skim over the surface of the water barely flapping their wings, saving energy. For such clunky looking birds, pelicans are also remarkably buoyant in the water. A dissection of two brown pelicans in the 1930s revealed a network of air sacs situated across the throat, chest and wings that are connected to their respiratory system. Although the exact mechanism of inflating the air sacs is unknown, the pelican can fill these sacs with air to help keep them afloat on the ocean with very little effort. There is also some research that suggests that pelicans can use these air sacs to cushion them as they dive into the water at high speed after their fish prey.
Most people living in the coastal regions that pelicans inhabit will have seen them plunge dramatically towards the water. This is the most common technique utilized by the brown pelican, who will dive headfirst from heights of up to 10-20 metres. The Australian and American pelicans use a different strategy, diving from a lower height, landing feet first and scooping up prey with their beak.
Pesticides and persecution: the issues faced by pelicans
The IUCN lists the brown pelican, Australian pelican and the Great White pelican as least concern, with the Peruvian pelican, Dalmatian pelican and spot billed pelican listed as near threatened, with populations in slight decline. But globally, there are still human driven threats that are affecting pelican populations including overfishing removing vital pelican prey from the oceans, human driven disturbance of nesting and feeding sites, entanglements in fishing lines and culling.
The Peruvian pelican is estimated to have increasing population trends, but there is still concern over their future, as they have had significant populations losses in the past. Scientists are pushing for better monitoring of this species and restricting access to breeding grounds. Both the Dalmatian and Spot Billed pelican have faced declines in the past due to the loss of critical breeding grounds and the drainage of vital wetlands, although increased legal protection in recent years has helped to stabilise the populations.
Pelicans are efficient fisherman thanks to their handy built-in fishing net pouches, but this expertise has put them in conflict with humans. Although they rarely predate on the same species that humans like to put on their dinner plate, since the 1880’s pelicans have regularly been shot and clubbed and their nesting sites destroyed. Although this attitude did change over time, there are still discussions around pelican culling any time they are perceived to threaten recreational or industrial fisheries. Interactions with fishermen are problematic in other ways; entanglement in fishing lines is particularly common as the hooks can easily catch in the thin skin of the pouch or webbed feet, and pelicans can also be crippled and even driven to starvation by microfilament fishing lines tangling around their bills.
Pelican populations took a serious hit in the 1950’s and 60’s when the now infamous pesticide DDT was frequently used across America. Birds in particular were the metaphorical canary in the mine when it came to the damage caused by the chemical. Much lauded conservationist Rachel Carson first brought attention to the damage the pesticide was wreaking on the environment in her famous 1962 book Silent Spring, where she lamented the loss of bird song. She was attacked by the pesticide industry, but when mass spraying of DDT to kill off beetles carrying Dutch Elm diseases caused a subsequent mass die-off of robins, people began paying attention to the pesticide and its harms.
DDT is so serious because it builds up in the food chain in a process called bioaccumulation. When DDT is sprayed over a habitat, the animals at the bottom of the food chain, such as insects, ingest the chemicals and store it in their tissues as it can’t be metabolised out. When a bird comes along looking for a tasty treat, they eat the insect and the DDT poison becomes more concentrated and dangerous in their bodies, where it builds up in fatty tissues. As birds will ingest a lot of insects in a day, the DDT contained in all that prey builds up into fatal levels. This is a particular issue for sea birds like the pelican, who ingest up to 4 pounds of fish per day, with each one of those fish containing accumulated toxins in their tissues. Even the slightest amount of environmental contamination can be transferred into huge toxin loads in birds and any other animals higher up in the food chain. Often, the pesticide won’t even kill the birds outright, but will sicken them and can affect their eggs, disrupting calcium metabolism and leading to thin shelled eggs that can’t support the weight of the developing chick.
DDT run off into the ocean was the major cause behind the massive decline in pelican numbers in the 1950’s and 60’s. It built up in the tissues of one of the most important pelican prey species, the anchovy, and led to mass failures of pelican nests as the thin shelled eggs were crushed under the brooding birds. Fortunately, with the overwhelming evidence against DDT, it was banned in the United States in 1972 and pelican numbers, alongside the many other birds and animals decimated by DDT, began to recover.
Pelicans are vulnerable to one of the most dreaded kinds of environmental pollution; oil spills. After the infamous Deepwater Horizon oil spill in April 2010, a report by the Centre for Biological Diversity recorded than 932 brown pelicans were collected for emergency care or rehabilitation, and they estimated that around 900,000 further pelicans were harmed, directly or indirectly, through loss of food resources, by the incident. Diving into the oil in search of fish can leave the pelicans feathers’ saturated, which can lead to hypothermia or even drowning. They can also become contaminated with oil an manage to fly back to their nesting grounds, affecting other birds and their young. Only a few weeks before this devastating event, the Brown Pelican had been removed from the Federal Endangered Species List after being listed in 1970 when DDT had crippled populations.
Pelicans, most particularly the brown pelican, is actually a conservation success story. No sooner had they recovered from the persecution of the early 20th century, when they were hunted for feathers or killed for their apparent interference with human fisheries, than they were being poisoned by the indiscriminate, mass spraying of DDT pesticide. Brown Pelicans recovered well, a testament to the workings of the Endangered Species Act (ESA), and their populations are relatively stable worldwide.
The Dalmatian Pelican is suffering some population declines across Europe, but Rewilding Europe, a not-for-profit conservation organisation, has developed the ‘Pelican Way of LIFE’ project, starting in Bucharest and focusing on the Black-Sea Mediterranean Flyway, where half the population currently resides and is a vital migratory corridor between Europe and Africa. They aim to tag and track pelicans to research their movements, reduce deaths from power line collisions, improve nesting sites and engage local stakeholders in the conservation of this charismatic bird.
The Spot Billed Pelican is also receiving conservation attention, as the only breeding populations currently exist in Sri Lanka, India and Cambodia, which are facing catastrophic habitat loss and destruction of key nesting habitat. There is also some evidence that pelicans are still hunted in this region, which local conservationists are hoping to tackle with awareness programmes aimed at local fishermen and schools.
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