The common or great cormorant is a large, top heavy and mostly black bird. They have an upright posture, a wingspan of more than 5 foot and large webbed feet. At the base of their powerful hooked beaks they have a yellow patch of skin and bright bluey green eyes. Young birds have a more washed out appearance with brown wings and heads and creamy grey chests. Throughout the breeding season adult birds develop white patches on their thighs and sometimes around the back of their necks. Their wing feathers become more of an iridescent bronze colour and they grow a small crest of black feathers which can be held upright but also flat to their heads. Their feathers are not waterproof and as they spend a lot of their time in water they have to dry them out by standing upright with their wings splayed.
A lot of the time Cormorants can be seen standing along waterways, sometimes high on the branches of waterside trees or nearby buildings. Their webbed feet aren’t great for walking and they can only move slowly on land, but don’t let that lure you in. they are exceptional swimmers. For birds, cormorants have really dense bones meaning they float very low in the water and as their paddle shaped webbed feet are towards the back of their bodies they can swim really fast both above and below the surface. Their diet is made up almost exclusively of fish which they catch by chasing down then gripping with their hook shaped beaks before swallowing them whole. Although each bird only consumes around 500grams of fish per day, they are so good at catching them that they often grab hold of and eventually release fish that are too large for them to swallow. This can leave the larger fish scarred or sometimes fatally injured and has netted the cormorants a bad reputation with anglers.
Cormorants can breed at any time of the year if there is enough food available but this is usually confined to the warmer months between April and September. They nest communally, often in tall waterside trees but occasionally on cliff edges and both coastal and inland islands. Cormorants are for the main part monogamous but as pairs sometimes spend long lengths of time apart, upon returning to the nest they must perform a courtship display to solidify their relationship. If their mate takes the bait, egg laying can begin. Each female produces between 3 and 6 pale blue or green coloured eggs. These are incubated for 28 to 31 days and just like penguins, sometimes the parent birds will lift the eggs on top of their feet to keep them closer to the warmth of their bodies. When the chicks hatch out they are covered in a layer of dark brown down and look remarkably like their parents, albeit more gangly versions. They are fed on regurgitated fish for 50 days before they can fledge. After fledging the young birds stay with their parents for several more weeks as they learn how to catch fish for themselves. Some of this is through copying their parents but a lot is on the fly through trial and error.
Long term studies have shown that cormorant numbers have increased by around 40 percent since 1986. There are now around 9100 breeding pairs and 41,000 individual birds. No one is exactly sure why these birds seem to have begun casting out into inland areas rather than their traditional coastal breeding sites, perhaps this was caused by a lack of food in the oceans or maybe they have been drawn in by the ready supply of fish in fisheries and stocked ponds and lakes.
Cormorants can be really long lived birds with the oldest individual making it to a whopping 27years and 2 months. Their average lifespan is around 15 years but they do have a high mortality rate in their first year.
Some of the footage and images used in this video were obtained through creative commons. The originals can be found at:
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"Smaller crowned cormorant eggs. Schaapen Island, Saldanha" by Mary Gillham Archive Project is licensed under CC BY 2.0 eggs
"man with cormorant" by suecan1 is licensed under CC BY 2.0
"Aalscholver - Great Cormorant" by Rob Zweers is licensed under CC BY 2.0
#britishbirds
#wildlife
#nature
30 июн 2024
