Whilst walking around Thornton Reservoir recently we saw a Great White Egret catch a large Perch, struggling for several minutes to subdue and swallow it. Perch are native species that are found throughout the country and have a fossil record going back several million years. They are readily identifiable with a greenish body with up to nine dark vertical stripes, red or orange pelvic and anal fins and a red tail. They have two dorsal fins with the first one being spiny, and it is this spiny fin that can make the fish rather difficult to swallow. Large Perch are predators that eat other fish and crayfish; small perch survive mainly on small invertebrates such as bloodworms and other insect larvae.

In contrast, Great White Egrets are comparatively recent additions to our fauna. During the last century they were rare visitors to this county, but over the last 30 years their range has expanded to include England and they have recently been seen nesting in Scotland. The first breeding pair in this country were documented in the Somerset Levels in 2012 and by 2019 the number of breeding birds had risen to up to 24 pairs; they have continued to prosper since then and are now found over much of England. It is a bird of marshes and wetlands and like its relatives, the Little Egret and the Cattle Egret, is now seen regularly in Leicestershire. Great White Egrets are carnivores that feed mainly on fish with occasional amphibians, small mammals and even small birds. They generally stand still or walk slowly through shallow water and stab and swallow prey that come in range.

Like all of the heron family, egrets have slender necks and swallowing a large fish can cause considerable problems. It took this egret around 5 minutes to get the fish into the right orientation as the fish has to be swallowed head first. In this way, the spiny fins and operculum (gill cover) are flattened and do less damage to the lining of the gut. The birds are unable to break the prey down into smaller parts so they have to rely on being able to swallow the catch whole. They are thought to require around 15-20% of their body weight each day, about 130-175 grams of food. This equates to several small fish, but a specimen like the perch seen here would be more than enough of allow the bird to survive for the day.

Having eventually swallowed the fish, the Great White Egret seemed for a while to have it stuck in its slender throat, although it did fly off a few minutes later with no apparent problem. Although the bird did have to put the fish back into the water a few times to reorientate it, the overall handling time would probably have been no more than would have been expended in catching several smaller fish. Part way down the neck of the egret is a wider area known as the crop where large prey can be stored before passing the food on to the gizzard. This is a thicker muscular sac with a rough, sand-like lining, used for grinding and mixing; it often contains sand and stones to help in this process. Egrets produce pellets consisting of indigestible parts of their prey, such as bones and fur, that are then coughed up and regurgitated whilst the edible parts continue through the digestive tract. Although the lump in the throat of our egret looks uncomfortable, I have no doubt that the bird would have made short work of its over-sized meal.