CATTLE EGRET - MIGRANT OR RESIDENT?

Bird watching in the 21th century took a different turn with many taking to digital bird photography. The old school birder who preferred to identify birds in the conventional way is now bypassed with photo identification. The advantage of having a picture for future reference is very much convenient to a hastily done field sketch. Bird photography today has advocated the need to review and revisit some bird behavior that show unusually high populations during a certain time of the year. Research studies on these aspects have now been undertaken on some commonly occurring bird species by local universities to determine their home ranges and migratory status. The Cattle Egret and the Indian Pond Heron are two such bird species under review.

 Both these species show off nuptial plumage changes of a breeding season with significant color change but no firm nest building behavior is recorded in any known heronry where much photography has emerged. Although it is adjudged a disapprobation to photograph nesting birds and their breeding behavior, the unscrupulous photographer still pursue his habit. There is literature on the breeding behavior and timelines with clutch sizes in old records of G M Henry and others ornithologists of the past but with no firm recordings at present time.

Cattle Egret

The Cattle Egret is of two subspecies. The Eastern Cattle Egret [Bubulcus coromandus] and the Western Cattle Egret [Bubulcus ibis]. The Eastern Cattle Egret; a species of heron is found in the tropics and subtropical warm temperate zones and the Western Cattle Egret is classified as those found outside these areas. Despite the similarities in plumage which is closer to the egrets of the genus Egretta,… they are more closely related to the herons of Ardea.

It is named for its habit in associating with grazing livestock to feed on the invertebrate prey disturbed by the hooves of moving cattle. But today with the shifting of grassland faming to closed house farming systems and overgrazing of grassland we don’t see them associating cattle very much. The cattle egret has a unique adaptation for catching its moving prey in flight …. Unlike most birds adapting to have its head stationary with their eyes focused on its prey, the Cattle Egret moves its head to either side in quick succession before it lunges forward in a stabbing gusto to grab the flying bug. At times it would hitch a ride on the animal’s back picking the ticks and fleas off its hide. There are times when it prefers to relax on the largest terrestrial beast when tired of following it.  

Galoya - Pic Uditha Wijesena

As mentioned above with the foraging livestock moving out and the tall grasses diminishing from overgrazing the Egret is now frequenting the ever increasing urban garbage dumps and landfills for grubs and bugs. Our Sri Lankan domestic garbage being wet and biodegradable is an ideal medium for breeding House Fly [Musca domestica] and the Bluebottle Fly [Protophormia terraenovae.] Both the flies are considered pest and disease transmitting vectors and the Cattle Egret is most welcome on these sites for vector control.

Kurunegala in July 2018 - No Cattle Egrets seen on Garbage

Urban garbage today is a national crisis and the biodegradable component of it is managed by turning it to compost through various programmes. The latest being a Japanese Technology introduced with comprehensive mechanical means to handle over 50 tons of garbage per day. The author is currently in this project on seven sites scattered in the country and is familiar associating the nauseating stench and the hordes of teeming flies swarming all over you in a humid locality. It’s so tricky to avoid them from getting into your garments. And when in the vehicle, its a task that would go on for 20 kilometers or more to rid the last fly out of the car.

This was normal on our site visits until during one visit it was significantly noticed that the flies had all gone. On close inspection it was seen that the flies had now been replaced by thousands of pure white plumage of Cattle Egrets that looked more like white sheets covering the dumps.

Dambulla grubbing alongside Elephants

Ampara - Deegawapi

The reason for the fly less atmosphere was the presence of the Cattle Egrets that feasted on them assisted with  Barn Swallows that crisscrossed the dumps regularly and rest on the roof trusses of the many sheds in these yards.

Barn Swallow - Kurunegala

The presence to the Ban Swallow prompted the beginning of the bird migration period for it being a regular winter visitor to the country……. But then the Cattle Egret? In such heavy numbers to have visited with the Barn Swallow suggests them also to be a group that migrated into the country? This notion had some confirmation with the bird being in all the seven locations in seven provinces at the same time in such large numbers.

Kurunegala February 2019 - Cattle Egrets grubbing inside yards

They initially feasted on the fly population and later picked on the maggots and the fly larvae, ridding the menace of irritation and the health hazard. They are still in the country but will soon be gone if they are migrants. I will keep watch for the increase in the fly population with the Cattle Egret gone in these sites. Their suspected migration was not significant until the number of people getting interested in birds and bird photography increased in the country I feel.

Pollonaruwa

Hambantota

There is scientific research to identify some populations of cattle egrets to be migratory and described as below;
"In many areas populations can be both sedentary and migratory. In the northern hemisphere, migration is from cooler climes to warmer areas. But Cattle Egrets breeding in Australia migrate to cooler Tasmania and New Zealand in the winter and return in the spring. Populations in southern India appear to show local migrations in response to the monsoons. They move north from Kerala after September. During winter, many birds have been seen flying at night with flocks of Indian Pond Herons [Ardeola grayii] on the South-Eastern coast of India, and a winter influx has also been noted in Sri Lanka."

As we have already commenced studies on the Cattle Egret it is high time that a comprehensive study be undertaken on the Indian Pond Heron as well, which also flaunt nuptial plumage sans any breeding noted recently…..there were some unusual flight patterns in large numbers of Indian Pond Herons along the sea coast flying in a Northerly path in and around the Colombo metropolis, observed sometime back.