Cattle Egret and Grazer

PHOTO FEATURE Cattle egrets feed on different preys ranging from insects such as ticks, Cattle Egret and grasshoppers, crickets, flies, moths, spiders, frogs and earthworms. They Grazer – Story of their have also been reported to feed on crustaceans, fish, lizards, rodents and vegetable matter. Relationship If a Cattle egret eats ticks off the hide of grazing mammals, then the M.C. Bindya relationship becomes mutualism. Cattle egrets also serve important ectoparasite biological control role by feeding on the ectoparasites found on their hosts (Blaker, 1969; Yadav, 1999; Seedikkoya et al., 2005; 2007). This has led to significant reduction in the associated irritation of dipterous cattle pests by pecking them directly from their skins (Blakar, 1969; Lever, 1987). This type of interaction represents mutualism. Here the egret essentially helps the mammal while at the same time getting food. It was also found that egrets with exclusive access to a cow always foraged better and caught significantly more number of preys than egrets who foraged away from the cattle (Grubb, 1976). If we were to clarify the nature of interaction between the Cattle egret and larger grazing mammals we can call it mutualism only when the egrets are in association with the cattle, that is if the A cattle egret former were within 2 to 3m distance of foraging cattle (Deep Novel Kour and D.N. Sahi, Acad. Journals, 2012) or HITE birds with yellow beaks other without affecting it, that is, neither perched on the back of the mammal. Since and slender legs are often benefitting nor harming. So, how is it egrets actually clean the area off annoying found in the vicinity of large that the Cattle egret shares two types of W pests, both the partners – the egret and the grazing mammals like cow, buffalo, relationships with cattle? mammal – are benefitting here. rhinoceros or elephants, especially if we pass by grasslands, wetlands or inundated fields. These are Cattle egrets, so called because unlike other types of egrets these are commonly found either riding on cattle or around them as they graze. For many years the interaction between the egret and a grazing mammal was described as ‘Mutualism’, a relationship between two organisms belonging to different species in which each individual benefits from the activity of the other. The same example is also often presented as ’Commensalism’, a relationship between two organisms belonging to different species in which one organism obtains benefits from the Egret and a wild water buffalo

34 | Science Reporter | June 2019 Egrets following wild Asian elephants once had a strong association with grazing cattle, but have now shifted themselves behind tractors especially in inundated agricultural fields. The egrets follow the tractor to feed on insects stirred up. A comparison between cattle and tractor in terms of capture per minute reveals the tractor to be more efficient in exposing the prey. Hence the egrets solely do not depend on walking or resting mammals to be fed, they are opportunistic feeders (Optimal Foraging Theory). They follow any cattle, or even tractors/mowers. This is called facultative Cattle egrets and rhinoceros commensalism, since the association of egrets with mammals is not obligate, the type of commensalism here in fact is loose; the egrets do not die if the relationship with cattle/a grazing mammal ends. In fact, Cattle egrets have been employed extensively as important biocontrol measures for cattle parasites (Telfair II, 1994; TelfairII and Raymond, 2006). Isaiah Oluwafemi Ademola et al. in the Journal of Environmental Extension (Vol. 12) in their article “Parasites of cattle egrets and the associated Haematological and biochemical changes”, says that “despite the beneficial roles of Cattle It can nevertheless be called 2007; Siegfried, 1971; Martinez and egrets in controlling cattle pests, they have facultative mutualism too because Motis, 1992) from grasslands and the been implicated in their potential role in the egrets and the mammals are not mammals do survive even in the absence the transmission of different diseases such exclusively dependent on each other for of egrets. Thus their relationship is not as heartwater, infectious bursal disease their survival (The American Heritage of obligate kind. and Newcastle disease (Fagbohun et al., Science Dictionary); egrets also feed These birds are able to easily obtain 2000a; 2000b). Isolation of salmonella in on vertebrates like frogs and other their diet (for instance insects, beetles cattle egret from Fernando de Noronha invertebrates like moths, spiders and and so on) when stirred up by their large Archipelago, Brazil (Silva M.A et al. Braz earthworms (Seedikkoya et al., 2005; herbivore hosts, which considerably J Microbiol., 2018) shows the possibility improves their foraging success compared of transmission of pathogens to human to when grazing alone. When in the beings and livestock. This is because Egrets following moving tractors company of cattle, their efficiency is Cattle egrets habitually come into close (www.ynotpics.com) 3.60 to 5.20 times more than when they proximity to cattle, sheep, goats and are not associated with cattle (Dinsmore horses (Lunardi V O, et al. Braz J Biol). 1973, Grubb 1976). In this case the egrets So, there is still a lot to be revealed are adjacent to the mammals but not very about the relationship between a Cattle close or perched on their bodies, thus the egret and a grazing wild or domesticated mammals are completely unaffected and mammal. get no benefit by the presence of egrets, while the egrets are getting fed. So, this interaction denotes commensalism. Ms M.C. Bindya is a Post Graduate Teacher Aeshita Mukherjee, Ornithologist, in Biology, Jawahar Navodaya Vidyalaya (MHRD, Dept of Education, Govt. of National Tree Growers Cooperative India), Mbajai, Jalukie, Peren District, Federation Limited, has drawn our Nagaland-797110. Email: bindyamcram@ attention to her abstract in her article gmail.com titled ‘Adaptiveness of Cattle egret’s Photographs shot by author in the Kaziranga foraging’, which says that Cattle egrets National Park, Assam

June 2019 | Science Reporter | 35