Foraging patterns and kleptoparasitism among three sympatric cormorants (Phalacrocorax spp.) from the Delhi region, North India

Abstract

Cormorants, described as 'foot-propelled pursuit divers', constitute an important component of aquatic food webs and exhibit unique foraging behaviour patterns, which can be properly understood through a comparative study. Since, after a foraging dive they surface to ingest the prey, the intensity of kleptoparasitic attacks on the surface can have a major impact upon the net energetic gain for each individual. Inspite of the fact that cormorants and their habitats are severely threatened in India, their foraging behaviour has not been adequately studied. Such considerations prompted us to undertake field studies on three sympatric cormorants (Phalacrocorax spp.) at 60 different sites in the Delhi region of North India, during 2004-2007. By means of video photography, some key foraging parameters including group size, prey size and patterns of kleptoparasitic attacks were quantified. Along a loose body size gradient, we observed significant differences among the three species with respect to not only their preference for wetland size but also prey size. The frequency of a kleptoparasitic attacks depended upon the group size and foraging behaviour of each species. It was observed that several foraging bouts were abruptly terminated due to human disturbances, mostly at sites lying outside the protected areas. This observation points towards the need to conserve small waterbodies in the countryside, currently threatened by pollution and urbanization, for the benefit of a variety of waterbirds including cormorants.

In situ measurements of animal morphological features: A non‐invasive method

“…In the case of museum bird specimens and free‐ranging chickens, we measured bill, head, tarsus and total body lengths, and the measurements ranged from 1.4 to 35.3 cm. Bill length was measured (Mahendiran & Urfi, ; Nagarajan, Lea, et al., ) as the distance from the tip of the upper mandible to the beginning of skin corners near nostrils, the proximal end of the beak (Figure a,b). Head length was measured as the distance from the nostrils to the back of the head region passing over the eye plane, and total body length was measured as the distance from the crest of the head to the base of the foot (Nagarajan, Thiyagesan, Natarajan, & Kanakasabai, ; Urfi & Kalam, ) (Figure a,b) with 0.01 mm accuracy using Vernier callipers and TPSDig2 in metric units.…”

“…Our experiment under field condition using free-ranging chicken (Figure 9a,b) also substantiates this. Here, it is worthy to mention that morphometric studies under field conditions have been coming up in the last few years using digital images (Foster et al, 2008;Mahendiran & Urfi, 2010;Sonnweber, Stobbe, Zavala, Slice, & Fieder, 2013). However, most of such studies were designed to quantify shape elements of model species rather than linear size dimension.…”

“…Remote techniques for measuring body sizes offer possibilities, but that co‐occurr either with errors or are costly to apply in the field studies. Remote estimation of prey sizes were done using bill or leg length as reference (Durell & Goss‐Custard, ; Magnusson, ; Nagarajan, Lea, & Goss‐Custard, ; Sutherland & Ens, ), and results of those studies were always associated with observer and other biases (Kalam & Urfi, ; Mahendiran & Urfi, ; Urfi & Kalam, ). van Rooij and Videler () used stereo‐photography to measure length in wild fish, but this method required costly and cumbersome equipment.…”

Intraspecific kleptoparasitism in flock-fishing Great Crested Grebes (Podiceps cristatus) and Great Cormorants (Phalacrocorax carbo) – a cost to participants?

“…(Bertelotti & Yorio 2000, Galván 2003. It can also be seen in flock-fishing Common Mergansers Mergus merganser (Källander 2006) and Great Cormorants Phalacrocorax carbo (Lekuona & Campos 2001, Mahendiran et al 2010, and one…”

The effect of kleptoparasite and host numbers on the risk of food‐stealing in an avian assemblage

“…Typically, host numbers have been reported, but the evidence for a relationship between host numbers and kleptoparasitism risk is mixed. Some studies have reported that the risk of kleptoparasitism rises with host numbers (Garrido et al , Mahendiran and Urfi ). However, other studies have reported that the numbers of hosts and kleptoparasites were poor predictors of kleptoparasitism risk (Woodall , Varpe ).…”