Breeding biology of the Short-toed Snake Eagle Circaetus gallicus

The Short-toed Snake Eagle Circaetus gallicus is a resident diurnal raptor that is widely distributed across India. We monitored the activities and behaviour of a breeding pair of Short-toed Snake Eagles for three continuous breeding seasons from 2013 to 2015. Information on the feeding habits and diet of the species, along with observations on hatchling growth, behaviour, and parental care are presented. Its incubation period lasted from 44 to 46 days. The Short-toed Snake Eagle feeds its hatchlings with 22 species of vertebrates, including, 69.63% of reptiles (16 species) and 14.28 of mammals (4 species), 3.57% of amphibian (1 species) and 0.59% of birds (1 species), excluding 11.90% of regurgitated food. The pair shares parental duties of incubation, feeding the chicks, hunting, and care of the young. 150 Indian BIRDS Vol. 12 No. 6 (Publ. 31 March 2017) Automatic cameras: The nests were also monitored using the automatic motion/time lapse (three minutes) cameras using Bushnell 119405 and Cudde back digital1200, for six weeks each, in 2013 and 2014. Our reason for using cameras after incubation, especially during hatching, was to minimise disturbance to the birds. The cameras were fixed on a nearby branch, above nest level, at a distance of one to two meters, ensuring that the breeding pair was minimally disturbed [145]. In 2015, we continued monitoring the nest for 12 weeks, documenting the breeding cycle from the hatching of the egg till the fledgling left the nest. All images captured on camera were scrutinised to identify the prey brought to the nest by the parents, by referring to published literature (Smith 1935, 1943; Whitaker & Captain 2004). The behaviour of the parent and the chick was noted, along with other relevant information. The behaviour of the chick, on the basis of our direct observation, and also from the image/video records was also analysed. The hatchling’s hourly activity (behaviour) was given numerical values of 1 to 6, wherein a value from 1 to 5 was ranked as a low level of activity, and above 5 as high, or intensitive activity. During the study we were especially cautious not to disturb the nesting birds. Therefore, measurements of egg size/weight, and hatchling size/ weight were not taken. Observations & results Nest site selection and nesting activities: Usually, in this area, STSE construct stick nests on khijada trees, choosing a different tree each year, within a radius of 1.5 km from the location of the previous year’s nest tree (pers. observ., DM). Nest dimensions, and other relevant information such as nest height from the ground, tree trunk girth, tree height, etc., are summarised in Table 1. Nests were placed either on the north-eastern, or on the eastern side in the canopy of the tree. During 2013, and 2015, nest construction activities were observed in the second, and first weeks of February, and January, respectively. But in 2014, it began in the first week of March. The pair was actively involved in its construction, which took them 10–15 days, (Table 2). Both birds were observed collecting nesting material from the ground, as well as by breaking twigs from off trees. Nesting material consisted of dry sticks, branches and twines of seven species of plants, including khijado, gando baval, gorad, desi baval, ingoriya, and cotton. The nesting material was available in the surroundings of the nesting tree. The birds also added some fresh, green leafy twigs and straws of piludi and khijado to the nest [146, 147]. Table 1. Morphometrics of the Short-toed Snake Eagle’s nests on khijado P. cineraria trees Year of nesting 2013 2014 2015 Height of tree (m) 12.5 10.6 12.0 Girth of tree-trunk (cm) 201 164 210 Height of nest above ground (m) 8.56 7.40 8.5 Diameter of branch supporting the nest (cm) 40 45 53 Diameter of nest’s outer circumference (Average cm) 38 42 48 Height of nest (cm) 22 25 24 Depth of nest cup (cm) 9 10 9 Nest orientation in relation to nest–tree– trunk North-east East North-east Table 2. Short-toed Snake Eagle: Summarised data of date of nest construction, egg laying, incubation period, and hatching dates.