Food composition of Indian Eagle Owl Bubo bengalensis Franklin ( Aves : Strigiformes : Strigidae ) from Tiruchirappalli District , Tamil Nadu , India

The diet of the Indian Eagle Owl was studied from April to September 2017 in Tiruchirapalli District, Tamil Nadu, India.  Analysis of 1082 regurgitated pellets yielded 2077 prey items; the mean prey items/ pellet was 1.91.  The diet constituted 65.1% of rodent prey and the remaining 34.83% of other groups of both vertebrate and invertebrate animals.  The mean percentage of prey composition was 31.15% Millardia meltada Soft-furred Field Rat, 12.95% Bandicota bengalensis Lesser Bandicoot Rat, 10.25% Mus booduga Indian Field Mouse, and 10.24% of other rodent species.  Of the 34.83% of non-rodent prey, the owls ingested insects (Rhinoceros beetles, 9.58%), Arachnida (Solifugae or Sun spider, Galeodes sp., 9.58%), reptiles (Calotes sp., 3.7%), amphibians (3.56%), shrews (Suncus murinus, 2.84%), and others (5.57%).  The Indian Eagle Owls consumed more than one prey per day and chiefly foraged in agricultural crop fields and consumed both small mammals and insects of agricultural importance under crop ecosystems.


INTRODUCTION
Owls are nocturnal birds and there are 241 (BirdLife International 2017) living species in the world.The Indian Eagle Owl Bubo bengalensis is one of the nocturnal raptors distributed only in the Indian subcontinent.Owls have evolved with many adaptations to occupy the top of the food chain in the ecological niche.Owls feed mainly on field rats, mice, shrews, bats, birds, reptiles, frogs, crabs, scorpions, and insects.The Indian Eagle Owls are terrestrial nesters of rocky hillocks of hill slopes, earth cuttings and bushes.Their hunting grounds consist of agricultural crop fields, water bodies, hills and rural habitats.Regurgitated pellets of owls have undigested body parts of prey like bones, fur of vertebrate and exoskeleton of invertebrate animals.These undigested food materials are oval in shape and greenish black or grey coloured and dropped in the nesting and roosting/ perching sites of owls.Regurgitated pellets are analyzed to understand and document the prey composition of Indian Eagle Owls and to find out the variations in their food habits over a period of time.Earlier studies have been carried out on Indian Eagle Owls such as information on the long call (Ramanujam 2003); methods of analyzing rodent prey (Ramanujam 2004); auditory and visual communicatory traits (Ramanujam 2007) (Ramanujam 2010); the time budget and behavioural traits of young and adult (Ramanujam 2015); and a comparative study on the diet (Ramanujam & Singh 2017).In India, prey spectrum of this species have been studied and reported from Tamil Nadu -Puducherry (ravines and gullies habitats) in southern India (Ramanujam 2006(Ramanujam , 2015) ) and Maharashtra (Pande et al. 2011;Pande & Dahanukar 2011b) in central India.It is understood from the review of literature that there is limited published information on the diet composition of Indian Eagle Owls from Tamil Nadu and hence the present study.

The Study Area
The present study was carried out in Musiri Taluk of Tiruchirappalli District, Tamil Nadu.The area consists of many hillocks, interspersed with villages and agricultural fields (Image 1).In the past, studies by Nagarajan et al. (1993), Taylor (1994) and Santhanakrishnan (1995) suggested use of indirect signs such as regurgitated pellets, milky white droppings and prey remains of Barn Owls for the identification of roosting/nesting sites.The same indirect signs were utilized in the present study for the identification of Indian Eagle Owls' nesting/ roosting sites.Information given by the local residents was also useful in locating the roosting/nesting sites of Indian Eagle Owls.It is apparent from the survey that the hillocks are the prime nesting and roosting/ perching habitats of Indian Eagle Owls (Image 2).The pellets of Indian Eagle Owls were collected from hillocks near three villages -Veliyanur (11.049 0 N & 78.586 0 E), Thuraiyur-Puthupatti-Pulikaradu (11.043 0 N & 78.580 0 E) and Thuraiyur-Puthupatti (11.037 0 N & 78.568 0 E) (Fig. 1) between April and September 2017.In total, 1082 pellets were collected during the study period.

Pellet Analysis
The pellets (Images 3 & 4) were collected once a month, and bagged in separate polybags, labelled and brought to the laboratory for analysis.Before analysis, the pellets were kept in an oven at 70 o C for 24h to kill the associated invertebrate parasites (Neelanarayanan et al. 1995;Santhanakrishnan 1995).The pellets were then placed in separate washing cups, containing 8% NaOH (by weight) sodium hydroxide solution, and then analysed (Neelanarayanan et al. 1998).Fur and other debris were dissolved in the 8% NaOH solution leaving only the osteous and chitinous remains of vertebrates and invertebrates, respectively.The solution was then carefully decanted by using a filter and the osteous remains were collected, oven dried at 60°C, labelled, bagged and preserved for prey species identification.
Vertebrate prey items were identified on the basis of lower jaws, skull, limb bones and pectoral and pelvic girdles (Neelanarayanan et al. 1998;Talmale & Pradhan 2009).We determined the number of prey individuals consumed per pellet based upon the number of skulls, lower jaws, or fore and hind limb bones found in each pellet.One set of lower jaws (left and right) (Image 5) or one skull or one pair of fore and hind limb bones were counted as remains of one prey item.In the absence of mandibles, other bones like skulls, limb bones, pectoral and pelvic girdles and synsacra (in the case of birds) were useful, especially for identifying and quantifying the mammalian, avian and amphibian prey (Neelanarayanan 2007).Insect prey items were identified up to order level on the basis of undigested pieces such as chitinous exoskeleton, heads, wings, legs, and stings (Images 6 & 7).A hand lens or low power binocular microscope was employed to identify insect exoskeleton (Marti 1987;Neelanarayanan 2007).In order to know the contribution of each prey species in the Indian Eagle Owl's diet, they were converted into proportions and presented in tables.The mean prey items per pellet were calculated as follows: Total no. of prey items observed in a month Mean prey items/pellet = - ----------------------------------Total no. of pellets collected in a month

RESULTS AND DISCUSSION
Analysis of 1082 regurgitated pellets yielded 2077 prey items (Table 1).The analyzed pellets revealedsmall mammals such as Bandicota bengalensis, B.  (Ramanujam 2006;Ramanujam & Singh 2017).The results of these studies corroborate the findings of the present study.It is obvious from the results of the present investigation that these owls hunt both commensal and field rodent pests and insect pests (particularly Rhinoceros beetle) from agricultural crop fields around their nesting/roosting habitats.
The Rhinoceros beetle is found on Coconut palms, occurring throughout the country and many regions of the world.Detection can be difficult due to the beetles' nocturnal activity within the trees.In the present study, rhinoceros beetle accounted for 9.58% of the Indian Eagle Owl's diet.In Maharashtra, 11.9% of this beetle was recorded in the owl diet (Pande & Dahanukar 2011b).Galeodes indicus was found to be 9.58% of the diet in this study, however, Pande & Dahanukar (2011b) reported it at 0.2%.The presence of the diurnal Threestriped Palm Squirrel F. palmarum in the diet may be due to the owls hunting behaviour during day time.Bats are also potential prey of owls, not surprising considering that both these animal groups are nocturnal (Marks et al. 1999).The other prey species groups like birds, reptiles including Calotes sp., amphibians, and scorpion  were rarely hunted by owls.
In the present study, a maximum of 1.94 prey items/ pellet was observed during June and July 2017 while a minimum of 1.84 prey items/pellet was observed during April 2017 (Table 2).The results of the present study indicate that the Indian Eagle Owls consumed more than one prey per day.

CONCLUSION
In conclusion, the results of the present study reveal that the Indian Eagle Owls are hunters of both rodent and insect pests.Steps should be initiated to protect and conserve Indian Eagle Owls in their natural habitats to increase their population and make use of their services in managing the pest populations in cropping ecosystems.

Figure 1 .
Figure 1.Location of the identified Indian Eagle Owl's roosting sites in the chosen study area.

Image 3 .
A pellet of Indian Eagle Owl observed in its roosting site.Image 4. Different sizes of Indian Eagle Owls' pellets collected during the present study.

Food
lower jaws or mandibles of rodents, an insectivore and Calotes sp.Image 6. Entire exoskeleton of Rhinoceros Beetle observed in the pellets.Image 7. Chelicerae of Galeodes indicus observed in the Indian Eagle Owl pellets.