M. Eric Ramanujam's continuing fascination with Indian Eagle-owls, particularly their behavioural traits, provides Sanctuary Asia readers with clues on how to better protect both species and habitats. What follows touches on his obsession with disentangling the ecological dynamics of his subjects, by going beyond collated statistics and encapsulating hours of field data. In his view, solid scientific reports not only fall short of embracing the experiences and joys of being out in wild nature, but also fail to link interpretations of animal behaviour that could greatly enhance our scientific understanding and the conservation of species and their habitats.
When I decided that I wanted to see an Indian Eagle-owl Bubo bengalensis, Rauf Ali, field biologist and ornithologist, frankly said that my quest was doomed. He had been living near ravines for over a decade and had seen the bird only once. I quite understood his point of view: the species, being an apex predator, occupies a large territory, and is not plentiful and more so, is secretive and nocturnal/crepuscular by nature. I actually managed to get my first decent view of the bird only after a year in the field (Sanctuary Asia, Vol. 36, No. 1, February 2015). But this did not faze me. There was plenty of indirect evidence of the species’ presence: night-time calls of the male, chalky droppings and most importantly, pellets and prey remains – pure manna for a biologist seeking to define trophic connections of the taxon. There was a lot of searching to do but this was not quite as impossible as looking for the proverbial needle in the haystack. Once the eyes were trained, it was relatively easy to pick out pellets from their surroundings. In fact, even unrelated objects began to look like pellets and prey remains! In such circumstances, I was reminded of Dr. Alan Rabinowitz, who undertook a study of jaguars in South America and never once had a proper sighting during his entire study period, yet came up with invaluable data from scats that enabled him to redefine conservation strategies concerning the great cat and its habitat.
The best time (perhaps the only time) to observe the Indian Eagle-owl is at the outset of the breeding season when their behaviour changes. The courtship begins in earnest after the monsoon, when individual males can be tracked and their territories explored by listening for their calls. Once eggs are laid (between January and March) the breeding owls turn strangely silent. The sudden shift from frenzied calling to near-absolute silence is so abrupt that it seems unnatural, but the behaviour serves a vital purpose as unobtrusiveness is a survival strategy during nesting. The males’ paternal instincts prompt them to stay in the vicinity of the nest, which will be protected by both parents from strategic lookout points. Their reluctance to move far from their nests makes it relatively easy to spot them, which soon get accustomed to the presence of an unthreatening human. The nests are not hard to find, though we were acutely aware of the need to stay silent and unobtrusive to avoid spooking the female during the incubation period and in the early stages of brooding. By the time the chicks are about 10 days old, it is possible to collect morphometric data and ethograms without unduly alarming the parents.
Between February 1998 and March 2006, we monitored four nests in and around the Union Territory of Puducherry (formerly Pondicherry). Ours was a small sample size (12 subjects) but more intensive studies, for example, those by Dr. Satish Pandey and Dr. Neelesh Dahanukar, are opening up new frontiers. In the not too distant future, it might be possible to arrive at generalisations on growth patterns and plumage variations, as was done in the case of the Eurasian Eagle-owl by Dr. Vincenzo Penteriani and his colleagues in Mediterranean Europe.
Rodents account for over half of the prey spectrum of the Indian Eagle-owl. The rest comprises birds, batrachians and other small mammals. Photo Courtesy: A. Lakshmikantan
The entire experience was interesting and fulfilling. We worked to holistically match climate variation, fruiting phenology, rodent abundance and breeding success of the Indian Eagle-owl in the region. The Coromandel coast exhibits a dissymmetric climatic regime. Most of the rain (up to 1,200 mm. per year) falls in October and November – the Northeast monsoon. This has given rise to drought-resistant coastal forests, the so-called (controversial) Tropical Dry Evergreen Forest that exists in a narrow belt from Visakhapatnam to Point Calimere. From the gut and stomach analysis, it was found that the rodents feed on 65 species of the 200 odd fruit species in the region. The fruiting season in this forest belt peaks in May and June (49 of the 65 species studied in this period, accounting for >75 per cent of the fruiting). Rodent trapping success also showed a marginal peak in the same period. I say ‘marginal’ because unlike temperate regions that exhibit highs and lows on account of food availability and prey abundance, here the frontiers are not so stark and there are always some plants fruiting or seeding, which provides rodents (the prime prey base of large owls) with a year-round supply of food. The lowest period is in December and January when only 26 or 27 species of trees fruit, accounting for 40 to 41.5 per cent.
Since the Indian Eagle-owl lays eggs at the beginning of the year, the young are well-grown by summer when they need more and more food. This period non-coincidentally coincides with a peak in rodent populations, which are in turn influenced by fruiting peaks. My studies were based in ravines surrounded by reforested plateaux, populated by essentially forest and grassland dwelling rodent species – Indian gerbil, lesser bandicoot or mole rat, tree rat and at least two species of mice. I grouped all the mice together because the Mus species complex is complex (pun unintended) and, despite the valuable work by Marshall and others, many anomalies continue to exist, with taxonomical details remaining unresolved. Though rodents accounted for over half the prey spectrum, the Indian Eagle-owl also fed on a variety of other creatures. These included birds (including a couple of Black Kites and a Spotted Owlet), batrachians (post-monsoon) and other mammals. Shrews and small bats were also regularly observed. Remarkably, black-naped hare constituted 30 per cent of the biomass in one area where a ban on hunting by Narikurava tribals was rigorously enforced. This gives rise to the question of whether the Indian Eagle-owl could possibly have started off as a lagomorph-hunter specialist like the Eurasian Eagle-owl and American Great Horned Owl, and only later shifted to a predominantly rodent-based diet. That owls are opportunistic feeders has been amply proved by other studies, and our preliminary findings on food consumption by the Indian Eagle-owl around the hillocks of Tiruvanamalai show that their prime prey is the field-dwelling soft-furred field rat. The hillocks are surrounded by fields and at dusk the owls can be seen descending to feed here – a phenomenon observed by Romulus Whitaker at Chingelpet. The Indian Eagle-owl also occasionally feeds on large beetles (predominantly Scarabaeidae), large centipedes and the Indian rock scorpion.
In 2004, we chanced upon another phenomenon – the effect of climate change on the owls’ breeding biology. May is the hottest month of the year when temperatures here can exceed 400C in the shade and precipitation is virtually non-existent. But in 2004, an unprecedented 212.2 mm. of rain fell in May. At that time we were monitoring rodents and two sets of nestlings in the Ousreri area, which were doing quite well. A week after the rains had abated we set out the usual 6 x 6 rodent trap lines and were surprised at the poor results that were almost negligible compared to previous years. Fruiting success also showed a steep decline – just 10.7 per cent, which is much lower than the normal lowest fruiting season of December and January. This imbalance led to nestling mortality and all we found in June were the remains of a single right-wing of one of the chicks. The parents survived and one pair bred successfully over the next two years, which provided us with more data on the growth and moulting patterns of the young.
Holistic data collection and interpretation was the backbone of our investigation, though statistical representation was never our forte. Our real challenge lay in recording and interpreting the behavioural traits of Bubo bengalensis, a facet severely overlooked in the Strigiformes. Behavioural ecology, though arguably still in its infancy, is steadily gaining credibility and it is imperative that changed methodologies and interpretation reflect the work of biologists. A relevant example is the ‘pellet analysis method’ adopted by most researchers who earlier dealt with food habit studies of owls. In this day and age, that methodology is outdated and it is imperative to take into consideration home range, nesting specifics and prey remains of large owls. Even among the smaller species that prey predominantly on arthropods and their larvae, the larval remains do not actually show up in the pellets.
Speaking for myself, the most important part of my study involved behaviour. This component of natural history study is not as easy as data collection for ecological purposes and demands many hours in the field and in the presence of the birds, The ‘trick’ of consolidation was to keep the data as simple as possible (easier said than done). Nevertheless, we did manage and at this point we have a manuscript ready for publication on the “time budget and behavioural traits of adult and young Indian Eagle-owls in and around the nest”.
The effects of climate change on the breeding biology of owls is only just being recognised. In 2004, unprecedented rainfall in May devastated fruiting success and therefore rodent populations. This had a direct, negative impact on nesting mortality. Photo Courtesy: A. Lakshmikantan.
It is necessary to observe behavioural patterns, which may at first seem not to have any relevant ecological functions. Examples might be vocalisations, ritualistic behaviour patterns, activity patterns, so-called aberrant behaviour and more.
King Solomon was reputed to understand the ‘language’ of animals and many a committed pet owner would agree. Fundamentalist biologists may not agree, but in my personal experience, ethology, the study of animal behaviour, has proved to be useful and served to remove barriers between my subjects and I. Essentially, I made sure to give my subjects the time and space to get used to my presence. Once this barrier was broken, a whole heap of insights were possible, provided I obeyed that unwritten, cardinal rule – I was in their space, had to keep my distance and be alone or at best with helpers and others who had managed to successfully habituate themselves to my subjects over many years, such as A. Lakshmikantan, whose images have been so intrinsic to my research.
We have made considerable progress documenting the vocalisations, displays and time budgets. My first and very fulfilling drill was to catalogue the various auditory and visual communicatory traits and patterns of progressive behaviour of the Indian Eagle-owl. This was followed by documenting the behaviour of adults and young to the approach of humans to the nest site. In the beginning, I took it for granted that the ‘spread-wing displays’ of the young and parents were what had been portrayed thus far in both scientific and popular literature. It took me a while (a decade) of studying ethograms to realise that there were, in fact, at least three distinct spread-winged agnostic displays! A recent revisiting of my raw data turned up a ‘broken-wing display’ in a young subject, but I have not seen that display in an adult, though others have indeed reported this in relevant literature. Nevertheless, I am not able to make a definitive statement about the difference – maybe, or obviously, there are different broken-wing displays and the nuances conditional upon causations and functions that are still to come to light. Hopefully, in the near future I shall be able to distinguish more nuances and contribute to behavioural ecology. But clearly, behaviouralists have a long way to go, especially concerning terminology. I would go so far as to say, we need a modern-day Linnaeus to begin the process of standardising behavioural nomenclature since such descriptions are currently beyond reasonable comprehension, leading to much confusion concerning even the most fundamental behaviour.
Animal communication studies are opening up great prospects and conservation biology is constantly redefining its parameters to more effectively incorporate holistic definitions and linkages with molecular analysis, taxonomy, even instinctive and ritualistic behavioural patterns (as separate from learnt patterns). These are the new tools of evolutionary biology, which include ethograms, sonograms and other molecular and taxonomic parameters that might augment and better authenticate the ‘tree of life’ so central to our understanding of Homo sapiens’ raison de etre.
After years of observing the behavioural traits of the Indian Eagle-owl, the author recognised three distinct spread-winged displays and one ‘broken-wing’ display exhibited by the birds! The underlying reasons for these displays is yet to come to light. Photo Courtesy: Vivek Vegda.
