This is the presentation about owl.

1. THE INDIAN EAGLE OWL
BUBO BENGALENSIS (FRANKLIN, 1831)
SCOPE OF OUR STUDIES AND EFFECTS
AFFECTING ITS BREEDING POTENTIAL DUE TO
UNSEASONAL CLIMATIC CHANGE IN THE
MONTH OF MAY 2004 IN THE AUROVILLE
INTERNATIONAL TOWNSHIP REGION
PITCHANDIKULAM FOREST, AUROVILLE INTERNATIONAL
TOWNSHIP

2. BRIEF INTRODUCTION TO THE SPECIES
BUBO BENGALENSIS – TAXONOMIC REVIEW
Most popular field guides in circulation find this species mentioned as the
Eurasian Eagle Owl Bubo bubo. For many years it was considered to be
the sub-species Bubo bubo bengalensis. It is in fact a taxonomically valid
species in its own right based on molecular analysis (Konjetal, 2000)
Superficial characteristics that differentiate it from the nominate taxon
include a black facial rim and the last digit of the phalanges and underside
of the feet bereft of feathering

3. DISTINGUISHING CALL
The call is distinct from the Eurasian Eagle Owl Bubo bubo. It has been
rendered as “a deep, resonant, hollow bu – bo (accent on second
syllable much prolonged” (Ali & Ripley, 1969). The call of Bubo bubo is
much the same, but the accent is on the first syllable

4. STUDY AREAS
The study areas were Aranya, Hermitage and Merveille near Ousteri Lake
(11°95’N & 79°73’E) and Success, Forecomer’s Canyon and Ravena in the
Auroville plateau (11°98’N & 79°81’E)

5. OUR INVESTIGATIONS
ETHOLOGY – AUDITORY COMMUNICATION
Owls being nocturnal species use a variety of calls to communicate.
We have recorded 9 distinct auditory traits in this species:
1) Long call – this is the distinguishing call
2) Intermediate call
3) Short call
4) Begging call
5) Alarm call
6) Anxiety call
7) Chick-like vocalizations
8) Hissing
9) Bill clicking or Bill clapping

6. ETHOLOGY - VISUAL COMMUNICATION
This species being crepuscular, it also uses a variety of visual cues
to advertise its moods and intentions
Some are shown herewith
Positions of ‘horns’

7. Bobbing and bowing behaviour
When approached by an intruder (either human or any other
animal it is interested in) it seems to take stock of it by looking
at the object of interest from all angles. This may look curious,
but makes perfect sense

8. Spread-winged displays
Perhaps the most spectacular of all displays are the spread winged
displays which most authors termed the “threat display” earlier

9. Spread-winged displays
Our investigations showed that there were at least three distinct types
of spread winged displays – viz. Intimidatory display, Intermediate or
transition display and threat display

10. TROPHIC CONNECTIONS
OTHER OWLS
Four species of owls occur in the Auroville region – viz. Collared Scops
Owl Otus bakkamoena, Indian Eagle Owl Bubo bengalensis, Spotted
Owlet Athene brama and Mottled Wood Owl Strix ocellata. We have
managed to study pellets of Otus bakkamoena and Athene brama and
have analysed food and niche overlap between these and Bubo
bengalensis

11. PREY ANALYSIS OF BUBO BENGALENSIS
Prey analysis was a combination of both pellet and prey remains to give
an accurate estimate of the number of animals predated on by a pair /
family of owls within their territory

12. Rodents, the prime prey base
Though hares, bats, shrews, birds, monitor lizards, snakes,
batrachians and invertebrates (including the venomous Rock
Scorpion Heterometrus swammerdami and Tiger Centipede
Scolopendra hardwickii) were preyed on, rodents were the prime
prey base accounting for 64.91%. Eight species of rodents were
recorded from owl pellets and carcasses. We have worked out a
simplified key to identify rodents based on their lower mandibles
alone

13. Rodent population estimates
The standard trapping method (Barnett & Dutton, 1995) was adopted.
Three trapping stations, each 100 sq m in extent and forming a grid of
6 x 6 trap lines were maintained from 2002 to 2004 in three types of
habitat (viz. ravine, grassland on plateau and forest plantation). Two
trapping nights every month was the practice adopted and monthly
trap success was the sum of traps entered on these two nights. The
percentage trap success and was calculated as follows:
% trap success = (traps entered / no.of traps set) x 100

14. BREEDING SEASON AND GROWTH RATES
Courtship usually began after the N.E. Monsoon in October / November. Eggs
were laid between December - February. Incubation (by the female alone) was
approximately 30 days. They attained the juvenile stage in approximately 60
days. The fact remains that, whatever the time of reproduction, the young
require enormous quantities of basic food at this time, especially the
months of April, May and June, if they were to survive to the ‘floater’
stage which precedes adulthood since they are not skilled enough until
that time to hunt by themselves. The young stayed with their parents until
the abatement of the S.E. Monsoonal showers (roughly, end of August /
beginning of September)

15. CO-RELATING RODENT ABUNDANCE TO FRUITING PHENOLOGY
We co-related rodent trap success to fruiting phenology of species whose
seeds / seed fragments were found in gut analysis of rodents. The species and
values concerning a normal time (2002 – 2003) are given below
F ruiting phenolog y & trap success for the year
2002 & 2003
0
10
20
30
40
50
60
70
80
Jan F eb Mar Apr May Jun Jul Aug S ep Oct Nov Dec
F ruiting
T.Indica
R .rattus
Mus spp.

16. Fruiting% T.Indica R.rattus Mus spp.
Jan 41.43 9.25 2.31 9.72
Feb 47.69 8.79 2.77 8.79
Mar 56.92 8.33 3.7 8.33
Apr 66.15 8.79 4.16 8.33
May 75.38 9.72 6.48 9.72
Jun 75.38 10.64 6.94 11.11
Jul 73.84 8.79 5.55 11.57
Aug 72.3 8.33 5.55 9.25
Sep 61.53 8.79 4.62 8.33
Oct 56.92 8.79 4.16 8.33
Nov 44.61 9.25 4.16 8.79
Dec 40 8.79 2.77 9.25

17. Eggs
Three to four eggs is the usual complement of eggs laid, but five is not
uncommon

18. Five and 10 day old chicks
The chicks hatch asynchronously which leads to great disparity in size. The
nidicolous and altrical young are covered in white natal down and their eyes are
closed

19. 15 day old nestling
The prejuvenile moult is in progress. A yellow iris is obvious. It can adopt
the intimidatory posture if threatened

20. 25 and 30 day old nestlings
These are the same two chicks seen the the slide before the previous
one
Although the elder will continue to be larger, there is not the vast
disparity of size

21. 45 day old young
The first prebasic moult is evident and the general aspect is more like an adult.
It has moved away from the nest site – a process called “branching”

22. 60 day old young
Though looking like an adult and able to fly, the aigrettes are not fully
developed and the underside is still covered with juvenile down. This is in
strong contrast to adults – and adult is shown on the right for comparison

23. UNSEASONAL CLIMATE CHANGE
The Coromandel Coast has a disymmetric climatic regime. Though it receives
some showers from the S.W. Monsoon, the bulk of the rains fall during the N.E.
Monsoon (October to December) due to depressions formed in the Bay of
Bengal. Up to 1,200 mm per year has been recorded
In the month of May in 2004 the areas had unprecedented rains – over 200 mm
in the hottest month
Precipitation for the years 2002-2004
0
100
200
300
400
500
600
Jan Feb Mar Apr May Jun Jul Aug S ep Oct Nov Dec
2002
2003
2004

24. 2002 2003 2004
Jan 31 0 43
Feb 154.4 0 0
Mar 0 0 0
Apr 0 0 0
May 19.6 40 212.2
Jun 35.4 20 50
Jul 36.5 71.8 45
Aug 37.6 204.1 67
Sep 77 52 202
Oct 247.7 156.3 411.6
Nov 305.5 510.4 253
Dec 141 12 12

25. EFFECTS OF CLIMATE CHANGE
This unusual rainfall led to a drop in fruiting and flowering. This in turn led to a drop
in rodent populations. This in turn affected the breeding of the owls that depend on
the rodent prey base. All the chicks of the three pairs of owls that bred that year
died
F ruiting phenology & trap success for the
year 2004
0
10
20
30
40
50
60
70
Jan F eb Mar Apr May Jun Jul Aug S ep Oct Nov Dec
AxisTitle
F ruiting%
T.Indica
R .rattus
Mus spp.

26. Fruiting% T.Indica R.rattus Mus spp.
Jan 41.5 7.3 2.5 8.9
Feb 47.6 7.9 2.7 9.1
Mar 56.9 8.1 3.9 8.4
Apr 66.1 8.4 3.9 8.6
May 10.7 0 0 3.2
Jun 13.8 0 0 4.1
Jul 32.3 1.8 0 5
Aug 40 2.7 0 7.4
Sep 61.5 6 0 9.7
Oct 59.9 5 0 11.1
Nov 44.6 8.7 0.4 17.1
Dec 40 9.7 0.4 17.5

27. FOR FURTHER DETAILS
Journal of Threatened Taxa
www.threatenedtaxa.org
Zoos’ Print Journal
www.zoosprint.org
Author bar: Ramanujam

28. THANK YOU