Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 December 2020 | 12(17): 17323–17329
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
doi: https://doi.org/10.11609/jott.5397.12.17.17323-17329
#5397 | Received 09 September 2019 | Final
received 20 October 2020 | Finally accepted 01 November 2020
Crepuscular hunting of swiftlets
(Family: Apodidae) by Besra
(Family: Accipitridae) in the urban areas of the
Andaman Islands, India
Amruta Dhamorikar
1, Dhanusha Kawalkar
2, Prathamesh Gurjarpadhye
3 & Shirish Manchi 4
1,2,3,4 Division of Conservation Ecology,
Sàlim Ali Centre for Ornithology and Natural History,
Anaikatty (Post), Coimbatore, Tamil Nadu 641108,
India.
1 ahdhamorikar@gmail.com, 2 dhanushakawalkar@gmail.com,
3 gurjarpadhyeprathamesh@gmail.com,
4 ediblenest@gmail.com
(corresponding author)
Editor: Anonymity requested. Date
of publication: 26 December 2020 (online & print)
Citation: Dhamorikar, A., D. Kawalkar, P. Gurjarpadhye &
S. Manchi (2020). Crepuscular hunting of swiftlets (Family: Apodidae) by Besra (Family: Accipitridae) in the urban areas of the Andaman Islands,
India. Journal of Threatened Taxa 12(17): 17323–17329. https://doi.org/10.11609/jott.5397.12.17.17323-17329
Copyright: © Dhamorikar et al. 2020. Creative Commons Attribution 4.0
International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: Ministry of Environment and Forest and Climate Change (MoEF&CC), Government of India.
Competing interests: The authors declare no competing interests.
Author
details: Amruta Dhamorikar, MSc, a researcher in the Edible-nest Swiftlet conservation
program (2017–2019) and is currently working as an ecologist in AECOM India
Pvt. Ltd. Dhanusha Kawalkar, Msc,
a researcher in the Edible-nest Swiftlet conservation program (2017–2020) and
currently engaged in studying the Indian Swiftlet towards its conservation in Maharahstra. Prathamesh Gurjarpadhye, PhD scholar and a researcher is
involved in the Edible-nest Swiftlet conservation program (2018 onwards). He is
presently exploring the population dynamics of the species through ecological
and molecular approach. Manchi Shirish, PhD, Principal Scientist is
involved in research and conservation of the Edible-nest Swiftlet in the
Andaman and Nicobar Islands for around two decades.
Author
contribution: AD—conceptualization,
data curation, methodology, writing – original draft; DK—conceptualization,
data curation, formal analysis, methodology, writing – original draft;
PG—conceptualization, methodology, data curation, writing – original draft;
SM—funding acquisition, investigation, project administration, resources,
conceptualization, supervision, validation, writing – review & editing.
Acknowledgements: We thank the Ministry of
Environment, Forest and Climate Change for funding the in situ and ex situ
conservation of endemic Andaman Edible-nest Swiftlet project under which the
present study was conducted. We are
grateful to the Department of Environment and Forests, Andaman and Nicobar
Island for providing the necessary permissions.
We especially thank Mr. Russogi (Divisional
Forest Officer, Mayabunder, WL) for his support
during the fieldwork. We are indebted to
Miss. Pallavi Poojari and Justin Sumit
Kumar for their help during the data collection. We acknowledge reviewers for their inputs to
improve the quality of the manuscript.
Abstract: We report the crepuscular hunting
behavior by the Besra
Accipiter virgatus, on the Glossy Swiftlets Collocalia esculenta affinis
and the Edible-nest Swiftlets Aerodramus fuciphagus inexpectatus in
urban areas the Andaman & Nicobar Islands.
Unlike other raptors in the islands, the Besra
hunts at twilight often in the absence of moonlight or/and artificial
light. Glossy and Edible-nest Swiftlets
have been ranched in human habitations and their nests harvested for livelihood
support of local communities under an ex situ conservation program. Using the focal animal sampling method, we
recorded the hunting behavior of the Besra (the predator) on the swiftlets (the prey) for 40h
(120 min/day for 20 days) at the ex situ swiftlet colony established in a house
in the Middle Andamans. The Besra made 84 hunting attempts, with the highest success
rate (15.4%) between 17.00–18.00 h. The
catch rate was a mean of 4±11 (SD) per day.
The maximum time that was used for attempt to kill the prey was two
hours. Depredation of the Edible-nest
Swiftlet by the Besra could affect ex situ
conservation efforts, which can also lead to economic losses and retaliation
against the raptor. Restricting perch
sites for the raptor around ranching houses might reduce predation risks for
the swiftlets.
Keywords: Andaman & Nicobar Islands, Besra, crepuscular hunting, Edible-nest Swiftlet, ex situ conservation,
predatory behavior.
INTRODUCTION
Availability of food and
potential nesting sites play an essential role in adapting birds to survive
urban environments (Marzluff 2016). Glossy Swiftlet Collocalia
esculenta affinis and the Edible-nest Swiftlet Aerodramus fuciphagus inexpectatus (Cranbrook et al. 2013) are examples of
birds that are adapted to urban habitats in the Andaman & Nicobar Islands (Manchi & Mane 2012).
This successful adaptation is due to the availability of nesting
locations and food. Some cave-dwelling
swiftlets such as the Edible-nest Swiftlet are of human interest and famous
worldwide for ‘bird’s nest soup,’ a delicacy in Chinese cuisine, and
traditional Chinese medicine (Koon & Cranbrook 2002; Chantler
& Boesman 2019).
The nests exclusively built using bird’s saliva have a high market value
due to their medicinal properties. These
birds are farmed for mass production of the edible nests to sustain
international demand (Hobbs 2004; Thorburn 2015).
In the past several decades, the
nests have been illegally harvested from caves in the Andaman Islands,
impacting the population. For
sustainable use of the birds’ nest and to reduce the pressure on wild
populations, an ex situ conservation program was started in urban houses, which
habituated the Edible-nest Swiftlet to nest in human-made structures. The Glossy Swiftlet also nests in abandoned
houses, bridges, and jetties. As part of
the conservation program, the swiftlets are attracted to human habitation and
reared in an artificial structure, known as ex situ swiftlet house (Manchi & Mane 2012).
Scientists and managers with years of efforts, have successfully
attracted the Edible-nest Swiftlet population to breed in one such ex situ
structure (henceforth ‘swiftlet house’) in the Middle Andamans by using the
sympatric Glossy Swiftlet as foster parents to hatch the eggs and rear the
chicks (Sankaran & Manchi 2008). This swiftlet house supports a colony of
Glossy Swiftlet (~1,000 individuals) and Edible-nest Swiftlet (8–10
individuals). The Edible-nest Swiftlet
(ENS) shares the nesting site with the Glossy Swiftlet. Some young ENS birds are also known to build
nests on existing Glossy Swiftlet nests.
During our study, the swiftlet
population in the house was hunted by the raptor, Besra
Accipiter virgatus abdulalii,
at dawn and dusk. Besra is a small, diurnal bird of prey of the Order Falconiformes. Out
of 11 subspecies of A. virgatus, A.v. abdulalii
is an endemic subspecies restricted to the Andaman Islands (Naoroji
2006; Clark & Marks 2020). Due to
the easy availability of the prey, and its nesting locations, Besra has adapted to the urban habitats in the Andaman
Islands. As the other members of the
genus Accipiter, the Besra is a swift and silent
hunter. The species is quick on the wing
in quest of prey, often twisting and turning to chase the bird and escape
hindrances. Besra
breeds from March to May and nests on roadside trees, near human habitation,
mangrove forests, and Padauk plantations (Ali & Ripley 1978). Being an opportunistic hunter, the diet of Besra includes small birds, insects, and some mammals and
reptiles, depending on the season and availability of prey. It primarily preys on birds during the
breeding season (Huang et al. 2004). In
the Andaman Islands, the Besra predates on poultry
near human habitation. It is also a
potential predator of swiftlets breeding in the limestone caves of the Andaman
Islands, according to Manchi & Sankaran (2009).
Foraging in twilight is generally
regarded as an end or beginning of diurnal or nocturnal activity. While crepuscular foraging is uncommon, many
nocturnal predators such as owls, nightjars, and waders begin hunting at
dusk. The circumstances under which
crepuscular hunting occurs are not well understood or documented (Martin
1990). Among diurnal raptors other than
owls, the smaller species of the genus Falco (Lesser Kestrel F. naumanni, Kestrel F. tinnunculus,
Hobby F. Subbuteo and Sooty Falcon F. concolor)
and large-bodied falcons such as the peregrine falcon hunt at night under
artificial lights such as street lamps, and moonlight (Ratcliffe 1980; Pierson
& Donahue 1983).
As the swiftlet ranching in the
ex situ houses aims to provide livelihood support for the economic development
of the local populations in the Andaman Islands, the threat from Besra can have significant implications. Therefore, we studied the crepuscular hunting
behavior of Besra. Further, we hypothesized that the successful
hunting of swiftlets by Besra is associated with i) time of day (diurnal vs. crepuscular), ii) availability
of perch sites, and iii) flock size of swiftlets.
MATERIALS
AND METHODS
Study Area
The Andaman group of islands is
in the northeastern Indian Ocean, along the southern
extension of the Arakan Yoma
mountain range, are peaks of a submerged continuous mountain ridge extending up
to Sumatra in the south, between latitude 6.75–13.68 0N and
92.20—93.95 0E. The Andaman
group of islands are divided into (a) South Andaman, (b) Middle Andaman, (c)
North Andaman, (d) Baratang, and (e) Rutland. The forest types range from the tropical wet
evergreen forest towards the south to tropical moist deciduous forest in the
North Andaman group of islands (Davidar et al. 2001;
Champion & Seth 2005). Parts of the
islands also have human settlements and agricultural fields surrounded by deciduous
forests. This island group, with a high
proportion of endemic flora and fauna, is one of the global biodiversity
hotspots in the world (Conservation International 2005). The archipelago has 19 identified Important
Bird and Biodiversity Areas (Rahmani et al. 2016) and
is also recognized as an endemic bird area (Birdlife International 2019). Including endemic species such as Andaman
Serpent Eagle Spilornis elgini,
Great Nicobar Serpent Eagle Spilornis klossi, Central Nicobar Serpent Eagle Spilornis minimus,
and Nicobar Sparrowhawk Accipiter butleri; the Andaman & Nicobar Islands have 22
raptor species.
We conducted the present study in
the northernmost part of Middle Andaman in Tugapur
near Mayabunder town (Figure 1). The temperature in Tugapur
during April was between 27oC and 35oC (Accuweather 2018).
Sunrise and sunset were between 05.01h & 05.16h and 17.31h &
17.33h, respectively (Time and Date 2018).
Human habitation and small patches of deciduous forest surround the
swiftlet house. Plant species such as Azadirachta indica A.
Juss, Gliricidia sepium (Jacq.) Walp., Calamus
sp. L., Tectona grandis
L.f., and Ficus religiosa L. are seen around the swiftlet house. We made daily visits to the swiftlet
house during the late summer season from 02 April to 28 April 2018 between
16.00h and 18.00h. The study period
coincided with the breeding season of the Besra (Ali
& Ripley 1978) and swiftlets (Manchi &
Sankaran 2014). The activities of the Besra near the swiftlet house were studied using focal
animal sampling (Altmann 1974). We made
observations from the moment the individual arrives around the swiftlet house
until it leaves the site.
Simultaneously, swiftlets around the house were observed to understand
the interaction between the prey and predator.
Three observers were stationed at different observation stations around
the house to observe and note the behavior of the Besra along with the time (Figure 2). With 120 min of observation every day, we
collected data for 2,400 min in 20 days.
Occasionally, we prolonged the observations until 18.30h to check the
presence and activity of Besra. Because of unfavorable
circumstances, we could make only one observation during the morning hours
(04.45–07.00 h). To process the
collected data, we used XL-STAT software (Ver. 2020, Addinsoft
2020). We excluded the set of data from
the single morning visit during analysis.
Ethograms of Besra was made based on behavioral observations.
No ethical approval was obligatory for this study.
RESULTS
The present study confirms the Besra as a predator of the swiftlets. Swiftlets being diurnal foragers, the
breeding individuals keep returning to the breeding location to feed their
nestlings, and the arrival of the Besra was at
16.00h. During the 20 days of
observations, the Besra made 84 hunting attempts per
day to catch swiftlets with 4±11 (Mean±SD). It preyed upon 1±0.5 swiftlets per day, with
14.92% (n=84) successful attempts. The
most hunting attempts were between 17.31–17.50 h (67.80 %), and most successful
(11.48%) and unsuccessful (56.32%) attempts were also made during the same
period (Figure 3). Comparing the sunset
timings (17.31h to 17.33h on observation days) and the period of most hunting
attempts were during the crepuscular (twilight) hours (Time and Date
2018). It confirmed the crepuscular
hunting behavior of Besra,
the predator. Out of the total time the besra spent near the ex situ house, 48% was spent
attempting a kill while 35% time was spent on the perch (Figure 4).
All the hunting attempts,
successful or unsuccessful, were on the flock of swiftlets swarming in the
lower canopy (2–5 m above ground) and never above the canopy. The number of attempts increased as the
swiftlet flock size increased (Table 1).
The Besra captured and carried its kill with
its claws. Immediately after capture,
the predator brought each kill to the same perch of attack (mostly Azadirachta indica)
or the nearest landing site (mostly Tectona
grandis within 10m). As the swiftlets gathered around the house
in small groups (15–20 birds), the Besra would chase
the selected prey with athletic ease, twisting, turning, and swooping close to
the ground (6 in Figure 2) as the aerodynamic swiftlet tried to break away from
its grasp. The predator and the prey are
swift flyers, and thus sometimes swiftlets managed to evade the predator
successfully. The height at which the
chase was made, particular areas around the swiftlet house , and the
time of the hunt influenced a successful kill.
The Besra
usually ripped off the feathers of its prey before consuming the kill. Occasionally, it would swallow the feathers
too. The Besra
spent 16% of its time in consuming the kill (Figure 4). By examining the kill remnants, we confirmed
that the prey species was Glossy Swiftlet, however, once the population of the
Edible-nest Swiftlet grows, we cannot deny the possibility of it being hunted
by the Besra.
The most hunting attempts by Besra were from a particular perch in the canopy of a large
Azadirachta indica
(46.17%), beside the swiftlet house, however, the Besra
was observed using other perching sites around the swiftlet house as well
(Table 2). After each attempt, it often
perched (30.76%) on Gliricidia sepium (2 in Figure 2).
The predator returned to the same perch on Azadirachta
indica for the next attempt to catch a swiftlet.
DISCUSSION
Swiftlets are known to flock near
their breeding and roosting sites during dawn and dusk while leaving or
returning to their roosts (Tarburton 2009; Mane &
Manchi 2017).
The cave-dwelling swiftlets are usually known to be vulnerable while
entering and exiting the caves (Mane & Manchi
2017). The present study, however, is
the first to document aerial predation of swiftlets by the Besra
around human-habitation. Flying in
flocks equips the swiftlets to successfully evade predators. The time of arrival at the roost (Mane & Manchi 2017, 2019) and the speed used for entering the
breeding/roosting sites (Tarburton 2009) are counted
as the anti-predatory behaviors of the swiftlets.
Approximately 20km from the
swiftlet house, we located a Besra chasing the
swiftlets during morning and evening twilight hours. This location hosts thousands of Glossy
Swiftlets. Here, we observed the
swiftlets forming to chase away the predator.
Therefore, we can see two anti-predatory mechanisms in the swiftlets,
one to escape the predator by forming groups, and secondly by mobbing the
predator by forming larger groups. The
anti-predatory behavior may limit the number of prey
obtained by the Besra. Apart from the Besra,
we noticed that the Shikra Accipiter badius attempting to hunt swiftlets near the
swiftlet house between 16.00 and 16.30 h from the Ficus
benghalensis L. trees which was the tallest in
the study site. The Shikra
chased the swiftlets swarming in the open air but was unsuccessful in catching
a bird.
As the number of Glossy Swiftlets
in the swiftlet house is greater than the Edible-nest Swiftlet, we can say that
the Besra may be preying on the more easily available
target. It makes the Edible-nest
Swiftlet as vulnerable to predation as the Glossy Swiftlets, putting the
already low population at risk.
Sparrow-hawks use at least a 15cm
circumference branch of a tree or a moderately flat surface for perching (Owen
1932). Although we could not confirm the
same for the Besra, the repetitive use of the same
perch shows some preference for perches.
To avoid predation of swiftlets, it is essential to avoid such ideal
‘perches’ or trees near the swiftlet house.
Removal of these ideal available perches might drastically reduce the
rate of predation of the swiftlets by the Besra, at
least till the individual finds and learn to use any other perching site and
hunting strategy. The predation behavior depends mostly on the cognitive ability of an
individual; it is challenging at present to ascertain the change in the
predation rates by the Besra after removal of the
perch trees around the house.
Many raptors have shown
adaptations in hunting and foraging behavior
according to the prey resources. The Bat
Hawk Macheiramphus alcinus
in sub-Saharan Africa, South Asia, and New Guinea, is known to hunt bats during
the twilight hours. The bat hawk’s adaptation
in morphology and behavior results from the prey’s
biology (Black et al. 1979). The Bat
Falcon Falco rufigularis, found in Mexico, and
Central and South America, is another bird that hunts bats at dusk. The Bat Falcon has also adapted to hunting in
urban environments (Seijas 1996). The Peregrine Falcon, a diurnal bird, is also
reported to prey on bats (Pierson & Donahue 1983), and some even during
dusk or at night (Rejt 2001). Mester & Oliver
(2018) reported an unusual fishing behavior of the Eurasian
Sparrowhawk during winter when the prey are
scarce. Their report suggested, ‘Raptors
may be able to adopt unusual hunting or foraging behavior
and prey selection in response to changing environmental conditions and
changing availability of potential prey resources.’ Therefore, with a more focused study and
observations throughout the islands, it can be concluded whether A. v. abdulalii of Andaman Islands has adapted to crepuscular
hunting owing to the swiftlet’s ecology, and whether this behavior
is limited to urban areas (in ex situ structures) or exists everywhere.
CONCLUSION
Since the swiftlet-farming
efforts are in the direction of livelihood development and economic growth in
the islands, any hindrance to such a program will ultimately affect the local
human populations. The raptor-human conflict that may arise from this is a
threat to the survival of both (prey and predator) species. Based on the
observations discussed, we now recommend maintaining the premises of the
swiftlet houses by restricting the vegetation growth for better management of
the swiftlet populations in urban areas and also to avoid future raptor-human
interaction.
Table 1. The hunting attempts by
the Besra (the predator) at a given time in relation
to the flock size of swiftlets (the prey) (Note: flock size: <50—small |
50–200—medium | 200–500—large)
Time (h) |
Flock size of swiftlets |
Total hunting attempts (%
success) |
16.20–16.30 |
small |
1 (0) |
16.30–16.40 |
small |
1 (0) |
16.40–16.50 |
small |
6 (50) |
16.50–17.00 |
large |
3 (0) |
17.00–17.10 |
large |
0 |
17.10–17.20 |
large |
6 (0) |
17.20–17.30 |
large |
11 (0) |
17.30–17.40 |
large |
35 (14.28) |
17.40–17.50 |
small |
21 (23.80) |
17.50–18.00 |
small |
0 |
|
Total |
84 |
Table 2. Perch sites used by Besra while hunting the swiftlets near the ex situ swiflet house, Middle Andaman.
|
Scientific name of the perch
tree |
Common name of the perch tree |
Height of perch (meters) |
Total hunting attempts (%
success) |
1 |
Azadirachta indica A. Juss |
Neem |
3.5 |
13 (46) |
2 |
Gliricidia sepium (Jacq.) Walp |
Gliricidia |
2.3 |
13 (15) |
3 |
Gliricidia sepium (Jacq.) Walp |
Gliricidia |
1.8 |
13 (8) |
4 |
Gliricidia sepium (Jacq.) Walp |
Gliricidia |
2.3 |
13 (8) |
5 |
Tectona grandis L.f. |
Teak |
3 |
7 (14) |
6 |
Ficus religiosa L. |
Peepal |
~7 |
26 ((8) |
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