Foraging behavior of selected insectivorous birds in Cauvery
Delta region of Nagapattinam District, Tamil Nadu, India
S.
Asokan 1 & A. Mohamed Samsoor Ali 2
1 Associate
Professor, Department of Zoology and Division of Wildlife Biology, A.V.C.
College (Autonomous), Mannampandal,
Mayiladuthurai,
Tamil Nadu 609 305, India.
2 Senior Research
Fellow, Owl Research Project, Department of Zoology, Saraswathi Narayanan College
(Autonomous), Perungudi, Madurai, Tamil Nadu 625 022, India.
Email: 1 beeasokan@yahoo.co.in, 2 amsamsoor@yahoo.co.in (corresponding author)
Date of
publication (online): 26 February 2010
Date of
publication (print): 26 February 2010
ISSN 0974-7907
(online) | 0974-7893 (print)
Editor: C. Srinivasulu
Manuscript
details:
Ms # o2201
Received 11 May
2009
Final received
06 December 2009
Finally accepted
08 February 2010
Citation: Asokan, S.
& A.M.S. Ali (2010). Foraging behavior of selected insectivorous birds in
Cauvery Delta region of Nagapattinam District, Tamil Nadu, India.Journal of Threatened Taxa 2(2): 690-694.
Copyright: © S. Asokan
& A. Mohamed Samsoor Ali 2010. Creative Commons Attribution 3.0 Unported
License. JoTT allows unrestricted use of this article in any medium for
non-profit purposes, reproduction and distribution by providing adequate credit
to the authors and the source of publication.
Author Detail: Dr. S. Asokanis currently teaching students, undertaking and supervising various research
activities. He has produced 7 PhD and 40 MPhil students in various fields of
Wildlife Biology and Zoology. He has
published more than 35 research papers in leading national and international
journals.
A. Mohamed Samsoor Ali obtained his MSc degree in Wildlife
Biology from AVC College, Mannampandal in 2003 and he has been working on
various fields of ornithology since 2004.
Author
Contribution:The field study was conducted by AMSA under the supervision of SA. AMSA
analyzed data and wrote the manuscript and SA provided necessary suggestions during
manuscript preparation.
Acknowledgements:Financial
support for this project was provided by the Ministry of Environment and
Forests, Govt. of India, New Delhi. We are grateful to Principal, Staff members
of Department of Zoology and Management of A.V.C. College (Autonomous),
Mannampandal for having rendered facilities and encouragement. We are thankful
to Mr. M. Chakravarthi, Mr. R. Manikannan and Mr. P. Radhakrishnan for their
field help.Thanks are also due to the anonymous
reviewer for his very constructive comments.
Abstract:This paper reports the foraging behavior of five insectivorous
birds, namely White-breasted Kingfisher Halcyon smyrnensis, Small Bee-eater Merops
orientalis, Indian Roller Coracias benghalensis, Common Myna Acridotheres
tristis and Black Drongo Dicrurus macrocercus in Nagapattinam
District of Tamil Nadu, India. The birds
used a variety of perch types for hunting insect prey; in general the electric
power line was a common perch type used by all species except the Common
Myna. The perching and foraging height
used by birds were classified into 3 meter categories, up to 12m. Aerial feeding or hawking in Bee-eaters and
ground feeding in Common Mynas were major feeding techniques, recorded 68% and
86% of the time respectively. The other
three species used gleaning as a feeding technique. The highest niche overlap was recorded
between Indian Rollers and Black Drongos and between White-breasted Kingfishers
and Indian Rollers.
Keywords: Feeding methods, foraging height,
perch types, perching height, substrates.
Introduction
Studies on the foraging ecology
of birds have been used to explain the community structure, resource use and
competition or co-existence in a particular habitat. The foraging guilds in a bird community are
described by the way species obtain food, the types of food taken, the foraging
substrates exploited, and the heights at which different species forage
(MacNally 1994). These data help to compare
communities within and between habitats (Recher & Davis 1998; Gokula &
Vijayan 2000) and also to assess the health of the ecosystem and management
needs for the conservation of species and ecosystems (Lawton 1996; Loyn 2002).
High-quality habitats for birds
have attributes that influence their hunting success, such as perch height,
perch abundance, vegetation density, and prey visibility. It is usually assumed that a perched bird
scans a circular area under each perch (Yosef & Grubb 1992) and that the
search area increases with perch height (Sonerud 1992). The significance of
perch characteristics (hunting perch) in birds has been highlighted by some
authors (Bell 1982; Bell & Ford 1986; Hutto 1990). The role of foraging substrates in prey
selection in insectivorous birds has been noted by Bell & Ford (1990),
Hutto (1990), Asokan (1995) and Gokula & Vijayan (2000).
The overlap among potential
competitors may be used to assess the extent of resource partitioning of the
niche dimensions measured (Gokula & Vijayan 2000). Resource partitioning
reduces the effect of competition by decreasing the amount of overlap between
the competing species. Some bird species
are generalists that will search for food at all heights, on a variety of
substrates, and use different methods to obtain food, while other species show
varying degrees of specialization (Somasundaram & Vijayan 2008). Studies of niche segregation have shown a
separation in foraging behavior of a few closely related species (Hartley 1953;
MacArthur 1958; Sturman 1968; Morse 1970).
Detailed study on the foraging
behavior of birds in and around agro-ecosystems of India is limited (Dhindsa
& Saini 1994; Parasharya et al. 1994; Subramaniya 1994). However, some detailed study on foraging
behavior has been conducted in the various forest regions of India and other
countries (Johnston 1971; Johnsingh et al. 1987; Gokula & Vijayan 2000,
2007; Amano & Eguchi 2002; Hino et al. 2002; Murakami 2002; Unno 2002;
Jayson & Mathew 2003; Oppel & Beaven 2004). Hence, the present investigation was designed
to study foraging behavior with special reference to selection of perch types,
perching height, foraging height, foraging substrates, foraging methods and
niche overlap of the White-breasted Kingfisher Halcyon smyrnensis, Small
Bee-eater Merops orientalis, Indian Roller Coracias benghalensis,
Common Myna Acridotheres tristis, and Black Drongo Dicrurus
macrocercus in the Cauvery delta region of Nagapattinam District, Tamil
Nadu, India.
Materials and Methods
This study was conducted in two
different villages, namely Mannampandal and Thiruvalangadu (18018’N & 79050’E),
of the Cauvery Delta region in Nagapattinam District of Tamil Nadu, India, from
February 2004 to December 2006. Agriculture is the major industry of this area,
and contributes a high share of the rice production in the state. Sugarcane, groundnut, green gram, black gram,
cotton, etc. are other major crops cultivated in the area. The river Cauvery and its tributaries are
major perennial water sources used for irrigation. Woody vegetation is sparse
in the form of groves and roadside trees. The predominant tree species found in the study area are Cocos
nucifera, Borassus flabellifer, Madhuca indica Mangifera indica, Enterolobium
saman, Tamarindus indicus, Ficus benghalensis, Ficus religiosa, Thespesia
populnea, Acacia arabica, Odina wodier and Azadirachta indica. Important
shrub species are Prosopis juliflora, Jatropha glandulifera andAdhathoda vesica. Plantations of Casuarina equisetifolia, Tectona
grandis and Bamboosa arundinacea are also found in the study area. Based on the north-east monsoon the study
area is divided into four seasons, namely post-monsoon, summer, pre-monsoon and
monsoon. Summer ranges from April to
June (with mean maximum temperature of 380C) and north-east monsoon starts
between October and December. The cold season starts in November and may last
until January.
The foraging behavior of birds
was observed at the study area mostly within the first five hours after
sunrise. Individual birds were observed through binoculars and type of perch
(electric power lines, trees, shrubs and ground), perching height (height at
which the bird was perched while feeding - grouped into 0-3m, 3-6m, 6-9m and
9-12m), foraging height (0-3m, 3-6m, 6-9m and 9-12m), foraging substrate (the
material from which food is taken by the birds - classified into air, plants
and ground) and foraging method (classified into aerial feeding - a bird
flew into air to catch flying prey; gleaning - a stationary food item is
picked from its substrate by a standing or hopping bird, and ground feeding- the bird picked prey from the ground) being used were noted (Bell & Ford
1990; Asokan 1995; Gokula 2001). The
heights were visually estimated. From
the data collected we determined and calculated percent use of different
foraging variables used by the insectivorous bird species.
The forage specialization of each
foraging variable was analyzed using the Shannon-Weaver index (Shannon &
Weaver 1949). The niche overlap values
between the foraging variables of birds were calculated by Pianka’s index
(Pianka 1973).
O = ∑ pxapya / √∑ pxa2 ∑ pya2
Where, pxa = proportion of
use of ‘a’th resource by species ‘x’ and pya = proportion of use
of ‘a’th resource by species ‘y’.
Results
In total, 1194 foraging
observations of White-breasted Kingfisher, 1052 of Small Bee-eater, 700 of
Indian Roller, 1277 of Common Myna and 1186 of Black Drongo were recorded in
the study area. Birds used a variety of
perches for hunting the prey. The
White-breasted Kingfisher, Small-Bee-eater, Indian Roller and Black Drongo
perched predominantly on electric power lines but Common Myna used mostly
ground (Table 1). The perching and foraging heights varied from 0 to 12m. In general, a perching height of 6-9m high
seemed to have been preferred by all bird species except the Common Myna. The White-breasted Kingfisher, Indian Roller,
Common Myna and Black Drongo fed predominantly at 0-3m. The Bee-eater is shown to forage at heights
of 0-3m and 3-6m at a similar percentage (Table 2). The White-breasted Kingfisher, Indian Roller
and Black Drongo used plants (herbs, shrubs and trees) as foraging substrate to
find insect prey while Small Bee-eaters used air and Common Mynas used ground
as substrates (Table 3). Foraging by gleaning was relatively higher than other
methods in White-breasted Kingfisher, Indian Roller and Black Drongo. The Small
Bee-eater foraged mainly by aerial feeding and the Common Myna was shown to use
ground feeding (Table 4).
Foraging niche
overlap: Niche
overlap values for variables associated with the insectivory of five bird
species are given in table 5.
Perch types: The Indian
Roller and Black Drongo had the highest overlap (0.99) while the lowest overlap
was between Small Bee-eater and Common Myna (0.11).
Perching height: The niche
overlap in perching height was highest between White-breasted Kingfisher and
Black Drongo (0.99) while the lowest was between Indian Roller and Common Myna
(0.19).
Foraging height:The highest
niche overlap in foraging height was between White-breasted Kingfisher and
Indian Myna; White-breasted Kingfisher and Common Myna and Indian Roller and
Black Drongo (0.99) while the lowest niche overlap (0.62) was found between
Small Bee-eater and Common Myna.
Foraging
substrates and methods: The highest overlap was found between
White-breasted Kingfisher and Indian Roller and Indian Roller and Black Drongo
(0.98) while the lowest was found between Small Bee-eater and Common Myna
(0.07) (Table 5).
Discussion
Our results indicate that the
five insectivorous bird species used different perch types in the study
area. All species, except the Common
Myna that preferred to use ground, showed high use of electric power
lines. The electric power lines are a
common feature in the study area especially around the agricultural
habitats. These structures provided
suitable perches to birds for detecting prey. The other dominant perch sites used by the birds in our study area were
trees and shrubs. With the absence of electric power lines in areas like
riverine habitats, birds preferred and readily utilized trees and shrubs as
perches. Lammers & Collopy (2007) stated
that avian predators are attracted to over-head utility power lines because
they provide perches for various activities, including hunting prey. The White-breasted Kingfisher, Small
Bee-eater, Indian Roller and Black Drongo were sit-and-wait predators and they
used perches mainly to locate prey and launch their attack. Brookers et al.
(1990), Asokan (1995) and Yosef (2004) documented the importance of perches for
prey detection / hunting, vigilance, resting as well as other activities of
insectivorous birds. However, preference
of perch type is dependent on the abundance, availability and type of prey; on
the habitat type; and also on the morphological and behavioural characteristics
of the bird species themselves.
The White-breasted Kingfisher,
Small Bee-eater, Indian Roller and Black Drongo in our study typically perched
at the height category of 6-9m to scan an area. The Common Myna perched at a height of 0-3m because they are generally
ground foragers. Similarly, Sivakumaran
& Thiyagesan (2003) found that Indian Rollers perched at heights of 3-9m
for locating insect prey. Higher perches
may provide a larger field of view and increase chances of detecting prey. However, Shafir & Roughgarden (1997) and
Butler et al. (2005) stated that distance to prey is a key factor influencing
the perching height selection in sit-and-wait predators. Bell & Ford (1986) suggested that the
nature and height of perches used by birds is related to the type of prey
captured and their seasonal variation. In this study the White-breasted Kingfisher, Indian Roller, Common Myna
and Black Drongo foraged mainly at 0-3m above the ground, and the Small
Bee-eater foraged at wide range of heights (0-12m). Brookers et al. (1990) suggested that
insectivorous birds in general are height generalists. Vegetation structure,
plant species composition, prey abundance and distribution, and interspecific
competition significantly affect the foraging height selection of insectivorous
birds (Holmes & Robinson 1981; Robinson & Holmes 1984).
Three major foraging substrates,
namely air, plants and ground, were recognized of which, the White-breasted
Kingfisher, Indian Roller and Black Drongo fell under the plant-guild because
plant offers a greater variety of insect food. The Small Bee-eater used air and
Common Myna used ground as major foraging substrates. In the present study, most of the foraging
observations were recorded in agricultural and riverine habitats. The birds
took insect prey in various foraging substrates viz., paddy/other crops,
small stumpy vegetation, and trees, from both habitats. Earlier, some
researchers, Holmes & Recher (1986), Craig (1990), MacNally (1994), Bhatt
& Kumar (2001), Gokula (2001), Murakami (2002), Gokula & Venkatraman
(2003), Gokula & Vijayan (2007) find out plants as
main foraging substrates in forest bird species.
Our results indicate that the
White-breasted Kingfisher, Indian Roller and Black Drongo foraged exclusively
by gleaning, which suggests that these species adopted a foraging technique
suitable to capturing slow moving insect prey on herbs and shrubs. Gleaning is also a common foraging technique
reported for many avian species (Recher & Gebski 1990; Beachly et al. 1995;
Amano & Euguchi 2002; Adamik et al. 2003; Adamik & Kornan 2004). The Common Myna foraged mainly on the ground
surface and the Small Bee-eater used an aerial mode of feeding. The use of foraging technique is determined
partly by the morphology of birds (Gokula & Vijayan 2000). Morphological characteristics are closely
related to ecological characters in some restricted taxa. Morphological constraints may restrict the
range of foraging techniques adopted by any given species. For example, the Small Bee-eater having a
long bill is suitable for capturing and firmly grasping aerial insects or those
of high mobility, the other bird species having short bills are found
predominantly to be gleaners. The
foraging technique of birds also changed according to habitat type and the
abundance of prey items (Poulin et al. 1994; Recher & Davis 1998; Murakami
2002).
High niche overlap was recorded
between Indian Roller and Black Drongo (perch type, foraging height, foraging
substrate and foraging method) and White-breasted Kingfisher and Indian Roller
(foraging height, foraging substrate and foraging method). Low and high niche overlap values shown by
each species can be attributed to the availability of food resources and
inter-specific competition in the habitat (Gokula & Vijayan 2000; Loyn
2002). Hartley (1953), Feinsinger (1976)
and Hutto (1981) stated that the distribution, abundance, and quality of food
may influence the extent of foraging niche overlap. However, there is no direct information on
food resources for this study.
In conclusion, many factors, such
as time of day, season, ambient temperature, availability of prey, breeding
season, and presence of predators, influence the foraging behavior of
birds. Kelly (1998) stated that weather,
especially temperature, affects the foraging behavior of insectivorous birds.
Several studies have found temperature-related changes in the foraging behavior
of birds. Gokula & Vijayan (2007)
stated that food availability, habitat structure, and interspecific competition
are also responsible for variation in the foraging behavior of birds.
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