CHAPTER VI

FFOORRAAGGIINNGG BBEEHHAAVVIIOOUURR

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6.1. Introduction

In a forest we are often caught by the sounds and movements of birds. As

we watch, it becomes obvious that species differ in their habits. Birds, whether

diurnal or nocturnal, show a characteristic rhythm of routine emergence, feeding,

interaction with others and roosting. Avian community ecology aims to identify

recurrent patterns of species composition, guild structure, diversity and other

parameters among co-occurring species and to reveal the factors promoting those

patterns (Wiens and Rotenberry, 1981b). Guild structure can be defined as the

pattern of resource use (similarities and differences) among bird species occurring in

a habitat. For birds, food is usually considered to be the important resource and

study of foraging behaviour is often linked with how, where and which food is

obtained.

Bird species have often been assigned to foraging guilds on the basis of a

general knowledge of their feeding behaviour (Eckhardt, 1979; Alatalo and Alatalo,

1979; Airola and Barret, 1985). Guilds are groups of more than one species that

seem to exploit the same kind of resources in similar ways. These guilds have been

used extensively in the analysis of many taxonomic groups in many types of biomes,

and ornithologists have been among the most active in interpreting assemblages of

species (Recher and Holmes 1985; MacNally, 1994; Wheeler and Calver, 1996).

Members of guild segregate themselves into specific ecological niches by adopting

foraging behaviour. They differ in microhabitat use and foraging strategy (Wiens,

1989). The foraging strategy includes various methods to exploit the resources.

Insectivore birds exhibit different methods of exploiting resources such as gleaning,

sallying, probing, pouncing and hawking (Crome, 1978; Homes et al., 1979; Gokula,

1998; Nirmala, 2002).

Understanding the effects of habitat structure on foraging is particularly useful

in the conservation of species and in making management decisions. Moreover, a

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knowledge of the ways in which birds exploit resources within a forest will not only

increase understanding of how they use their environment but also the essential

requirements for their survival. This information, in turn, is required for the

development of sound, scientifically based plans of management for protected areas.

This chapter examines the feeding behaviour of birds in Parambikulam Wildlife

Sanctuary.

6.2. Methods

6.2.1. Foraging guild

Foraging records were collected at the study area during December, 2002 to

November 2003. Sixteen days were spent in a month to record foraging behaviour of

birds of the Sanctuary. Most of the observations were done within four hours after

sunrise. Additional observations were made throughout the day time for some rare

species. Only one foraging record was taken for any individual encountered as done

by Morrison (1984) and MacNally (1994). For each foraging attempt microhabitat

details such as the height above ground level, substrate and species of plant with the

prey and foraging method were recorded.

6.2.2. Foraging height

Foraging attempts were observed for different height categories from ground

level.

6.2.3. Foraging substrate

A substrate is the material from which food is taken by birds. Foraging

substrates are classified as

1. Ground: Including debris, litter and grass

2. Trunk/main branches: The main axes of trees

3. Foliage: Leaves including leaf blades and petioles

4. Twigs: Small branches to which leaves were attached

5. Flower and Fruits

6. Air.

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Among these, flower (nectar), fruits and seeds form the food of nectivorous,

frugivorous and granivorous birds respectively. The other five categories of

substrates are meant purely for insectivore species. The plant on which foraging

attempts were made was identified upto species or genus or category level.

6.2.4. Foraging methods

The foraging of birds were categorized as

1. Glean: A stationary food item is picked by the bird from its substrate by standing or

hopping.

1.2 Probe: As glean, only the bird’s beak penetrates or lifts the substrate to locate

covered food.

1.3 Pounce: A bird flies from a perch and grabs the food items as it lands on the

substrate similar to flycatcher gleaning explained by Croxall (1977).

1.4 Sally: A bird flies into air to catch flying prey.

To cluster the species on a micro level, the sally, probe and glean were

classified further into finer levels based on the substrate (Table 6.1). The fruit and

flower were related to all behaviours of frugivores and nectarivores and the use of

plants by omnivorous birds was of relevance in comparison to their insectivore

behaviour (Wheeler and Calver, 1996). Eighteen categories of foraging activity

(Table 6.1), which encompasses the behaviour described by Crome (1978) and

expanded by Holmes et al. (1979) and MacNally (1994) were used in the present

study.

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Table 6.1. Description of foraging activities used to assess the guild structure of avifauna Sl. No. Activity (description)

1. Above canopy sally Sally to airborne insect in or above the main canopy

2. Below canopy sally Sally from perched position to airborne insect below the main canopy

3. Bush sally Sally to airborne insect from the bushes

4. Ground sally Sally to airborne insects from the ground

5. Leaf glean Gleaning of perched prey from leaves of trees

6. Twig glean Gleaning of perched prey from twigs of trees

7. Wood search Gleaning of perched prey on trunks or main branches

8. Wood probing Probing the bark

9. Bark tear Searching for prey by tearing the bark

10. Bush gleaning Gleaning of perched prey from bush

11. Litter search Scratch and search through litter for insects

12. Fallen log gleaning Searching fallen logs

13. Ground pounce Attack on grounded prey from perched position

14. Ground search Searching ground for insects

15. Arboreal granivore Consumption of seeds in trees

16. Ground granivore Consumption of seeds in ground

17. Fruit exploiting Consumption of fruits

18. Flower exploiting Consumption of pollen and nectar or blossoms

For the purpose of getting sufficient sample size, the information was pooled

irrespective of years. At least 20 foraging observations on each species (29 in moist

deciduous forest; 22 in evergreen forest; 28 in teak plantation) were made for the

most appropriate clusters explained as foraging guilds in each habitat.

6.2.5. Statistical analysis

Specialist Index (J')

The foraging specialization of each bird category for each foraging dimension

and forage height was analysed using the Shannon-Weiner Index (H'). These values

were converted to a standardized range using the formula

J' = H' / H max

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Where J' denotes Specialization and H max is equal to the H' values obtained

when the observations are distributed equally across all subsets of the foraging

dimension (Crome, 1978 and Recher and Holmes, 1985). J' values range between

‘1’ to ‘0’, with foraging specialization increasing as J' falls.

Diversity

Diversity index (H') was calculated using the programme SPDIVERS.BAS

developed Ludwig and Reynolds (1988).

Cluster analysis

To compare the foraging behaviour, substrate use and height between the

species, cluster analysis were performed on a data matrix (species * characteristics),

as followed by Holmes et al., (1979). This analysis is used for unweighed pair group

clustering method with arithmetic averages (UPGMA) and Squared Euclidean

Distance (Legendre and Legendre, 1983, Rohlf, 1987).

6.3. Results

In the moist deciduous forest, evergreen forest and teak plantation in

Parambikulam Wildlife Sanctuary foraging behavior of only common resident and

migrant bird species were made. A total of 2905 observations were made on 29

species in moist deciduous forest, 23 in evergreen forest and 28 in teak plantation

(Table 6.2)

Table 6.2. Number of foraging records made in different habitats

Number of observations Sl.

No. Common name Species name MDF EVN PLN

1. Ashy prinia Warbler Prinia socialis Sykes 28 25 39 2. Asian Paradise Flycatcher Terpsiphone paradisi

(Linnaeus) 22 - 45

3. Baya Weaver Ploceus philippinus (Linnaeus) 38 42 44

4. Black-headed Oriole Oriolus xanthornus (Linnaeus) 42 34 35

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Number of observations Sl.

No. Common name Species name MDF EVN PLN

5. Blue winged Parakeet Psittacula columboides (Vigors) 25 22 32

6. Chestnut-Headed Bee-eater Merops leschenaulti Vieillot 22 34 35

7. Common Hoopoe Upupa epops Linnaeus 40 32 55 8. Common Iora Aegithina tiphia (Linnaeus) 32 - 75 9. Common Myna Acridotheres tristis

(Linnaeus) 35 38 42

10. Common Tailor Bird Orthotomus sutorius (Pennant) 30 32 35

11. Greater Racket-tailed Drongo Dicrurus paradiseus (Linnaeus) 40 42 65

12. Grey Jungle Fowl Gallus sonneratii Temminck 30 - 25

13. Heart-Spotted Woodpecker Hemicircus canente (Lesson) 35 22 22

14. Jungle Babbler Turdoides striatus (Dumont) 22 30 50

15. Jungle Myna Acridotheres fuscus (Wagler) 42 40 30

16. Plain Flowerpecker Dicaeum concolor Jerdon 32 - 40 17. Plum-headed parakeet Psittacula cyanocephala

(Linnaeus) 32 20 40

18. Red-vented Bulbul Pycnonotus cafer (Linnaeus) 38 30 35

19. Red-whiskered Bulbul Pycnonotus jocosus (Linnaeus) 40 32 55

20. Scarlet Minivet Pericrocotus flammeus (Forster) 45 22 -

21. Small Bee-eater Merops orientalis Latham 28 - 40 22. Small Yellownaped

Woodpecker Picus chlorolophus Vieillot 35 48 22

23. Spotted Dove Streptopelia chinensis (Scopoli) 25 28 52

24. Thick-billed Warbler Acrocephalus aedon (Pallas) 35 - 32

25. White-bellied Drongo Dicrurus caerulescens (Linnaeus) 38 - 58

26. Whitebrowed Fantail Flycatcher Rhipidura aureola Lesson 35 42 42 27. White-eye Zosterops palpebrosus

(Temminck) - 42 -

28. Whiteheaded Babbler Turdoides affinis (Jerdon) 35 48 62 29. Yellowfronted Pied

Woodpecker Dendrocopos mahrattensis (Latham) 22 30 30

30. Yellowthroated Sparrow Petronia xanthocollis (Burton) 42 33 35

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6.3.1. Foraging patterns of bird species in moist deciduous forest

Foraging height (in meter)

Totally nine categories of foraging height were recognised such as ground

(G), 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7 and 7-8 m and 29 species of birds were observed

in the moist deciduous forest (Table 6.3). Most of the species foraged over a broad

height range, they were grouped according to the layer of vegetation in which

majority of their foraging was recorded.

The foliage was apportioned between the 3 layers of strata viz. ground (0 m),

shrub and short trees (0 – 2 m) and tree (> 2 m). five ( %)species foraged mainly

on the ground, namely, Grey Jungle Fowl, Spotted Dove, Common Hoopoe,

Whiteheaded Babbler and Jungle Babbler (Table 6.3).

Nine species utilized the 0 - 2 m height. They are Heart-spotted Woodpecker,

Common Myna, Red-vented Bulbul, Red-whiskered Bulbul, Ashy Wren warbler,

Indian Tailor bird, Thick-billed Warbler and Blossom headed Parakeet (Table 6.3).

15 species of birds like Black-headed Oriole, White-bellied drongo, Racket-

tailed Drongo etc were recorded at the tree layer height (>2 m)(Table 6.3).

Foraging substrate

Seven substrates were categorized in the moist deciduous forest, such as

ground, trunk, foliage, twigs, flower, fruit and air (Table 6.4).

Ground: Among the seven substrates, ground was largely used by eight species of

birds. They were Grey Jungle fowl, Spotted Dove, Common Hoopoe, Common

Myna, Jungle Myna, White-headed Babbler, Jungle Babbler and Yellow throated

Sparrow. Both insectivores and granivores used this substrate (Table 6.4).

Trunk: Four species viz., Yellownaped Woodpecker, Yellowfronted Pied

Woodpecker, Heartspotted Woodpecker, and Black headed Oriole used the trunk

substrate (Table 6.4).

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Foliage: Whitebrowed fantail Flycatcher, Ashy Wren Warbler, Indian Tailor Bird,

Nilgiri Flowerpecker and Common Iora utilized foliage for collecting their prey

(Table 6.4).

Twigs: In this substrate no absolute usage by any one of the bird was recorded. But

less than 50 percent were found utilizing this substrate (Table 6.4).

Flower and Fruit: Four species utilized this substrate for catching their prey. They

were Malabar Parakeet, Blossom headed Parakeet, Red vented Bulbul and Red

whiskered Bulbul (Table 6.4).

Air: Insectivore species like Chestnut headed Bee eater, Green Bee eater, White

bellied Drongo, Racket tailed Drongo were found to catch their prey in the air (Table

6.4).

Foraging methods

Out of the 18 foraging techniques employed by birds, 9 major methods were

distinguished for the birds in the moist deciduous forest. The major prey attack

manoeuvores used by birds in the moist deciduous forest were sallying, pouncing,

foliage-gleaning, wood gleaning, wood probing, carnivores, nectar exploiting, fruit

exploiting and grain exploiting (Table 6.5).

Sallying: Five species of birds were recorded as salliers (Table 6.5). They are

Malabar Parakeet, Chestnut-headed Bee-eater, Green Bee-eater, White-bellied

Drongo and Racket- tailled Drongo.

Pouncing: No bird was found strictly confined to this method and only 10 percent

among the selected species shared this mode of feeding (Table 6.5).

Foliage gleaning: Four species of birds were recorded under this guild (Table 6.5).

Majority warblers (about 90%) like Ashy wren Warbler, Thick billed Warbler and

Indian Tailor Bird used this method.

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Wood gleaning: Four species of birds were found to come under the wood gleaning

guild. They are Yellow-napped Woodpecker, Yellow fronted Pied Woodpecker, Heart

Spotted Woodpecker and Scarlet Minivet (Table 6.5).

Wood probing: This guild included Woodpeckers only (Table 6.5).

Ground Carnivores: Hoopoe, White-headed Babbler and Jungle Babbler were

found in this guild. Of these Hoopoe was a complete ground carnivore (Table 6.5).

Nectar exploiting: Birds like Nilgiri Flower pecker and Common Iora were grouped

under this guild, of these the former was found to be about 98 percent nectar

exploiting (Table 6.5).

Fruit exploiting: Only four species (Red vented Bulbul, Red whiskered Bulbul,

Common Myna and Jungle Myna) constituted this group. Common Myna used this

guild only for about 20 per cent of its feeding activity (Table 6.5).

Seed exploiting: Six species were found to use this method. They were Grey

Jungle Fowl, Spotted Dove, Common Myna, Jungle Myna, Yellow throated Sparrow

and Baya Weaver (Table 6.5).

Table 6.3. Height distribution of birds in moist deciduous forest based on percentage of prey attacks

Foraging heights (m) Species name/guild

G 1 2 3 4 5 6 7 8 Ashy wren Warbler 0 8 31 45 16 0 0 0 0 Baya Weaver 0 0 0 0 0 0 23 42 35 Black-headed Oriole 0 0 4 19 27 49 1 0 0 Blossom-headed parakeet 0 70 0 0 0 0 0 23 7 Chestnut-Headed Bee-eater 3 8 12 14 18 22 11 12 0 Common Hoopoe 100 0 0 0 0 0 0 0 0 Common Iora 0 2 24 49 22 3 0 0 0 Common Myna 1 14 32 21 14 12 4 2 0 Green Bee-eater 0 19 0 0 47 22 0 0 12 Grey Jungle Fowl 100 0 0 0 0 0 0 0 0 Heart-Spotted Woodpecker 0 2 32 44 22 0 0 0 0

90

Foraging heights (m) Species name/guild

G 1 2 3 4 5 6 7 8 Indian Tailor Bird 0 5 32 15 2 46 0 0 0 Jungle Babbler 88 8 4 0 0 0 0 0 0 Jungle Myna 0 2 13 25 28 32 0 0 0 Malabar Parakeet 0 4 8 6 8 43 15 11 5 Nilgiri Flowerpecker 0 10 24 20 22 24 0 0 0 Paradise Flycatcher 0 0 2 50 48 0 0 0 0 Racket-tailed Drongo 0 1 6 51 19 22 1 0 0 Red-vented Bulbul 0 50 15 16 18 1 0 0 0 Red-whiskered Bulbul 0 25 30 42 2 1 0 0 0 Scarlet Minivet 0 0 1 23 22 34 20 0 0 Spotted Dove 55 23 20 2 0 0 0 0 0 Thick-billed Warbler 0 2 22 33 43 0 0 0 0 White-bellied Drongo 0 5 3 21 37 32 2 0 0 Whitebrowed Fantail Flycatcher 0 0 8 32 30 28 2 0 0 Whiteheaded Babbler 100 0 0 0 0 0 0 0 0 Yellowfronted Pied Woodpecker 0 0 15 32 45 8 0 0 0 Yellownaped Woodpecker 0 0 8 20 60 2 8 2 0 Yellowthroated Sparrow 0 2 32 48 18 0 0 0 0

Table 6.4. Use of substrate (%) by birds in the moist deciduous forest

Species name Ground Trunk Foliage Twigs Flower Fruit Air Ashy wren Warbler 0 0 95 0 5 0 0 Baya Weaver 0 0 30 55 15 0 0 Black-headed Oriole

0 80 0 12 0 8 0

Blossom-headed parakeet

0 0 0 0 3 97 0

Chestnut-Headed Bee-eater

0 0 15 0 0 0 85

Common Hoopoe 98 0 2 0 0 0 0 Common Iora 0 0 0 0 99 1 0 Common Myna 98 0 0 2 0 0 0 Green Bee-eater 0 0 5 0 0 0 95 Grey Jungle Fowl 99 0 1 0 0 0 0 Heart-Spotted Woodpecker

0 99 0 1 0 0 0

Indian Tailor Bird 0 0 90 0 10 0 0 Jungle Babbler 100 0 0 0 0 0 0

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Species name Ground Trunk Foliage Twigs Flower Fruit Air Jungle Myna 100 0 0 0 0 0 0 Malabar Parakeet 0 0 0 0 1 99 0 Nilgiri Flowerpecker

0 0 75 0 15 10 0

Paradise Flycatcher

0 0 14 51 35 0 0

Racket-tailed Drongo

0 0 0 12 0 0 88

Red-vented Bulbul 2 12 0 0 12 74 0 Red-whiskered Bulbul

0 25 2 0 20 53 0

Scarlet Minivet 0 0 78 12 10 0 0 Spotted Dove 100 0 0 0 0 0 0 Thick-billed Warbler 0 0 85 0 15 0 0 White-bellied Drongo

0 0 0 0 0 0 100

Whitebrowed Fantail Flycatcher

0 0 74 12 14 0 0

Whiteheaded Babbler

100 0 0 0 0 0 0

Yellowfronted Pied Woodpecker

0 88 0 12 0 0 0

Yellownaped Woodpecker

0 98 0 2 0 0 0

Yellowthroated Sparrow

91 2 7 0 0 0 0

Table 6.5. Prey attack manoeuvores (%) by birds in moist deciduous forest

Species name

Salli

er

Poun

cer

Folli

age

glea

ner

Woo

d gl

eane

r

Woo

d pr

ober

Gro

und

carn

ivor

e

Nec

tari-

vo

re

Frug

i- vo

re

Gar

ni-

vore

Ashy wren Warbler 0 0 96 0 0 4 0 0 0

Baya Weaver 0 0 0 0 0 0 0 0 100 Black-headed Oriole 18 0 82 0 0 0 0 0 0 Blue winged Malabar Parakeet 98 2 0 0 0 0 0 0 0 Chestnut-Headed Bee-eater 90 10 0 0 0 0 0 0 0 Common Hoopoe 0 0 0 0 0 100 0 0 0 Common Iora 0 0 25 0 0 0 75 0 0 Common Myna 0 0 0 0 0 0 0 23 77 Green Bee-eater 95 5 0 0 0 0 0 0 0 Grey Jungle Fowl 0 0 0 0 0 0 0 0 100 Heart-Spotted Woodpecker 0 0 0 6 94 0 0 0 0 Indian Tailor Bird 0 0 98 0 0 2 0 0 0

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Species name

Salli

er

Poun

cer

Folli

age

glea

ner

Woo

d gl

eane

r

Woo

d pr

ober

Gro

und

carn

ivor

e

Nec

tari-

vo

re

Frug

i- vo

re

Gar

ni-

vore

Jungle Babbler 12 0 0 0 0 88 0 0 0 Jungle Myna 0 0 0 0 0 0 0 24 76 Nilgiri Flowerpecker 0 0 2 0 0 0 98 0 0 Paradise Flycatcher 39 0 61 0 0 0 0 0 0 Plum headed parakeet 0 0 0 0 0 0 0 100 0 Racket-tailed Drongo 98 8 0 0 0 0 0 0 0 Red-vented Bulbul 0 0 21 0 0 0 0 79 0 Red-whiskered Bulbul 0 0 23 0 0 0 0 77 0 Scarlet Minivet 22 0 28 50 0 0 0 0 0 Spotted Dove 0 0 0 0 0 0 0 0 100

Thick-billed Warbler 0 0 94 0 0 6 0 0 0

White-bellied Drongo 90 10 0 0 0 0 0 0 0

Whitebrowed Fantail Flycatcher 38 0 62 0 0 0 0 0 0

Whiteheaded Babbler 14 0 0 0 0 86 0 0 0 Yellowfronted Pied Woodpecker 0 0 0 2 98 0 0 0 0 Yellownaped Woodpecker 0 0 0 5 95 0 0 0 0 Yellowthroated Sparrow 0 0 0 0 0 0 0 0 100

Specialist Index

Out of the three specializations, highest was observed in foraging method

followed by foraging substrate and foraging height (Table 6.6). Grey Jungle Fowl

and Common Hoopoe were found specialists in all the three categories, as their J’

values are ‘0’. Spotted Dove and Jungle Myna were specialists in foraging method

and foraging substrate.

Table 6.6. Extent of specialization of birds in foraging height, foraging substrate and foraging method as shown by J' values in Moist deciduous forest (J' values ranges from 0 -1, specialist are in bold)

Foraging height Foraging method

Foraging substrate Species name

H' J' H' J' H' J'

Ashy wren Warbler 1.22 0.53 0.67 0.34 0.42 0.18

Baya Weaver 1.07 0.47 0.00 0.00 0.30 0.15

Black-headed Oriole 1.19 0.52 0.54 0.28 0.37 0.16

Blossom-headed parakeet 0.77 0.34 0.33 0.17 0.00 0.00

Chestnut-Headed Bee-eater 1.98 0.86 0.20 0.10 0.13 0.06

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Foraging height Foraging method

Foraging substrate Species name

H' J' H' J' H' J'

Common Hoopoe 0.00 0.00 0.00 0.00 0.00 0.00

Common Iora 1.21 0.53 0.51 0.26 0.06 0.02

Common Myna 1.75 0.76 1.04 0.53 0.37 0.16

Green Bee-eater 1.26 0.55 0.10 0.05 0.06 0.02

Grey Jungle Fowl 0.00 0.00 0.00 0.00 0.00 0.00

Heart-Spotted Woodpecker 1.14 0.49 0.27 0.14 0.10 0.04

Indian Tailor Bird 1.23 0.54 0.17 0.09 0.73 0.32

Jungle Babbler 0.44 0.19 0.00 0.00 0.99 0.43

Jungle Myna 1.41 0.61 0.00 0.00 0.00 0.00

Malabar Parakeet 1.74 0.76 0.20 0.10 0.06 0.02

Nilgiri Flowerpecker 1.57 0.68 0.23 0.12 0.97 0.42

Paradise Flycatcher 0.78 0.34 0.66 0.34 0.33 0.14

Racket-tailed Drongo 1.25 0.54 0.55 0.28 0.64 0.28

Red-vented Bulbul 1.28 0.56 0.54 0.28 0.81 0.35

Red-whiskered Bulbul 1.20 0.52 0.40 0.21 1.08 0.47

Scarlet Minivet 1.41 0.61 0.56 0.29 0.68 0.29

Spotted Dove 1.07 0.46 0.00 0.00 0.00 0.00

Thick-billed Warbler 1.14 0.50 0.10 0.05 0.35 0.15

White-bellied Drongo 1.39 0.61 0.00 0.00 0.06 0.02

Whitebrowed Fantail Flycatcher 1.36 0.59 0.37 0.19 0.20 0.09

Whiteheaded Babbler 0.00 0.00 0.00 0.00 0.75 0.33

Yellowfronted Pied Woodpecker 1.21 0.53 0.33 0.17 0.10 0.04

Yellownaped Woodpecker 1.19 0.52 0.47 0.24 0.20 0.09

Yellowthroated Sparrow 1.10 0.48 0.00 0.00 0.10 0.05

H’- Diversity index, J’ – Specialist indix

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Determination of foraging guilds

The relationship among the 29 species of birds based on the foraging

methods, foraging substrate and foraging height on a multidimensional analysis is

summarized in the cluster dendrogram (Fig. 6.1).

Fig. 6.1. Cluster dendrogram showing interspecific relationship of 29 species in the moist deciduous forest based on multivariate analysis of foraging method, foraging substrate and foraging height.

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6.3.2. Foraging patterns of bird species in evergreen forest Foraging height (in meter)

Nine height categories such as ground, 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7 and

7-8 m consisting of 22 species of birds were observed in evergreen forest (Table

6.7). Most of the species foraged over a broad height range, they were grouped

according to the layer of vegetation in which majority of their foraging was recorded.

The foliage was apportioned between the 3 layers of strata viz., ground (0 m),

shrub and short trees (0 - 2 m) and tree (> 2 m). Four species of birds foraged mainly

on the ground namely Common Hoopoe, White headed Babbler, Jungle Babbler and

Spotted Dove (Table 6.7).

Eighteen species of birds were found to utilize 0 - 2 m height, Out of these

Spotted Dove, Heart spotted Woodpecker, Racket tailed Drongo, Common Myna,

Red vented Bulbul and Indian Tailor Bird represented most dominantly (Table 6.7).

The tree layer (> 2 m) height was used by 18 species of birds (Table 6.7).

Foraging substrate

Seven substrates were categorized in the evergreen forest namely, ground,

trunk, foliage, twigs, flower, fruit and air (Table 6.8).

Ground: Eight species of birds were recorded in this substrate. They were Common

Hoopoe, Common Myna, Jungle Myna, White-headed Babbler, Jungle Babbler, Red-

vented Bulbul, Yellow-throated Sparrow and Spotted Dove (Table 6.8).

Trunk: Three species of birds such as Yellownaped Woodpecker, Yellowfronted Pied

Woodpecker and Heartspotted Woodpecker were found to use the trunk substrate

(Table 6.8).

Foliage: Eight species of birds found this substrate. Out these, four of them, such as

Whitebrowed Fantail Flycatcher, Ashy Wren Warbler, Indian Tailor Bird and Scarlet

Minivet utilize 70% of the feeding activity here (Table 6.8).

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Twigs: Five species were observed in twig substratum, performed only less than 25

percent of their prey attacks in this substratum (Table 6.8).

Flower and Fruit; Seven species of birds - Malabar Parakeet, Blossom headed

Parakeet, Red-vented Bulbul and Red-Whiskered Bulbul, Ashy Wren Warbler, Indian

Tailor bird, Yellow throated Sparrow were found to utilize this substratum for catching

that prey (Table 6.8).

Air: Insectivore species like Chestnut-headed Bee eater, Green Bee eater, White-

bellied Drongo, Racket-tailed Drongo were found to catch their prey in the air

(Table 6.8).

Foraging methods

Nine major methods were adopted by the birds in the evergreen forest, out of

the 18 foraging techniques. The major prey attack manoeuvores used by birds in the

evergreen forest were sallying, pouncing, foliage-gleaning, wood gleaning, wood

probing, carnivores, nectar exploiting, fruit exploiting and grain exploiting (Table 6.9).

Sallying: Five species of birds were observed as salliers (Table 6.9). They were

Chestnut-headed Bee-eater, Black-headed Oriole, Racket tailed Drongo, Scarlet

Minivet and Whitebrowed Fantail Flycatcher.

Pouncing: No complete pouncers were recorded and only 10 per cent used this

guild (Table 6.9).

Foliage gleaning: Six species of birds were found as foliage gleaners (Table 6.9).

Only warblers predominantly used this guild (> 90 per cent).

Wood gleaning: In this guild there were seven species of birds, namely, Yellow-

napped Woodpecker, Yellow-fronted Pied Woodpecker, Heart Spotted Woodpecker,

Scarlet Minivet, Black-headed Oriole, White-headed Babbler and Jungle Babbler

(Table 6.9).

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Wood probing: Three species of woodpeckers were found under this guild

(Table 6.9).

Ground Carnivores: Hoopoe, White headed Babbler and Jungle Babbler

constituted in this guild (Table 6.9).

Fruit exploiting: Six species of birds, Blossom headed Parakeet, Malabar Parakeet,

Red vented Bulbul, Red whiskered Bulbul, Common Myna and Jungle Myna were

recorded as fruit exploiters (Table 6.9).

Seed exploiting: Spotted Dove, Yellow throated Sparrow and Baya Weaver Bird

were found to come under this guild (Table 6.9).

Table 6.7. Height distribution of birds in evergreen forest based on Percentage of prey attacks

Foraging height (m) Species name/Guild

G 1 2 3 4 5 6 7 8 Ashy wren Warbler 0 9 19 54 12 6 0 0 0 Baya Weaver 0 0 0 0 0 0 23 55 22 Black-headed Oriole 0 5 20 32 33 6 4 0 0 Blossom-headed Parakeet 0 0 0 55 32 0 0 13 0 Chestnut-Headed Bee-eater 5 9 10 13 18 22 11 12 0 Common Hoopoe 100 0 0 0 0 0 0 0 0 Common Myna 1 14 32 21 14 12 4 2 0 Heart-Spotted Woodpecker 0 2 32 44 22 0 0 0 0 Indian Tailor Bird 0 8 45 14 2 31 0 0 0 Jungle Babbler 80 12 3 5 0 0 0 0 0 Jungle Myna 0 2 13 25 28 32 0 0 0 Malabar Parakeet 0 2 10 28 0 32 14 12 2 Racket-tailed Drongo 0 5 33 32 30 0 0 0 0 Red-vented Bulbul 0 40 42 16 1 1 0 0 0 Red-whiskered Bulbul 0 34 20 44 2 0 0 0 0 Scarlet Minivet 0 0 12 22 12 32 22 0 0 Spotted Dove 48 30 22 0 0 0 0 0 0 Whitebrowed Fantail Flycatcher 0 0 15 32 38 15 0 0 0 Whiteheaded Babbler 100 0 0 0 0 0 0 0 0 Yellowfronted Pied Woodpecker 0 0 15 32 45 8 0 0 0 Yellownaped Woodpecker 0 0 8 20 60 2 8 2 0 Yellowthroated Sparrow 0 3 31 55 11 0 0 0 0

98

Table 6.8. Use of substrate (%) by birds in the evergreen forest

Species name Ground Trunk Foliage Twigs Flower Fruit AirAshy wren Warbler 0 0 80 0 20 0 0 Baya Weaver 0 0 45 25 30 0 0 Black-headed Oriole 0 90 0 10 0 0 0 Blossom-headed Parakeet

0 0 0 0 23 77 0

Chestnut-Headed Bee-eater

0 0 25 0 0 0 75

Common Hoopoe 100 0 0 0 0 0 0 Common Myna 100 0 0 0 0 0 0 Heart-Spotted Woodpecker

0 100 0 0 0 0 0

Indian Tailor Bird 0 0 70 0 30 0 0 Jungle Babbler 100 0 0 0 0 0 0 Jungle Myna 100 0 0 0 0 0 0 Malabar Parakeet 0 0 0 0 12 88 0 Racket-tailed Drongo 0 0 0 22 0 0 78 Red-vented Bulbul 20 20 0 0 60 0 0 Red-whiskered Bulbul 0 45 2 0 44 9 0 Scarlet Minivet 0 0 80 20 0 0 0 Spotted Dove 98 2 0 0 0 0 0 Whitebrowed Fantail Flycatcher

0 0 86 14 0 0 0

Whiteheaded Babbler 100 0 0 0 0 0 0 Yellowfronted Pied Woodpecker

0 100 0 0 0 0 0

Yellownaped Woodpecker

0 100 0 0 0 0 0

Yellowthroated Sparrow

90 0 10 0 0 0 0

Table 6.9. Pery attack manoeuvres (%) by birds in evergreen forest

Species name

Salli

er

Poun

cer

Folli

age

glea

ner

Woo

d gl

eane

r

Woo

d pr

ober

Gro

und

carn

ivor

e

Nec

tari-

vore

Frug

i-vo

re

Gar

ni-

vore

Ashy wren Warbler 0 0 98 0 0 2 0 0 0

Baya Weaver 0 0 0 0 0 0 0 0 100

Black-headed Oriole 23 0 47 30 0 0 0 0 0

Blue Winged Parakeet 0 0 6 0 0 0 0 94 0

Chestnut-Headed Bee-eater

94 6 0 0 0 0 0 0 0

99

Species name

Salli

er

Poun

cer

Folli

age

glea

ner

Woo

d gl

eane

r

Woo

d pr

ober

Gro

und

carn

ivor

e

Nec

tari-

vore

Frug

i-vo

re

Gar

ni-

vore

eater

Common Hoopoe 0 0 0 0 0 100 0 0 0

Common Myna 0 0 0 0 0 0 0 69 31

Heart-Spotted Woodpecker

0 0 0 7 93 0 0 0 0

Indian Tailor Bird 0 0 94 0 0 6 0 0 0

Jungle Babbler 3 0 0 15 0 82 0 0 0

Jungle Myna 0 0 0 0 0 0 0 75 25

Racket-tailed Drongo 94 6 0 0 0 0 0 0 0

Red-vented Bulbul 0 0 0 0 0 6 23 34 37

Red-whiskered Bulbul 0 0 0 0 0 0 12 32 56

Scarlet Minivet 21 0 34 45 0 0 0 0 0

Spotted Dove 0 0 0 0 0 0 0 0 100

Plum -headed Parakeet 0 0 2 0 0 0 0 98 0

Whitebrowed Fantail Flycatcher

98 2 0 0 0 0 0 0 0

Whiteheaded Babbler 2 0 0 12 0 86 0 0 0

Yellowfronted Pied Woodpecker

0 0 0 2 98 0 0 0 0

Yellownaped Woodpecker

0 0 0 6 94 0 0 0 0

Yellowthroated Sparrow 0 0 0 0 0 0 0 0 100

Specialist Index

Out of the three specialization, highest was observed in foraging method

followed by foraging substrate and foraging height in the evergreen forest (Table

5.10). Common Hoopoe was observed as specialist in all the three categories, as

their J’ values are ‘0’. White-headed Babbler was specialist in foraging height and

foraging method.

100

Table 6.10. Extent of specialization of birds in foraging height, foraging substrate and foraging method as shown by J' values in evergreen forest (J' values ranges from 0 -1, specialist are in bold)

Foraging height

Foraging method

Foraging substrate Species name

H' J' H' J' H' J'

Ashy Wren Warbler 1.29 0.56 0.50 0.22 0.06 0.03

Baya Weaver 1.00 0.43 1.07 0.46 0.00 0.00

Black-headed Oriole 1.50 0.65 0.33 0.14 1.05 0.54

Blossom-headed Parakeet 0.96 0.42 0.54 0.23 0.10 0.05

Chestnut-Headed Bee-eater 2.00 0.87 0.56 0.24 0.23 0.12

Common Hoopoe 0.00 0.00 0.00 0.00 0.00 0.00

Common Myna 1.75 0.76 0.00 0.00 0.62 0.32

Heart-Spotted Woodpecker 1.14 0.49 0.00 0.00 0.25 0.13

Indian Tailor Bird 1.28 0.56 0.61 0.27 0.23 0.12

Jungle Babbler 0.69 0.30 0.00 0.00 0.55 0.28

Jungle Myna 1.41 0.61 0.00 0.00 0.56 0.29

Malabar Parakeet 1.64 0.71 0.37 0.16 0.23 0.12

Racket-tailed Drongo 1.24 0.54 0.53 0.23 0.35 0.18

Red-vented Bulbul 1.12 0.49 0.95 0.41 1.24 0.64

Red-whiskered Bulbul 1.13 0.49 1.02 0.44 0.94 0.49

Scarlet Minivet 1.54 0.67 0.50 0.22 1.05 0.54

Spotted Dove 1.05 0.46 0.10 0.04 0.00 0.00

Whitebrowed Fantail Flycatcher 1.30 0.57 0.40 0.18 0.10 0.05

Whiteheaded Babbler 0.00 0.00 0.00 0.00 0.46 0.24

Yellowfronted Pied Woodpecker 1.21 0.53 0.00 0.00 0.10 0.05

Yellownaped Woodpecker 1.19 0.52 0.00 0.00 0.23 0.12

Yellowthroated Sparrow 1.04 0.45 0.33 0.14 0.00 0.00

H’- Diversity index, J’ – Specialist index

101

Determination of foraging guilds

The guild formed in the evergreen forest based on the use of substrates,

method and height and their relationship among the 22 species of birds are

summarized in the cluster dendrogram (Fig. 6.2). The species are separated into a

number of distinct groups, which exploit their food resources from similar substrates.

Fig. 6.2. Cluster dendrogram showing interspecific relationship of 22 species in the evergreen based on multivariate analysis of foraging method, foraging substrate and foraging height

102

6.3.3. Foraging patterns of bird species in Teak Plantation Foraging height (in meter)

Nine height categories such as ground, 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7 and 7-

8 m with 28 species of birds were observed in the teak plantation (Table 6.11).

The foliage was apportioned between the 3 layers of strata viz., ground (0 m),

shrub and short trees (0 - 2 m) and tree (> 2 m). Five species, such as Grey Jungle

Fowl, Spotted Dove, Common Hoopoe, White-headed Babbler and Jungle Babbler

foraged mainly on the ground (Table 6.11).

Twenty three species utilized the 0 - 2 m height, out of these Thickbilled

Warbler and Nilgiri Flowerpecker were dominantly represented (Table 6.11). The tree

layer (> 2 m) height category was used by twenty six species of birds (Table 6.11).

Foraging substrate

Seven substrates were categorized in the teak plantation, namely, ground,

trunk, foliage, twigs, flower, fruit and air (Table 6.12).

Ground: Eight species of birds were recorded in this guild. They were Grey Jungle

Fowl, Spotted Dove, Common Hoopoe, Common Myna, Jungle Myna, White-headed

Babbler, Jungle Babbler and Yellow-throated Sparrow (Table 6.12).

Trunk: Four species of birds were found in the trunk substrate. They are

Yellownaped Woodpecker, Yellowfronted Pied Woodpecker, Heartspotted

Woodpecker and Black headed Oriole (Table 6.12).

Foliage: Ashy Wren Warbler and Indian Tailor Bird highly prevalent in this guild

(Table 6.12).

Twigs: Three species were noted in this guild, namely, White browed Fantail

Flycatcher, Paradise Flycatcher and Baya Weaver (Table 6.12).

103

Flower and Fruit: Four species, such as Malabar Parakeet, Blossom-headed

Parakeet, Red-vented Bulbul and Red-whiskered Bulbul occupy this substratum

(Table 6.12).

Air: Insectivore species like Chestnut-headed Bee-eater, Green Bee-eater, White-

bellied Drongo, Racket-tailed Drongo were found to resort to this substratum (Table

6.12).

Foraging methods

Nine foraging methods were noted for birds in the teak plantation. The major

prey attack manoeuvores used by birds in the plantation were sallying, pouncing,

foliage-gleaning, wood gleaning, wood probing, carnivores, nectar exploiting, fruit

exploiting and grain exploiting (Table 6.13).

Sallying: Seven species of birds were recorded as salliers, namely, Chestnut-

headed Bee eater, Green Bee eater, White bellied Drongo, Racket tailled Drongo,

Common Iora, Whitebrowed Fantail Flycatcher and Paradise Flycatcher (Table 6.13).

Pouncing: Six species of birds found to be pouncers (Table 6.13).

Foliage gleaning: Eleven species of birds were observed in this guild and mainly

warblers and flycatcher used this method (Table 6.13).

Wood gleaning: Three species of birds constituted the wood gleaning guild. They

were Yellow-napped Woodpecker, Yellow-fronted Pied Woodpecker and Heart-

Spotted Woodpecker (Table 6.13).

Wood probing: Only Woodpeckers found to use this foraging method (Table 6.13).

Ground Carnivores: Hoopoe, White headed Babbler and Jungle Babbler were

observed under this guild (Table 6.13).

104

Fruit exploiting: Nine species found in this group, namely, Blossom headed

Parakeet, Malabar Parakeet, Black headed Oriole, Red vented Bulbul, Red

whiskered Bulbul, Common Myna and Jungle Myna (Table 6.13).

Seed exploiting: Four species were completely (100%) seed exploiters. They were

Grey Jungle Fowl, Spotted Dove, Yellow throated Sparrow and Baya Weaver

(Table 6.13).

Table 6.11. Height distribution of birds in teak plantation based on percentage of prey attacks

Foraging height (m) Species name/Guild

G 1 2 3 4 5 6 7 8 Ashy Wren Warbler 0 9 18 29 32 12 0 0 0 Baya Weaver 0 0 0 0 0 5 15 32 48Black-headed Oriole 0 0 6 29 17 47 1 0 0 Blossom-headed Parakeet 0 70 0 0 0 0 0 23 7 Chestnut-Headed Bee-eater 3 8 12 14 18 22 11 12 0 Common Hoopoe 100 0 0 0 0 0 0 0 0 Common Iora 0 2 24 49 22 3 0 0 0 Common Myna 1 14 22 31 14 12 4 2 0 Green Bee-eater 0 19 0 0 47 22 0 0 12Grey Jungle Fowl 100 0 0 0 0 0 0 0 0 Heart-Spotted Woodpecker 0 2 45 34 18 1 0 0 0 Indian Tailor Bird 0 15 23 25 12 25 0 0 0 Jungle Babbler 90 8 2 0 0 0 0 0 0 Jungle Myna 0 0 43 15 31 10 1 0 0 Malabar Parakeet 0 4 8 6 8 43 15 11 5 Nilgiri Flowerpecker 0 12 34 16 32 6 0 0 0 Paradise Flycatcher 0 0 2 50 48 0 0 0 0 Racket-tailed Drongo 0 1 16 41 19 22 1 0 0 Red-vented Bulbul 0 55 23 12 10 0 0 0 0 Red-whiskered Bulbul 0 45 22 12 21 0 0 0 0 Spotted Dove 55 23 20 2 0 0 0 0 0 Thick-billed Warbler 0 3 32 23 30 12 0 0 0 White-bellied Drongo 0 5 13 11 37 32 2 0 0 Whitebrowed Fantail Flycatcher 0 0 12 18 12 32 26 0 0 Whiteheaded Babbler 78 22 0 0 0 0 0 0 0 Yellowfronted Pied Woodpecker 0 0 15 32 45 8 0 0 0 Yellownaped Woodpecker 0 0 25 18 35 18 2 2 0 Yellowthroated Sparrow 0 0 0 0 0 0 33 47 20

105

Table 6.12. Use of substrate (%) by birds in the teak plantation

Species name Ground Trunk Foliage Twigs Flower Fruit Air

Ashy Wren Warbler 0 0 100 0 0 0 0

Baya Weaver 0 0 30 20 50 0 0

Black-headed Oriole 0 100 0 0 0 0 0

Blue winged Parakeet 0 0 0 0 23 77 0

Chestnut-Headed Bee-eater

0 0 10 0 0 0 90

Common Hoopoe 100 0 0 0 0 0 0

Common Iora 0 0 0 0 99 1 0

Common Myna 100 0 0 0 0 0 0

Green Bee-eater 0 0 15 0 0 0 85

Grey Jungle Fowl 100 0 0 0 0 0 0

Heart-Spotted Woodpecker

0 100 0 0 0 0 0

Indian Tailor Bird 0 0 100 0 0 0 0

Jungle Babbler 100 0 0 0 0 0 0

Jungle Myna 100 0 0 0 0 0 0

Nilgiri Flowerpecker 0 0 75 0 15 10 0

Paradise Flycatcher 0 0 11 20 69 0 0

Plum -headed Parakeet

0 0 0 0 2 98 0

Racket-tailed Drongo 0 0 0 0 0 0 100

Red-vented Bulbul 2 12 0 0 74 12 0

Red-whiskered Bulbul 0 25 2 0 20 53 0

Spotted Dove 100 0 0 0 0 0 0

Thick-billed Warbler 0 0 90 0 10 0 0

White-bellied Drongo 0 0 0 0 0 0 100

Whitebrowed Fantail Flycatcher

0 0 74 12 14 0 0

Whiteheaded Babbler 100 0 0 0 0 0 0

Yellowfronted Pied Woodpecker

0 100 0 0 0 0 0

Yellownaped Woodpecker

0 100 0 0 0 0 0

Yellowthroated Sparrow

80 20 0 0 0 0 0

106

Table 6.13. Prey attack manoeuvores (%) by birds in teak plantation

Species name

Salli

er

Poun

cer

Folli

age

glea

ner

Woo

d gl

eane

r

Woo

d pr

ober

Gro

und

carn

ivor

e

Nec

tari-

vo

re

Frug

i-vo

re

Gar

ni-

vore

Ashy Wren Warbler 0 0 92 0 0 8 0 0 0

Baya Weaver 0 0 0 0 0 0 0 0 100

Black-headed Oriole 0 0 33 0 0 0 0 77 0

Blue winged Parakeet 0 0 4 0 0 0 0 96 0

Chestnut-Headed Bee-eater 93 7 0 0 0 0 0 0 0

Common Hoopoe 0 0 0 0 0 100 0 0 0

Common Iora 0 0 36 0 0 0 0 64 0

Common Myna 0 0 0 0 0 0 0 26 74

Green Bee eater 99 1 0 0 0 0 0 0 0

Grey Jungle Fowl 0 0 0 0 0 0 0 0 100

Heart-Spotted Woodpecker 0 0 0 16 84 0 0 0 0

Indian Tailor Bird 0 0 94 0 0 6 0 0 0

Jungle Babbler 0 0 0 0 0 100 0 0 0

Jungle Myna 0 0 0 0 0 0 0 14 86

Nilgiri Flowerpecker 0 0 88 0 0 0 0 12 0

Paradise Flycatcher 5 6 89 0 0 0 0 0 0

Plum -headed Parakeet 0 0 2 0 0 0 0 98 0

Racket-tailed Drongo 88 12 0 0 0 0 0 0 0

Red-vented Bulbul 0 0 0 0 0 0 0 87 13

Red-whiskered Bulbul 0 0 0 0 0 0 0 88 12

Spotted Dove 0 0 0 0 0 0 0 0 100

Thick-billed Warbler 0 0 98 0 0 2 0 0 0

White-bellied Drongo 81 19 0 0 0 0 0 0 0

Whitebrowed Fantail Flycatcher

12 16 72 0 0 0 0 0 0

Whiteheaded Babbler 0 0 0 0 0 100 0 0 0

Yellowfronted Pied Woodpecker 0 0 0 14 86 0 0 0 0

Yellownaped Woodpecker 0 0 0 82 18 0 0 0 0

Yellowthroated Sparrow 0 0 0 0 0 0 0 0 100

107

Specialist Index

Out of the three specialization, highest was observed in foraging method

followed by foraging substrate and foraging height in Plantation (Table 6.14). Grey

Jungle Fowl and Common Hoopoe can be considered as specialist in all the three

categories, as their J’ values are ‘0’. Spotted Dove, White-headed Babbler and

Jungle Babbler were specialists in foraging height and foraging method.

Table 6.14. Extent of specialization of birds in foraging height, foraging substrate and foraging method as shown by J' values in teak plantation (J' values ranges from 0 -1, specialist are in bold)

Foraging height

Foraging method Foraging substrate

Species name H' J' H' J' H' J'

Ashy Wren Warbler 1.50 0.65 0.00 0.00 0.28 0.12 Baya Weaver 1.15 0.50 1.03 0.53 0.00 0.00 Black-headed Oriole 1.23 0.53 0.00 0.00 0.61 0.27 Blue winged Parakeet 1.74 0.76 0.54 0.28 0.17 0.07 Chestnut-Headed Bee-eater 1.98 0.86 0.33 0.17 0.25 0.11 Common Hoopoe 0.00 0.00 0.00 0.00 0.00 0.00 Common Iora 1.21 0.53 0.06 0.03 0.65 0.28 Common Myna 1.75 0.76 0.00 0.00 0.57 0.25 Green Bee-eater 1.26 0.55 0.42 0.22 0.06 0.02 Grey Jungle Fowl 0.00 0.00 0.00 0.00 0.00 0.00 Heart-Spotted Woodpecker 1.16 0.50 0.00 0.00 0.44 0.19 Indian Tailor Bird 1.57 0.68 0.00 0.00 0.23 0.10 Jungle Babbler 0.38 0.16 0.00 0.00 0.00 0.00 Jungle Myna 1.29 0.56 0.00 0.00 0.40 0.18 Nilgiri Flowerpecker 1.45 0.63 0.73 0.38 0.37 0.16 Paradise Flycatcher 0.78 0.34 0.82 0.42 0.42 0.18 Plum -headed Parakeet 0.77 0.34 0.10 0.05 0.10 0.04 Racket-tailed Drongo 1.40 0.61 0.00 0.00 0.37 0.16 Red-vented Bulbul 1.15 0.50 0.81 0.42 0.39 0.17 Red-whiskered Bulbul 1.27 0.55 1.08 0.56 0.37 0.16 Spotted Dove 1.07 0.46 0.00 0.00 0.00 0.00 Thick-billed Warbler 1.42 0.62 0.33 0.17 0.10 0.04 White-bellied Drongo 1.47 0.64 0.00 0.00 0.49 0.21 Whitebrowed Fantail Flycatcher 1.53 0.67 0.75 0.39 0.78 0.34 Whiteheaded Babbler 0.53 0.23 0.00 0.00 0.00 0.00 Yellowfronted Pied Woodpecker 1.21 0.53 0.00 0.00 0.40 0.18 Yellownaped Woodpecker 1.49 0.65 0.00 0.00 0.47 0.20 Yellowthroated Sparrow 1.04 0.45 0.50 0.26 0.00 0.00

H’- Diversity index, J’ – Specialist index

108

Determination of foraging guilds

The guild in the teak plantation based on the substrates, method and height

used and their relationship among the 28 species are summarized in the cluster

dendrogram (Fig. 6.3). The bird species were separated into a number of distinct

groups, which exploited their food resources from similar substrates.

Fig. 6.3. Cluster dendrogram showing interspecific relationship of 28 species in the plantation based on multivariate analysis of foraging method, foraging substrate and foraging height

109

6.4. Discussion

Bird community studies employing guild analysis frequently involve circular

reasoning. From many foraging axes a few were subjectively chosen for

quantification. The relevancy of axes depends upon the observers knowledge of the

organisms studied. As a result of defining this foraging axe, species were divided into

different guilds. The subsequent analysis could yield meaningful information about

community organization, but only to the extent that chosen axes were important in

real life species interaction. Typically in community studies overlap in resources were

quantified and patterns of partitioning elucidated, with competition evoked as a

causative mechanism.

Eventhough the species broadly overlap, which forage in similar ways or

exploit the same substrates, were grouped together. By organizing the species within

a community into groups a picture of community organization or structure emerges

which can be compared with communities in other types of forest or on other

continents. In this way it is possible to identify the important resources for birds, to

detect the communities where the basic structure might have been disturbed by

human activities and compare the patterns of evolution among the communities. The

hierarchical and schematic groupings are useful in summarizing the ways in which

(moist deciduous forest, evergreen forest and teak plantation) birds forage for food in

different habitats and which resources are important for the survival of particular

species.

In addition to understanding the species composition of the assemblages, it is

essential to find out how they utilize the resources available by partitioning these

effectively in order to reduce the competition and co-exist peacefully (Cody, 1974).

Assuming that the food is an important limiting resource (Lack, 1966 and Cody,

1974) it can be proposed based on the present study that communities should be

structured on the basis of how food is partitioned and that the species should differ in

110

physical or behavioural characteristics resulting in different food utilization. Foraging

method is specialized because it is depending on the morphological features, which

have been evolved over a long period. Many species fed from the different strata

and positions in the canopy layer with others who were specialists.

In many ecological studies, communities have been divided into guilds (Root,

1967). As grouping members are the most likely potential competitors, it is

appropriate to study the competitive interactions and resource partitioning within a

guild frame work (Feinsinger, 1976 and Pearson, 1977). The guild analysis in the

community studies frequently involves circular reasoning. Many foraging axes are

subjectively chosen for quantification. The relevancy of axes depends upon the

observer’s knowledge of the organisms studied (Landers and MacMahon, 1980).

Foraging method, foraging substrate and foraging height were studied to understand

the foraging pattern of birds in the moist deciduous forest, evergreen forest and teak

plantation.

Among the bird species recorded in the moist deciduous forest, evergreen

forest and teak plantation, four major groups were recognised based on the food

eaten, namely, insectivore, nectarivores, granivores, and frugivores. The important

factors dividing the bird community into the foraging guilds relate to the physical

structure of the habitats. The height and height related characteristics separate the

ground foragers from all other species. There are four major foraging environments in

the different habitats at Parambikulam Wildlife Sanctuary (forest floor, shrub, tree and

air).

Four substrates such as air, ground, wood, foliage and nectar/seed/fruit are

known in the moist deciduous forest, evergreen forest and teak plantation. It can be

further reduced into air, ground and plant. A large number of bird species fall under

the plant guild because plant offers a greater variety of microhabitats for the birds to

find suitable food for them. In the moist deciduous forest, wood was utilized by more

111

number of birds, it could be due to the fact that wood provides larger provision for

suitable food. In addition to this, most of tall trees drop their leaves during the dry

season which enables better visibility of prey.

A total of nine foraging methods were used by birds in different habitats at

Parambikulam Wildlife Sanctuary. Wood probing was recognized as the major

method for Woodpeckers in all the habitats. Searching patterns are largely a function

of the morphological and perceptual traits of each species, which allow the birds to

move through the foliage, locate, detect and capture the prey in specific ways. The

feeding methods are more specialized in each species notwithstanding the habitat

structure. Resource partitioning reduces the effect of competition by decreasing the

amount of overlap between the competing species (Wiens, 1989). The incidence of

overlap surrounded by potential competitors may be used to assess the extent of

resource partitioning on the niche dimensions. All the birds in these habitats

overlapped with other dimensions or exploited different categories of food with

overlapping microhabitat and method. It can be said that partitioning of foraging

dimensions among the birds occurred in different habitats which are comparable with

earlier studies (Recher and Holmes, 1985; Wheeler and Calver, 1996). The guild

structure of this community is suggested to result from a division of broad adaptive

strategies into detailed strategies, from which species may be divided into guilds

based on the patterns of microhabitat foraging preferences. Ecological partitioning in

the community can be attributed mostly to differing adaptive strategies among guilds,

indicative of evolutionary commitment to the physical structure of the habitats

(Holmes et al., 1979).

The analysis of the guild structure in this community helped to clarify the

functional relationships of species and thus interpretation of ecological process of

coexistence. Foliage gleaners exhibit a narrow range of foraging behaviours, but

overlap species in other guilds have extensive range due to their distinctive foraging

112

technique and food site and this overlap may be probably ecological unimportant.

Determinants of community organization have been investigated recently by studies

of similar disjunctive habitats. The resource axes found to be important in avian

communities (Cody, 1975). The patterns of community changes may be viewed as

shifts in the number and composition of species. Communities change in their

structure over time and between geographic locations. Quantifying changes in the

number of species per guild may provide how resources are used in different

communities (Orians, 1969).