SPATIO-TEMPORAL PATTERNS OF NESTING WITHIN A BREEDING COLONY OF GUDAVI BIRD SANCTUARY IN WESTERN GHAT REGION OF KARNATAKA

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1 2 (2) : , 2008 SPATIO-TEMPORAL PATTERNS OF NESTING WITHIN A BREEDING COLONY OF GUDAVI BIRD SANCTUARY IN WESTERN GHAT REGION OF KARNATAKA G.Y. DAYANANDA,* A. NAVEED, K.L. NAIK AND B.B. HOSETTI Department of P.G. Studies and Research in Applied Zoology, Bio-Sciences Complex, Jnana Sahyadri, Shankaraghatta , Shimoga dayananda_gy@yahoo.co.in ABSTRACT INTRODUCTION Many species aggregate for feeding, roosting or nesting behavior which are especially prevalent among waterbirds. Factors commonly identified to explain aggregations are the spatial availability of food and defense against predators (Brown et al., 1990). Other studies suggest that ectoparasitism and abiotic factors (tidal level, precipitation etc) affect habitat quality and may become a dominant force influencing aggregation behavior in birds (Boulinier and Lemel, 1996) the interaction between these factors could affect reproductive success and it could explain its inter annual variation in the same place. A large population of nesting birds and competition for nest sites may lead to high nesting density. Because nests located on the periphery of a colony are more exposed to predation, birds nesting in relatively smaller colonies are more likely to experience a greater predation risk (Brown et al., 1990). A large colony may benefit in terms of food acquisition due to the increase in the number of breeding pairs that can provide information of food availability. Large colonies are believed to have a tendency to grow indefinitely. However, excessive growth of a colony causes a decrease in the populations breeding rate due to intensive competition, mainly for nest sites (Parrish, 1995). The ideal size of colonies will vary among species and habitat. The response of wild populations to their resources is not always predictable because of the outcome of a number of interacting factors, which may go since a single until multiple factors. Food scarcity often leads to foraging in distant areas, which may result in formation of small colonies or the division of populations breeding period. Strong seasonal peaks in food resources may limit breeding to a single season of the year and cause synchronized breeding of the population. In these cases, large colonies are formed and intense competition for food occurs. Competition might be lessened by a strategy of fine-scale temporal and spatial segregation in the use of habitat among species with similar feeding habits (Hill and Lein, 1989). This paper deals with the study of temporal and spatial patterns of nesting by five species of water birds at a breeding colony of Gudavi. Specifically, we document and compare the number of breeding pairs in each population during the time of stay in the colony, the temporal period of breeding and height of nests. We also discuss the implications of these results regarding the factors that may explain the patterns of temporal segregation between Breeding colonies of Anhinga melanogaster, Phalacrocorax niger, Nycticorax nycticorax, Ardea purpurea and Platalea leucorodia were monitored during 2001 to 2003 for number of breeding pairs, beginning of the breeding period and during peak of nesting. Similarities and dissimilarities in these three parameters were analyzed to explain temporal and spatial patterns of nesting within the colony. A temporal segregation occurred between the two greatest populations of Nycticorax nycticorax and Phalacrocorax niger. The reproductive temporal sequence observed was Nycticorax nycticorax, Phalacrocorax niger, Anhinga melanogaster, Ardea purpurea and Platalea leucorodia. Such sequence may be due to the fact that more piscivorous species breed during low water period. The analysis of nests locations showed a vertical stratification of the populations. These results support the notion of species that overlap temporally, segregate vertically in their nest location. Reproductive success of the studied populations was similar to results found in temperate regions. It is suggested that the temporal and vertical structure of the breeding colony is associated with the local structure of the vegetation. KEY WORDS Breeding colony Spatial and temporal pattern Reproductive success Nesting Gudavi sanctuary Received : Revised : Accepted : *Corresponding author 143

2 G.Y. DAYANANDA et al., reproductive populations and differences among species for nest sites. MATERIALS AND METHODS Gudavi bird sanctuary is one of the well known bird sanctuaries of Karnataka, with notification, AHFF-262-fwl 86/ on 10:07:1989. It is located at 13 km away from Sorab city and 0.5 km away from Gudavi village. This sanctuary occupies the water spread area of about 33 ha, in rainy season, out of the total ha (Map 1). There are three wetlands and were connected in series such as Kallambi, Vaddekere and Gudavi ponds. The rainfed water from Kallambi flows for a distance of 2 km through irrigation channel and enters into the Vaddekere. The outflow of water from Vaddekere enters into Gudavi pond, from their it is again used for irrigation at the downstream croplands. Vaddekere and Gudavi ponds are separated by a common bund. The sanctuary lies between latitude 14 o 25' 59" to 14 o 26' 41" and longitude 75 o 6' 43" to 75 o 25' 28". Map 1: Gudavi Bird Sanctuary Vegetation The entire area was covered with dense moist deciduous forest and due to intensive protection efforts by the Forest Department, the area has maintained greenery. Apart from thi s, Gudavi sanctuary embodies diversif ied vegetation that favors the migratory birds to take shelter and provides the space to construct their nests during breeding. The vegetation of GBS comprised of marshy plants and microphytes. The trees and shrubs partially submerged and provide suitable nesting grounds for birds. These nesting sites also provide the highest security from the predators. Methods The present study was carried out for three successive breeding seasons of 2001, 2002 and 2003 from June to November every year. The systematic censuses were conducted to monitor the number of breeding pairs and nests at the site with 5x50 binoculars and available field guides (Sonobe and Usui, 1993; Salim Ali, 1996). The methods used to estimate the number of nests depend on how a species responds to the presence of humans (Tremblay and Ell ison, 1979). Populati ons of species accustomed to humans were accurat ely estimated by walking through the colony and counting marked individuals. Those distributed by the presence of humans were estimated by watching the nest and count ing individuals from a distance. Methods were combined in order to best score nests within the colony. Average number of nests observed over all days to be used estimates the population size of breeding birds. The number of active nests was multiplied by two to determine the total number of birds (Custer and Osborn, Table 1: Aspects of the breeding biology and development of eggs and nestlings for five species breeding in the colony Breeding Variables Anhinga melanogaster Phalacrocorax niger Nycticorax nycticorax Ardea purpurea Platalea leucorodia Population size 43 pairs 250 pairs 160 pairs 18 pairs 8 pairs Beginning of breeding June June July June August Location of nests Fork of emergent trees Fork of emergent trees Platform of twigs Fork of emergent trees Platform of twigs Mean height of nests(m) 8.71± 2.23(n=10) 5.94 ± 1.38(n=15) 2.03 ± 0.66(n=24) 6.22 ± 1.13(n=10) 5.95 ± 1.18(n=6) Laying eggs per pair 3.6 ± 0.52(n=10) 4.1 ± 0.74(n=10) 3.4 ± 0.52(n=10) 2.7 ± 0.48(n=10) 3.57 ± 0.53(n=7) Hatched eggs per pair 3.7 ± 0.67(n=10) 4.1 ± 0.74(n=10) 3.3 ± 0.67(n=10) 2.3 ± 0.48(n=10) 2.4 ± 0.55(n=5) Number of young 1.9 ± 0.57(n=10) 3.5 ± 1.08(n=10) 2.1 ± 0.57(n=10) 1.4 ± 0.52(n=10) 1.8 ± 0.45(n=5) 144

3 SPATIO-TEMPORAL PATTERNS OF NESTING Table 2: Comparison of nest height (Mean ± SD) among five species of water birds breeding at Gudavi Bird Sanctuary Species Height of No. of nest nest (m)* observed Anhinga melanogaster 8.71 ± 2.23 a 10 Phalacrocorax niger 5.94 ± 1.36 b 10 Nycticorax nycticorax 2.03 ± 0.67 c 12 Ardea purpurea 6.22 ± 1.13 b 10 Platalea leucorodia 5.95 ± 1.18 b 6 F -value: (p=0.0001) * The superscript of letter represent the means with the same letter are not significantly different at p= 0.05 (Tukey class) 1978). Only nests with eggs or nestlings were considered active. The height of nests was measured from the nest to the ground and for all species in the colony. The number of eggs laid and number of young fledged were recorded. Censuses were performed twice a week over of the breeding season observed in the colony. RESULTS Temporal pattern of breeding The colony occupied in 2 ha area (Vaddekere) within the moist deciduous forest and the nests were generally concentrated within a site. Based of nests classes a total of 1848 individuals were estimated for the five species present in the colony. The number of breeding individuals varied widely from 615 Phalacrocorax niger to 6 Platalea leucorodia (Fig 2). Breeding occurred between June and November. The total colony breeding season lasted six months, with the average stay of each species four months. Although there was considerable overlap in breeding phenology, the most common species Phalacrocorax niger and Nycticorax nycticorax bred largely at different times (Fig 2). The other three species overlapped with both Nest height (m) Am Pn Nn Ap Pl Species Figure 1: Average nest height of water birds breeding at Gudavi Bird Sanctuary Am - Anhinga melanogaster, Pn - Phalacrocorax niger, Nn - Nycticorax nycticorax, Ap - Ardea purpurea and Pl - Platalea leucorodia Am Am - Anhinga melanogaster, Pn - Phalacrocorax niger, Nn - Nycticorax nycticorax, Ap - Ardea purpurea and Pl - Platalea leucorodia Figure 2: Average number of bird population breeding at Gudavi Bird Sanctuary Phalacrocorax niger and Nycticorax nycticorax. There appears to be a temporal separation between the two largest breeding populations. Spatial stratification of nests Vertical placement of nests differed among the five species (F=32.39) and formed three groups distinct (Table 2). Phalacrocorax niger, Platalea leucorodia and Ardea purpurea nests height did not differ, with most nests being placed at heights from 5.94 to 6.22 m. The Anhinga melanogaster placed their nests higher in the foliage, generally 8.71 m high (Table 2). Anhinga melanogaster placed their nests preferentially in the canopy, on the open platforms formed at the top of the trees covered by the leaves. Ardea purpurea, occupied the same height as 6.22 (Fig 2), but placed their nests in branched forks located immediately under emergent trees. Phalacrocorax niger occupied the forks formed by the branches below tree tops with leaves. Platalea leucorodia and Nycticorax nycticorax nested on Kirganelia mats, at a lower height, just above water surface levels. Reproductive effort and success The average number of eggs laid by each species varied from 2.7 to 4.1 (Table 1). The average number was 3.6 for Anhinga melanogaster, 4.1 for Phalacrocorax niger 3.3 for Nycticorax nycticorax, 2.3 for Ardea purpurea and 2.4 for Platalea leucorodia respectively. The average number of nestlings survived in this colony was 1.9 for Anhinga melanogaster 3.5 for Phalacrocorax niger, 2.6 for Nycticorax nycticorax, 1.4 for Ardea purpurea and 1.8 for Platalea leucorodia respectively. The loss of nestlings averaged 48% for Anhinga melanogaster, 15% Phalacrocorax niger, 22% for Nycticorax nycticorax, 40% Ardea purpurea and 25% Platalea leucorodia. DISCUSSION Temporal segregation was found in between the species that breed in the study area. Rodgers Jr (1980) suggested that asynchronous nest building phases of bird is reflecting on the breeding cycle. Frederick and Collopy (1989) have shown a strong difference for the nesting chronology of four species (Casmerodius albus, Egretta tricolor, Egretta Pn Nn Ap Pl 145

4 G.Y. DAYANANDA et al., caerulea and Eudocimus albus) in Florida. They discussed the possibility that such results could be artifacts from the sampling period, since water level and rainfall data did correlate with the differences among nest initiations. Presumably this would be associated with other variables, such as temperature, prey activity and reproductive cycle. Food or space-nest limitations might be expected to lead to asynchronous breeding behavior, especially for conspecifics that overlap more closely in food and nesting characteristics. However, temporal segregation may also occur due to different peaks in the availability of food items used by nesting species within a colony. In relation to population size in the colony, differences in the numbers of pairs were observed. Availability of food or environmental conditions may explain variance in the number of individuals breeding both within and among colonies. Anthropogenic changes are expected to affect the breeding colonies of bird species and the food density was closely related to the reproductive success of Ciconiformes (Erwin et al., 1996). The results showed a temporal segregation among species of the breeding colony. All the five species were bred during the time when the water levels were at the highest. Reduced water levels likely to facilitate food acquisition by these species. Anhinga melanogaster, Phalacrocorax niger and Ardea purpurea bred at the beginning of the rainy period. The temporal segregation for these species is not likely to be due to prevalent food competition. Instead, limitation of nesting space differences during breeding period. The asynchrony is probably due to temporary differences in food availability caused by large territories that decrease colony space availability ( Rodgers. Jr, 1980). The nests of Egretta thula and Bulbucus ibis showed average nests height from 2.04 m to 2.59 (Maxwell and Kale, 1977). Results of this work support the notion that species that overlap temporally in breeding, also segregate vertically in nest placement within the colony. Anhinga melanogaster and Phalacrocorax niger occupied the same nest height within the colony and breed at same time. Vegetation structure at a site may influence nest placement within the colony, so dense vegetation could retrain large birds from build in their nest deep in the canopy. The Anhinga melanogaster and Phalacrocorax niger occupied same height for placing the nests, and Ardea purpurea had nests located, higher in the canopy when compared to the others. The absence of statistical differences among herons in the Gudavi colony was likely due to the fact that these observations occurred in a colony located in other vegetation, characterized by a uniform environment with a low height and diversity of species. The vegetation structure can be an important factor in the placement of nests in the colony area and associated with food supply and density, may also influence reproductive success (Cezilly et al., 1995). On the other hand, the results obtained in this research may be reflecting the small sample size. According to Maxwell and Kale (1977), eggs laid during the incubation phase were of 28.8% for Egretta thula (n=186), 30.9% for Bulbucus ibis (n=73) and 33.3% for Casmerodius albus (n=28) respectively. Hence, results from the present study in south India are comparable to those from temperate areas. Avian clutch size is likely to be influenced by a species evolutionary history, where as mortality of eggs and young is probably varies according to local environmental conditions, nest collapse or predation (Brown et al., 1990). The competition and nest location as limiting factors responsible for the low breeding success of heron species. For the other species these factors may result in an increase of the survival rate, as is shown in Phalacrocorax niger and Nycticorax nycticorax, considering that these species maintain a clear temporal segregation. On the other hand, food may be an important resource to the reproductive success in Ciconiformes (Erwin, 1996). Thus, the temporal nesting segregation of species during the breeding season within and individual colony may have influenced the increase of breeding success in the two larger populations which nest at the same height. The results of this study of the reproductive success, spatial stratification of nests and temporal pattern of breeding suggest that the facility of food acquisition considering the low water level and prey activity and availability of nest site due to the vegetation structure, leads to an optimization of the colony area. Phalacrocorax niger and Nycticorax nycticorax have consequently obtained a slightly higher nesting success when compared to Platalea leucorodia, Ardea purpurea and Anhinga melanogaster, possibly due to temporal segregation. SUMMARY The systematic censuses were conducted to monitor the number of breeding pairs and nests viz. Darter (Anhinga melanogaster), Little Cormorant (Phalacrocorax niger), Night Heron (Nycticorax nycticorax), Purple Heron (Ardea purpurea) and Spoonbill (Platalea leucorodia). Documented and compared the number of breeding pairs in each population during the time of breeding season and temporal period, height of nests and reproductive success. Availability of food or environmental conditions may explain variance in the number of individuals breeding both within and among colonies. All the five species were bred during the rainy season. The temporal segregation for these species is not likely to be due to present day food competition. The competition and nest location as factors responsible for the low breeding success of these species and food may be an important limiting factor to the reproductive success. The reproductive success, spatial stratification of nests and temporal pattern of breeding suggest that the facility of food acquisition considering the low water level and prey activity and availability of 146

5 SPATIO-TEMPORAL PATTERNS OF NESTING space due to the vegetation structure, leads to an optimization of the breeding colony. REFERENCES Ali, S The book of Indian birds. Oxford University Press, Bombay. Barta, Z and T. Szep Frequency dependent selection on information transfer strategies at breeding colonies: a simulation study. Behavioral Ecology. 6(3): Boulinier, T and J.Y. Lemel Spatial and temporal variations of factors affecting breeding habitat quality in colonial birds: some consequences for dispersal and habitat selection. Acta Ecologica, 17(6): Brown, C.R., B.J. Stutchbury, and P.D. Walsh Choice of colony size in birds. Trends in Ecology and Evolution, 12(5): Cezilly, F.V., R.E. Boy, Green, G.J.M. Hirons and A.R. Johnson Interannual variation in great flaming breeding success in relation to water levels. Ecology, 1(76): Custer, T.W and R.G. Osborn Feeding habitat use by colonially breeding herons, egrets and ibises in north Carolina. Auk, 95: Erwin, R.M Reproductive success, growth and survival of black-crowned night-heron (Nycticorax nycticorax) and snow egret (Egretta thula) chicks in coastal Virginia. Auk., 1(113): Frederick, P.C and M.W. Collopy Nesting success of five ciconiiforms species in relation to water conditions in the Florida everglades. Auk., 106: Hill, B.G and M.R. Lein Territory overlap and habitat use of sympatric chickadees. Auk., 106: Maxwell, G.R. and W.Kale Breeding biology of five species of herons in coastal florida. Auk., 94: Parrish, J.K Influence of group size and habitat type on reproductive success in common murres (Uria aalge). Auk., 112(2): Rodgers Jr, J.A Breeding ecology of the little blue herons on the west coast of Florida, USA. Condor, 82: Satish Pande, Saleel Tambe, M.Clement Francis, and Niranjan Sant Text book of Birds of Western Ghats, Konkan & Malabar. BNHS. Oxford University Press, New Delhi. Sonobe, K. and S.Usui A field guide to the water birds of Asia. Wild Bird Society of Japan, Tokyo. Tremblay, J and L.N. Ellison Effects of human disturbance on breeding of black-crowned night herons. Auk. 96:

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