Nesting Tree Characteristics of Heronry Birds of Urban Ecosystems in Peninsular India: Implications for Habitat Management
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Current Zoology, 2017, 63(6), 599–605 doi: 10.1093/cz/zox006 Advance Access Publication Date: 17 February 2017 Article Article Nesting tree characteristics of heronry birds of urban ecosystems in peninsular India: implications for habitat management a, a,b Ramesh ROSHNATH * and Palatty Allesh SINU aDepartment of Animal Science, Central University of Kerala, Padannakad, Kerala, PO 671314, India and bDepartment of Ecology and Evolutionary Biology, Bioscience West, University of Arizona, Tucson, AZ 85721, USA *Address correspondence to Ramesh Roshnath. E-mail: [email protected]. Received on 9 September 2016; accepted on 28 January 2017 Abstract Wetland ecosystems, particularly the mangrove forest, are the primary wild habitat of heronry birds. However, urban ecosystems have become a favorite breeding habitat of these birds. To pro- vide inputs into the habitat management for conservation of these birds, we investigated the quan- titative and qualitative characteristics of nesting trees of heronry birds in the urban environment of the North Kerala region of peninsular India. Census on nesting trees was done in 3 major micro- habitats of the urban ecosystem: avenues of national highways and towns, nonresidential plots, and residential areas apart from the mangrove islets in the peri-urban locality. The study found that 174 trees of 22 species hosted 1,928 heronry bird nests in the urban habitats; mangrove forests, al- though plentiful in the study area, hosted only about 20% of the total nests encountered in the study. Rain trees Samanea saman (43.7%) were the most available nesting tree. The greatest num- ber of nests and nesting trees were encountered on the roads of urban areas, followed by nonresi- dential areas and residential areas. The differences in the observed frequencies of nesting trees in 3 microhabitats and in 3 types of roads (national highways > state highways > small pocket road) were significant. Canopy spread, girth size, and quality of the trees predicted the tree selection of the heronry birds in urban environments. Therefore, we recommend proper management and noti- fication of the identified nesting trees as protected sites for the conservation of herorny birds. Key words: avenue trees, heronry, management, urban ecosystem. Urbanization is generally perceived as a bane for the decline of bio- et al. 1994; Subramanya 1996; Urfi 1997). Monitoring the popula- diversity. However, lately it has been widely accepted that the ur- tion ecology of heronry birds is particularly useful to understand the banization is unrelenting, and sustainable development is the only impact of urbanization (Urfi 2010). way to mitigate it. Therefore, there is a great deal of research on Heronry (¼ rookery) is group nesting of colonial waterbirds of urban habitat management to make urban areas inhabitable for the orders Ciconiformes, Pelecaniformes, and Suliformes, which wildlife. Even though birds have always been dwelled in cities, the comprises of herons, egrets, storks, pelicans, ibises, spoonbills, dar- concept of urban ecosystem and biodiversity conservation did not ter, and cormorants, which shows spatial and temporal clustering of emerge until the late 1990s (Collins et al. 2000; McKinney 2002; nests (Roshnath et al. 2013). Even though heronry birds vary in their Miller and Hobbs 2002). Studies show that the created urban cli- habitat preference, diet, and behavior, their fundamental require- mate is no longer a lost habitat for birds as many wild birds are ments for nesting remain more or less the same (Hafner 2000). acclimated to it, but often with some physiological stress in the birds Multiple factors affect habitat selection and colony site dynamics of (Shochat et al. 2010). Colonial waterbirds, for example, use cities waterbirds (Kharitonov and Siegel-Causey 1988; Fasola and Alieri for nesting and foraging (Parasharya and Naik 1990; Jamgaonkar 1992; Boulinier and Lemel 1996; Erwin et al. 1998); habitat quality, VC The Author (2017). Published by Oxford University Press. 599 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact [email protected] 600 Current Zoology, 2017, Vol. 63, No. 6 including the nesting tree quality, has been demonstrated as one of the most important habitat selection criteria (Fasola and Alieri 1992; Baxter and Fairweather 1998). Therefore, studying nesting ecology of the birds in urban ecosystems can suggest methods to im- prove their urban habitats. Kannur corporation is the youngest corporation of Kerala state in peninsular India (11520N, 7525 E), but the oldest port city of the Malabar region during the Portuguese and the British colonial periods. Being the youngest corporation, it is now gearing up for the expansion of the city that will determine the fate of the old avenue trees. The city has been developed close to the Arabian ocean and several backwaters with mangrove islets. It has many large trees and green spaces in the streets, highways, and other public places, such as the premises of historical forts, railway station, and temples. We have been monitoring the nesting trees of heronry birds in Kannur and adjacent Kasaragod districts for about a decade (Roshnath et al. 2014). The objectives of the present study are the following: (1) to identify the nesting tree species of heronry birds; (2) to identify the tree characteristics crucial for nest tree selection and nest abun- dance; and (3) to understand the bird species participating in the heronries of city streets and the adjoining mangrove islets. Materials and Methods Kerala has about 15 species of resident and breeding waterbirds nesting Figure 1. Map of North Malabar (Kannur and Kasaragod) shows the heronry in various heronries across the state (Sashikumar et al. 2011). Little cor- sites dealt in this study. morant Microcarbo niger, Indian cormorant Phalacrocorax fuscicollis, Oriental darter Anhinga melanogaster, Indian pond-heron Ardeola Table 1. Scores assigned to different qualitative characters of trees grayii, black-crowned night-heron Nyctricorax nycticorax, little egrets to derive the qualitative value of the host trees Egretta garzetta, intermediate egrets Ardea intermedia,greategrets Ardea alba, purple heron Ardea purpurea, and grey heron Ardea cinerea Parameters High Medium Low are the 10 species that are found nesting in North Kerala region Protection from predators 3 2 1 (Roshnath et al. 2014). Nesting materials acquired within the tree 3 2 1 We used historical bird census data (Sashikumar and Jayarajan Suitable branching pattern 3 2 1 2007, 2008; Sashikumar et al. 2011; Roshnath et al. 2013, 2014) Adequate space (canopy) 3 2 1 and the citizen responses to our newspaper advertisements for her- Withstand wind (chance of nest not to be fallen) 3 2 1 onry bird sites to select the nesting sites for the present investigation. Protection from rain (chances of nest 321 We followed Sutherland’s (1996) method of counting nests in heron- not getting wet) ries to assess the bird population. A total of 52 heronry sites were identified in Kannur and standard lengths (7 and 9 m) were used as the references. The GBH, Kasaragod districts of North Kerala, which include both the human- canopy length (L), and breadth (B) were estimated using a meter influenced areas, such as roads in urban and rural towns, residential tape. Average canopy spread (hereafter canopy spread) was esti- and nonresidential areas, and the wild habitats, such as mangrove mated using the formula (L þ B)/2 (Blozan 2006). islets (Figure 1). These heronries were visited during the peak breed- Trees were assigned qualitative scores based on the sum score ing period (monsoon months of June–August 2015) to identify the obtained from the scores assigned to following qualitative variables composition of the birds in the heronries, and to record the charac- of the nesting trees: canopy’s adequate space (canopy spread area) teristics of the nesting trees. Nesting bird species were identified for nest placement, and suitable branching pattern, which supports using binoculars (Celestron’s Nature DX 8 Â 42) and a standard field guide (Ali 2003). The number of nests of each species was re- nests, offers nesting materials, and protects nests from rain, wind, corded in each heronry. Wherever possible an aerial survey was and predators (Table 1). made on trees in urban and residential sites from the terrace of the adjacent tallest buildings. Based on the long-term data we identified Statistical analysis following “microhabitat” types for sampling the nesting trees and to Number of nests per tree was used as a measure of nest tree occupancy study the tree characteristics: road, residential area, nonresidential and as the response variable in the analyses to study the effect of public places, wetland, and riverside (Figure 1). Whenever a nesting urban habitat type and nesting tree species on heronries. Since an ac- tree was located tree characteristics (tree species, tree height, girth at curate number of nests per mangrove tree was not available, man- breast height [GBH] of the tree, and tree crown spread) and the age grove habitat is not included in the analyses. We also studied the of the heronry (only for those trees that were occupied by the birds effect of road type (national highway, state highway, and pocket as seen in the historical data) were recorded. road) on the number of nests of the heronries per tree. We used gener- The tree height was measured using a 1-m graded pole (Datta alized linear mixed models (GLMM) with Poisson error as the distri- and Pal 1993; Gopi and Pandav 2011); electricity poles of 2 bution to compare the effects of habitat (road, residential site, and Roshnath and Sinu Á Nesting tree characteristics of heronry birds 601 nonresidential site) and the road type (streets in the cities, state high- another tree in Parapuram, a wetland habitat had only 1 nest.