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The composition and status of waterbirds of Perur Lake in Tamil Nadu , India

The composition and status of waterbirds in Perur-Sundakamuthur Lake, a wetland in Coimbatore, Tamil Nadu, was studied from May 2014 to April 2016. This wetland is home to resident and local migrant birds throughout the year and is also used by winter migrant birds during a part of the year (September to March). From the data collected so far, the highest number of birds and species diversity was recorded from February to April. It is, therefore, imperative to maintain adequate water levels in these wetlands during these crucial months for the benefit of the northward migrating waterbirds. During the study period, it was also found that activities like road building could have had a deleterious effect on the number of birds that used this wetland. We recommend that similar studies be carried out in some of the adjoining wetlands of the area in a synchronous manner to further understand the subtlety of local avian movements within the greater Coimbatore area.


INTRODUCTION
Birds occupy a range of habitats and are responsive and sensitive to environmental changes. Wetlands are one of the most productive ecosystems and waterbirds play a vital role in its effective functioning. Urban habitats that include wetlands are continuously disturbed by development activities, which affect bird populations (Raju 2015). Although most urban wetlands in India are considered to be extremely polluted, they still attract a large number of winged visitors (Reginald et al. 2007). Our conclusions are based on the compilation and interpretation of data gathered during monthly bird counts in Perur-Sundakamuthur Lake from May 2014 to April 2016.

STUDY AREA
This study was carried out in Perur-Sundakamuthur Lake (Perur Lake henceforth) (10.968 N & 76.928 E), a wetland complex located in the urban fringe of metropolitan Coimbatore, Tamil Nadu. According to Pragatheesh & Jain (2013), the wetland complex in Coimbatore consisting of around 30 lakes was constructed during the Kongu-Chola regimes in 8 th and 9 th Century AD in the vicinity of the Noyyal River basin. Considering the nature of the river to flood downstream near Noyyal villages and to exploit the scanty rainfall typical of this region, the Kongu-Chola kings channelized the fury of the monsoon by creating a system of lakes and anicuts to aid the recharging of groundwater. Over a period of time, these wetlands came to house a lot of species of birds, fish, and other forms of life. Thus, the wetlands in this dry region not only provide the much-needed water for agriculture but also perform functions such as flood control, groundwater recharge, water purification, nutrient retention, and biodiversity conservation.
The Perur Lake, which has a catchment area of 5.768km 2 , is fed by Kuniyamuthur anicut channel from Noyyal River as an overflow of excess water from Ganganarayanasamudhram Lake, located further upstream. The length of the road that adjoins the Perur Lake on the eastern side is approximately 2km (formerly a mere bund), which is shaped like a crescent and filled with partial vegetation on one side and residential areas on the other. Given the lack of industrial activity in the area and non-flow of sewer into this lake, it is relatively unpolluted and contains a rich diversity of molluscs and fish that provide food for waterbirds. According to Wetland (Conservation and Management) Rules, 2010, the violations in this lake are encroachment and road construction as presented in Table 3 (Pragatheesh & Jain 2013).
Local migrant (LM) -A species that stays in an area throughout the year or most of the year whose adult population moves outside the area to breed (e.g.: Painted Stork Mycteria leucocephala).
Winter migrant (WM) -A species that spends its non-breeding winter months (mostly from September to April) in the area (e.g.: Wood Sandpiper Tringa glareola).
Vagrant (V) -A species that occasionally visits an area and whose pattern cannot be discerned (e.g.: Woollynecked Stork Ciconia episcopus).

RESULTS
The bird species recorded in Perur Lake during this period were 112, belonging to 44 families and 18 orders. Since this study focuses exclusively on waterbirds, which are 49 in number belonging to 14 families and seven orders, only their status is discussed in detail and listed in Table 1.

Lesser Whistling-duck Dendrocygna javanica
is a species that has the potential to breed in this area when conditions are favourable and to not do so when they are not. Therefore, it has the dual status of a possible resident or a local migrant, based on local factors like water levels in the wetland (Ali 2002). This species was recorded throughout the year except during the dry months from April to June (the only exception being that in May 2015 when five birds were recorded due to favourable water conditions). The highest numbers of this species were seen during the winter months of January 2015 and February and March 2016 when 97, 159, and 74 species were recorded, respectively. Based on these observations, this possible breeder in the area during the southwestern monsoon months (Rasmussen & Anderton 2012) is primarily a local migrant during winters in Perur Lake (Fig. 1).

Cotton Pygmy-goose Nettapus coromandelianus
is a local migrant duck in the area that was recorded only during winter months in an erratic manner. They were sighted from November 2014 to January 2015; a single individual was sighted in December 2015 (Fig. 2).

Indian Spot-billed Duck
Anas poecilorhyncha is a resident species that was recorded every month since the count began in March 2014. Its highest counts were recorded during the migratory months of September and October during autumn and also in February, March, and April during spring. In September and October 2014, however, its numbers were depressed due to very high water levels, which were devoid of shoreline exposure. This dabbling duck favours shallow freshwater lakes with extensive emergent vegetation (Madge & Burn 1988) and shoreline exposure. This characteristic helps to explain its low numbers in September and October of 2014, which were 14 and 22. During similar periods in 2015, however, the numbers of this species were 227 and 114, respectively, due to favourable conditions (Fig.  3). In January 2015, a pair was observed in courtship behaviour, which terminated in copulation. In the October 2015 bird count, when 114 individuals of this species was recorded, an adult bird with a crèche of five chicks was also observed, confirming the breeding status of this bird in this lake.

Northern Shoveler
Anas clypeata is a winter migrant species (Fig. 4a) that was recorded during the winter months between December 2014 and March 2015. The numbers were 113, 140, 131, and 99 in each month of this period. Due to some inexplicable reason, three and nine individuals of this species were recorded only in October 2015 and February 2016, respectively, of the second season.

Northern Pintail
Anas acuta is also a winter migrant duck (Fig. 5a) that was recorded from December 2014 to March 2015, whose numbers were 71, 218, 436, and 30, respectively. Similar to Northern Shoveler, the Pintails were also reduced in numbers during the subsequent year; only two and 14 individuals were recorded in January and February 2016, respectively. 6. Garganey Anas querquedula, according to our records for Perur Lake, is the most numerous winter migrant duck (Figs. 6a,b). It was recorded every month from December 2014 to April 2015, with peak sightings in February and March 2015, which were 532 and 436, respectively. Its sightings, however, dwindled during the winter months of 2015-2016 as only 21 and 152 individuals were recorded in February and March 2016, respectively. Note: Species 4, 5 & 6 that are winter migrant ducks were recorded in lesser numbers in 2015-2016 when compared with similar months in 2014-2015. Only continued monitoring can possibly reveal the reasons behind these annual variations.

Common Teal
Anas crecca is a winter migrant species with erratic presence in the lake. The species was recorded in January and February 2015 and a pair was observed in October 2015 (Figs. 7a,b).

Little Grebe
Tachybaptus ruficollis is a resident species recorded throughout the year, except in the months of May and June. This bird is extremely water  (Rasmussen & Anderton 2012). Accordingly, its highest counts were recorded during the months when the water level was high, such as 33 in September 2014, 50 and 29 in January and February 2015, respectively (Fig. 8). The breeding season of this species ranges principally between April and October (Ali 2002). This species could probably breed in this lake when water levels are medium to full, which occurs usually after the arrival of the southwestern monsoon. Its breeding status was confirmed in the lake when a flock with three chicks was observed in September 2014. This is evidence of post-breeding dispersal when they were recorded in low numbers from September onwards; however, only future observations can verify this behaviour.
Ciconiiformes: Ciconiidae 9. Asian Openbill Anastomus oscitans is a local migrant stork that breeds in southern India mostly from November to March (Ali 2002). This bird was consistently recorded in Perur Lake from May to July 2014 and again from January to June 2015, with a brief presence in September and October 2015 and then being sighted in sufficient numbers from March 2016 onwards. This pattern indicates that the breeding adults migrate out of the area during its breeding season, which could vary from September to March. High water levels with unexposed shoreline are a deterrent to its presence, as indicated

Dry
The absence of water in the lake or the presence of a negligible amount of wetness

Low
The presence of a small amount of water in a few isolated puddles

Medium
The presence of water in the whole lake with shoreline exposure in the periphery Full Lake completely filled with water without any shoreline exposure      by the full water levels from August to December 2014 when very few individuals of the species were recorded. In contrast, in September and October 2015, when water levels were less than full with some shoreline exposure, 24 and 17 individuals of this species were recorded, respectively ( Fig. 9). Exposed shoreline makes prey-finding possible for this species. Subsequently, when water levels became higher from November 2015 onwards, very few numbers of this species were sighted. This species, however, started to return during the winter months after the full water level receded to expose the shoreline and gradually increased in numbers as the lake dried out.            highest counts were recorded in September and October 2015 and in April 2016 when 30, 34, and 35 individuals were sighted, respectively ( Fig. 11), when the water level was between shallow and medium, which made preyfinding possible. In the study area, it was present mostly from September to May. This species is listed as Near Threatened due to its moderate population reduction owing to hunting, drainage, and pollution (Rahmani 2012).

Indian Cormorant
Phalacrocorax fuscicollis is a resident cormorant species and its presence is sparse in Perur Lake. This species was observed in all months of the year except during the summer months of May, June, and July 2014 and from March to June 2015. The highest number was recorded in February 2016 when 11 individuals of this species were sighted. Its absence in October 2014 even when the water level was full shows the erratic presence of this species in Perur Lake. This species probably breeds in the area in other water bodies.

Great Cormorant
Phalacrocorax carbo is a local migrant cormorant species that was sighted twice during our count period, in December 2015 and January 2016.
In both the occurrences, only a single bird was recorded ( Fig. 13). 14. Little Cormorant Phalacrocorax niger is a resident cormorant species that was recorded every month since the count began in March 2014. Its highest counts were recorded in the winter months of January and February 2015 when 252 and 203 individuals were sighted, respectively (Fig. 14). The population of this species drastically reduced when the water levels were low, especially during the summer months from April to July. This species could be a possible breeder in this lake when conditions are favourable. The breeding season of this bird in southern India chiefly lies between November and February (Ali 2002 17). Cinnamon Bittern was recorded in February 2015 and April 2016; in both occurrences, a single bird was sighted (Fig. 18). These are possibly local migrants that are sparsely recorded in the lake during winter months.

Grey Heron
Ardea cinerea is a resident species that was recorded year-round in Perur Lake. Its highest counts were recorded in September and October 2015 when 46 and 21 individuals were sighted, respectively, when the water conditions were probably favourable. Their habitat preferences are brackish water, wetlands, reedbeds, and paddy fields (Rasmussen & Anderton 2012). Its breeding season in southern India ranges from November to March (Ali 2002). It is probable that in September and October this species might be using this lake as a transit point (Fig. 19). 20. Purple Heron Ardea purpurea is a resident species that was recorded year-round except in May 2014 and July 2015. Its highest counts were recorded in April 2015 and February 2016 when nine and 11 individuals of this species were sighted, respectively. Its breeding season in India ranges from June to March depending on locality (Ali 2002), and in neighbouring Kerala, it reportedly breeds in July and August (Sashikumar et al. 2011).          numbers ranging from one to eight in this lake; however, the highest count was recorded in April 2016 when 31 individuals of this species were sighted (Fig. 21). This observation shows that this species might be using Perur Lake as a transit point during spring migration.

Intermediate Egret
Mesophoyx intermedia is a local migrant species in the lake. It was recorded yearround in the lake, except for the dry months of May and June 2014 and the months from September to November 2014 when the water level was full. Its highest count was recorded in April 2016 and December 2015 when 24 and 17 individuals of the species were sighted, respectively.

Little Egret
Egretta garzetta is another local migrant species in the lake that was recorded yearround. The highest counts of this species were recorded in the spring migration period of March and April 2015 and April 2016 when 60, 116, and 215 individuals were sighted, respectively (Fig. 23).
Note: In analysing the numbers of the three white egret species, namely Great, Intermediate, and Little, it can be deduced that these species probably use Perur Lake as a transit point mostly during the months of March and April. This can be clearly seen in the respective figures (Figs. 21,22 & 23) when their numbers are at the highest levels.

Western Reef-Heron
Egretta gularis is a vagrant species in the area. This bird was recorded once in Perur Lake when a sole bird was sighted in March 2015 (Fig.  24).

Cattle Egret
Bubulcus ibis is a resident species that was recorded year-round in the lake. The highest counts of this species were recorded in November 2014 and April 2015 when 37 and 40 individuals of this species were sighted, respectively (Fig. 25). Birds with breeding plumage were observed during its breeding months of November to March; however, no nests were recorded in the vicinity of the lake. It builds untidy stick nests in mixed colonies with Cormorants and Pond Herons, often in the vicinity of little villages (Ali 2002).

Indian Pond Heron
Ardeola grayii is a resident that was recorded year-round in the lake. Its highest counts were recorded in January 2015 and April 2016 when 65 and 64 of this species were sighted, respectively (Fig. 26). According to Ali (2002), its breeding season in southern India is from November to January and its nesting behaviour is similar to that of Cattle Egret. We, however, sighted some birds of this species displaying its breeding plumage in April and May 2015 though no nests were recorded in the vicinity of the lake. Its presence is higher in winter and also during spring migration, indicating that some of them might be using this lake as a transit point.

Striated Heron
Butorides striata is a resident species in our area that was recorded in the months of August 2014, March 2015, June to August 2015, and April 2016. The highest count of this species was recorded in April 2016, when four birds were sighted. Even though a resident breeder, it was unrecorded for many months during our count (Fig. 27), due to its secretive and crepuscular behaviour. Occasionally, however, it may be also active during the daytime, particularly in cloudy overcast weather. Its breeding season is from March to August with local variations (Ali 2002). In April 2016, a single bird in breeding plumage was observed in this lake.

Black-crowned Night-Heron
Nycticorax nycticorax is a resident species and its presence is sparse in Perur Lake. Its highest count was recorded in February 2016 when 18 individuals of this species were sighted flying overhead (Fig. 28). Most of them were immature or juvenile birds, indicating its possible breeding in the area. This species, however, is largely unrecorded during our counting sessions due to its nocturnal and crepuscular nature similar to that of the Striated Heron. According to (Ali 2002), this species breeds from December to February in southern India.

Pelecaniformes: Threskiornithidae
29. Glossy Ibis Plegadis falcinellus is a winter migrant species that was recorded in the lake during the winter months from September to March. The highest counts were recorded in September and October of 2015 when 53 and 68 of this species were sighted, respectively. During September and October of 2014, however, this species was not recorded in the lake. A plausible explanation can be arrived at by analysing its sight recordings in conjunction with the water level variations. When water levels were shallow with shoreline exposure that facilitated prey-finding, this species was recorded in large numbers as was the case in September and October 2015. When water levels were full in September and October of 2014, however, they were absent. This fact can be clearly seen in Fig. 29b where the water level was medium and its numbers were higher.

Black-headed Ibis
Threskiornis melanocephalus is a local migrant species that was recorded erratically in the lake. The highest count was recorded in April 2016 when six of this species were sighted. According to (Ali 2002), its nesting season is largely "ill-defined" and it may nest in southern India from November to December. This species was unrecorded in the lake during those months. According to Rahmani (2012), this species is nomadic and migratory in nature depending upon the availability

12477
of water. Since its population reduction in Asia due to an entire gamut of threats from hunting, disturbances at the breeding colonies to drainage, and conversion of foraging habitats to agriculture lands, it is listed as Near Threatened.

Eurasian Spoonbill
Platalea leucorodia is a local migrant species that was recorded only once in October 2015 when 11 individuals of the species were sighted. It is not possible to conduct an analysis based on this single observation.

Gruiformes: Rallidae 32. White-breasted Waterhen
Amaurornis phoenicurus is a resident species that was recorded yearround except during the drier months in the lake from May to July. Its highest count was recorded in February 2015 when six individuals of this species were sighted ( Fig. 32). Its breeding season is from June to October or during southwestern monsoon (Ali 2002). respectively. It is worth noting that during this period, the water levels were favourable for breeding, which ranged from medium to full. During a similar period in 2015-2016, however, its numbers were significantly reduced due to unfavourable water levels. Even though Ali (2002) states that Eurasian Coots breed during the monsoonal months of July and August, according to Rasmussen & Anderton (2012) March to August (Ali 2002). A juvenile of this species was observed in July 2015 38. Little Ringed Plover Charadrius dubius has two subspecies that are called C.d.curonicus, which is entirely a winter migrant in India, and C.d.jerdoni, a possible breeder and resident (Hayman et al. 1986). This species the resident subspecies C.d. jerdoni could be a possible breeder in this lake. In May and June 2015, three and one individuals of this subspecies were recorded, respectively. Due to changing water levels, however, its nesting could not be confirmed.

Charadriiformes: Jacanidae 39. Pheasant-tailed Jacana
Hydrophasianus chirurgus is a local migrant species that was infrequently recorded in the lake. Its numbers when sighted were very few such as one, one, and two in September, October, and December 2014, respectively; however, 17 individuals of the species were sighted in January 2015, which is an inexplicable anomaly. It is not been recorded in the lake since then.

Bronze-winged Jacana
Metopidius indicus is a local migrant species that is infrequently recorded in the lake, similar to Pheasant-tailed Jacana. A single individual of this species was sighted in January and August 2015.
Charadriiformes: Scolopacidae 41. Common Sandpiper Actitis hypoleucos is a winter migrant species that was recorded from August to     April. Its highest count was recorded in March 2015 when 21 individuals of this species were sighted. According to Ali (2002), it is one of the earliest wader migrants to arrive (August) and also one of the last to leave (May). The sightings of this species in this lake match this statement to a large extent.                 shoreline exposure. This pattern usually happens during the spring migration months from February to April. Its highest counts were recorded in February to April 2015 and April 2016, when seven, six, and 14 of this species were sighted, respectively.

Marsh Sandpiper
Tringa stagnatilis is a winter migrant species that was sighted sparsely in the lake. Most of the sightings were during the spring migration months of February and March 2015 and March 2016 when three individuals were sighted on each occasion.

Wood Sandpiper
Tringa glareola is the most numerous winter migrant sandpiper species in the lake. Even though it was recorded from September to April, it is primarily a species that is sighted during the spring migration months from February to April. Its highest counts during this season were in March 2015 and 2016 when 62 and 100 individuals were sighted, respectively. When water level conditions are favourable with shoreline exposure, as was the case in October 2015, 86 individuals of this species were recorded.

Temminck's Stint
Calidris temminckii is a winter migrant species that was recorded only twice in the lake during the count period of February and March 2015 when four and eight of this species were sighted, respectively; this correlates with the spring migration season.

River Tern
Sterna aurantia is a winter migrant species that was recorded only twice in the lake when a single bird in November 2014 and a couple in January 2016 were sighted. The water levels of the lake during both the sightings were full.

Types of Encroachments
Waterbirds usually avoid areas with extensive disturbance, choose roosting or foraging sites with fewer disturbances, and generally prefer wetlands with features that maximise the abundance and accessibility of their food (Khan et al. 2016). The types of habitat encroachments in Perur Lake that impair its functionality are road construction and its use for motor vehicles, illegal and unauthorised dumping of waste material, conversion to an artificial reservoir for agricultural use, and establishment of hutments.
For instance, road construction was carried out on the eastern bund of the Perur Lake covering the entire eastern border of 2km for use by motor vehicles. The probable effect of road construction on bird population and species diversity can be interpreted from the graphs given below. The road building activity appears to have reduced the sightings of the number and diversity of birds during the construction period, which lasted from March to August 2014.

DISCUSSION
From the analysis of the data collected from May 2014 to April 2016, it is clear that it is the resident/ local migrant birds that utilise this wetland throughout the year (Figs. 50-53). In addition, this wetland complex is also home to at least 17 species of winter migrant birds. Relations between habitat characteristics and waterbird abundances are often difficult to interpret as different factors act simultaneously, confounding the effects of individual ones, as birds frequent wetlands not only for food but also for rest and shelter. Migratory waterbirds are, however, opportunistic and adapt to utilise various habitat types during migration and colonisation (Khan et al. 2016).
Our conclusions from the observations can be stated as follows: · As far as Perur Lake is concerned, the presence or absence of water and its levels is a key determining factor of the avian species composition, the details of which are discussed in the individual species accounts.
· It appears from the data collected so far that the bird species diversity and actual numbers are at their highest (Figs. 51,52 & 53) during the months of February, March, and April, thus possibly pointing towards the highest avian diversity and numbers during their northward migration in spring. A mere two years' set of data, however, is simply insufficient to substantiate this possible pattern.
Nevertheless, it behoves us to maintain adequate water levels in these wetlands for all birds, especially for migrant birds, during the critical months of March, April, and May. Local communities too might derive benefits