An annotated checklist based on a decadal study on the waterbirds in Perur-Sundakamuthur Lake, Coimbatore, Tamil Nadu, India (Supplementary)

1 An annotated checklist based on a decadal study on the waterbirds in Perur-Sundakamuthur Lake, Coimbatore, Tamil Nadu, India (Supplementary) G. Parameswaran(1)(4), R. Sivashankar(2)(4) and Vridhi. R(3)(4) (1) G. Parameswaran, 438/11, Mayflower Apartments, 130, Vivekananda Road, Ramnagar, Coimbatore – 641009, Tamil Nadu, India. Email: [email protected]. (2) R. Sivashankar, 5690/18, Halasova, Jihlava, Czech Republic – 58601. Email: [email protected] [Corresponding author]. (3) Vridhi. R, 5690/18, Halasova, Jihlava, Czech Republic – 58601. Email: [email protected]. (4) Associated with “Kovai Birders” a volunteer organization that is involved in community-based Citizen Science in Coimbatore (https://kovaibirders.org/) Introduction: This supplementary paper provides an annotated checklist of the waterbirds recorded in Perur-Sundakamuthur Lake (Perur Lake henceforth), Coimbatore, Tamil Nadu, India, from May 2014 till April 2024. Out of 129 bird species recorded, we analyzed the status and population of 51 waterbirds. Methodology: We conducted a total of 108 counts in Perur Lake once a month in the period from May 2014 to April 2024, usually on second Saturdays. We walked along the fixed 2 km road during the morning for approximately two hours and counted all birds that were seen or heard and recorded the information in a checklist. This count can be characterized as a “total count” because visibility is nearly 100%. We recorded 51 waterbirds species comprises of 13 winter migrants and 14 local migrants (Table 6 of main publication). We pared down this list to 37 species by eliminating 14 species falling under rare category (Table 3 of main publication) because they are statistically insignificant. The 37 species are further categorized as 10 guilds and 8 individual species (Pearce et al. 2007). The annotation is provided with following information: a) Status of all the waterbird species (Table 2 in main publication). b) Population abundance (Table 3 and 3A in main publication). c) Dashboard visualization for 37 statistically important waterbirds comprising basic statistics about their population, monthly trend chart, bar chart showing population distribution across months and yearly trend chart indicating the population variation. d) The variation in their numbers with high counts and water levels. e) Notable behaviors including breeding. Results: The bird species recorded in Perur Lake during the study period are 129, belonging to 50 families and 19 orders (Table 14). Of these only the 51 waterbirds are annotated. A dashboard visualization is provided for selected 37 waterbird species that provides statistical information on their population and distribution. The error bar depicted in the yearly trend chart is a “Standard Error (SE) of the Sample Mean” calculated using following formula: The x-axis of these line graphs represents the calendar year from May to April and the y-axis represents the mean of the species with the error bars recorded in that period. For example, May 2015 to April 2016 is denoted as 2015-16 and similarly for the rest. The species accounts are based entirely on the results derived from our monthly counts. Impact of Water Level: The water level in this wetland plays a key role in determining the species composition and their numbers (Table 11). The highest counts of waterbirds were obtained when the water level of the lake was ‘Medium’ (Table 12) when large flocks of dabbling ducks, egrets, and shorebirds are seen feeding in the mudflats, shore and shallow water pools. 2 Table 11: Summary of waterbird counts in Perur lake (WB=Waterbird) Period (No. of counts) Details May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr Summer Southwest Monsoon Northeast Monsoon Winter Summer 2014–15 (12) Water level Low Dry Dry Full Full Full Full Full Full Med Med Med No. of WB species 11 11 12 20 20 18 28 26 29 36 36 25 Total count of WBs 146 61 104 265 786 774 410 709 1598 2045 1278 605 2015–16 (12) Water level Med Low Full Full Med Med Full Full Full Med Med Med No. of WB species 20 14 19 21 25 29 21 20 23 27 30 24 Total count of WBs 275 90 150 295 780 612 165 153 202 660 868 624 2016–17 (12) Water level Low Low Low Low Low Low Low Low Low Low Low Low No. of WB species 15 16 17 19 14 13 21 22 22 17 15 16 Total count of WBs 345 195 124 134 142 211 277 280 380 176 192 139 2017–18 (8) Water level Low Survey not done Med Med Low Low Low Low Low No. of WB species 8 21 31 15 17 14 12 17 Total count of WBs 58 165 218 246 122 110 36 33 2018–19 (12) Water level Low Low Full Full Full Full Full Full Full Med Med Med No. of WB species 9 15 19 19 18 18 19 22 23 30 25 28 Total count of WBs 80 164 219 299 297 293 466 413 283 296 351 382 2019–20 Water level Low Low Low Full Full Full Full Full Full Full Full Survey not done No. of WB species 17 14 16 17 16 15 15 14 15 22 20 (11) Total count of WBs 178 237 382 90 149 131 94 80 121 218 332 2020-21 Water level Survey not done Med Full Full Full Full Full Full Full Full Full No. of WB species 14 17 14 14 12 14 18 17 18 16 (10) Total count of WBs 114 141 121 63 79 50 109 301 179 210 2021-22 Water level Survey not done Med Full Full Full Survey not done Full Full Full No. of WB species 21 12 15 13 17 20 18 (7) Total count of WBs 442 121 99 239 252 193 223 2022-23 Water level Med Med Full Full Full Full Full Full Full Full Full Full No. of WB species 19 20 19 18 18 15 21 18 21 21 22 26 (12) Total count of WBs 243 270 222 113 103 128 240 205 233 392 557 774 2023-24 Water level Full Med Med Med Med Low Low Full Full Full Med Low No. of WB species 22 21 14 21 15 23 23 18 19 19 21 21 (12) Total count of WBs 815 952 484 353 795 764 1068 169 162 519 509 959 Table 12: Mean count of waterbirds across water levels Water level Number of occurrences Sum of bird count Mean count Standard Error Dry 2 165 82.5 21.5 Low 28 7268 259.6 48.6 Med 23 13322 579.2 89.3 Full 55 16004 291 35.9 Anthropogenic actions in Perur Lake: The three major anthropogenic actions in Perur Lake are following and their detailed impacts are provided in the main publication. 1. Commercial fishing: The Commercial fishing operation was started in October 2018 and is primarily carried out in the eastern part of the wetland covering approximately 69% of the water spread area. This has significantly impacted the waterbird population especially the winter migrant ducks and shorebirds, because the shallow pools and mudflats where prey is located is absent. The logical validity of this inference along with the hypotheses is provided in the “Logical Validity of inference of various hypotheses” section and Table 13 of this supplementary paper and the overall results in Table 9 of the main publication. In the main publication, Figure 5 shows the annual variation of water level across the decade indicating the higher water levels in the last five years to aid “Commercial fishing”. 3 2. Road expansion: From March 2019 onwards the wetland was subjected to an encroachment in the form of expansion which was finished in February 2021. This entailed the removal of vegetation and the appropriation of the wetland’s area for a two-lane roadway. An estimated 0.1 sq. km (c. 9% of water coverage area) has been encroached for the construction of a containment wall of 1.5m in height along the perimeter of the wetland. Even though there was an overall decline of waterbirds, the birds that were dependent on the periphery of the wetland like the Rails declined sharply based on our data (Parameswaran et al., 2023). 3. Sandmining: From June 2017 to September 2017, Perur Lake was subjected to sandmining, technically called reclamation (O’Connell 2000), which altered the character of the core area of the wetland. Deep pits and ravines that resulted from this operation disfigured 69% of the water spread area. The topography of the gentle-sloping bowlshaped wetland that was once hospitable to various waterbird groups like ducks, shorebirds, and egrets, deteriorated significantly (Parameswaran et al., 2023). Anseriformes: Anatidae 1. Lesser Whistling-Duck (Dendrocygna javanica) has the distinction of being a Resident (R) and as well as a Local Migrant (LM). According to our records the population of this species increases in winter, specifically from January to March denoting its local migratory nature. While it is recorded throughout the year it is absent during the dry months. Therefore, it has the dual status based on its nomadic habits in search of adequate water levels (Ali 2002). The highest count of this species occurred in the wetland year 2022-23, for three months in a row from February-April 2023 99, 105 and 99 individuals were sighted. Also, chicks in the company of adults were also observed in November 2022 and March 2023, proving its occasional breeding in Perur Lake when conditions are favorable. 2. Cotton Pygmy-Goose (Nettapus coromandelianus) is a Local Migrant (LM) duck in the area that has not been recorded during the last four years from May 2020 to April 2024. 3. Garganey (Spatula querquedula) is the most numerous of all the Winter Migrant (WM) ducks seen in Perur Lake. It is also the earliest to arrive such as in the month of August and the last to leave, which is by mid-April of the following Based on our data set, we can unequivocally state that the winter migrant ducks, and winter migrant shore birds have declined in the lake since commercial fishing started in October 2018. 4 year. During the time frame from May 2020 to April 2024, this once numerous winter migrant has been sighted only on four occasions, which are 2 in September 2021, 12 in November 2022, 7 in October 2023 and 6 in November 2023. 4. Northern Shoveler (Spatula clypeata) is a Winter Migrant (WM) duck species that has no records in the last four-year time frame from May 2020 to April 2024. 5. Indian Spot-billed Duck (Anas poecilorhyncha) is primarily a Resident (R) species that has been consistently recorded since the inception of the survey in March 2014. In winter some additional birds add to the existing resident population increasing its numbers from September to April. This species’ numbers have steadily increased from September 2021 onwards and dramatically from April 2023 to April 2024 and is the only bird classified as Abundant. During the wetland 5 year of 2023-24, this species had triple digit numbers on eight of the twelve counts ranging from a low of 102 to a high of 345. It is worth noting on four separate occasions the count exceeded the two hundred mark and they are 208 in June2023, 345 in September 2023, 211 in March 2024 and 241 in April 2024. 6. Northern Pintail (Anas acuta) is a long distant Winter Migrant (WM) duck species that has no records in the last fouryear time frame from May 2020 to April 2024. 7. Common Teal (Anas crecca) is a Winter Migrant (WM) species that also that has no records in the last four-year time frame from May 2020 to April 2024. 8. Common Moorhen (Gallinula chloropus) is a Resident (R) species that was sighted throughout the year and when the water level was either full or medium. From September 2020 till March 2021, its counts were depressed despite 6 favourable water conditions and the most probable reason was the disturbance caused by road expansion which ended in February 2021. The species has made a comeback especially from May 2022 till March 2024. The highest counts were 6,6,7 and 17 on November 2022, March 2023, April 2023, and June 2023 respectively. A chick and a juvenile were spotted in November 2020 and two chicks were seen on March 2023 and thereby establishing its breeding in this lake. 9. Eurasian Coot (Fulica atra) This Resident (R) species was once recorded in large numbers, but its number has significantly reduced. It is mostly present when there is sufficient water, especially in high numbers, when its level is between medium and full. From December 2019 till June 2022, there were only two records of birds numbering three and two. The removal of vegetation and road expansion along the lake bund could be the probable reasons for their long absence, despite favorable water levels. From July 2022 onwards until April 2023 has species has made a spectacular comeback. In the wetland year 2022-23 the highest counts were 37, 49, 52, 42 and 58 from December 2022 to April 2023. During the same wetland year, there were seven monthly counts when juvenile and immature chicks were also recorded in the presence of adults confirming its breeding status which spanned from September 2022 till April 2023. During the wetland year 2023-24, the significant counts were 200 in May 2023, 257 in June 2023 and 61, 68 and 67 in July 2023, August 2023 and February 2024 respectively. In March 2024 a juvenile accompanied by adults was also recorded confirming its breeding status. The Eurasian Coot is a breeder during the monsoonal months of July and August (Ali 2002) and in South India this breeding season can extend up to November (Rasmussen and Anderton 2012). 7 10. Grey-headed Swamphen (Porphyrio poliocephalus) is a Resident (R) species and recorded in large numbers until April 2016 when the water levels mostly vary from medium to full. Since then, their presence in the lake was erratic due to disturbances like unregulated commercial fishing and road expansion. A slight increase in their population has been observed since February 2022 possibly due to the cessation of road expansion. The highest count was 45 recorded in June 2023 when the water level was Medium. In August 2023, a juvenile bird of this species was seen in the company of two adults confirming its breeding status in this wetland. 11. White-breasted Waterhen (Amaurornis phoenicurus) is a Resident (R) species that has been found year-round in the lake until 2019. From June 2019 till April 2024 covering a span of almost 5 years, there had been only 8 8 instances when this bird was seen in the lake. The major reason for its long absence is probably due to road expansion and the permanent loss of vegetation along the bund. The highest counts were three, two and two in September 2023, April 2022, and November 2022 respectively. 12. Black-winged Stilt (Himantopus himantopus) is ideally classified as a Local Migrant (LM), but it is predominantly seen only in winter from January onwards. Its presence maybe extended to September in this location, in order to breed if the situation is favourable. This long-legged shorebird is an ideal indicator to establish the necessary condition of medium water levels and exposed mudflats. Its sporadic absence may be due to lack of such conditions. Its high counts were 13, 15, 15, and 20 in March 2021, September 2021, June 2022, and April 2024 respectively. In June 2022 four juveniles were seen, in August 2023 a young fledgling was recorded and in April 2024 a few birds were seen sitting on possible eggs indicating its breeding success and potential in this location. 9 13. Little Ringed Plover (Thinornis dubius) is predominantly a Winter Migrant (WM) species in our lake. However occasionally, the resident subspecies C.d.jerdoni had also seen between May and August indicating its probable breeding in the wetland. From June 2019 till April 2024, we have had only 7 occasions of the bird being recorded and the probable cause for decline is the high-water level in the lake due to commercial fishing that continues to the present day. The highest counts were five and four in July 2020 and August 2023. 14. Red-wattled Lapwing (Vanellus indicus) is a Resident (R) species that was recorded throughout the year in our lake. Its absence indicates that the water level is either too full with unexposed mudflats or too dry when there is hardly any prey to consume. Its high counts were 15, 8, 17, and 15 in October 2021, May 2022, August 2023, and September 2023. Breeding records in the form of immature birds were recorded in May 2022 and in August 2023. 16 33. Little Cormorant (Microcarbo niger) This Resident (R) cormorant species is recorded around the year and had the distinction of being the benchmark waterbird from May 2014 to April 2020, which is the highest average count over the specified period. Their population is stable during the last four years of count and they were recorded in high numbers when the water levels are high. However, they were seldom recorded feeding in the lake and the probable explanation based on their behavior is that they either roost or nest in the trees located at the far end of the lake by using the water as a predatory barrier (Subramanya 2005 and C Sashikumar et al. 2014). Their highest counts were 120 and 150 in March 2023 and February 2024 respectively. 17 34. Great Cormorant (Phalacrocorax carbo) is a Resident (R) species that is a wanderer in search of water and its sighting is based on this feature in our lake. It had been sparse and low in number till August 2021. Since then, the sightings have regularly increased. The highest counts are 23, 23 and 24 in September 2021, December 2021 and February 2024. 35. Indian Cormorant (Phalacrocorax fuscicollis) is a Resident (R) species in Perur Lake. From the start of the survey in May 2014 till July 2018, this species was sparsely present. Its population dramatically increased from August 2018 onwards and has been frequently recorded since then. Similar to the Oriental Darter, the species favour high water levels which has been the case in Perur Lake since July 2018. The highest count during the last 4 years is 81, 80 and 113 in May 2023, March and April of 2024. 18 36. Glossy Ibis (Plegadis falcinellus) is a Winter Migrant (WM) in our area that was recorded in higher numbers mostly during September to March. The highest counts of this species were 49 and 60 recorded in February and November of 2022 and 2023 respectively. This species had been using the lake for the initial two years of our study (May 2014 till April 2016) and had been largely absent with sporadic occurrences till August 2021. The species has started using the lake again in the winter months during the last 3 years of the study. 37. Black-headed Ibis (Threskiornis melanocephalus) is a Local Migrant (LM) species that was recorded erratically and in lower numbers. Its highest counts were 16 in June 2022 and 13 in October 2023 respectively. 19 38. Eurasian Spoonbill (Platalea leucorodia) is a Local Migrant (LM) species which is also nomadic and erratic in its occurrence. Its preference is for standing water with shallow depth where it is often seen feeding in the company of Painted Storks and Little Egrets. The highest counts were 32 in April 2019 when the water level was at medium and 25 in June 2019 at low water level. The species had been absent since August 2019 till April 2024 except in June 2022 when 5 individuals were spotted in the lake when we had Medium water level. Pelecaniformes: Ardeidae 39. Yellow Bittern (Botaurus sinensis) and 40. Cinnamon Bittern (Botaurus cinnamomeus) are two species that occurred very rarely in our lake till April 2016. Both species had been absent in the lake for the past 8 years. 41. Black-crowned Night Heron (Nycticorax nycticorax) is a Resident (R) species with sparse sightings in our lake, which is also secretive and nocturnal. It has never been recorded in the last decade during the dry months of May and June and was largely absent from May 2016 till July 2019 except three occasions. The highest count in the last five years was 16 on March 2020. 20 42. Little Egret (Egretta garzetta) is a Local Migrant (LM) species which is recorded consistently throughout the year in the wetland. Its highest numbers are usually recorded when the water level varies from medium to low. The highest count during this time frame was in April 2019 and April 2024 when 29 and 32 birds were sighted. Due to sand mining and water impoundment for commercial fishing its overall population has reduced since May 2017. However, the species was recorded throughout the year except November 2022 till January 2023 in this study period. The population reduction of this species between the first and last 5 years is nearly 45%. 43. Western Reef Egret (Egretta gularis)is a species with Uncertain (U) status. This bird was recorded only once in our whole ten-year study period in March 2015 where a single species was observed. 21 44. Striated Heron (Butorides striata) is a species with Uncertain (U) designation in Perur Lake. In the first six years of the count, this species was recorded at eight instances with the highest count of four in April 2016. It was recorded only four times in the last four years where we spotted a single individual at each of these instances. These low records are possibly due to its shy and retiring nature along with its secretive behavior. 45. Indian Pond Heron (Ardeola grayii) This species is a widespread Resident (R) that is recorded throughout the year. The water level preference is medium or low with exposed mudflats. From May 2020 to April 2024 the highest counts were 29, 29 and 36 in November 2022, December 2022, and June 2023. The population of this species has significantly dropped since May 2016 and the plausible reasons could be disturbances due to sand mining of the wetland, the removal of vegetation for road building and commercial fishing. The population reduction is nearly 37% between the first and last 5 years. 46. Eastern Cattle-Egret (Ardea Coromanda) This species is principally a Resident (R)/Local Migrant (LM) in our area. It used to be recorded throughout the year between May 2014 till May 2017. Since then, its population has dropped and has been recorded only intermittently including brief absences in our lake. The highest counts in the last 4 years are 15, 12 and12 in August 2020, September 2020, and February 2024. The population reduction is nearly 53% between the first and last 5 years of our 10-year study. 22 47. Great Egret (Ardea alba) is a Local Migrant (LM) species that has been recorded year-round in Perur Lake from May 2014 to April 2016. Its counts usually ranged between one and eight, with a notable exception being in April 2016, when it was an astounding 31 individuals possibly due to local migration through the area. It was recorded in low numbers from June 2016 till April 2024, which included many months when they were absent. The highest counts in the last 4 years were five each in April and September of 2021. The population reduction of this species between the first and last 5 years is nearly 49%. Our data shows that commercial fishing might be the probable cause for this decline. 23 48. Intermediate Egret (Ardea intermedia) This medium sized white egret is a Local Migrant (LM) species whose highest count was an unusually high 61 in April 2023 possibly due to the local migration in the area. From July 2016 to March 2021 its sightings were reduced with an intermittent pattern. However, since then, the bird has been consistently recorded with only a brief absence between July till October 2023. The population has slightly increased by nearly 19% when comparing the first and last five years. 49. Grey Heron (Ardea cinerea) is a Resident (R) species that is seen consistently in our lake throughout the year in all water conditions. However, the highest counts are usually registered when the water levels are either Low or Medium and they are 41 and 51 in June 2023 and November 2023 during the last 4 years. 24 50. Purple Heron (Ardea purpurea) is a Resident (R) species that was observed consistently from June 2014 to August 2016. Since then, its sightings have reduced and were inconsistent compared with the first two years of our study. The highest counts during the last 4 years were 6 birds each in February 2021 and April 2024. The population reduction between the first and last 5 years is nearly 48%. This species is largely crepuscular, perhaps shy, and secretive, keeping to dense reed cover where it may be easily overlooked (Ali 2002). Pelecaniformes: Pelecanidae 51. Spot-billed Pelican (Pelecanus philippensis) is a Local Migrant (LM) species that was an irregular visitor to our lake and was recorded only at five occurrences before November 2016 with a highest of 25 in September 2015. In January 2017, when there was low water level, a record 170 individuals of this species were recorded. In April 2019, 95 birds were registered at medium water level. The species had been absent in the lake since September 2019 till April 2024 except for a single instance where a single bird was spotted on March 2022. 25 Logical Validity of inference of various hypotheses: If P = Commercial fishing is carried out Q = Water level is full R = Shallow pools and mudflats where prey is found are non-existent S = Winter migrant ducks and shorebirds decline Then, the following are the implications (based on field observation and data analysis) 1. P → Q : If commercial fishing is to be carried out, then the water level must be full. 2. Q → R : If the water level is full, then shallow pools and mudflats where prey is found are non-existent 3. R → S : If shallow pools and mudflats are non-existent where prey is found, then the winter migrant ducks and shorebirds population decline. 4. A complete set of possibilities are enumerated in the truth table below, from which the relevant inference from row 1 is extracted to establish the logical validity of our argument (rows 9,13,15 and 16 are technically called vacuous truths, which are irrelevant) Table 13: Truth table No. P Q R S P→Q Q→R R→S P→S Rows 1,9,13,15 and 16 have all truth instances. By logical transitivity P → Q Q → R R → S Therefore, P→S is a valid inference. 1 T T T T T T T T 2 T T T F T T F F 3 T T F T T F T T 4 T T F F T F T F 5 T F T T F T T T 6 T F T F F T F F 7 T F F T F T T T 8 T F F F F T T F 9 F T T T T T T T 10 F T T F T T F T 11 F T F T T F T T 12 F T F F T F T T 13 F F T T T T T T 14 F F T F T T F T 15 F F F T T T T T 16 F F F F T T T T By the rule of logical transitivity derived from above table the conclusion is P → S, i.e., If commercial fishing is conducted, then the winter migrant ducks and shorebirds populations decline. Table 14: Birds of Perur Lake, Coimbatore Sl.No Common name Scientific name Status Population trend in Perur Lake (Average) Distribution status ANSERIFORMES: Anatidae 1 Lesser Whistling-Duck Dendrocygna javanica R / LM Stable Fairly Common 2 Cotton Pygmy-Goose Nettapus coromandelianus LM Last sighted in Dec-2015 Rare 3 Garganey Spatula querquedula WM Declining Fairly Common 4 Northern Shoveler Spatula clypeata WM Declining Uncommon 5 Northern Pintail Anas acuta WM Declining Uncommon 6 Common Teal Anas crecca U Last sighted in Feb-2019 Rare 7 Indian Spot-billed Duck Anas poecilorhyncha R Increasing Common GALLIFORMES: Phasianidae 8 Indian Peafowl Pavo cristatus R Stable Uncommon 9 Grey Francolin Ortygornis pondicerianus R Stable Uncommon PODICIPEDIFORMES: Podicipedidae