Current World Environment

Introduction

Shorebirds are well known for their long distance migration ¹ and they are travelling thousands of kilometer annually from breeding grounds to wintering grounds vice versa ^2,3. Shorebirds use different aquatic habitats and they are intensely dependent on various stop over sites for rest and refuel during their migration ⁴. Several wetlands which are situated along the coastal regions are showing critical foraging sites for various species of shorebirds during their migratory periods ^5,6, coastal wetlands regarded as a most productive and are energetic habitats for numerous species of shorebirds ⁷. Shorebirds are always consuming larger quantity of prey in relation to their body size and to fulfil their metabolic requirements ⁸. Hence, shorebirds always selecting their foraging sites on the basis of abundance and distribution of prey and they could deplete greater extent of prey within shortest time ^9,10,2.

Generally the shorebirds and waterbirds are categorised into various groups on the basis of their ecology and behaviour in which the wading birds are one of the major categories of shorebirds. In addition to that the wading birds are classified as two different groups on the basis of the length of their legs and other morphological and behavioural characteristics i.e. large wading (long legged) and small wading (small legged) birds. The wading birds are prominent predators in the coastal wetland habitats ¹¹. The wading birds require proper water level and distribution of prey to fulfil their energetic demands ¹². For instance the wading birds are using large home ranges it might be due to their energetic demands since they are travelling thousands of kilometre during their migration ^13,14. The abundance and diversity of preys could reasonably influence the use of feeding grounds by wading birds and the density of prey also playing major role on the viability of wading bird population in the coastal wetlands ^15,16,17,18. The wading birds are functioning as one of the top positions in the trophic structure of food pyramids in an aquatic ecosystem the shorebirds are regarded as a important functional components in the aquatic habitats ¹⁹. Due to their trophic status the wading birds are also considered as one of the significant indicators of the quality of the wetland habitats ^20,21.

In this perspective the Pichavaram Mangrove Forest (PMF) is one of the vital wetlands in the east coast of southern India and the PMF is situated along the Central Asian Flyway routes of migratory shorebirds. The PMF is attracting several species of wading birds and the birds are using the PMF as a vital stop over sites during their migration since they are providing sufficient nutrient for the wading birds ^22,23,24,25. The current study aimed to carry out the seasonal variations of population characteristics of small wading birds in the PMF and to suggest management recommendations and conservation wading birds visited PMF seasonally.

Study Area

The study was undertaken in the Pichavaram Mangrove Forest (PMF), which is situated at 11°23? to 11°30?N, and 79°45? to 79°50?E, India (Fig. 1). The total area of the PMF is 11 km², in which 50% is tidally conquered, 40% has urban waterways and 10% is sheltered by tidal flats. The annual temperature of PMF is ranging from 18 to 36 °C ²⁶. Annually several species of shorebirds were visiting the PMF ²⁷. Various species of waterbirds were using the PMF as effective foraging grounds ²⁷. PMF attracts rare and near-threatened shorebirds annually ²⁸.

Figure 1: Map showing the Pichavaram Mangrove Forest, Tamil Nadu, India. Click here to view Figure

Methodology

Assessment of Small Wading Birds

The study was conducted from July 2015 to March 2016. The study periods were categorised into three different seasons on the basis of the migration chronology of shorebirds such as pre-migratory (July-September), migratory (October-December) and post migratory (January-March) seasons. The birds were identified and counted by using the 7 × 50 binocular and 20 x 60 spotting scope ^{29,30, 31}. The bird census was carried out fortnightly for each month (monthly two censuses) at the randomly selected three different sites of the PMF. Each site one hectare area was chosen on the basis of the greater congregation of shorebirds foraging in the PMF. The bird census was undertaken 6 hours in a day during the morning hours from 06.00 am to11.00 am³⁰.

Data Analysis

The bird density was calculated for each month and season and results were expressed as number per hectare ³⁰. Species richness was arrived on the basis of the number of species recorded for each month ³². The bird diversity was calculated by using Shannon and Wiener diversity Index, ³³. The Analysis of Variance (ANOVA) was applied to understand the impact of temporal factor (seasons and months) on the population characteristics of large wading birds such as density, diversity and species richness. The SPSS 25.0 used for the analysis of the data and the results were interpreted using standard statistical procedures ³⁴.

Results

In total, 27 species of small wading birds were recorded from the Pichavaram Mangrove Forest during the study. The Little stint showed the highest density 177.24±20.515 (No./ha.) and the Bar-tailed godwit showed lowest density 0.13±0.099 (No./ha.), when compared to the other small wading birds recorded from the Pichavaram Mangrove Forest during the entire study periods (Table 1). In addition to that the Little stint showed greater density relatively when compared to the other 26 species of small wading birds for all the three seasons studied. However, the Bar-tailed godwit not recorded during the pre and post monsoon seasons and the Dunlin, Grey plover and Great sand plover not observed during post-monsoon season (Table 2). Indeed the monsoon season showed highest density, diversity and species richness of small wading birds. The density, diversity and species richness of small wading birds showed significant differences among the seasons (P<0.001) (Figs.2-4).

Table 1: Density of Small Wading Birds (No./Ha) Recorded in the Pichavaram Mangrove Forest (PMF) from August 2015- April 2016. (Values are Mean ± SE).

Table 2: Seasonal Variation of Small Wading Bird Density (No./Ha) Recorded from the Pichavaram Mangrove Forest, from August 2015- April 2016. (Values are Mean ± SE).

Figure 2: Overall Seasonal Variations of Bird Density of the Small Wading Bird Recorded from the Pichavaram Mangrove Forest from August 2015- April 2016. (Values are Mean ± SE) Click here to view Figure

Figure 3: Overall Seasonal Variations of Bird Diversity of the Small Wading Bird Recorded from the Pichavaram Mangrove Forest from August 2015- April 2016. (Values are Mean ± SE)  Click here to view Figure

Figure 4: Overall Seasonal Variations of Bird Richness of the Small Wading Bird Recorded from the Pichavaram Mangrove Forest from August 2015- April 2016. (Values are Mean ± SE) Click here to view Figure

Discussion

The study found that 27 species of small wading birds were recorded from the Pichavaram Mangrove Forest (PMF). However, the density, diversity and species richness varied significantly among the seasons (P<0.001). In fact the study found that the temporal factors could influence the population characteristics such as density, diversity and species richness of wading birds in the PMF. Generally the abundance and distribution of shorebirds might have determined by the various attributes of aquatic habitats such as water and soil quality characteristics, abundance, density and distribution of prey, presence of predators and other ecological factors ^35,36. However the density and distribution of prey could be varied during particular, which will facilitate the reproduction and growth of the prey species of a given aquatic habitat, whereby the number and diversity of predators could be fluctuated ^{37,38, 39, 30}.

Studies are insisted that the population of waterbirds including wading birds could vary depends on the various seasons ^{40,41, 42}. Another study revealed that the population characteristic of avian communities fluctuated on the basis of temporal factors and habitat quality including the availability, distribution and density of food, and the availability of suitable sites for reproduction or resting ⁴³. The present study found that the monsoon season showed greater density, diversity and species richness of small wading birds and the study also found that the density, diversity and species richness of small wading birds varied significantly (P<0.05), it might be due to the immigration of various species of shorebirds since the monsoon season is the migratory season for various waterbirds³⁰. During migratory season several species of waterbirds visiting the wetlands as effective feeding and refuel sites or stop over sites during their migration and it could be reason the monsoon showed highest bird density, diversity and species richness than the pre-monsoon and post-monsoon reasons. A study inferred that the variations of avian species diversity may be correlated with the arrival of seasonal migratory species, and monsoon season harbouring of various species dwelling in the wetland habitat ^44,45.  Studies revealed that variations of waterbirds in a given wetland habitat is due to immigration and emigration of avian communities seasonally ^46,47,48,49.

In fact the current study found that the Little stint showed highest density among the other species of small wading birds recorded from the PMF. The bird density variations among the shorebird species in a given wetland habitat is determined by various ecological factors such as prey choice, foraging techniques, tolerance against various disturbances and predatory pressures, inter and intra species competition during their foraging and other ecological factors including water depth, niche partitioning and overlapping etc. In addition to that the Little stint could forage, hunting and consuming their prey along with the other species of plovers and sandpipers when they are foraging it could be the reason that the density of Little stint was greater than the other species recorded from the PMF, but intensive study should be carried out to understand the variations of wading birds population characteristics in a given wetland habitat. However the density, diversity and species richness of small wading birds is moderately declining when compared to the studies already undertaken in the PMF ^50,51,23,52. Another study also inferred that the population of shorebirds are declined in the PMF due to various ecological threats²⁴.

Conservation Implication

The Pichavaram Mangrove Forest (PMF) is a Central Asian Flyway (CAF) routes and supporting various species of waterbirds as a viable feeding, roosting and breeding grounds ^26,50. But the studies stated that the PMF is under severe threat due to various factors influencing the PMF including anthropogenic pressures. A study reported that the PMF is highly polluted through various contaminants ⁵³ and a study revealed that the toxic pollution is threatening shorebirds in India ⁵⁴. A recent study explained that the PMF is degrading and the habitat is losing to support various species of shorebirds which are visiting the PMF annually ^3,25 and the current study is also revealed that the population characteristics of wading birds declined. Therefore need of the hour to take proper management and conservation measures including assessment of the soil and water quality characteristics, assessment of prey species, various pollution, and threats both natural and man-made etc., to preserve the PMF to sustain the fauna and flora which are depend on the PMF.

Acknowledgment

The authors RJ, JP and GK express their sincere thanks to DST-SERB for funding the project (Ref No. SERB/LS-512/2013 dated 20.09.2013). The authors also thank to the Management of AVC College and Department of Zoology and Wildlife Biology for providing necessary facilities for the said project.

References

1. Goss-Custard JD. Feeding dispersion in some overwintering wading birds. Social behaviour in birds and mammals. 1970:3-5.
2. Pandiyan J. Ecology of shorebirds in the tidal flats of Cauvery deltaic region of southern India, M.Phil. thesis submitted to Bharathidasan University, Tiruchirappalli, Tamil Nadu, India. 2000;
3. Pandiyan J, Mahboob S, Jagadheesan R, Elumalai K, Krishnappa K, Al-Misned F, Kaimkhani ZA, Govindarajan M. A novel approach to assess the heavy metal content in the feathers of shorebirds: A perspective of environmental research. J of King Saud University, Science. 2020a; 32, 3065-307.
   CrossRef
4. Battley P, Piersma T, Rogers DI, Dekinga A, Spaans B, Van Gils JA. Do body condition and plumage during fuelling predict northwards departure dates of Great Knots Calidris tenuirostris from north-west Australia? Ibis. 2004; 146,46–60.
   CrossRef
5. Schneider WA. Integral formulation for migration in two and three dimensions. Geophysics. 1978 Feb; 43(1):49-76.
   CrossRef
6. Evans PR, Herdson DM, Knights PJ, Pienkowski MW. Short-term effects of reclamation of part of Seal Sands, Teesmouth, on wintering waders and shelduck, Oecologica, Berlin. 1979; 41:183.
   CrossRef
7. Masero JA, Pe´ rez-Gonza´ lez M, Basadre M, Otero- Saavedra M. Food supply for waders (Aves: Charadrii) in an estuarine area in the Bay of Ca´ diz (SW Iberian Peninsula). Acta Oecologica. 1999; 20: 429–434.
   CrossRef
8. Schneider D. The food and feeding of migratory shorebirds. Oceanus. 1983; 26: 38-43.
9. Goss-Custard JD. Competition for food and interference amongst waders, Ardea. 1980; 68:31.
   CrossRef
10. Goss-Custard JD, Durrell SEA, le V. Feeding ecology, winter mortality and the population dynamics of Oystercatchers on the Exe estuary, in “Coastal Waders and Wildfowl in Winter”, Cambridge University Press, Cambridge.1984;
11. Davis SM, Ogden JC. Everglades: The Ecosystem and Its Restoration. St. Lucie Press, Delray Beach, FL. 1994.
12. Powell GVN, Habitat us by wading birds in a subtropical estuary: implications of hydrography. The Auk 1987; 104:740–749.
    CrossRef
13. Goss-Custard JD, Jones RE, Newbery PE. The ecology of the WashI. Distribution and diet of wading birds(Charadrii).J.Appl. Ecol. 1977. 14:681-700.
    CrossRef
14. Burger JM, Howe A, Hahn DC,  Chase J. 1977. Effects of tide cycles on habitat selection and habitat partitioning by migratory shorebirds. Auk 94:1977;743-758.
    CrossRef
15. Davis CA,  Smith LM. Ecology and management of migrant shorebirds in the Playa Lakes region of Texas. Wildlife Monographs. 1998; 140:1–45.
16. Taft OW, Haig SM. The value of agricultural wetlands as invertebrate resources for wintering shorebirds. Agriculture, ecosystems & environment. 2005; 1;110(3-4):249-56.
    CrossRef
17. Pandiyan J, Asokan S, Thiyagesan K, Nagrajan R. Use of tidal flats in the Cauvery Delta region of SE India by shorebirds, gulls and terns. Wader Study Group Bull. 2006; 109: 105-111.
18. Hartke KM, Kriegel KH, Nelson GM, Merendino M.T. Abundance of wigeongrass during winter and use by herbivorous waterbirds in a Texas coastal marsh. Wetlands.  2009; 29:288–293.
    CrossRef
19. Frederick PC, Ogden JC. Monitoring wetland ecosystems using avian populations: seventy years of surveys in the Everglades. Monitoring ecosystems: interdisciplinary approaches for evaluating ecoregional initiatives. Island Press, Washington, DC. 2003; 321-50.
20. Kushlan JA. Colonial waterbirds as bioindicators of environmental change. Colonial waterbirds. 1993; 1:223-51.
    CrossRef
21. Frederick P, Gawlik DE, Ogden JC, Cook MI, Lusk M. The White Ibis and Wood Stork as indicators for restoration of the everglades ecosystem. Ecological indicators. 2009; 9(6):S83-95.
    CrossRef
22. Sampath K, Krishnamurthy K. Shorebirds of the salt ponds at the Great Vedaranyam Salt swamps, Tamilnadu, India. Stilt. 1989; 15:20-3.
23. Nagarajan, R. and Thiyagesan, K. 1996. Waterbird population and substrate quality of Pichavaram wetlands, southern India. Ibis 138:710–721.
    CrossRef
24. Sandilyan, S. Habitat quality and waterbird utilization pattern of Pichavaram wetlands southern India. Ph.D. Thesis, Bharathidasan University, Tiruchirapalli, India. 2009;287 p.
25. Pandiyan J, Mahboob S, Govindarajan M,  Al-Ghanim  KA, Ahmed Z, Mulahim N, Jagadheesan R, Krishnappa K. An assessment of level of heavy metals pollution in the water, sediment and aquatic organisms: A perspective of tackling environment threats for food security. Saudi Journal of Biological Sciences: https://doi.org/10.1016/j.sjbs.2020; 11.072  (In press).
26. Kathiresan K.  A review of studies on Pichavaram mangrove southeast India. Hydrobiologia. 2000b; 430(1–3):185–205.
    CrossRef
27. Sampath K, Krishnamurthy K. Shorebirds (Charadriiformes) of the Pichavaram mangroves, Tamil Nadu, India. Wader Study Group Bulletin. 1990; 58: 24-27.
28. Sandilyan, S. and Kathiresan, K. Density of waterbirds in relation to habitats of Pichavaram mangroves, Southern India. J Coast Conserv. 2015; 19-131-139.
    CrossRef
29. Yates MG, Goss-Custard JD. A comparison between high-water and low water counts of shore birds on the wash, East England. Bird Study. 1991; 38: 179-187.
    CrossRef
30. Pandiyan J, Asokan S. Habitat use pattern of tidal mud and sand flats by shorebirds (charadriiformes) wintering in southern India. J Coast Conserv. 2015; 20, 1–11 (2016). https://doi.org/10.1007/s11852-015-0413-9.
    CrossRef
31. Ali  S. The book of Indian birds, 13th edn. Bombay Natural History Society, Bombay. 2002.
32. Verner J. Assessment of census techniques. In Johnston, R.F. (ed.). Current ornithology, Plenum Press, New York. pp. 1985;  247–302.
    CrossRef
33. Shannon CE, Wiener W. The mathematical theory of communication. Illinois University Press, Urban III. 1949.
34. Sokal R R, Rohlf  F I. Biometry: the principles and practice of statistics in biological research. (eds Sokal and Rohlf). 2012; 1-776 .
35. Pandiyan J. Factors influencing waterbird use of coastal sandflats and mudflats of Napaipattinam District, Tamilnadu, Sothern India, M.Phil. Thesis submitted to Bharathidasan University, Trichy- 24. 2000.
36. Nagarajan R, Thiyagesan K. Waterbirds and substrate quality of the Pichavaram wetlands, southern India. Ibis.1996; 138, 710-721.
    CrossRef
37. Goss-Custard  JD, Jenyon  RA, Jones RE, Newberry PE, Williams RL. The ecology of Wash II: seasonal variation in the feeding conditions of wading birds (Charadrii). J Appl Ecol. 1977; 14:701–719.
    CrossRef
38. Pienkowski MW. Differences in habitat requirements and  istribution patterns of plovers and sandpipers as investigated by studies of feeding behaviour, Verhandlung Ornithol. Ges. Bayern, 1981; 23:105.
39. Pandiyan J. Ecology of Shorebirds in the tidal flats of Cauvery deltaic region of Tamlnadu, Southern India, Ph.D. Thesis submitted to Bharathidasan University, Trichy- 24. 2002.
40. DuBowy PJ. Waterfowl communities and seasonal environments: temporal variability in interspecific competition. Ecology. 1988;  69:1439–1453.
    CrossRef
41. Bethke RW. Seasonality and interspecific competition in waterfowl guilds: a comment. Ecology. 1991;  72:1155–1158.
    CrossRef
42. Lo´ pez de Casenave J, Filipello AM. Las aves acua´ ticas de la Reserva Costanera Sur: cambios estacionales en la composicio´ n espec?´fica y en la abundancia de poblaciones y gremios. Hornero. 1995; 14:9–14
43. Wiens  JA. The ecology of bird communities. Cambridge University Press, Cambridge.1989.
    CrossRef
44. Filipello AM, Lo´ pez de Casenave J. Variacio´ n estacional de la comunidad de aves acua´ ticas de la Reserva Costanera Sur.Rev Mus Arg Cs Nat B Rivadavia Ecolog?´a. 1993; 4:1–15.
45. Pandiyan J, Asokan S, Nagarajan R. Habitat utilization and assemblage patterns of migratory shorebirds at stop-over sites in Southern India. Stilt. 2010; 58- 36-44.
46. Garc?´a CM, Garc?´a-Ruiz  R, Rendo´ n  M, Xavier Niell F, Lucena  J. Hydrological cycle and interannual variability of the aquatic community in a temporary saline lake (Fuente de Piedra, Southern Spain). Hydrobiologia. 1997;  345:131–141.
    CrossRef
47. Caziani SM, Derlindati E. Abundance and habitat of high Andes flamingos in northwestern Argentina. Waterbirds. 2000;  1:121-33.
    CrossRef
48. Vijaya Kumar KM Vijaya Kumara. Species diversity of birds in mangroves of Kundapura, Udupi District, Karnataka, Southwest Coast of India, Journal of forestry Research, Springer Berlin Heidelberg, 2004; 25: 661-666, DOI10.1007/s11676-014-0450-5 Print ISSN 1007-662X.
    CrossRef
49. Vijaya Kumar KM, Vijaya Kumara. Avifaunal diversity of mangrove ecosystem, Kundapura, Udupi district, Karnataka, India. Recent Research in Science and Technology, 2011; 3: 106-110
50. Nagarajan R. Factors influencing the wader (Ciconiiformes and Charadriiformes) populations in the wetlands of Pichavaram,Tamilnadu, south India. M.Phil. Thesis, A.V.C. College, Mayiladuthurai. 1990.
51. Sampath K, K rishnamurthy k. Birds of the Pichavaram mangroves and the adjoining coastal environs. J Ecol Soc. 1993; 6:23–38
52. Nagarajan R, Thiyagesan K. Significance of adjacent croplands in attracting waterbirds to the Pichavaram Mangrove forests. In: Dhinsa MS, Rao PS, Parashrya BM (eds) Birds in agriculture ecosystem. Society for Applied Ornithology (India), Hyderabad, 1998; pp172–181.
53. Agoramoorthy G, Fu-An Chen, Minna J, Hsu. Threat of heavy metal pollution in halophytic and mangrove plants of Tamil Nadu, India. Environmental pollution. 2008; 155.2, 320-326.
    CrossRef
54. Agoramoorthy  G, Pandiyan J. Toxic pollution threatens migratory shorebirds in India. Environmental Science and Pollution Research. 2016; 23(15), 15771-15772.
    CrossRef