1.1 Background
“The restlessness of shorebirds, their kinship with distance and swift seasons, the wistful signal of their voices down the longest coastlines of the world make them, for me, the most affecting of wild creatures. I think of them as birds of the wind, as wind birds.”
~ Peter Matthiessen (Matthiessen, 1973)
The Shorebirds, also known as Waders, a diverse group of birds, belong to the order Charadriiformes, which encompasses 386 species worldwide divided into 19 families. Among these families, Laridae boasts the highest number of species with 101, followed closely by Scolopacidae with 97 species and Charadriidae with 71 species. Unfortunately, many shorebird species face significant threats to their survival. According to the IUCN Red List of threatened species (IUCN, 2023), a comprehensive assessment of the conservation status of various organisms, the shorebird group has been greatly affected. Among the shorebirds, seven species have been declared extinct, meaning that they no longer exist in the wild. Additionally, eleven species are classified as Critically Endangered, which indicates they face an extremely high risk of extinction in the wild. Furthermore, fifteen species are considered Endangered, signifying a very high risk of extinction (HBW and BirdLife International, 2022). The detailed list of the order Charadriiformes along with their IUCN status is given in Table 1.
Table 1. Total number of species comprising 19 families of the order Charadriiformes (Shorebirds)
| Family | English Name | No. of Species | IUCN |
| EX | CR | EN | VU | NT | LC | DD |
| Alcidae | Auks | 25 | 1 | 0 | 2 | 4 | 3 | 15 | 0 |
| Burhinidae | Thick-knees | 10 | 0 | 0 | 0 | 0 | 2 | 8 | 0 |
| Charadriidae | Plovers | 71 | 0 | 3 | 1 | 4 | 8 | 54 | 1 |
| Chionidae | Sheathbills | 2 | 0 | 0 | 0 | 0 | 0 | 2 | 0 |
| Dromadidae | Crab-plover | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Glareolidae | Coursers, Pratincoles | 17 | 0 | 1 | 0 | 0 | 2 | 14 | 0 |
| Haematopodidae | Oystercatchers | 11 | 1 | 0 | 1 | 0 | 1 | 8 | 0 |
| Ibidorhynchidae | Ibisbill | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Jacanidae | Jacanas | 8 | 0 | 0 | 1 | 0 | 0 | 7 | 0 |
| Laridae | Gulls, Terns, Skimmers | 101 | 0 | 1 | 4 | 9 | 8 | 79 | 0 |
| Pedionomidae | Plains-wanderer | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 |
| Pluvianellidae | Magellanic Plover | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
| Pluvianidae | Egyptian Plover | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Recurvirostridae | Avocets, Stilts | 7 | 0 | 1 | 0 | 0 | 0 | 6 | 0 |
| Rostratulidae | Painted-snipes | 3 | 0 | 0 | 1 | 0 | 0 | 2 | 0 |
| Scolopacidae | Sandpipers, Snipes, Phalaropes | 97 | 5 | 3 | 4 | 6 | 20 | 59 | 0 |
| Stercorariidae | Skuas | 7 | 0 | 0 | 0 | 0 | 0 | 7 | 0 |
| Thinocoridae | Seedsnipes | 4 | 0 | 0 | 0 | 0 | 0 | 4 | 0 |
| Turnicidae | Buttonquails | 18 | 0 | 2 | 0 | 2 | 0 | 13 | 1 |
(EX-Extinct, CR-Critically Endangered, EN-Endangered, VU-Vulnerable, NT-Near Threatened, LC-Least Concern, DD-Data Deficient)
Shorebirds are found in diverse habitats ranging from intertidal mudflats, sandy beaches, and rocky coastlines to freshwater wetlands, grasslands, ploughed fields, and flooded agricultural lands. These adaptable birds have successfully colonized a wide array of ecosystems worldwide. One of the defining characteristics of shorebirds is their specialized feeding behaviour. They primarily rely on a diet composed of molluscs, small crustaceans, marine worms, and insects. This diet variation reflects the vast array of feeding strategies and adaptations observed among different species of shorebirds.
Figure 1. Some typical attributes of a shorebird (In picture: Calidris minuta)
In terms of physical characteristics, shorebirds exhibit remarkable diversity (Figure 1). They come in various sizes, ranging from small sandpipers to larger species like godwits and curlews. This size diversity corresponds to differences in bill shapes and leg lengths, allowing each species to exploit their preferred food sources in their specific habitats. For instance, species with long, probing bills can effectively reach deep into mud or sand to extract hidden invertebrates, while those with shorter bills may specialize in catching insects or surface-dwelling prey (Figure 2). Similarly, leg lengths play a crucial role in navigating different types of terrain, such as wading through shallow waters or traversing open fields.
Figure 2. Different species of shorebirds exhibiting the diversity of shapes and sizes.A - Numenius arquata, B - Tringa totanus, C - Calidris ferruginea, D - Calidris alpina, E - Pluvialis fulva, F - Arenaria interpres.
Shorebird migrations are awe-inspiring feats that showcase the remarkable endurance and navigational abilities of these avian travellers. Among the shorebird species that engage in extraordinary migrations are Red Knots (Calidris canutus), Buff-breasted Sandpipers (Tryngites subruficollis), and Hudsonian Godwits (Limosa haemastica) (Burger et al., 2012; Senner, 2012; Faria et al., 2023). These species breed in the Arctic regions and undertake astonishing journeys to reach their wintering grounds at the southern tip of South America. These shorebirds migrate over great distances every year, covering around 20,000 miles total. This amazing voyage often entails crossing several continents, travelling through many ecosystems, and overcoming a variety of environmental obstacles. The necessity to escape adverse weather conditions during breeding and non-breeding seasons as well as the availability of food supplies are the driving forces behind these migrations. These shorebirds use a mix of their intrinsic navigational abilities and acquired actions to get where they are going throughout their protracted migrations. They are able to make such arduous journeys because to incredible physiological adaptations. This entails having efficient flight mechanisms, specialised fuel storage options, and the capacity to control metabolism for extended durations of flight. These shorebirds halts at several stopover sites throughout their migratory routes in order to rest and refuel to replenish their energy levels. These resting sites are vital to the success of their migrations because they provide them essential food resources to sustain their travel. The survival and reproductive success of these migratory shorebird populations may be significantly impacted by the loss or deterioration of these vital stopover sites.