IF you have spent time near the river Wharfe during the spring and summer months there is little doubt that you will have heard the shrill call of an Oystercatcher. During the breeding season, they frequently fly up and down the river, and the volume and piercing nature of their call make this an attention-grabbing characteristic. However, they also have a very striking appearance.

One of Britain’s largest waders (40-45cm in length, and with an 80-85cm wingspan) (see photograph, with Mallard, for reference), Oystercatchers have black and white plumage, with white wingbars showing in flight. This is complemented by a red/orange bill, pale pink legs, and a red eye ring. Archaically they were referred to as ‘Sea-pies’ (amongst other names), alluding to similarities of plumage with magpies. Consistent with this, in Sweden they are known as ‘Strandskata’ which means ‘beach magpie’.

Locally, we have a small contingent during the breeding-season but they can be found, year-round, sometimes in large numbers, in the estuaries and along the coastlines of Britain. There they will feed on molluscs (especially Cockles, Mussels, and Baltic Tellins), worms (e.g., Ragworms and Lugworms – although some move a little way inland where they will take Earthworms), and other invertebrates (marine and terrestrial).

Their bills are well suited to dealing with this diversity of prey, being sufficiently robust to deal with shellfish (Oystercatcher opening a mussel: https://youtu.be/JRZDznBNJLI), but also sufficiently long to probe mud/sand/soil (https://youtu.be/CkkvnYpgXhE). However, individual Oystercatchers may specialise in taking certain types of prey, with the effects of abrasion leading to differences in bill shape that betray their dietary preferences and tend to reinforce those feeding behaviours. For example, hammering open shellfish eventually produces a blunter bill profile that is better suited to this task, while continuously probing the sand/mud leads to a slenderer bill shape that also better suits the behaviour. These ‘specialisations’ are not fixed and if needed, perhaps because of scarcity of a certain type of prey or increased competition, over time the bill shape will adapt to new requirements.

As the breeding season gets underway, in Scotland, the north of England and, to a lesser extent, the east of England, some Oystercatchers head inland to find nest sites. Nearby sections of the river Wharfe have met with the Oystercatchers’ approval. They pick secluded areas, generally with a gradually shelving stony shoreline and some vegetative cover nearby. There the Oystercatchers make a ‘scrape’ in the ground (a small depression), where the female will lay a single clutch of usually three eggs (https://youtu.be/9RhA8b__mVs). If they are successful in guarding their nest, the chicks will hatch about four weeks later.