The marshes are the flood plain of the Biebrza River, and form a mosaic of different wetland habitats, including reedbeds, sedges, hay meadows, flooded marsh and wetland forest. Although the marshes support birds the whole year round, most people choose to visit in the spring. Late April sees a huge passage of Ruff, and is also the best time to see one of the area's two speciality birds, Great Snipe . To see this bird, arrangements can be made to visit the famous lekking site near Dobarz, in the southern part of the marshes. There is a platform built by local birder Marek Borkowski, from which good views of the snipes' lek can be had shortly before and after dusk.
Fine evenings are best, as the birds are disturbed by wind and rain.
April is also a good time to see Corncrakes, which breed here in huge numbers, but as ever are generally heard rather than seen. As with the Great Snipe lek, you have a better chance of seeing them earlier in the season when the vegetation is less well grown. Most birders come to Biebrza in mid to late May, when the breeding season is in full swing. The variety and numbers of birds are extraordinary, with a wide range of common and rare marsh birds. There are also colonies of White-winged Black Terns , which can often be seen from the roads.