WB#2: Mute Swan - Mega Waterfowl
The cache, a magnetic camo-taped sample tube, is hidden alongside this short trail leading from the Wharfebank Mills complex west alongside the river to Mickel Ings Beck (Norse: mickel = large, ings = water meadow or marsh). It is along this stretch that Mute Swans built a nest and raised 7 young this spring, activities followed through Twitter photos by people working in the area close to the old mill sluice gates.
To reach the cache location: park in the visitor car park @ N 53 54.212 W 1 42.471 and head west along the riverside trail the short distance to the cache location.
The mute swan (Cygnus olor) is a very large member of the waterfowl family Anatidae native to much of Eurasia. It is an introduced species in North America, Australasia and southern Africa, where in some locations it has become an invasive species (see here). The name 'mute' derives from it being less vocal than other swan species.
Its plumage is all white with a long S-shaped neck and an orange beak bordered with black. It is recognisable by its pronounced knob atop the beak, which is larger in males.
Adults are 125-170 cm with a 200-240 cm wingspan. Males are larger than females and have a larger knob on their bill. It is one of the heaviest flying birds. Male swans (cobs) average around 11 kg. While the top normal weight for a big cob is roughly 15 kg, one unusually big Polish cob weighed almost 23 kg making it the largest weight ever verified for a flying bird, although it was doubtful whether this heavyweight could still take flight.
Young birds (cygnets) grow quickly, reaching near adult size around 3 months after hatching. They usually 
keep their grey feathers until they are at least a year old, with the down on their wings having been replaced by flight feathers.
Although white when mature, the neck & head feathers are often stained orange-brown by iron and tannins in the water.
They nest on large mounds that they build with waterside vegetation in shallow water on islands in the middle or at the very edge of a lake. They are monogamous and often reuse the same nest each year, restoring or rebuilding it as needed.
Male and female swans share the care of the nest, and once the cygnets are fledged whole families may be seen seeking food. They feed on a wide range of vegetation, both submerged aquatic plants which they reach with their long necks, and by grazing on land. The food commonly includes agricultural crop plants such as oilseed rape and wheat, and feeding flocks in the winter may cause significant crop damage, often as much through trampling with their large webbed feet, as through direct consumption.
They are usually strongly territorial with just a single pair on smaller lakes, though in a few locations where a large area of suitable feeding habitat is found they can be colonial with the largest colonies having over 100 pairs. UK breeding population is about 6,400 pairs and wintering population around 74,000 birds.
Once adults are mated they seek out their own territories and often live close to ducks and gulls, which may take advantage of the swan's ability to reach deep water weeds, which tend to spread out on the water surface. They eat water plants, insects and snails.
Although less vocal than the noisy whooper and Bewick's swans, they make a variety of grunting, hoarse 
whistling, and snorting noises, especially in communicating with their cygnets, and usually hiss at competitors or intruders trying to enter their territory (see/listen here). Its most familiar sound is the vibrant throbbing of the wings in flight - unique to the species - and heard from up to 2 km away, indicating its value as a contact sound between birds in flight (listen here). Cygnets are especially vocal, and communicate through a variety of whistling and chirping sounds when content, as well as a harsh squawking noise when distressed or lost.
From about 1960-early 1980s, numbers declined significantly mainly due to lead poisoning from birds swallowing discarded lead fishing sinkers. After these were replaced by less toxic alternatives, numbers increased rapidly.
See here for more (comprehensive) information on this magnificent bird.
See here for a good short video on swans fighting for territory, here for slow-mo of taking off and landing, and here for a wonderful short video close-up of swans in flight (filmed with David Attenborough).