they become available. The Dearne Valley reserves have no statutory protection, but as of 2019, the process to become a Site of Special Scientific Interest (SSSI) is under way. Fauna and flora Birds Since the 1990s the RSPB has been attempting to create improved habitats for the formerly endangered UK bittern population, with major reed bed creation at their Ham Wall and Lakenheath Fen reserves being a key part of the bittern recovery programme initiated in 1994 as part of the United Kingdom Biodiversity Action Plan. At Old Moor, in addition to the creation of new reed beds, 23,000 small fish were introduced between 2010 and 2016, mainly of species such as rudd and eels that are preferred as food by bitterns. This project increased the fish biomass more than twenty-fold to . Breeding waders include lapwings, redshanks, snipe and avocets, the last species having bred on the reserve since 2011. Predation of wader chicks by foxes has been a problem, so deep ditches and electric fences are being introduced to exclude mammals. Black-headed gull numbers have increased from 183 breeding pairs in 2006 to 2,385 pairs in 2017, and have been joined by Mediterranean gulls, eight being present in 2018. Old Moor is an important wintering site for golden plovers, although numbers have dropped from 6,000–8,000 to 2,000–3,000 in about twenty years. Passerine birds include a small colony of tree sparrows, currently stable at about ten pairs, and good numbers of willow tits. Willow tits are in steep decline in the UK, disappearing completely from many areas, but numbers are increasing in the Dearne Valley, particularly at Old Moor, where a breeding density of 6.7 territories per square km (17.4 territories per square mile) was the highest in the locality. The post-industrial landscaping and planting in the area have created a suitable habitat for the species containing willow, alder and clumps of bramble close to water and linked by linear features such as railways, canals and streams. Cetti's warbler and bearded tit have recently colonised the reserve, and up to three pairs of barn owls breed there. A calling male little bittern summered in 2015 and 2016, and appeared for a few days in 2017. Other recent rarities include a Baird's sandpiper in 2016, a thrush nightingale and gull-billed tern in 2015, and a black stork in 2014. Other animals and plants Lesser noctule bats and water voles figure