The best times to listen are in the early mornings and evenings but at first the ‘boom’ is seldom more than a cough or a croak.
It takes time for a bittern to build up to his full resounding boom which can carry for up to three miles. He needs powerful muscles in his oesophagus to vibrate the air inside and breathe this out, producing two or three deep notes, one of the loudest sounds produced by any bird.
He also needs to have fed well during the winter to reach peak breeding condition and for some bitterns the flooding of reedbeds has caused them considerable disruption.
Bitterns need to feed in water between 15cms and 30cms and any sudden inundation of reedbeds forces them to move elsewhere. Now that the floods have receded it remains to be seen what the impact will be on bitterns this year.
Flooding can rejuvenate reedbeds, washing out dead litter from the base of the reeds and bringing in more invertebrates and small fish for bitterns and other birds to feed on.
But these days floods can wash nutrient rich sediments into reedbeds from surrounding arable land which can cause problems such as algal blooms and lead to the loss of plants which help maintain a balanced reedbed ecology. Also invasive plant and fish species can be introduced which can become dominant.
Not all the region’s reedbeds were flooded and hopefully those that were will not be affected so that this will turn out to be yet another record year for bitterns.
Last year there were more than 150 booming males across England and Wales compared with 140 in 2014 and the highest number for more than 200 years.
Ducks from North America have been a feature of the past week with a drake green-winged teal at the North Cave Wetland, East Yorkshire, the drake American wigeon relocating from Scarborough to the main lake at Castle Howard, North Yorkshire and the drake surf scoter still at Filey.
A first winter female ferruginous duck was on the nature lake at Pugney’s Country Park, West Yorkshire while up to four redhead smews and two scaups were among large numbers of wildfowl at Bubwith Ings near Selby.
Up to seven bearded tits have been seen in the reedbeds at the Old Moor reserve near Barnsley while a firecrest has been showing well near the Silkstone sewage treatment works.
A long-eared owl was roosting in bushes at the Blacktoft Sands reserve where up to 27 marsh and two hen harriers, merlins and sparrowhawks are coming in to roost.
Pink-footed geese have continued to move north across Yorkshire while 13 white-fronted geese were at Wykeham South Lake near Scarborough and eight, along with 400 plus pink-footed geese at Carthorpe Mires, North Yorkshire.