Apart from being one of Britains rarest birds, the fascination of the Bittern is the challenge of finding it. The brown mottled, streaky plumage blends in with the reedbeds especially when they freeze, often sky pointing. You can give yourself a better than average chance by visiting Tring Reservoirs in the winter.
It has been shown from ringing records that there is some movement within the UK but the extra numbers of overwintering birds arrive from Northern and Eastern Europe at the end of November and leave early March.
Each breeding male holds a large territory, at least 20,000 sq.m if the conditions are very favourable. The males, which are polygamous, can have 1-5 mates within his territory and these can nest quite closely together. After mating the male doesn't have anything much else to do with rearing the young except in holding territory against other males, which he can do extremely aggressively. The female tends the young until shortly after fledging.
They need a reasonably constant water level.
Bitterns regularly overwinter at Marsworth Reservoir, with occasional sightings at Wilstone Reservoir. The best place to see one is by standing on the causeway between Marsworth and Startops Reservoirs looking over the Marsworth reedbed to see one flying short distances over the reeds. If you stand where the reedbed almost comes up to the causeway and peer into the reedbed you might get a good close-up view like this photo taken by Mike Collard on 10-1-03 at Marsworth Reservoir. The best time is between December and February late afternoon and dusk.
Normally they leave in early March and there is no booming by the males, however a Bittern was booming at Marsworth Reservoir in 1999 from 1st March to 3rd April. Mostly this was heard in the evening during and after dusk and overnight fishermen have told us it kept them awake at night. A Bittern was also booming at Wilstone Reservoir on 4th March, possibly the same bird.
Since 1999 we have not received any more records of Bitterns booming (in earnest) and interestingly the latest sighting in subsequent years is early March (9th March latest). Perhaps the booming male in 1999 had some intent to breed instead of just overwintering here. If so, he must have given up and gone to try his luck elsewhere because the last sighting that winter was on the 23rd April.
So, listen out for booming from end of February and through March, mainly during and after dusk. Good luck, and please let us know via the Sightings links on this web site if you see, or hear, anything interesting.