Breeding Bitterns at Minsmere 1977 ROB
BRRRY
Introduetion In c o n t r a s t with the high bittern, Botaurus stellaris population of 1976 w h e n t h i r t e e n pairs were r e c o r d e d breeding, n u m b e r s in 1977 d e c l i n e d dramatically with only seven pairs p r e s e n t , their success o r failure being u n k n o w n for obvious reasons. A f t e r t h e c e n s u s of 1976, the main emphasis in 1977 was on establishing first the n u m b e r of b r e e d i n g pairs and secondly locating t h e i m p o r t a n t f e e d i n g a r e a s t h r o u g h o u t the season. T h e r e a s o n f o r the 1977 decline may have b e e n that it was simply a n a t u r a l fluctuation in the p o p u l a t i o n , or it could have b e e n associated with the general decline that a p p e a r s to be t a k i n g place with the bittern p o p u l a t i o n s in East Anglia. H o w e v e r o n e can only wait to see what transpires during the Coming s e a s o n (1978). Nest Site Distribution A s can be seen f r o m m a p 1 the reserve lost a pair of bitterns b r e e d i n g in the N o r t h M a r s h , f o u r f r o m the M a i n Marsh and also o n e f r o m t h e M e a d o w M a r s h which is 800 metres west of the M a i n M a r s h . T h e losses occurred in both wet a n d dry r e e d b e d sites. In all a r e a s w h e r e t h e r e was a loss of a b r e e d i n g pair, b o o m i n g s a n d sightings were n e v e r r e c o r d e d during the c e n s u s p e r i o d (19th J a n u a r y to 31st A u g u s t ) , indicating that no birds e v e r a t t e m p t e d to establish a territory at any time during the b r e e d i n g s e a s o n . O f t h e two pairs b r e e d i n g in the N o r t h M a r s h below the D u n w i c h C o m m o n (see m a p 1), o n e pair m a d e regulär flights f r o m t h e r e e d b e d to the grazing m e a d o w s s o m e 1800 m e t r e s s o u t h , but t h e s e w e r e m a d e only in the m o r n i n g and were not so f r e q u e n t as t h o s e r e c o r d e d in 1976, usually consisting of just o n e flight out a n d back. Twice the point of descent was i n s p e c t e d but no trace of the adult bird, or a nest was ever f o u n d , possibly b e c a u s e the y o u n g may have been moving a r o u n d t h e r e e d b e d having left t h e nest site. Booming T h e first b o o m i n g r e c o r d e d was on 25th F e b r u a r y at 08.00, five d a y s later t h a n t h e first r e c o r d e d b o o m i n g in 1976, the second