Reedbed management and breeding bitterns
Botaurus stellaris in the UK
G.A. Tyler, K.W. Smith *, D.J. Burges
Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK
Received 21 November 1996; received in revised form and accepted 6 November 1997
Abstract
A survey of habitats at 17 reedbed sites in the UK which currently hold or have recently held breeding bitterns Botaurus stellaris
has shown signi®cant dierences between sites with decreasing and sites with increasing numbers of birds over the period 1979 to
1994. Those sites where bitterns have declined had signi®cantly higher values for variables describing scrub encroachment and the
presence of wet herb species than those where the bitterns have increased. A model describing bittern numbers in 1990 at the 17 sites
included reed area and a measure of scrub encroachment as the signi®cant predictive variables. It is concluded that hydroseral suc-
cession has been a key factor in the recent decline in breeding bitterns in the UK. # 1998 Elsevier Science Ltd. All rights reserved.
Keywords: Bittern; Botaurus stellaris; Breeding; Reedbed; Habitat
1. Introduction
The bittern Botaurus stellaris is a scarce breeding bird
in the UK, entirely restricted to reedbed Phragmites
australis sites, with a declining population of fewer than
20 males in the early 1990s (Batten et al., 1990; Smith
and Tyler, 1993; Ogilvie et al., 1995). Having been lost
as a breeding species in 1886 as a result of drainage of
its wetland breeding sites and persecution, re-colonisa-
tion took place during the ®rst half of the 20th century,
with numbers rising to a peak of about 70 males in the
1970s (Riviere, 1930; Seago, 1967; Sharrock, 1976; Day
and Wilson, 1978) but subsequently falling to the cur-
rent low numbers. Elsewhere in Europe the bittern is
classi®ed as `vulnerable', having suered large declines
(Tucker and Heath, 1994) and with what are now small
and declining populations in most countries. Only in
parts of eastern Europe, the Baltic states and Scandina-
via are populations reported to be stable or increasing.
The factors causing the recent decline in the UK have
remained unclear, although habitat degradation and,
particularly in the Broadlands of East Anglia, pollution
were suspected. In an extensive survey of reedbeds in
England and Wales, Bibby and Lunn (1982), found
several habitat factors associated with the presence of
breeding bitterns at a site. Compared with the overall
sample of sites, those with breeding bitterns were large
wet reedbeds with open water within them, had dyke
systems within the reeds and were not under tidal in¯u-
ence. Bibby and Lunn suggested that bittern numbers in
Britain were limited by the availability of suitable
breeding habitat and not by winter weather, although
the latter could still cause short term declines (Sharrock,
1976; Bibby, 1981; Bibby and Lunn, 1982).
Although Bibby and Lunn's analysis gave pointers to
determinants of bittern numbers, their habitat variables
were limited to descriptive categories and, because they
covered all reedbeds in England and Wales >2 ha in
area, they included many sites which had never been
known to hold bitterns and were probably not likely to
do so. Further, since the early 1980s the bittern has
continued to decline in both numbers and range in the
UK and so the need to understand the factors deter-
mining its numbers and distribution has become more
acute. In 1981 they bred at 22 sites, whereas by the early
1990s this had fallen to 12 (Smith and Tyler, 1993).
One of the factors that has been proposed as an
explanation for this decline is changes in reedbed habi-
tat as a result of succession and other processes such as
pollution (Tyler, 1994). To test this idea, in the autumn
and winter of 1990/91, detailed habitat surveys were
carried out at 17 reedbeds, all of which held breeding
bitterns at the time or had done so in the previous 10 yr.
BIOLOGICAL
CONSERVATION
Biological Conservation 86 (1998) 257±266
0006-3207/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved.
PII: S0006-3207(97)00174-2
* Corresponding author. Tel.: 01767 680551; fax: 01767 692365;
e-mail ken.smith.research@rspb.org.uk