LEIGHTON MOSS BEARDED TITS HAVE AN EXCELLENT YEAR
This year has turned out to be a record year for the
Leighton population of bearded tits. We have ringed 165 juveniles by early
September compared with a previous record high of 158 in 1997. At Leighton the
first brood which flies in late April is always the most successful, and this
year was no exception. The second and third broods are much smaller but this
year they have done the best yet and so far we have ringed 35 from the 3rd
brood compared with a previous record of 24 in 1995, and there are probably
several yet to ring.
Other reedbed birds have also had an excellent season we
have ringed 604-reed warbler compared with 403 in 1998 and 324 sedge warblers
against 147, with roughly similar effort. However blue tits, which usually enter
the reedbeds in late summer and autumn, have been very few with only 50 ringed
compared with 179 last year. It has been a good year for reed aphids and some
sedge warblers have obviously been feeding up and putting on weight, prior to
their departure for Africa. In early September we caught one which weighed 20.6
grams, the normal weight is only ca 10 grams!
The new design of nest box
(or wigwam) has worked well. This onion shaped box without the wooden
floor has meant that all nests are inside the box and not under the floor as
happened with some nest boxes in the previous two years. A total of 40 nests
were recorded and the success rate was high with ca 70% of birds ringed as
nestlings being retrapped as juveniles.
In the 1998 season we caught 92 adult males and 52 adult
females, In previous years there has been a small excess of males, but never to
the extent recorded last year. This
year to date of the 166 juveniles ringed 101 are males. The imbalance has been
especially marked in the third brood, with 25 of the 35 being males. Why this
should be so is interesting Dr. Ian Hartley from Lancaster University (remember
he gave us the fascinating talk on dunnock behaviour). He has taken DNA samples
from almost all the successful broods to see what the sex ratio is in the nest.
Male bearded tits are about a gram heavier than females so perhaps they survive
the winter better than the females. A limited analysis of our ringing data does
suggest that males live longer than females but we really need more data.
To date this year we have caught 43 adult males and only 14 females but
we will catch many more adults during the autumn but the early indications are
that the preponderance of males is continuing.
This year we have individually colour ringed all birds
caught as part of the above DNA study. So if you see beardies away from Leighton
look carefully for rings, each bird has four rings on and it is important to
record the position and on which leg the BTO metal ring is located. If you want
to see bearded tits at their best we have Bearded Tit Watches on Sunday October
3rd and 10th. Otherwise pick a calm morning in October and
visit the Causeway between 09.00 and ca 10.30.
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