NLRG was formed in 1957 to help in the study of birds in the Lancaster and District Birdwatching Society area. There are currently 12 active ringers. Species currently being studied include: Pied Flycatcher, Bearded Tit, Sand Martin, Twite, Goosander, Oystercatcher and Grey Wagtail. Migration has been studied for 28 years at Heysham. We welcome anyone who wants to observe, help or perhaps wish to become a ringer. Photo: A Heysham-ringed Twite on the Mull of Kintyre (thanks to Eddie Maguire)

Wednesday, 22 July 2009

Do Male Bearded Tits Live Longer than Females?


To date, this year we have caught 24 adult Bearded Tits at Leighton Moss . Of the 24, 14 are males and 10 Females. Of the 14 males 5 are 3 years old or older but the oldest female is only in its third year. This is obviously a small sample so I looked at our records since 2000

In total up to the end of 2008 we had caught 1395 juveniles of which 723 were males and 672 females. Of these 298 males (41%) had been caught or sighted as adults. By contrast of the 672 females only 171 ( 26%) were caught or sighted as adults. So it appears as though males survive better in the first year.

I then looked at the numbers of each sex as to how long they live and the table below shows the results.
7 + years 1 Male
6+ years 2 Males
5+ years 5 males 2 female
4+ years 6 males 4 females
3+ years 18 males 9 females

Of course these results need testing statistically, but it does appears that males survive better than females.
John wilson

1 comment:

Matt said...

There's quite a lot of literature about differential survival rates among birds. But females usually disperse further than males, so you may simply be losing more females to the outside world and not getting many immigrants back in. But, generally, male passerines do live longer than females. That's because males dominate females when food is tight, and also because females get nobbled on the nests by weasels etc. But there can also be issues of catchability that can't easily be ignored. So simple % calculations are of limited use and a survival program such as MARK is needed to work out more robust figures that takes these variables into account.