batboxes.files.wordpress.com  · web view04/03/2015  · the mix of big and little groups varies...

Bats Wilson Reserve 14 March 2015Another fine, windless afternoon and a good-sized team assembled. Steve and Stanley checked the Burke Rd tubes first and captured two Gould’s males, then did the last few boxes at Wilson Reserve, with Emily helping.

Kristin had a broken ulna and radius from a fall, but wouldn’t miss batting anyway, and we had a new recruit in Katrina Sofo, with her husband and little daughter

There were bats in six boxes, and we had a couple of escapees, possibly recaptured later. Jessica Whinfield joined us with a university friend, Maddy Woodruff, who has been vaccinated and was eager to start learning bat-handling skills, as was Katrina. Helen Reilly has been having her vaccinations and is keen to start next month. So Jessica helped Maddy get started while I helped Katrina, whose little daughter very much wanted to pat a bat and feel its soft fur, and even hoped she’d be allowed to hold one (which she wasn’t). Stanley went off to release his two bats once they’d been done, so missed the news that another Burke Rd bat had emigrated to a Wilson Reserve box. There were two unbanded bats, so Steve dealt with them.

Katrina’s daughter wanted to get up very close to see what her mum was doing. Katrina works at Biosis. She assessed several Gould’s, and the one Broadnose before her little girl’s attention span was exhausted.

Maddy made good progress in overcoming beginner’s nervousness by the end of the afternoon, and was very pleased about it.

One of the 2-year-old Gould’s females, banded in Dec ’13, and captured 11 times by now, had a serious band-

ing injury: the band had slipped far down her arm and cut through the wing membrane. Steve removed it and put a new band on the other arm. It is unusual for a banding injury to occur so long after banding. 93288 struggled in her first year to put on adult weight, but went through her first pregnancy last spring, had two healthy pups and is now a healthier weight.

Most Gould’s females get to 15+ grams before their first winter, but 93288 was well below that. She had a severe abdominal injury last March, so wasn’t weighed, and had two attached young in November.

She’s having a tough time with adulthood.

The one Broadnosed bat is our 21st of this species, so there are now 10 females and 11 males, with nearly all the repeat visitors being males. This is a big contrast to the Gould’s whose colony is dominated by the females.

Jessica was keen to be involved in releasing the bats after dark, so she, Maddy, and mother Brigitte all came along and Maddy opened most of the bags to let little bats fly off into the night. I got many photos of white bags, and one of a bat leaving.Box Bats Species Adult Esc M FB19 12

1Gould’s Broadnose

21

10 1

B12 9 Gould’s 1 8 2B05 5 Gould’s 3 2B01 2 Gould’s 2B06 1 Gould’s 1B16 1 Gould’s 1

31 Total 7 24 3For Burke Rd:Tube Bats Species Adult M FT04 1 Gould’s 1T07 1 Gould’s 1

33 Total 9 24

Over eleven years, March captures have fluctuated

quite a bit, peaking in 2006 then settling between 40 and 60 most years, but down in 2013 and again this year to little more than 30 bats.

Eleven of the Wilson Reserve bats were post-lactating females and there were 16 other Gould’s, so some must have died already from the probably 22 young born in October. The remainder of the year’s young will probably emigrate in search of breeding colonies in May.

Which boxes do they prefer in March?Some of the boxes are in shadowy woodland, others out in the open meadow edges, three are narrow-chambered and one is made of thicker timber. Generally in March the meadow boxes are favoured, but not this year. The woodland and narrow-chambered boxes had the bulk of the 31 bats this March.

What happens to group size in autumn?Each month we get some solitary bats, some in quite small groups and sometimes we get big groups of over 40. The mix of big and little groups varies through the year, the big groups far more prominent in the breeding season, when the females gather in maternity groups.

The chart shows the typical change from summer to autumn, with fewer bats in big groups and more in smaller groups. This shift continues to the end of winter.

Life experience and a bat’s weightYoung bats take a few months to become experienced insect hunters and reach adult weight. Mother bats,

having been through pregnancy and succeeded in catching enough insects to maintain their own weight and also produce milk for growing young, tend to be heavier.

But there is a fair bit of overlap – some young bats grow fast, some mother bats still struggle to keep their weight up. So this month we had a 16-gram young bat and a 14-gram post-lactating mother. Bats are variable in their life skills and their inherited predispositions.

Community structureThe 31 bats captured this month have been members of our colony for variable lengths of time, some just arrived, others around nearly 4 years.

The three “old ladies” who have been in the colony over 40 months have been joined by some of their daughters who didn’t emigrate, and some immigrants who became long-term stayers. And there is a very large group of this year’s young in the first column, present for up to 5 months since banding. Most of these are likely to emigrate by May to seek breeding opportu-nities elsewhere. But the long-term structure probably has several generations plus several immigrants who dispersed from other colonies elsewhere.

Next box check: Saturday 18 April 2:30 p.m.