No Ringing: Something To Pass The Time: Saturday, 17th December 2022

Marsh Tits in the Braydon Forest

I was planning to go ringing at Somerford Common with Ellie this morning. It looked hopeful, with the forecast for a higher temperature than we have seen for over a week, and looking like our last chance before the wind and rain sweep in from tomorrow. We decided to start later, at 8:00, to give the birds time to wake up, warm up and get some feeding in before we started catching. I had filled up empty feeders on Monday, and they were empty again yesterday. Arriving on site this morning, they had already been reduced by one-third since 11:30 yesterday, so they are clearly being taken full advantage of.

I left home with the temperature at 0oC, but by the time I got to site it was down to -4oC and, after another 40 minutes, it was still -2oC, with no sign of the sun to warm the air. After this week of hard weather, we decided it would not be fair on the birds to set the nets and subject them to any additional stressor, no matter how small that stress might be. We had a good chat whilst waiting to see if the weather was going to warm up, and it was Ellie who first raised that we shouldn’t set the nets. Nice to know your trainees know what they are doing. So, rather than do nothing (or “household chores” as my wife refers to them), once I got home and thawed out, I decided to have a look at how things have been going with Marsh Tits in the Braydon Forest.

Since I got my C-permit and started ringing in the Braydon Forest mid 2012, I have been running a colour-ringing scheme across five sites. It has helped me to get a number of additional sightings from other local birders. However, the major contribution to the analysis has come from my team’s ringing activities. For the purpose of this analysis I have used ringing and recapture data only.

The first thing I looked at is, naturally, the numbers of Marsh Tits ringed by site by year:

Clearly it shows that the main sites for ringing Marsh Tits are Ravensroost Wood, Somerford Common and Red Lodge. They are three very different woodlands. Ravensroost comprises 40 hectares of primarily deciduous woodland. Of that 10 hectares is given over to an 8-year Hazel coppice cycle, with 4 coupes cut on two year rotations; 10 hectares given over to a 25-year coppice scheme, with the remainder being designated as ancient woodland. Somerford Common is more than twice the size of Ravensroost Wood, but over 50 hectares are given over to commercial conifer forestry, completely unsuitable for Marsh Tits. However, the eastern side of the complex is being returned to native deciduous trees and, as can be seen from the numbers, is as active as Ravensroost Wood. Coincidentally, since 2020, 10 hectares of this managed habitat is mulched on an 8-years cycle, in an attempt to encourage Marsh Fritillary butterflies. Red Lodge is an old commercial plantation, which is predominantly beech at the western end and oak at the eastern end. Our ringing is currently restricted to about 20 hectares of the beechwood area.

Webb’s Wood is a similar size to Somerford Common. It was clear felled soon after World War 2 and replanted by the Forestry Commission. It was previously split between a commercial conifer plantation and a commercial beechwood plantation. Most of the conifer has now been removed, with the land left boggy or planted with native species. During winter 2020 / 21 a major thinning of the beechwood was undertaken and there is very little under-storey. Bar two quite surprising years in 2017 and 2018, it has been a poor site for the species. Immediately north of Webb’s Wood, lies the Firs. This is the smallest woodland, at 11.5 hectares and is colloquially known as the “Braydon Bog”. This is because it sits on Oxford Clay and the lower reaches of the reserve are wet all year round. It was the first site that I ever ringed a Marsh Tit after I got my C-permit. It has a very mixed habitat only, unfortunately, this winter the owner has decided that all of the Ash has to be removed and that a lot of the Oak can be removed by way of payment, so it will be interesting to see what is left once I can get access again.

Giving the bald figures for numbers of birds caught can be misleading: it has to depend upon the amount of effort put into working at the site:

The reduction in the number of sessions in Ravensroost Wood was as a result of restrictions put in place following some issues after the Covid lockdown in 2020. Taking the effort into account enables you to get a more accurate picture of the number of birds ringed per session:

From this you can see quite clearly that the best performing sites for ringing Marsh Tits, in terms of effort expended are, Somerford Common and Red Lodge. The situation at Ravensroost Wood is actually reflected across all species for 2022: I have no idea what has depressed the catch in the wood. We might get another session in before year end.

Ringing them is one thing, but how many are being recaptured at each site. The crude figures are:

However, these can represent the same bird being caught multiple times, including those ringed that year. The best indication of how these sites are performing is to look at the number of individual birds caught. i.e. the number of birds ringed, plus birds from previous years recaptured and counted just once:

This, expressed as average number caught per session, shows:

The proportion of sessions in which Marsh Tits were caught is:

So, what does all of this mean: the catches are small but regular. Somerford Common and Red Lodge are the strongest sites for the bird, closely followed by Ravensroost Wood. I can’t help thinking that the performance for Ravensroost Wood has been adversely affected by the lack of activity in 2020 and the astonishingly low catches across the board in 2022.

I have had a look at the number of birds ringed in any particular year that have been caught in subsequent calendar years, i.e. those that have survived one or more winter period:

For a bird that, according to BTO BirdFacts, has a typical lifespan of just two years, that we have birds living to 3, 4 or 6 years is encouraging, especially when the survival rate for juveniles of the species in their first year is less than 20% (again, courtesy of BTO BirdFacts). However, the record age from date of ringing is 11 years and 3 months, set in 2015.

Of the two birds extant after 6 years had elapsed, D056930, it is one of only two Marsh Tits that has moved site. This bird was ringed in Webb’s Wood on the 2nd February 2013, recaptured in the Firs on the 21st April 2016, was subsequently caught again in Webb’s Wood on four more occasions, the last being the 15th February 2019: 6 years and 13 days after being ringed as age unknown. The distance moved is less than 700m, which fits with the proposition that Marsh Tits are highly sedentary. There was one other bird ringed that moved somewhat further: D983277, ringed on 13th June 2014 as a juvenile and retrapped in Red Lodge on the 24th January 2015, a distance of approximately 4km. Presumably this was a slightly longer juvenile dispersion.

The other long lived bird, D056635, was ringed, age unknown, in Ravensroost Wood on the 13th October 2012, and recaptured on 15 other occasions, the last being on 6th January 2018. It was only the third Marsh Tit I had ringed since getting my C-permit, and only the second in Ravensroost Wood.

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