New 'Thermal' season up and running

Last night we ventured forth for our first evening visit to a local farm to see what we could find in the field using our thermal imaging camera provided by the WMBC.
The first three field we looked at produced nothing avian--a few mice, rabbits and a badger were the only animals we saw.
However, in the next field--stubble, there were between 20 and 30 skylark of which we managed to ring 6 --the first of the season.
This was our first session at a new farm where the farmer is interested in monitoring how his developing no till practice is affecting wild life. We propose to visit systematically through the winter to provide him with as much data as possible
For generally ' little brown birds'--Skylarks are rather handsome in a subtle, understated way--as you can see from this picture:-

Over recent years we have noticed a great variation in the length of the hind claw. Birds which live on the ground for long periods tend to have long hind claws--but we're not quite sure if there is anything other than normal variation behind the large variation in hind claw length. The picture tries to show this from two birds last night. You need to look carefully at the bottom picture to see just how long the claw is; it's not far short of twice the length of that in the top pic:-