Low level, low light, slow shutter speed and high ISO

Yesterday (22nd October 2017) I went for a walk up the hill behind our house. Twice I passed a spot where I have stopped many a time to watch birds. It is at the edge of a clear-fell, where there was forest 3 or 4 years ago. There are a few patches of deciduous trees with had been left by the woodcutters. One area of mixed alders, birch, rowan and rose bushes is often a good spot for birds, and both times I checked the area there was plenty to be seen.
On my second visit I discovered that as well as feeding on various seeds and berries that birds were also bathing along a ditch with slow-flowing water. So I sat down to see what was coming down to feed and then drink / bathe in the ditch.
Using a tripod and with the camera at low level, I was able to lie on the ground and photograph some of the birds there. I needed to use a high ISO value of 1600-2500 due to poor light, also a relatively slow shutter speed. Even though the lighting was not ideal and the images were a bit grainy I still managed some half-decent shots (or at least I was surpised that they were not absolutely awful under the circumstances).

Great Tit Parus major (N=kjøttmeis)

Blue Tit Cyanistes caeruleus (N=blåmeis)

Mealy Redpoll Carduelis flammea (N=gråsisik)

The rig used for above shots: Canon 50D, 300mm L-lens, 1.4x teleconverter. Tripod is a cheapo bought in a local Co-op about ten years ago, with a Manfrotto head. Works well for low-level stuff.