A little info
I had a few hours in La Brenne on 19 May: obviously this is nowhere near enough but just a couple of observations :
1. For the first-time visitor, I would recommend the Chérine NNR and its visitor centre, the "Maison de la nature et de la Réserve", on the D6a a little east of Saint-Michel-en-Brenne. There are several hides and trails, very well waymarked and well-placed, with good notices explaining what's going on. I was particularly taken with the Etang de la Sous, on the same road, with a very well-placed carpark and hide: here I had superb close-up views of Purple Heron, Red-crested Pochard and Great Reed Warbler.
2. The Etang Purais, near Lingé, is drained this year for its decennial maintenance.
3. There is a smallish heron colony at the Etang Massé, not quite so easy to find but it is on the D17a just west of Le Blizon. The colony seems to contain mostly Cormorants but there are also Grey Herons, Night Herons, Little Egrets and Cattle Egrets.
My guess is the whole area is worth dedicating at least a couple of days.
Recommended !