La Rouvière is a forest near the town of Montarnaud, northwest from Montpellier. The population has been monitored since 1991 with all nest boxes within the same site. The habitat is mainly composed of deciduous downy oaks (Quercus pubescens) but some small areas are dominated by evergreen holm oaks (Quercus ilex). There are currently 272 nest boxes weekly monitored during the breeding season. The main birds monitored are the blue tit (Cyanistes caeruleus) and the great tit (Parus major). About half of the nest boxes are equipped with small entry (28 mm) to favor blue tits, while the other half is equipped with larger entry (32 mm) that great tits can use.