The Asserbos, a forest in the city of Assen, partly consists of oak stands up to 350 years old. This type of old forest is rare in the province of Drenthe. Breeding birds were counted in 1993. A previous count was carried out in 1984. In the meantime some species typical of mature deciduous forests (Nuthatch, Marsh Tit and Hawfinch) increased substantially in Drenthe. The Nuthatch in the Asserbos increased likewise, from 5 to 19 territories. The Marsh Tit, on the contrary, decreased from 14 to 4 territories and the Hawfinch was more or less stable in numbers. This partly different development in the Asserbos, as compared to the regional trend, is hard to explain, especially because the habitats of the Asserbos were thought to be optimal for the afore-mentioned species. It seems that the increase of the Marsh Tit is still mostly confined to southern Drenthe, whereas Hawfinches thrive in mixed forest (and not so much in pure deciduous forests).