A little confusing. Two birds were at the hollow; one on top while the other went into the hollow. The first bird then flew to a nearby tree while I waited for its mate to come out. However, after quite a while two birds actually came out of the hollow, so perhaps the other bird wasn't the mate after all. In the meantime there were two other birds present. Earlier there had been a lot of noise among all birds. Then while I watched the birds in the hollow, the other two flew around with one constantly being pursued by the other.