The gradual loss and episodic creation of Palm Cockatoo (Probosciger aterrimus) nest-trees in a fire- and cyclone-prone habitat

Abstract

We present information regarding the rate of loss of nest-hollows over a long period in the tropics, and a dramatic episode of nest-hollow creation following two tropical cyclones. We followed the fate of 61 Palm Cockatoo (Probosciger aterrimus) nest-trees over a period of 6 years (1999 to 2005). On average, 48 trees were monitored each year. During this time 16 (26.2%) were rendered unusable for Palm Cockatoos; their final cause of loss was fire (n = 10; 62.5%), wind (n = 4; 25%), and intense decay where the tree was left standing but unusable (n = 2; 12.5%). On average, 5.2% of nest-trees were lost each year. Dead trees were more likely to be destroyed than living trees. Individual Palm Cockatoos build nests in multiple hollows, a subset of which are used for actual breeding whereas the rest are used for display purposes only (inactive nest-trees). Inactive nest-trees were also more likely to be destroyed than active trees, suggesting Palm Cockatoos actually breed in nest-trees that are more durable. We revisited our study area in July 2006, following two severe tropical cyclones. Most of the known nest-trees that we visited after the cyclones were still standing. The first cyclone created ~0.02 new nesting opportunities per hectare, whereas the second created 0.19. The differences between the two cyclones can be explained by their different paths and different radii of destructive winds in relation to our study area. While the loss of nest-trees owing to fire is significant, and should be monitored given that they are a limiting resource (Murphy et al. 2003), our results suggest that fire management should focus more on maintaining adequate recruitment of large trees, which could be affected by excessively frequent burning.