Background information and definitions
Birds can consume seeds or physically damage trees. However, insectivorous birds may also control invertebrate herbivore populations. Some territorial species (such as bell-miners) may also displace other insectivorous birds and hence affect the impact of invertebrates on forests.
Supporting evidence from individual studies
A controlled study in 1992–1995 in three sites in narrow-leaved peppermint Eucalyptus radiata forest in south eastern Victoria, Australia (Clarke & Schedvin 1999) found that the removal of bell miners Manorina melanophrys did not improve tree health. The change in tree health (an index based on crown size, crown density, the presence of dead branches and the shoot growth) did not differ between the plots where bell miners had been removed (-0.6), were present (-2.3) and a control plot where no bell miners occurred (-0.7). In June 1993, a total of 189 bell miners were removed from the experimental site and the surrounding area (2.7 ha), by mist netting and culling. The tree health index was based on the visual assessment of the health of 10 trees at each plot (50 x 50 m), following a standardized protocol.Study and other actions tested