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The effects of mistletoe on occurrence of insectivorous birds: Insights from a removal experiment

Wednesday, 26 June 2013: 11:03
La Paz - B West (Herradura San Jose)
David M Watson , Environmental Science, Charles Sturt University, Australia
Numerous studies have documented positive relationships between diversity and mistletoe occurrence, with a recent experimental study revealing that mistletoe removal caused mean losses of 35% of resident bird richness in remnant eucalypt woodlands in southern Australia.  Rather than nectarivores or frugivores, the guild that exhibited the greatest change was insectivores, but the mechanisms underlying this response are unclear.  Here, I quantify changes in canopy-feeding and ground-foraging insectivores in woodlands where all mistletoe was removed, comparing them with patterns in control woodlands to determine which group is more sensitive, and infer whether canopy or litter-dwelling arthropod assemblages are more influenced by mistletoe occurrence.  In terms of species richness, both canopy and ground-feeding insectivores exhibited similar responses, declining by 34% and 30% (respectively) three years after all mistletoes were removed.  Changes in incidence were less marked, with 18% and 19% declines in the two groups.  When only residents were considered (occurring in at least two of the four seasonal surveys), the ground foraging insectivores exhibited the greatest change, losing on average 37% of their initial species number.  These congruent responses suggest both canopy and litter-dwelling arthropod assemblages are boosted by mistletoe presence, with the greater sensitivity of ground-foraging insectivores further highlighting the role of nutritional limitation in driving widespread declines in this group.  As well as evaluating shortcomings with the five-year dataset, I consider the implications of these findings for the management of remnant, restored and replanted vegetation, with mistletoe potentially enabling persistence of resident insectivores in otherwise poor quality habitat.