Beetle Epidemic a Short-lived Boom for Birds
While British Columbia's mountain pine beetle epidemic is shaping up to be a gold rush for some cavity-nesting birds, it appears the boom will soon bust. As beetles moved into healthy, mature, mixed forests in the Interior Douglas-fir biogeoclimatic zone near Williams Lake, woodpeckers that relish beetle larvae and adults prospered.
Several species of woodpeckers, chickadees and other cavity-nesting birds that are year-round residents and consume bark beetles increased their densities over ten years as the number of beetle-attacked-trees grew. Once 40 percent of the conifers had succumbed to beetles, though, red-breasted nuthatch and black-capped chickadee numbers declined, likely due to a collapse in the supply of insects they eat.
Altogether, populations of 40 out of 100 bird species shifted significantly in size during the 11 years that the proportion of beetle-attacked conifers in the forests climbed from 2 to 40 percent. These also include birds that from the start dropped in numbers, such as northern flickers and red-naped sapsuckers who eat ants and tree sap.
At least 24 species of birds and mammals feed on bark beetles in BC's interior forests, possibly enough to accelerate the retreat of an insect epidemic after it peaks. Many of these birds rely on mature, mixed-species forests since they nest in aspen trees while foraging on insects living in conifers. The authors of this study recommend that beetle-infested forests be managed to retain patches of mature trees as these could form refuges after the epidemic for animals that prey on beetles.
Kathy Martin, Andrea Norris and Mark Drever. 2006. Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: Implications for critical habitat management. BC Journal of Ecosystems and Management. 7(3): 10-24.