Northern Pygmy Owl
Limiting Factors
Limiting factors for the Northern Pygmy Owl are considered to be those that increase juvenile or adult mortality, decrease productivity or nesting success, or reduce
habitat quality. Only those limiting factors that result from the direct or indirect activities of humans are discussed below.
Habitat loss and degradation is the primary limiting factor for the Northern Pygmy Owl throughout its range in North America. Pygmy owls are not primary excavators, so they rely on primary cavity nesters,
such as woodpeckers, or holes created by fungal decay or insects for nesting cavities. In Alberta, the cavities excavated by Black-backed Wodpeckers, Hairy Woodpeckers, Northern Flickers, and to a lesser extent Pileated Woodpeckers
are of prime importance to pygmy owls given the large diameter of entrance holes created by these species. Shortages of older, large diameter trees limit the numbers of woodpeckers, wood boring insects, and fungal decay, thereby limiting the numbers of secondary cavity nesters. In Alberta and elsewhere older forests are being harvested first, and the structural complexity and heterogeneity of these older stands has been correlated with high species diversity and specialization. The removal of snags and large diameter trees through intensive logging practices is detrimental to cavity-nesting birds. Current provincial operating rules for harvesting of mixedwood forest in Alberta make no provisions for the retention of areas of forest older than 70 years, or greater than 10
hectares in size, except where they exist along riparian buffer strips and other limited reserve lands.
The preference for logged areas by some woodpecker species may limit and reduce the amount of suitable nesting cavities for the Northern Pygmy Owl in preferred forest habitat. Further research into the habitat requirements of pygmy owls will be necessary before the magnitude of these differences in habitat preferences can be assessed fully. The careful placement of nest boxes can potentially help to alleviate shortages in nesting cavities, although their use by the Northern Pygmy Owl has not been documented.