Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities?

Published source details Brawn J. & Balda R. (1988) Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities?. The Condor, 90, 61-71.
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This study is summarised as evidence for the following.

	Action	Category
	Thin trees within forests Action Link
	Provide artificial nesting sites for songbirds Action Link

Thin trees within forests

A controlled before-and-after study in 1973-1983 in pine- Pinus spp. oak Quercus spp. woodlands in Arizona, USA (Brawn & Balda 1988), found that over 90% of nests on two managed plots were in nest boxes, compared to 30% on an unmanaged plot. This study is discussed in more detail in ‘Provide artificial nesting sites’.
Provide artificial nesting sites for songbirds

A controlled before-and-after study in pine-oak woodlands in Arizona, USA (Brawn & Balda 1988), found the population density six cavity-nesting songbirds more than doubled from on two out of three experimental plots (one thinned, one with 75% of the oak and pine foliage removed), following the installation of 60 nest boxes on each plot in 1979 (21-46 pairs/40 ha in 1973-5 and 1979 vs. 64-108 pairs/40 ha in 1980-3). A third plot with no management showed a small but non-significant increase in population density. Violet-green swallows Tachycineta thalassina, pygmy nuthatches Sitta pygmaea and western bluebirds Sialia mexicana all showed significant increases in population density. Nest box use by five of the species was significantly higher in open and thinned forest plots, with more than 85% of nests of violet-green swallow, pygmy nuthatch and mountain chickadee Parus gambeli in nest boxes, compared to 30-35% in dense forests. White-breasted nuthatches S. carolinensis used a lower proportion of boxes in all habitats (approximately 63% of nests in open and thinned forests in nest boxes and almost none in dense forest). Bluebirds nested almost exclusively in nest boxes in all habitats. Boxes were 1,900 cm³, made of woodcrete with entrance holes 3.2 or 3.8 cm in diameter and placed 5-11 m above ground.