Three secondary cavity nesters on the Penn State Campus that often nest in artificial nestboxes are the eastern bluebird (Sialia sialis), the tree swallow (Tachycineta bicolor), and the house wren (Troglodytes aedon). The objective of my study was to examine artificial nestboxes as a limiting resource within the three species and to determine the method of niche partitioning used to reduce competition. To test this, I examined 59 established nestboxes during the summer of 2009. Species nestbox selection was analyzed to determine significant differences in the time of box choice and habitat type. Timing of nestbox selection differed significantly among the three species (F = 20.94, p < 0.001). Eastern bluebird mean nest date was May 29 (+/- 3.00 days S. E.), for tree swallows: May 15 (+/- 1.27 days S. E.), and for house wrens: June 14 (+/- 3.62 days S. E.). I plotted box occupancy over time to examine the breeding techniques of the three species and found that eastern bluebirds occupy nestboxes throughout the season, tree swallows occupy during early season, and house wrens occupy during late season. Tree stem count within 11.3 m, shrub stem count within 5 m, percent forb, brush, and grass cover within 5 m, and percent coverage of entrance hole were analyzed for each nestbox. It was determined that only tree stem count had a significant difference in the boxes chosen by house wrens when compared to tree swallows and eastern bluebirds (F = 5.60, p = 0.008). It was determined that temporal separation between the three species was used to reduce direct competition while habitat separation was somewhat secondary.
