Use of cavities excavated by Syrian woodpeckers ( <i>Dendrocopos syriacus</i> ) by other birds and mammals in a forest in Boyer Ahmad County, Iran

Most cavity-nesting birds are considered limited by the availability of nesting sites, either in terms of obtaining suitable cavities for nesting or the time or energy to excavate new cavities. We investigated the rate of nest cavity reuse in a cold, multispecies forest for cavity-nesting birds in southwestern Iran. We measured 80 Syrian Woodpecker ( Dendrocopos syriacus ) nest trees for 9 years and their cavity reuse by 6 cavity-nesting bird and mammal species. Analysis examined the relationship between nest cavity reuse and the characteristics of the cavities and nest trees. In all cases, cavities that were abandoned after a year of re-occupancy remained unoccupied for the subsequent years thereafter. Once a species had adopted a cavity then it was used by the same species thereafter, with only seven (2.5% of 282) exceptions – in one nest, the occupying species changes in three successive years. Over the entire study period, for all the cavities and occupancies, the average number of years a cavity was reused was highest for the Eastern rock nuthatches and lowest for the Syrian woodpecker, but this was unaffected by species. The Mount Atlas Mastic was used by Syrian woodpeckers most frequently followed by Narrow-laved Ash trees and then Wild Pear trees (n = 54, 22, and 4, respectively). Almost all of the physical characteristics of the tree or cavity did not correlate with the proportion of nest re-occupied, except for circumference at breast height and diameter at breast height, which exhibited significant positive relationships. Vertical depth of the nest cavity was significantly affected by species reusing the cavity, largely because the Eastern rock nuthatches ( Sitta tephronota ) reused swallower nest cavities. As agriculture increases, logging and the removal of older trees decrease the availability of suitable nesting cavities for birds.