Twelve Rock Wren Nests in New Mexico

Facultative Nest Modification by Rock Wrens (Salpinctes obsoletus)

“…Rather than taking any available stones, Rock Wrens preferentially select thin, flat stones which they use to occlude cavity entrances. Though we did not sample available stones in the wider environment, observations indicated that the shape of ambient stones near nesting sites showed a wide range of dimensions approaching Includes 20 nest stones from nest B32790 collected by Florence Bailey in 1903, and catalogued at the Smithsonian Institution (Bailey, 1904).…”

“…Facultative placement and assembly of stones suggests flexibility and greater cognitive complexity than is sometimes attributed to nest construction behaviours (Lefebvre et al, 2004;Raby and Clayton, 2009). This flexible approach to cavity modification likely improves nest protection, and allows Rock Wrens to nest in a wide variety of cavity types and sizes (Bailey, 1904;Warning and Benedict, 2014).…”

“…Rock Wrens exhibit high variation in the size and type of nest cavities, and in the amount of stones that they add to nest cavities, which has led to much speculation as to the function(s) that the stones serve (Bailey, 1904;Smith 1904;Brewer 2010). Our previous work has shown that stones occlude cavity entrances and alter nest microclimates by keeping them drier during simulated rainfall events (Warning and Benedict, 2014).…”

Full Issue

“…They build cup nests of grasses and sticks typically located in natural cavities between boulders and rock fissures (Harrison 1979, Lowther et al 2000. Since the first descriptions of Rock Wren nests, workers have noted that many flat stones (1) are used to line the nest cavity, (2) are placed as a foundation under the nest cup, and (3) often extend beyond the nest cavity in a nest pavement (Bailey 1904, Merola 1995, Lowther et al 2000. Research in other species has shown that stones are used to augment avian nests for 4 primary functions: thermoregulation (hypothesized in at least 18 desert species), dryness, predator defense, and mate communication (Orr 1970, Afik et al 1991, Moreno et al 1994.…”

“…Early researchers hypothesized that the primary function of Rock Wren stone pavements was to decrease the effective size of the nest cavity and cavity entrance, referring to this outcome as ''cavity occlusion'' (Bailey 1904). We tested whether stones occlude cavity entrances and hypothesized that cavity occlusion may occur among Rock Wrens as a proximate mechanism that provides 3 benefits demonstrated in other species: (1) temperature amelioration, (2) nest dryness, and (3) predator defense.…”