Chris Kirkpatrick

Distribution and Relative Abundance of Forest Birds in Relation to Burn Severity in Southeastern Arizona

Abstract The frequency of wild and prescribed fires in montane forests of the southwestern United States has increased after a century of fire suppression and subsequent fuels accumulation. To assess the effects of recent fires (median time since fire = 6 yr) on the montane forest bird community, we surveyed birds in 8 Sky Island mountain ranges in southeastern Arizona, USA, and examined how the distribution (i.e., presence–absence) of 65 species and relative abundance of 16 species correlated with evidence of severe and less severe fire at >1,500 survey points. We detected associations between fire and bird presence–absence for 17% of the 65 species analyzed and between fire and bird relative abundance for 25% of the 16 species analyzed. Most species (73%) were positively associated with burned areas and displayed stronger associations (i.e., more extreme odds ratios) with survey points that had evidence of severe as opposed to less severe fire. Positive associations with severe fire were strong (>3 to 1 odds) for western wood-pewee (Contopus sordidulus) and house wren (Troglodytes aedon), and negative associations with severe fire were strong for warbling vireo (Vireo gilvus) and red-breasted nuthatch (Sitta canadensis). Although recent fires appear to have had a positive effect on the distribution and relative abundance of several montane forest bird species in the region, these species are not the open-woodland birds that we would have expected to have benefited from fire based on previous research. Nevertheless, our results confirm associations between fire and bird presence–absence and relative abundance reported previously for 7 species of birds. Our results also provide new information for Graces warbler (Dendroica graciae) and greater pewee (C. pertinax), 2 species for which fire data were formerly lacking. Managers can use these data to make and test predictions about the effects of future fires, both severe and less severe, on montane forest birds in the southwestern United States.

Effect of Forest Fire Suppression on Buff-Breasted Flycatchers

Abstract Buff-breasted flycatchers (Empidonax fulvifrons) are rare in the United States due to a >90% reduction in breeding distribution. Previous authors have implicated fire suppression in montane woodlands as the underlying cause of population declines and range contraction. We examined the effect of fire suppression on population declines of buff-breasted flycatchers by comparing both presence and abundance of flycatchers in areas with and without evidence of recent fire in 9 mountain ranges in southern Arizona, USA. We also replicated previous survey efforts conducted in 1980–1983 and 1995–1996 to determine population trajectory. Twenty-two (63%) of 35 survey routes had negative trends, and the average slope of the declines was −0.105 (10.5% annual decline). The number of buff-breasted flycatchers detected at a survey point was positively associated with severity of recent fires, and flycatchers were particularly associated with areas that had evidence of high-severity surface fire. However, we failed to detect flycatchers in 5 canyons that recently burned, which suggests one or more of the following: 1) fire suppression is not the cause (or is not the main cause) of population decline and range contraction, 2) flycatchers do not colonize burned areas until >10 years postfire, 3) low- or medium-severity fires are insufficient to make fire-suppressed areas suitable for breeding flycatchers, or 4) local recruitment and immigration are insufficient to allow buff-breasted flycatchers to expand into recent fire-restored areas. Continued suppression of high-severity forest fires in the southwestern United States may eventually result in the extirpation of buff-breasted flycatchers. A landscape that includes a mosaic of recently burned and unburned forest patches appears to be most suitable for buff-breasted flycatchers. Prescribed burning is unlikely to help restore flycatcher populations unless burns are of high severity, conditions typically avoided during prescribed burns for safety reasons.

Trends in abundance of grassland birds following a spring prescribed burn in southern Arizona

We examined short-term trends in relative abundance and species richness of breeding and wintering grassland birds before (1996) and after (1997, 1998) a prescribed burn in a mesquite-invaded, desert grassland at Buenos Aires National Wildlife Refuge, Arizona. We surveyed birds and sampled vegetation along 1-km line transects bisecting 14 (7 control, 7 burn) 25-ha plots located randomly within a burn and adjacent control unit. Following a spring burn that was moderate in intensity and patchy in areal extent, we observed that ground cover was affected more strongly by burning than mesquite (Prosopis) cover, smaller mesquite were affected more strongly by burning than larger mesquite, and mortality of mesquite was low. No change in total abundance of birds was detected on the burn unit following fire for either wintering or breeding birds; however, species richness of breeding birds decreased in the first year post-burn. During the breeding season, mourning doves (Zenaida macroura) increased, whereas Botteris sparrows (Aimophila botterii), Cassins sparrows (Aimophila cassinii), and cactus wrens (Campylorphynchus brunneicapillus) decreased in relative abundance following fire. During the wintering season, ladder-backed woodpeckers (Picoides scalaris) and vesper sparrows (Pooecetes gramineus) increased and cactus wrens decreased in relative abundance following fire. Beyond species-level trends, we found stronger evidence of trends and greater magnitudes of relative change for breeding species associated with open grasslands compared to those associated with shrubs. The use of spring burns on the Refuge will likely improve conditions for open-grassland species that were historically more abundant by killing smaller mesquite and reducing mesquite recruitment. However, more intense and extensive fires will be required to reduce the presence of larger mesquite. Such fires would likely have a greater impact on birds associated with shrubs, and consequently, a greater impact on the avian community as a whole.

Probability of detecting band-tailed pigeons during call-broadcast versus auditory surveys

Abstract Estimates of population trend for the interior subspecies of band-tailed pigeon (Patagioenas fasciata fasciata) are not available because no standardized survey method exists for monitoring the interior subspecies. We evaluated 2 potential band-tailed pigeon survey methods (auditory and call-broadcast surveys) from 2002 to 2004 in 5 mountain ranges in southern Arizona, USA, and in mixed-conifer forest throughout the state. Both auditory and call-broadcast surveys produced low numbers of cooing pigeons detected per survey route (x̄ ≤ 0.67) and had relatively high temporal variance in average number of cooing pigeons detected during replicate surveys (CV ≥ 161%). However, compared to auditory surveys, use of call-broadcast increased 1) the percentage of replicate surveys on which ≥1 cooing pigeon was detected by an average of 16%, and 2) the number of cooing pigeons detected per survey route by an average of 29%, with this difference being greatest during the first 45 minutes of the morning survey period. Moreover, probability of detecting a cooing pigeon was 27% greater during call-broadcast (0.80) versus auditory (0.63) surveys. We found that cooing pigeons were most common in mixed-conifer forest in southern Arizona and density of male pigeons in mixed-conifer forest throughout the state averaged 0.004 (SE = 0.001) pigeons/ha. Our results are the first to show that call-broadcast increases the probability of detecting band-tailed pigeons (or any species of Columbidae) during surveys. Call-broadcast surveys may provide a useful method for monitoring populations of the interior subspecies of band-tailed pigeon in areas where other survey methods are inappropriate.

Importance of Montane Riparian Forest and Influence of Wildfire on Nest-Site Selection of Ground-Nesting Birds

Abstract We studied breeding populations of 2 coexisting ground-nesting birds, the red-faced warbler (Cardellina rubrifrons) and yellow-eyed junco (Junco phaeonotus), in high-elevation (>2,000 m) forested drainages of the Santa Catalina Mountains, Arizona, USA. From 2004 to 2005, we 1) estimated density and nesting success of breeding populations of red-faced warblers and yellow-eyed juncos, 2) identified nest-site characteristics for each species (i.e., used sites vs. random plots), 3) compared nest-site characteristics between the 2 species, and 4) examined effects of a recent (2003) wildfire on distribution of nests of both species. In addition, we estimated the areal extent of montane riparian forest (the preferred breeding habitat of both species) within high-elevation forests of the Santa Catalina Mountains. We found that red-faced warblers and yellow-eyed juncos were the 2 most common ground-nesting birds within our study area with an average density of 2.4 and 1.4 singing males/ha, respectively, along drainage bottoms. Compared to random plots, most red-faced warbler and yellow-eyed junco nests were located close (≤30 m) to drainage bottoms within a strip of montane riparian forest characterized by abundant brush, small woody debris, ferns, and forbs (both species), high number and diversity of saplings and small trees (red-faced warblers), and abundant shrubs and downed logs and less canopy cover (yellow-eyed juncos). Although both species nested in close proximity within montane riparian forest, nest-site characteristics differed between the 2 species, especially at finer spatial scales. For example, most yellow-eyed juncos nested adjacent to grass (principally Muhlenbergia spp.), whereas red-faced warblers nested adjacent to a variety of plant species, including grass, bigtooth maple (Acer grandidentatum), white fir (Abies concolor), and Douglas-fir (Pseudotsuga menziesii). Both red-faced warblers and yellow-eyed juncos avoided nesting in areas burned during a recent wildfire. In addition, nesting success was low for red-faced warblers (13%) and yellow-eyed juncos (19%) following the wildfire, suggesting an indirect negative effect of fire on breeding populations in the short-term. Montane riparian forest appears to provide important breeding habitat for red-faced warblers and yellow-eyed juncos. However, little research or conservation planning has been directed toward montane riparian forest in the region, even though this forest type is limited in its areal extent (<11% of high-elevation forest in the Santa Catalina Mountains) and increasingly threatened by disturbance. Results from our study can be used to facilitate the management and conservation of breeding populations of red-faced warblers and yellow-eyed juncos in high-elevation forests of the southwestern United States.

Nest Predators of Ground-nesting Birds in Montane Forest of the Santa Catalina Mountains, Arizona

Abstract We used time-lapse video cameras and track plates to identify nest predators of Red-faced Warblers (Cardellina rubrifrons) and Yellow-eyed Juncos (Junco phaeonotus) in high-elevation (> 2,300 m) forests of the Santa Catalina Mountains in southeastern Arizona. Mammals, especially gray fox (Urocyon cinereoargenteus) and cliff chipmunk (Tamias dorsalis), were the principal nest predators of Red-faced Warblers and Yellow-eyed Juncos within our study system, accounting for 89% of all nest depredations. Our study is one of the first to use video cameras at real nests to document the prevalence of nest predators in montane forest ecosystems. Additional research is needed to learn if mammals are the dominant nest predators in other montane environments.

RANGE EXPANSION OF THE BUFF-BREASTED FLYCATCHER (EMPIDONAX FULVIFRONS) INTO THE RINCON MOUNTAINS, ARIZONA

Abstract We detected buff-breasted flycatchers (Empidonax fulvifrons) while conducting surveys in the Rincon Mountains, Arizona, in 2000 (n  =  2), 2004 (n  =  4), and 2005 (n  =  5). Our detections represent the first records of buff-breasted flycatchers in the Rincon Mountains since 1911, suggesting that this rare species has recolonized a portion of its historical breeding range.

Response to Nestling Throat Ligatures by Three Songbirds

Abstract We attempted to collect diet samples using throat ligatures from nestlings of three songbird species in a riparian woodland in southeastern Arizona from May to August 2009. We had success with Song Sparrows (Melospiza melodia), observed adult Yellow-breasted Chats (Icteria virens) reclaim food from nestlings, and discontinued the use of throat ligatures when we observed an adult Aberts Towhee (Pipilo aberti) remove two, 3–4-day-old ligatured nestlings from its nest. Previous studies have reported problems (e.g., aggression toward nestlings by adults) with throat ligatures, but we are the first to document removal (and subsequent nestling mortality) in response to this technique. We urge investigators to exercise caution when using throat ligatures on species for which evidence of the safety and efficacy of this method are lacking, especially when nestlings are small in size relative to adults.