The Journal of Wildlife Management 76(2):382–390; 2012; DOI: 10.1002/jwmg.270 Habitat Relations Nesting Characteristics Of Mourning Doves in Central New Mexico: Response to Riparian Forest Change D. MAX SMITH,1 USDA Forest Service Rocky Mountain Research Station 333 Broadway SE, Suite 115, Albuquerque, NM 87102, USA DEBORAH M. FINCH, USDA Forest Service Rocky Mountain Research Station 333 Broadway SE, Suite 115, Albuquerque, NM 87102, USA DAVID L. HAWKSWORTH, USDA Forest Service Rocky Mountain Research Station 333 Broadway SE, Suite 115, Albuquerque, NM 87102, USA ABSTRACT Riparian forests of the American Southwest are especially prone to changes in composition and structure due to natural and anthropogenic factors. To determine how breeding mourning doves (Zenaida macroura) respond to these changes, we examined nest site use and nest survival in control plots, fuel reduction plots before and after mechanical thinning, and post-wildfire sites. The greatest number of nests (50%) were located in post-wildfire sites where resprouted vegetation and woody debris provided numerous nest sites in the understory. We found fewer nests in post-treatment fuel reduction plots (17%), where most were constructed in cottonwoods, and an intermediate number of nests in control and pre- treatment plots (33%), where most were constructed in exotic plants. The best-supported logistic-exposure nest survival model indicated that survival varied among years and with date. Models containing effects of forest type, study block, and nest site selection received little support, suggesting that survival was constant among plot locations, disturbance types, and nest sites. Our nest survival estimates were low relative to those from other studies, but productivity could offset mortality if adults make numerous nest attempts each year. Our results highlight the utility of woody vegetation and debris as understory nest sites for mourning doves and other riparian birds. Managers should devise methods to preserve or reestablish these nest sites when conducting fuel reduction, exotic vegetation removal, or post-fire restoration activities. ß 2011 The Wildlife Society. KEY WORDS fuel reduction, mourning dove, nest survival, New Mexico, riparian, wildfire, Zenaida macroura. Riparian forests are critical to conservation of breeding altered conditions (Howe and Knopf 1991, Busch and Smith bird populations in the American Southwest (Knopf and 1995, Shafroth et al. 2002). Previous studies have found that Sampson 1994, Rich et al. 2004). Owing to high levels of changes to riparian forests have increased nesting densities structural and species diversity in lowland riparian forests, of some bird species, such as Bewick’s wrens (Thryomanes this vegetation type provides greater numbers of nest sites for bewickii) and other species that occupy dense vegetation, generalist and riparian specialists than adjacent upland hab- but have decreased densities of others, such as yellow-billed itats, resulting in high densities of breeding birds (Carothers cuckoos (Coccyzus americana) and other broadleaf-obligates et al. 1974, Knopf et al. 1988). These forests have received (Hunter et al. 1987, Taylor 2003, Sogge et al. 2008). Few attention by land managers and researchers because they are studies, however, have compared nest site use and nest subjected to changes in composition and structure brought survival between areas undergoing multiple disturbances. upon by natural and anthropogenic factors (Stromberg This information is required to understand how changes et al. 2010). For centuries, humans have altered disturbance in structure and composition influence bird populations regimes along southwestern rivers by decreasing the magni- (Martin 1992). tude and frequency of floods and introducing novel distur- Mourning dove (Zenaida macroura) populations have de- bances such as intensive livestock grazing, wildfire, and clined in many areas of the United States including the manual vegetation removal (Busch 1995, Periman and Central Management Unit (CMU; Baskett 1993, Dolton Kelly 2000). In response, flood-dependent native vegetation et al. 2007, Sauer et al. 2008). In the western United States, has declined in some areas and has been replaced by exotic declines in mourning dove productivity have been linked to species, such as Russian olive (Elaeagnus angustifolia) and changes in natural and anthropogenic habitats that lower saltcedar (Tamarix ramosissima), that are better adapted to nest site availability (Miller et al. 2001). New Mexico is 1 of 2 states within the CMU where dove populations have Received: 31 July 2010; Accepted: 15 June 2011; Published: 2 December 2011 increased in recent years (Dolton et al. 2007) or remained relatively stable (Sauer et al. 2010). These trends suggest that 1E-mail: [email protected] nest sites have remained abundant and juvenile survival rates 382 The Journal of Wildlife Management 76(2) are high enough to compensate for adult mortality. Riparian extensive changes to hydrology and vegetation to increase forests provide much of the nesting habitat for mourning agricultural production and support population growth. doves and other land bird species in arid portions of the Historically, multi-aged stands of flood-dependant species, CMU (Carothers et al. 1974, Drobney et al. 1998, Hayslette such as Rio Grande cottonwood (Populus deltoides wislizenii) et al. 2000). An understanding of factors affecting nest and willow (Salix spp.), were created when germination sites site availability, nest site use, and nest survival of mourning were left exposed throughout the floodplain by flooding and doves in riparian forests is needed to understand population channel movement. In the early 20th century, levees, channel trends in New Mexico. stabilization devices, and conveyance canals were installed to The riparian forests of the Middle Rio Grande in central reduce flood damage and provide irrigation. The completion New Mexico provide an ideal opportunity to examine the of Cochiti Dam in 1974 further reduced the frequency and effects of vegetation change on mourning dove reproduction. intensity of floods (Howe and Knopf 1991, Scurlock 1998). During the last century, magnitude and spatial extent of Because of these changes, cottonwood stands are largely flooding has decreased, lowering recruitment of flood-de- confined between the levees and undergo little to no recruit- pendant, native plants (Howe and Knopf 1991). At the same ment (Howe and Knopf 1991, Molles et al. 1998). time, exotic vegetation and woody debris have accumulated As part of a large-scale fuel reduction experiment, we in the forest understory. These changes have contributed to divided the study area into three blocks (Smith et al. increased frequency of catastrophic wildfire (Stuever et al. 2009b). The north block was located in Bernalillo County 1995, Molles et al. 1998). Managers have begun mechanical on land owned and managed by City of Albuquerque Open clearing of exotic vegetation and woody debris to reduce fuel Space and the Middle Rio Grande Conservancy District loads and restore a native-dominated forest along the Middle (MRGCD). The middle block was in Valencia and Rio Grande. Such activities drastically change the structure Socorro Counties on MRGCD land and the south block and composition of the forest and alter the density of various was in Socorro County on MRGCD land and Bosque Del animals (Bateman et al. 2008). Wildfire also alters the struc- Apache National Wildlife Refuge (Fig. 1A). Each experi- ture and composition of riparian forests, creating shrub-like mental block contained 1 control plot and 3 fuel reduction conditions that support high densities of generalist birds treatment plots. Fuel reductions were applied between 2002 including mourning doves (Busch 1995, Smith et al. and 2005 (Table 1) and involved manual clearing of exotic 2009a, Stromberg et al. 2009). To examine nesting biology vegetation and woody debris from the understory (Smith of mourning doves in response to changes in structure and et al. 2009b). composition, we monitored nests in undisturbed riparian Control and pre-treatment plots typically consisted of a forest plots, plots cleared for fuel reduction, and post-wildfire cottonwood canopy with some Goodding’s willow (Salix sites. Our objectives were to 1) determine if nest site use gooddingii) also present in the canopy. Some exotic trees differs between forest types, 2) compare nest survival among including Siberian elm (Ulmus pumila) and white mulberry forest types, and 3) identify factors influencing nest survival. (Morus alba) were in the canopies of the north and middle blocks. Saltcedar and Russian olive were the most common exotic plant species and grew as large shrubs or small trees STUDY AREA (Fig. 2A). Russian olive is the dominant exotic species in the We established study sites along the Middle Rio Grande in north reaches of the Middle Rio Grande and saltcedar is central New Mexico (Fig. 1), where humans have made dominant in the south (Mortenson and Weisberg 2010). Figure 1. Location of (A) fuel reduction blocks and (B) post-wildfire sites in the Middle Rio Grande study area, New Mexico where we monitored mourning dove nests from 2000 to 2007. Each block contained 1 control plot and 3 fuel reduction plots. Smith et al. Mourning Doves in Central New Mexico 383 Table 1. Treatment status and number of mourning dove nests found at control and fuel reduction (FR) plots along the Middle Rio Grande, New Mexico from 2000 to 2007. Years searched Number of nests per year Plot Plot type Size (ha) Treatment year Pre-treatment Post-treatment Pre-treatment Post-treatment NO1a Control 16.1 2000–2007 1.1 NO2 FR 18.3 2002 2000–2002 2003–2007 1.7 1.0 NO3 FR 17.0 2003 2000–2003 2004–2007 1.8 0.8 NO4 FR 23.4 2002 2000–2002 2003–2007 2.0 1.4 MI1 FR 19.4 2003 2000–2003- 2004–2007 0.8 0.3 MI2 FR 29.2 2004 2000–2004 2005–2007 4.6 2.0 MI3 FR 13.2 2003 2000–2003 2004–2007 1.5 4.3 MI4–MI7b Control 35.0 2000–2007 6.8 SO1 Control 28.9 2000–2007 3.5 SO2 FR 15.5 2002 2000–2002 2003–2007 1.7 2.2 SO3 FR 26.7 2002 2000–2002 2003–2007 2.3 2.4 SO4 FR 15.5 2002 2000–2002 2003–2007 1.0 3.6 a Control plots did not receive fuel reduction treatments.