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Contributing variables to nest survival, and the breeding biology, of the western wood-pewee (Contopus Sordidulus) in southwestern Colorado.

Anthropogenic landscape changes associated with increased human population in the southwestern United States have resulted in destruction and degradation of numerous habitats including riparian zones (Fleischner, 1994; Stromberg, 2001; Miller et al., 2003) and Gambel oak (Quercus gambelii) woodlands (Marquiss, 1972; Engle et al., 1983; Lauver et al., 1989; Odell and Knight, 2001). Although a fairly rare habitat (<1% of surface area), riparian areas are disproportionately important for birds throughout the year. Johnson et al. (1977) reported that 77% of 166 avian species depend on riparian areas during at least part of their life cycles, and 51% are riparian obligates. Gambel oak woodlands occupy considerably more surface area, nearly 4 million ha in Arizona, Colorado, New Mexico, and Utah (Harper et al., 1985). Unlike riparian areas, fewer studies have focused on Gambel oak habitat (Marti, 1977; Rosenstock, 1998; Leidolf et al., 2000); therefore, we have comparatively little knowledge of the importance of this widespread habitat to birds.

Coupled with direct loss and destruction of these two habitats, global climate change has resulted in numerous alterations on a landscape level, often with cascading effects on bird communities. Climate, in part, orchestrates the distributions of many species (Simberloff, 2000), and changes in distribution have already been documented (Kelly and Goulden, 2008; Brusca et al., 2013). Climate change has also been implicated in the establishment and proliferation of invasive plant communities (Dukes and Mooney, 1999; Simberloff, 2000), beetle infestations (Waring et al., 2009; Williams et al. 2013), and catastrophic wildfires (Dale et al., 2001; Schoennagel et al., 2004), and it could become the most important contributor to loss of biodiversity (Dale et al., 2001; Jetz et al., 2007).

A growing concern focuses on management of biodiversity in the face of climate change (Heller and Zavaleta, 2009). However, basic natural history information that informs management is often lacking, even for common species occupying multiple habitats such as western woodpewees (Contopus sordidulus). According to the Breeding Bird Survey (Sauer et al., 2014), populations of western wood-pewees significantly declined throughout the United States and Canada between both 1966-2013 (-1.57%/y, [CI.sub.95%] = -2.20 to -1.09) and 2003-2013 (-0.19%/y, [CI.sub.95%] = -0.88 to -0.53%). Also, the National Audubon Society (The Climate Report, http://climate.audubon. org/birds/wewpew/western-wood-pewee) suggested a possible 74% decrease in the summer range of the western wood-pewee by 2080.

A decline of this magnitude is particularly alarming for a generalist species and suggests that its habitat requirements are not being met. Western wood-pewees are Nearctic-Neotropical migrants (Bemis and Rising, 1999); therefore, it is unclear whether their needs are not fulfilled within the breeding grounds (western United States and Canada), wintering grounds (in general, from Costa Rica through much of western South America), or along migratory routes. Few studies have focused on western wood-pewees (Chace et al., 1997; Curson et al., 1998; Bemis and Rising, 1999), yet understanding their habitat requirements within the context of nest success and potential effects of climate change is essential for effective management.

In this study we examined numerous habitat, land use, and nest-site variables that potentially contribute to nest survival of western wood-pewees in two of their common habitats: riparian areas and Gambel oak woodlands in southwestern Colorado from 1992-1998 and in 2001 and 2004. Examination of contributions to nest survival is particularly important because habitat quality can best be evaluated through demographic metrics (Powell and Steidl, 2000), as surveys without additional demographic studies can result in misleading conclusions (Johnson and Temple, 1986). Vegetation structure appears to shape bird communities in general, and large trees found in riparian areas add structural complexity (Powell and Steidl, 2000) and prey base (Bock and Bock, 1984). With a greater structural diversity providing more nest placement choices and foraging opportunities, we predicted nest survival would be higher in riparian areas than in adjacent upland Gambel oak habitat.

MATERIALS AND METHODS--Study Area--We studied the breeding biology (during 1992-1998, 2001, and 2004) of the western wood-pewee at the San Juan Basin Research Center in La Plata County, Colorado (37[degrees]14'N, 108[degrees]3'W; 2,316 m elevation; 2,541 ha). At our study site, western wood-pewees nested in two habitats: riparian habitat and Gambel oak-dominated woodland. Riparian habitat, which was 5-200 m in width, occurred along the La Plata River where narrow-leaf cottonwood (Populus angustifolia) was the dominant tree and where riverbirch (Betula fontinalis), thinleaf alder (Alnus tenuifolia), and willows (Salix species) also occurred in the comparatively sparse understory. Gambel oak-dominated woodland occurred in upland pastures with different grasses, and ponderosa pine (Pinus ponderosa), junipers (Juniperus species), and quaking aspen (Populus tremuloides) occurred infrequently; also, understory cover was low. In these two primary habitats, and depending upon pasture and year, cattle grazed at a density of 0-3.3 head/ha (Ortega and Ortega, 2009).

Data Collection--We searched for, and followed, western wood-pewee nests from early May into early August. Nests were followed every 1-3 d by direct observation or by use of mirror and pole. During each visit, we recorded nest contents (i.e., eggs or nestlings) and nest outcome (i.e., chicks fledged, depredation, abandonment, lost to weather, etc.). To determine mean incubation period, we calculated the length of time from laying of the last egg until hatching of the first egg (Ortega and Ortega, 2003a, 2003b). We determined nests as successful if they fledged at least one western wood-pewee chick (Chace et al., 1997; Ortega et al., 1997; Ortega and Ortega, 2000). We confirmed nest success directly by observing a fledging or locating fledglings in nearby vegetation. For nests in which nestlings were no longer present, if the nest was intact, flattened, or stretched (or some combination), with fecal material on the nest and nearby substrate and at an appropriate time for fledging, we determined these nests as successful.

Statistical Analyses--We used Program MARK (Colorado State University, Fort Collins, Colorado) to analyze nest survival in western wood-pewees (Dinsmore and Dinsmore, 2007; Rotella, 2016). Our primary covariates included habitat (riparian or Gambel oak-dominated woodland), grazing intensity (determined by forage utilization) by cattle within a pasture (moderate-to-high grazing intensity, low grazing intensity, and no grazing), nest substrate (live Gambel oak, live narrow-leaf cottonwood, or other substrate), nest height (m), nest substrate height (m), the ratio of nest height to substrate height, and year. Because our yearly sample sizes of nests over the period of 1992-1997 were small (range = 1-7 nests per year), for the covariate examining the effect of year on nest survival, nests for the years 1992-1997 (n = 22 nests) were combined into a single "early years'' designation (compared to 1998, 2001, and 2004) to increase our overall sample size of nests used in our Program MARK analyses. However, by doing this, interpretation of a possible year effect could be limited. Our first candidate model involved solely a constant daily survival rate (DSR), which is essentially the same as the maximum likelihood method for calculating nest success according to the Mayfield method (Mayfield, 1961, 1975; Rotella, 2016). We included seven other a priori candidate models that included each of the above-indicated covariates along with a constant DSR. These initial eight models were compared using an information-theoretic approach by using their Akaike Information Criterion values corrected for small sample size (AICc [Burnham and Anderson, 2002]). Comparison of a model's AICc value to the most supported model (i.e., the model with the smallest [AIC.sub.c] value) yields a [[DELTA]AIC.sub.c] value, and any models with a [[DELTA]AIC.sub.c] value [less than or equal to] 2 also had some support in explaining nest survival of western woodpewees (Burnham and Anderson, 2002). An additional MARK analyses output is the model weight ([w.sub.i]) and, in comparison to all models examined, it is a measure of the likelihood that a particular model has the most support. In addition, the ratio of one model with a larger model weight to another model with a smaller model weight provides a comparison of relative support of the former model to the latter model (Rotella, 2016; see Tables 1 and 2). After we obtained [[DELTA]AIC.sub.c] values and model weights for these eight a priori models, we then examined other exploratory models (i.e., we combined covariates) based upon a covariate's initial possible strength in explaining nest survival with a constant DSR (Table 1). We also allowed DSR to vary throughout the breeding season (this is the effect of date) and with respect to nest age (the possible effect of age of the nest within the nesting attempt; these two covariates are continuous variables). Allowing DSR to vary indicated that such models were much more supported than those with a constant DSR. Therefore, we also analyzed a wide variety of exploratory models (with a varying DSR and covariates in Table 2) to best explain nest survival in western wood-pewees.

We collected nest concealment data only in 1998, 2001, and 2004, and these data could not be obtained for all nests from all perspectives of a nest (see below); therefore, we did not include nest concealment as a covariate in our Program MARK analyses. To examine potential effects of nest concealment on nest success, we determined the percentage of a nest covered by vegetation from photos taken 1 m from the nest: above, from the side of a nest looking toward the center of the nest substrate, and below (Ortega et al., 2002). Using two-tailed Kruskal-Wallis tests (Zar, 1996), we found no differences in nest concealment among years from a photographic perspective and based upon nest success; therefore, we pooled years and used two-tailed Mann-Whitney U-tests to compare concealment values, within a photographic perspective, between successful and unsuccessful nests (Zar, 1996). We used nonparametric tests because much of our data were not normally distributed (Zar, 1996). Mean values were reported with [+ or -]1 SE, and P [less than or equal to] 0.05 was considered significant. Besides our use of Program MARK, we completed our other statistical analyses by our own calculations or by using SPSS, version 21 (SPSS: An IBM Company, Chicago, IL).

RESULTS--We found 118 active western wood-pewee nests. We did not know the final outcome of two nests, so they were not included in our Program MARK analyses (see below). Of 116 nests, 47 (40.5%) were not successful: of these, 44 (93.6%) were depredated, 1 (2.1%) was abandoned, and 2 (4.3%) were lost for other reasons. Sixty (51.7%) of 116 nests were in Gambel oak-dominated woodland and 56 (48.3%) were in riparian habitat. Similarly, 59 (50.9%) nests were constructed in Gambel oak, 34 (29.3%) were placed in live narrow-leaf cottonwoods, and 23 (19.8%) nests were in another substrate.

The earliest western wood-pewee eggs were laid on 2 June in both 1998 and 2004, and the latest clutch was initiated on 11 July 2001. The mean date for laying the first egg in the first seven nests within a breeding season (seven nests was our sample size in 1992) progressed earlier from a mean date of 14 June ([+ or -] 1.3 days) in 1992, to 10 June ([+ or -] 1.6 days) in 1998, to 7 June ([+ or -] 0.4 days) in 2001, and to 4 June ([+ or -] 0.5 days) in 2004; there was a significant difference in mean date for initiation of egg laying in the first seven nests among these 4 y of study (H3 = 18.376, P < 0.0001). For these seven initially active nests in these 4 y, apparent nest success (the ratio of successful nests to all nests in a year) did not differ among years ([G.sub.adj.,3] = 1.301, 0.75 > P > 0.50).

For nests discovered during incubation or earlier, and with confirmed clutch size, mean clutch size was 2.89 [+ or -] 0.04 (n = 97 nests, range = 2-4 eggs). In successful nests, the mean number of eggs hatched was 2.64 [+ or -] 0.08 (n = 66 nests, range = 1-4 eggs), and the mean number of chicks fledged was 2.48 [+ or -] 0.08 (n = 69 nests, range 1-4 chicks). The mean incubation length was 14.71 [+ or -] 0.17 d (n = 33 nests, range = 12-17 d), and the mean minimum and maximum nestling periods were 14.52 [+ or -] 0.17 d (n = 56 nests, range = 12-17 d) and 15.49 [+ or -] 0.19 d (n = 56 nests, range = 12-18 d), respectively. Six nests were parasitized with a single brown-headed cowbird (Molothrus ater) egg, and all parasitized nests occurred in Gambel oak-dominated woodland. Within this habitat, parasitized nests were at a mean height of 3.08 [+ or -] 0.33 m compared to a mean nest height of 2.80 [+ or -] 0.16 m (n = 54 nests) for unparasitized nests; however, the distributions of nest heights in parasitized and unparasitized nests were not significantly different (U = 203.0, P = 0.327). Brown-headed cowbird chicks hatched in only two nests, and these chicks were depredated. In two nests, cowbird eggs never hatched, and in two nests the parasitic eggs were also depredated.

We included 114 western wood-pewee nests in our Program MARK analyses. We excluded the two nests with unknown outcomes and two nests discovered at fledging and, therefore, these two nests had no exposure days. Our initial Program MARK analyses most supported a model with a constant DSR and with the covariate of the ratio of nest height to nest substrate height in describing nest survival in western wood-pewees (Table 1). The secondmost supported model included only a constant DSR, but three other candidate models (with a constant DSR and one other covariate) had [[DELTA]AIC.sub.c] values <2, suggesting there were several other covariates (substrate height, year, and grazing intensity) that were nearly equal in their support for describing western wood-pewee nest survival (Table 1). Combining these three covariates individually with the most supported model, and in one case combining two of these indicated covariates with the most supported model (constant DSR, the ratio of nest height to substrate height, grazing intensity, and year), resulted in several additional models with [[DELTA]AIC.sub.c] values [less than or equal to] 2 (Table 1).

However, when we allowed for a varying DSR, this initially produced a model far more supported in describing nest survival than those with a constant DSR (Table 2). In this secondary series of analyses, adding individually our primary seven covariates to our model of varying DSR also resulted in models with far more support in describing nest survival than did any of the models with a constant DSR. For example, of the eight presented models with a constant DSR compared to the 18 candidate models with a varying DSR, none have any support as indicated by their model weight values, [w.sub.i], of 0.000 (Table 2). Initially, nest age also resulted in a model with some support for explaining nest survival in western wood-pewees (Table 2). Therefore, we combined a varying DSR, and nest age, with our four most-supported individual covariates, and we suggested a few other models with combinations of covariates. Ultimately, with a varying DSR, our first six most-supported models all included either year, the ratio of nest height to substrate height, substrate height, or some combination of these covariates; however, models with the covariate of nest age were not as strongly supported (Table 2).

A closer examination of year revealed that apparent nest success (not the same as nest survival) was comparatively high from 1992-1997 (72.9%, n = 22 nests) and in 2004 (69.8%, n = 43), and it was lower in both 1998 (45.4%, n = 22) and 2001 (44.8%, n = 29). In fact, in four of the five most supported models, and where year was a covariate (Table 2), 1998 had a negative effect on nest survival (i.e., the p value varied from -0.460 [[+ or -] 0.407] to -0.521 [[+ or -] 0.418]); similarly, the year 2001 also had a negative effect on nest survival (i.e., the [beta] value varied from -0.946 [[+ or -] 0.388] to -0.995 [[+ or -] 0.389]).

In addition to year, the ratio of nest height to substrate height was a covariate in three of our five most-supported models (Table 2), and in all models it had a negative effect on nest survival (i.e., the [beta] value varied from -1.180 [[+ or -] 0.796] to -1.331 [[+ or -] 0.804]). That is, nests relatively lower in the tree had a higher nest survival. More specifically, in riparian habitat successful western woodpewee nests were placed relatively lower in the substrate (mean = 0.42 [+ or -] 0.03, n = 34) compared to unsuccessful nests (mean = 0.52 [+ or -] 0.04, n = 21), but the difference in relative nest placement was not quite significant (U = 251.0, P = 0.066). However, in Gambel oak woodlands, no difference existed in this ratio between successful (mean = 0.53 [+ or -] 0.02, n = 33) and unsuccessful nests (mean = 0.56 [+ or -] 0.03, n = 26, U = 381.0, P = 0.463).

The covariate substrate height had a small positive effect on nest survival (third most-supported model: [beta] = 0.028 [+ or -] 0.028; sixth most supported model: [beta] = 0.040 [+ or -] 0.028). That is, nests in taller trees had a higher nest survival. Specifically, in riparian habitat successful nests were placed in taller trees (mean = 13.82 [+ or -] 1.01 m, n = 34) than were unsuccessful nests (mean = 11.00 [+ or -] 1.71 m, n = 21), though these values were not significantly different (U = 454.0, P = 0.093). However, no difference occurred in Gambel oak habitat in substrate height between successful (mean = 5.25 [+ or -] 0.35 m, n = 33) and unsuccessful nests (mean = 5.25 [+ or -] 0.39 m, n = 26, U = 424.5, P = 0.945). Lastly, including only habitat, nest height, grazing intensity, or substrate in a model with a varying DSR did not result in supported models ([[DELTA]AIC.sub.c] = 3.707-5.068) for describing nest survival in western wood-pewees (Table 2).

Among years, and from a particular photographic perspective, there were no significant differences in nest concealment values in either successful or unsuccessful nests, respectively (Hg [less than or equal to] 5.337, P [greater than or equal to] 0.069). When combining nest concealment values among years, we found no significant differences in nest concealment between successful and unsuccessful western wood-pewee nests (from 1 m above the nest: successful nests, mean = 46.6 [+ or -] 8.6%, n = 25 vs. unsuccessful nests, mean = 51.7 [+ or -] 9.6%, n = 15, U = 178.5, P = 0.804; from 1 m from the side of the nest: successful nests, mean = 33.1 [+ or -] 5.4%, n = 23 vs. unsuccessful nests, mean = 35.2 [+ or -] 6.0%, n = 19, U = 206.5, P = 0.762; or from 1 m below the nest: successful nests, mean = 61.6 [+ or -] 3.4%, n = 40 vs. unsuccessful nests, mean = 60.8 [+ or -] 3.4%, n = 25, U = 496.5, P = 0.962).

DISCUSSION--Our Program MARK analyses suggests that no single covariate is most supported in describing nest survival in western wood-pewees. However, when we allowed the DSR to vary (effect of date across season), all models with a constant DSR lacked support. With respect to a varying DSR, in our most parsimonious model the estimated DSR decreased from 0.999 on the first day of the western wood-pewee breeding season to a value of 0.905 by the last daily interval. Therefore, western wood-pewee nests earlier in the breeding season have a higher probability of survival than nests later in the breeding season.

The other most-supported variables for western woodpewee nest survival include year, ratio of nest height to substrate height, and substrate height. We do not know why study years varied in nest survival. Chace et al. (1997) found similar nest success values for western wood-pewees in 1990 (83.3%, n = 12) and 1992 (80.0%, n = 10). Using the Mayfield method (Mayfield, 1961, 1975), Liebezeit and George (2002) witnessed a decline in nesting success in dusky flycatchers (Empidonax oberholseri) over a 3-y study period (1998 to 2000) from 36% (n = 53 nests) to 19% (n = 49 nests), but their DSRs did not differ. These two studies, along with our results, could simply demonstrate stochastic variation among years in the predator community. Perhaps the longer the study, the more likely one will observe chance variation among years.

Within riparian habitat at our study site, successful nests tend to be in taller trees and relatively lower in the nest tree (ratio of nest height to substrate height) compared to unsuccessful nests. In Gambel oak habitat, we found no differences in either tree height or ratio of nest height to tree height between successful and unsuccessful nests. Mature Gambel oaks are considerably shorter than mature narrow-leaf cottonwoods; therefore, pewees have more nest placement choices within the riparian habitat. If pewees throughout their range experience greater nest success in taller trees of riparian zones, this could suggest a conservation concern, as tamarisk (Tamarix species) and Russian olive (Elaeagnus angustifolia) invasions currently dominate many western riparian areas (Katz and Shafroth, 2003; Evangelista et al., 2007), and these nonnative trees are short compared to native cottonwoods. Also, many cottonwood galleries of the west are failing to generate new recruits due to lack of natural flooding regimes, channel incision, and lower water tables (Stromberg, 2001; Friedman et al., 2006; Lovell et al., 2009). As these decadent cottonwoods die, they might not be replaced by equally tall trees (Howe and Knopf, 1991).

The main sources of nest mortality for North American songbirds include predation (Martin, 1988, 1993; Martin and Li, 1992) and brown-headed cowbird parasitism (Friedmann and Kiff, 1985; Ortega, 1998). We found a very low level of cowbird parasitism on western woodpewees at our study site even though other species, such as yellow warblers (Setophaga petechia) and warbling vireos (Vireo gilvus), experienced moderate to heavy parasitism at the same site (Ortega and Ortega, 2000, 2003a). The low parasitism levels are consistent with zero-to-low levels others have found in western and eastern wood-pewees (Contopus virens, Chace et al., 1997; references in Ortega, 1998; Underwood et al., 2004; Swanson and Baker, 2016).

Some investigators have found higher concealment among successful nests compared with unsuccessful nests (Murphy, 1983; Martin and Roper, 1988; Kelly, 1993). However, similar to other findings (Best and Stauffer, 1980; Filliater et al., 1994; Howlett and Stutchbury, 1996; Burhans and Thompson, 1998), we found no relationship between concealment and success in pewees. The common known predators of arboreal nests at our study site include rock squirrel (Spermophilus variegatus), chipmunk (Neotamias species), deer mouse (Peromyscus maniculatus), raccoon (Procyon lotor), long-tailed weasel (Mustela frenata), black-billed magpie (Pica hudsonia), Steller's jay (Cyanositta stelleri), western scrub-jay (Aphelocoma californica), Cooper's hawk (Accipiter cooperii), sharp-shinned hawk (Accipiter striatus), and great horned owl (Bubo virginianus). The moderate level of observed predation by these potential predators at our study site is within the range of predation levels of other songbirds at our study site, from warbling vireos (25.7%, n = 35 nests, Ortega and Ortega, 2003a) to chipping sparrows (Spizella passerina, 52.6%, n = 76 nests, Ortega and Ortega, 2001).

We observed an increasingly early clutch initiation date, which could have been a response to climate change. At our study site, total precipitation and total snowfall amounts decreased steadily over the study years (1992-2004) and have decreased significantly to the current date (1992-2016; Western Regional Climate Center, http://www.wrcc.dri.edu/cgi-bin/cliMAIN. pl?co3016). Decreased water availability throughout the year, coupled with warmer June and July months (Western Regional Climate Center, http://www.wrcc.dri.edu/ cgi-bin/cliMAIN.pl?co3016), might have affected vegetative growth, insect availability, and the predator community. At least 20 avian species have responded similarly to global temperature increases (Crick et al., 1997; Dunn and Winkler, 1999; Winkler et al., 2002; Sanz, 2003). However, not all avian species (Torti and Dunn, 2005), or even all populations of the same species (Sanz, 2003), have responded in exactly this same manner to increasing global temperatures.

Variable DSR better explained nest success in western wood-pewees than did constant DSR. Our analysis suggests western wood-pewees nesting earlier in the season were more successful than those nesting later in the season. Although we do not fully understand the effects of global climate change on western wood-pewees, advancing the start of the breeding season, as we observed, appears to result in a higher probability of nest success.

With nest success well within the normal range, western wood-pewee population declines might be explained by variables not investigated in this study, such as changes in their food base and changes in the structure of habitats. Western wood-pewees feed on aerial insects (Daily et al., 1993). We did not measure the availability of various species of flies (Diptera) and wasps, bees, and ants (Hymenoptera) that make up the majority of the diet of western wood-pewees (Bemis and Rising, 1999), so we do not know if peak prey production coincided with advanced egg-laying date (Jones and Creswell, 2010), but nest success did not differ among years for the first seven nests of the year. However, we do not know if the life-cycle timing of various insects in their diet have changed with climate change, but it is crucial for many birds to time their breeding activities with peak availability of insects (Visser and Both, 2005; Charmantier et al., 2008).

We also did not quantify the angles of branches used for nest placement, but we believe that all western woodpewees in our study placed their nests on open horizontal branches, consistent with their nest placement throughout their range (Bemis and Rising, 1999). Both Russian olive and tamarisk trees have shrub-like branching patterns that do not favor formation of open horizontal branches appropriate for western wood-pewee nests. While western wood-pewees are not considered a riparian obligate, they often use these habitats (Skagen et al., 2005) but might not find suitable nesting sites in areas dominated by tamarisk and Russian olive.

The importance of understanding contributing factors to nest survival in species with declining populations is unequivocal. With loss and degradation of habitat throughout the arid Southwest, including Gambel oak woodlands and riparian areas, for management purposes it is important to understand the value of these habitats to declining populations (Bock, 1997). While we did not find a difference between our two habitat types in nest survival of western wood-pewees, we did not explore their use of other habitats with various land-use patterns. However, as a habitat generalist, relatively free from cowbird parasitism and with apparent flexibility in timing of their breeding season, their enigmatic population declines were not explained by this study and would require investigations of potential causes of population declines within their wintering grounds or along migratory routes (Bemis and Rising, 1999).

Field work was conducted with the help of many field assistants including S. Allerton, J. Amett, S. Backensto, J. Cable, S. Hena, T. Kreykes, H. Lyon, A. Maurer, B. Merris, J. Nardelli, P. Nylander, D. Palmer, C. Salaz, D. Sekayumptewa, F. Sforza, A. Skromme, C. Thornton, J. Vagneur, M. Vivalda, and S. Vorisek. A grant from the Howard Hughes Medical Institute to the Departments of Biology and Chemistry, Fort Lewis College, provided major funding from 1992-1997. Early in this period, J.C.O. also received funding from a Ford Foundation Fellowship (administered by the National Research Council). Funding in 1998, 2001, and 2004 was provided by grants to C.P.O. from the National Geographic Society, the National Fish and Wildlife Foundation, and the Colorado Wetlands Program. In 1998, C.P.O. and J. Amett received additional funding by Colorado Alliance for Minority Participation (National Science Foundation) grants. We thank A. Denham, D. Schafer, and D. Zalesky for granting permission to use the San Juan Basin Research Center, which at the time was under the direction of Colorado State University.

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Submitted 15 August 2016. Accepted 5 December 2016.

Associate Editor was Eddie Lyons.

<ADD> Joseph C. Ortega * and Catherine P. Ortega Department of Biology, Fort Lewis College, Durango, CO 81301 </ADD>

* Correspondent: ortega_j@fortlewis.edu Present address of CPO: 2507 County Road 220, Durango, CO 81303
TABLE 1--Summary statistics for the candidate models (all with a
constant daily survival rate, DSR) initially analyzed in Program MARK
for nest survival of 114 western wood-pewee (Contopus sordidulus)
nests at the San Juan Basin Research Center, La Plata County,
Colorado, 1992-1998, 2001, and 2004. [[DELTA]AIC.sub.c] is Akaike's
Information Criterion corrected for small samples sizes, [w.sub.I] is
the model weight, K is the number of model parameters, and Dev is the
model deviance.

Model                            [[DELTA]      [w.sub.i]   K   Dev
                                 AIC.sub.c]

Constant DSR + ratio nest        0.000         0.144       2   382.768
height to substrate height (a)

Constant DSR                     0.463         0.114       1   385.235

Constant DSR + ratio nest        0.647         0.104       7   373.374
height to substrate height +
grazing intensity + year

Constant DSR + ratio nest        0.726         0.100       4   379.482
height to substrate height +
grazing intensity

Constant DSR + substrate         0.746         0.099       2   383.514
height

Constant DSR + ratio nest        1.026         0.086       5   377.774
height to substrate height +
year

Constant DSR + year              1.053         0.085       4   379.810

Constant DSR + grazing           1.082         0.084       3   381.845
intensity

Constant DSR + ratio nest        1.778         0.059       3   382.541
height to substrate height +
substrate height

Constant DSR + nest height       2.104         0.050       2   384.872

Constant DSR + habitat           2.136         0.050       2   384.904

Constant DSR + substrate         3.585         0.024       3   384.348

(a) [AIC.sub.c] for the best model = 386.773.

TABLE 2--Summary statistics for the candidate models (most with a
varying daily survival rate, DSR) analyzed in Program MARK for nest
survival of 114 western wood-pewee (Contopus sordidulus) nests at the
San Juan Basin Research Center, La Plata County, Colorado, 1992-1998,
2001, and 2004. [[DELTA]AIC.sub.c] is Akaike's Information
Criterion corrected for small samples sizes, [w.sub.I] is the model
weight, Kis the number of model parameters, and Dev is the model
deviance.

Model                            [[DELTA]      [w.sub.i]   K   Dev
                                 AIC.sub.c]

Varying DSR + ratio nest         0.000         0.172       6   355.020
height to substrate height +
yeara

Varying DSR + year               0.194         0.156       5   357.224

Varying DSR + substrate height   1.556         0.097       6   356.176
+ year

Varying DSR + ratio nest         1.559         0.079       3   262.604
height to substrate height

Varying DSR + nest age + ratio   2.010         0.063       7   355.019
nest height to substrate
height + year

Varying DSR + substrate height   2.084         0.061       3   363.129

Varying DSR + nest age + ratio   2.161         0.058       9   351.142
nest height to substrate
height + grazing intensity +
year

Varying DSR + nest age + year    2.195         0.057       6   357.216

Varying DSR                      2.334         0.054       2   365.384

Varying DSR + ratio nest         3.403         0.031       4   362.441
height to substrate height +
habitat

Varying DSR + nest age + ratio   3.487         0.030       4   362.525
nest height to substrate
height

Varying DSR + habitat            3.707         0.027       3   364.752

Varying DSR + nest height        3.902         0.025       3   364.946

Varying DSR + nest age +         3.988         0.023       4   363.026
substrate height

Varying DSR + grazing            4.065         0.023       4   363.103
intensity

Varying DSR + nest age           4.187         0.021       3   365.232

Varying DSR + substrate          5.068         0.014       4   364.106

Varying DSR + nest age +         6.034         0.008       5   363.064
grazing intensity

Constant DSR + ratio nest        19.718        0.000       2   382.768
height to substrate height

Constant DSR                     20.182        0.000       1   385.235

Constant DSR + ratio nest        20.365        0.000       7   373.374
height to substrate height +
grazing intensity + year

Constant DSR + ratio nest        20.444        0.000       4   379.482
height to substrate height +
grazing intensity

Constant DSR + substrate         20.465        0.000       2   383.514
height

Constant DSR + ratio nest        20.774        0.000       5   377.774
height to substrate height +
year

Constant DSR + year              20.771        0.000       4   379.810

Constant DSR + grazing           20.800        0.000       3   381.845
intensity

(a) [AIC.sub.c] for the best model = 367.055.

(b) All constant DSR models have model weights, wi, of 0.00001.
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Date:Dec 1, 2016
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