San Luis Valley Regional Habitat Conservation Plan Draft for Public Review
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2.0HCP SettingThe San Luis Valley is a high mountain desert valley in south-central Colorado. The Valley is about 125 miles long and 65 miles wide, and is between the Sangre de Cristo Mountains to the east and the San Juan Mountains to the west, extending into the upper Rio Grande headwaters area of Mineral County. Most of the Valley is relatively flat, at an elevation of about 7,500 feet above sea level, while the upper portions within the HCP plan area in Mineral County reach about 9,000 feet. This arid Valley receives an average of 7 inches of precipitation a year, most of which is in the form of mid-summer rain. The growing season averages 90 days (Service 2003). 2.1Covered SpeciesSouthwestern Willow FlycatcherListing Status and HistoryThe southwestern willow flycatcher (Empidonax traillii extimus) was listed as endangered on March 29, 1995 (Service 1995). Critical habitat was initially designated on July 22, 1997 (Service 1997a), and corrected on August 20, 1997 (to clarify the lateral extent of the designation) (Service 1997b). Critical habitat units were initially designated in Arizona, California, and New Mexico. Areas in Colorado, Nevada, Texas, and Utah were not designated because of the limited range of the bird in those States. On May 11, 2001, the Tenth Circuit Court of Appeals revisited the critical habitat ruling and instructed the Service to issue a new critical habitat designation. On October 12, 2004, the Service published a proposal to designate critical habitat for the flycatcher in California, Arizona, Nevada, Utah, Colorado, and New Mexico (69 FR 60706). On October 19, 2005, the Service issued its final critical habitat designation, which excluded the Valley from critical habitat (70 FR 60968-60970). In response to a lawsuit, the Service agreed to reconsider the critical habitat designation by July 31, 2011, with a final rule to be published by July 2012. 12 The flycatcher also is listed as endangered by the State.
DescriptionThe flycatcher is a riparian obligate species, about 5¾ inches long, with a light olive-green back and wings, a whitish throat, a lighter olive-green breast, a pale yellowish belly, two indistinct wing bars, a faint eye-ring, and a beak that is dark on the upper mandible and lighter on the lower mandible, becoming dark at the tip. The flycatcher is confirmed by its wheezy “fitz bew” or “fit-za-bew,” song during nesting season. Flycatchers winter in southern Mexico, Central America, and probably northern South America (Stiles and Skutch 1989; Ridgely and Gwynn 1989; Howell and Webb 1995; Unitt 1997; Koronkiewicz et al. 1998; Unitt 1999). Recent genetic analysis of wintering birds (Paxton et al. 2008) suggests that the four subspecies occupy finite areas of the wintering grounds, but with overlapping ranges. The southwestern willow flycatcher (E.t. extimus) appears to be largely restricted to the center of the winter range (in the vicinity of Costa Rica). There are four currently recognized subspecies of E. traillii distributed throughout North America as summer residents (AOU 1998; Phillips 1948; Unitt 1987; Browning 1993). E.t. extimus (Aldrich 1951; Unitt 1987) can be distinguished from the other three subspecies, E.t. brewsteri, E.t. adastus, and E.t. traillii, through its morphology, song type, habitat use, structure and placement of nests (Aldrich 1953; Gorski 1969; Sogge et al. 2010), eggs (Walkinshaw 1966), ecological separation (Barlow and McGillivray 1983), and genetics (Seutin and Simon 1988; Winker 1994). The taxonomic status of E.t. extimus has been critically reviewed and confirmed multiple times based on morphological, genetic, and song data (Unitt 1987; Browning 1993; Paxton 2000; Sedgwick 2001). Although the overall subspecies’ ranges are distinct, Sedgwick (2001) and Paxton (2008) noted interbreeding/gradation zones in the boundary area between E.t. extimus and E.t. adastus. The Valley is within this interbreeding/gradation zone. According to recent research, within the probable range of E.t. extimus in Colorado, flycatchers appear to be very localized and uncommon. Breeding flycatchers within the probable range of E.t. extimus have only been confirmed on tributaries of the San Juan River and within the Valley (Owen and Sogge 1997; Sogge et al. 2001). However, considerable potential flycatcher habitat remains to be surveyed, and undiscovered breeding populations may exist.
Flycatcher Breeding BiologyMost flycatchers arrive at their breeding areas from early May to early June and depart in late July and August after nesting (Service 2002a). Male flycatchers generally arrive first at a breeding site, followed by females a week or two later. Male flycatchers are highly territorial, and establish territories by singing and interacting aggressively with other flycatchers after arrival at a breeding site (Service 2002a). Female flycatchers build an open cup-shaped nest about 3.15 inches high and 3.15 inches wide of grass, leaves, fibers, feathers, animal hair, and coarser materials in a fork of branches (Bent 1940). Nest height can range from 1.6 to 60 feet above the ground. Flycatchers lay three or four eggs, and the young fledge about 25 days after the last egg is laid. Flycatchers are insectivores, feeding on a wide variety of insects including wasps; bees; flies; beetles; butterflies; moths; caterpillars; flying insects; Hymenoptera, Diptera, and Hemiptera (true bugs); and spittlebugs (Beal 1912; McCabe 1991; Drost et al. 1997; Durst et al. 2008). Flycatchers glean prey from foliage, or catch them on the ground (Service 2002a). Genetic studies conducted by Paxton (2000) indicate that the northern boundary for the southwestern willow flycatcher is generally consistent with that proposed by Unitt (1987) and Browning (1993), and described in the Recovery Plan (Service 2002a). Within Colorado, the past and current status of the flycatcher is unclear (Service 1995; Service 2002b). Genetic studies have recently evaluated the genetic composition of flycatchers including those captured in the Valley (Paxton et al. 2008). Early genetic studies of flycatchers from throughout their range suggest that considerable genetic diversity exists within the extimus subspecies and within local breeding sites (Owen and Sogge 1997), and that flycatchers sampled on the Alamosa NWR and BLM’s McIntire Springs belong to the endangered extimus subspecies (Busch et al. 2000). However, studies on vocal identities of flycatchers found that pure forms of E.t. extimus apparently do not occur in Colorado, and that the southernmost populations in Colorado are acoustically similar to more northerly populations known to be adastus, suggesting moderate introgression between extimus and adastus (Sedgewick 2001). More recent genetic studies could not identify a distinct genetic boundary line between the two subspecies and suggest that the boundary between the two subspecies should be thought of as a region of genetic overlap (Paxton et al. 2008; Paxton 2000). The Valley is within the region of genetic overlap. Flycatcher Breeding HabitatIn general, flycatchers breed in tall dense riparian habitat with low gradient streams, wetlands, or saturated soils usually nearby, at least early in the breeding season (Bent 1940; Stafford and Valentine 1985; Harris et al. 1987; Spencer et al. 1996). The Service has reported that “occupied sites always have dense vegetation in the patch interior. These dense patches are often interspersed with small openings, open water, or shorter, sparser vegetation, creating a mosaic that is not uniformly dense (Service 2002a, p. 11; Appendix D). In most cases, this dense vegetation occurs within the first 10 to 13 feet (3 to 4 meters) above ground. The canopy density at nests generally ranges from 75 to 90 percent. Thin strands of dense vegetation are generally not suitable; and patch size, arrangement of patches, and open areas appear to influence whether an area is occupied. Breeding habitat at high elevation sites (greater than 6,200 feet) is characterized by one distinct vegetation layer and no over or understory layer. However, most breeding habitat contains dense branching and twig structure within the lower 6.5 feet (2 meters). In addition, proximity to water is important to flycatchers, with breeding territories often near slow-moving or standing water, a marsh, and/or saturated soils. The average canopy heights range from 10 to 23 feet (3 to 7 meters) (Sogge et al. 1997a). Site Fidelity, Movement, and Territory SizeBanding studies over several years have shown that most flycatchers return to their former breeding sites; however, they regularly move among sites within and between years (Service 2002a). From 1997 to 2000, 66 to 78 percent of flycatchers known to have survived from one breeding season to the next returned to the same breeding site (Id.). From studies at Roosevelt Reservoir in Arizona, site fidelity, where a site is defined as all patches within a specified area, is higher than patch fidelity — site fidelity ranges up to 92 percent depending on the method of calculation, while patch fidelity ranges up to 54 percent (Newell et al. 2005; Koronkiewicz. 2002). Flycatchers that move to new sites more commonly move within-drainages than between-drainages (Kenwood and Paxton 2001; Newell et al. 2005). Individual movements of banded flycatchers have been recorded over distances of up to 160 miles from the original banding site (McKernan and Braden 2001; Newell et al. 2005). Depending on the vegetation type, quality of the habitat, nesting stage, and population density, territory size can range from 0.25 to 5.7 acres (Service 2002a; Sogge et al. 1997b). Home range data for the flycatcher have been collected from radio-tracking studies at Roosevelt Reservoir in recent years (Cardinal 2005; Cardinal and Paxton 2004, 2005). Information from 23 flycatchers that were tracked using radio telemetry indicates a wide variation range of movement among individuals and before, during, and after nesting. Prior to nesting, home ranges were generally small, with a mean of about 1.4 acres (Cardinal 2005). During nesting, the mean home range was slightly less than 1 acre (Id.). Territories are often unevenly distributed within a habitat patch and tend to be clumped together. Some biologists consider flycatchers semicolonial nesters (Service 2002a). Cardinal (2005) summarized territory and home range sizes from several studies of other flycatcher subspecies, which range from less than 1 acre to more than 4 acres. At a landscape scale, Hatten and Paradzick (2003) report that dense patches of vegetation within an 11.1-acre (4.5 hectare (ha)) neighborhood provide refuge, foraging, and dispersal habitat for juvenile and adult flycatchers. This includes surrounding meadow and upland habitat. The home range and territory size has not been determined for the flycatcher; however, studies conducted on SWAs in 2007 showed that territory size may be small and immediately adjacent to or overlap other territories (WEST 2007). Based on the above information, this HCP conservatively assumes that the average territory size for breeding flycatchers in the Valley is 1 acre nested within a larger breeding neighborhood of approximately 11 acres that overlaps and is shared with other breeding flycatchers. Local Habitat ConditionsThe flycatcher Recovery Plan notes that most high elevation (greater than 6,230 feet/1,900 meters) sites are found in habitat dominated by native trees and shrubs, are dominated by a single species of willow, and generally consist of less vertically structured and narrower habitat patches (Service 2002a, p. 12). Four habitat types have been identified as appropriate for breeding flycatcher pairs throughout their range: (1) monotypic high-elevation willow, (2) monotypic exotic, (3) native broadleaf dominated, and (4) mixed native/exotic. Along the Rio Grande in the northern portion of the Valley, two of these habitat types have been identified: (1) native broadleaf dominated and (2) monotypic high-elevation willow (WEST 2007). The native broadleaf dominated habitat type is composed of a single species of willow, or a mixture of broadleaf trees and shrubs such as narrowleaf cottonwood and sandbar willow. This habitat type exhibits heights ranging from 10 to 13 feet (3 to 4 meters) and contains a distinct overstory with an easily identifiable subcanopy layer and a dense mixed understory (Id.). Measurement of habitat characteristics at flycatcher detection locations along the Rio Grande (WEST 2007) found that flycatchers were associated with:
Habitat characteristics along the southern portion of the Rio Grande and Conejos River may vary slightly from the northern Rio Grande. The Environmental Assessment for the Lillpop Ranch addition to the Alamosa NWR (Service 2002b) describes the habitat on the Alamosa NWR as monotypic stands of sandbar willow and peachleaf willow with little narrowleaf cottonwood overstory bordering the Rio Grande. These willow stands typically range from 10 to 40 feet (3 to 12 meters) in width. Local agency biologists (Stone, pers. comm. 2005; Lucero, pers. comm. 2005) who are familiar with occupied flycatcher habitat conditions in the Valley have observed the following habitat patterns that vary from the guidance in the Recovery Plan, yet are important for nesting success and site fidelity for flycatchers in the Valley:
Overall, vegetation characteristics of occupied flycatcher habitat across the Valley consists of smaller sized native vegetation patches, both in patch width and height, than the overall habitat conditions described in the Recovery Plan. Additionally, the adjacent foraging habitat (such as standing water, wet meadows, and tall grasses) appears to have a greater influence on site use in the Valley than the Recovery Plan suggests. This juxtaposition of willow patches to foraging habitat may explain the occurrence and reoccurrence of territories at sites that otherwise provide marginal habitat structure (Lucero, pers. comm. 2005). These observations suggest that a diverse riparian structure, and the surface water infrastructure that supports that structure (such as natural stream channels and irrigation canals/ditches), are important components of flycatcher habitat in the Valley. Abundance within the San Luis ValleyAccording to the Recovery Plan (Service 2002a), territory is the unit of measure. Flycatchers are a territorial species, where males select and defend exclusive breeding territories in which they attempt to attract a mate and breed. Because it can be difficult to determine whether a particular male is paired with a female, the Service selected “territory” as the unit of measure for recovery goals (rather than “pairs”), recognizing that generally one territory equates to two flycatchers (one male and one female). This HCP uses this definition of territory to maintain consistency with the Recovery Plan and U.S. Geological Survey (USGS) reporting. Based on regional survey data through 2003 compiled by the USGS, Durst et al. (2005a) estimated the Valley flycatcher population at 73 territories (the Recovery Plan set a goal of 50 territories for the San Luis Valley Management Unit). Subsequent surveys in 2004, 2005, 2007, 2009, and 2010 (BLM 2005, 2009, West 2007, 2010) did not include all known occupied sites for flycatchers. Data from 2004 (Durst et al. 2005b) identified six sites with 57 territories in the plan area. The Service, CPW, U.S. Forest Service (USFS), and BLM conducted surveys at a variety of locations in the Valley from 2002 to 2004. The survey results from 2004 indicate 84 individual flycatchers were observed in the Valley; however, caution should be used when interpreting these results since not all locations were surveyed every year. Flycatchers have been consistently observed at McIntire -Simpson (BLM), Alamosa NWR, Higel SWA, and Rio Grande, SWA. Willow flycatchers have also been occasionally detected at La Garita (BLM) and Hot Creek and Sego Springs SWAs. Additionally, surveys conducted on a private ranch along the Rio Grande in 2010 yielded a single flycatcher detection (WEST 2010). No flycatchers have been observed during numerous surveys conducted on USFS land. The general locations of known flycatcher detections are shown in Figure 2. Survey data from 2005 suggest that the number of flycatcher territories on SWA lands and the McIntire/Simpson properties are consistent with the 2003 results. Surveys conducted in 2005 identified 28 probable and six possible territories on the Rio Grande/Shriver-Wright SWA, while no territories were identified at the Hot Creek or Sego Springs SWAs (Hawks Aloft 2005). Surveys were not conducted at the Alamosa NWR in 2005. Surveys conducted on the Rio Grande and Higel SWAs in 2007 identified 14 flycatcher territories. This number is less than reported from previous surveys (Hawks Aloft 2003, 2004, 2005), but may be a reflection of slightly different survey goals and methods. The 2007 survey focused on specific sampling areas to correlate flycatcher detections with vegetation characteristics, and followed strict criteria to avoid double counting. Thus, the total survey area and number of territories recorded may not be as extensive as previous surveys (WEST 2007). Figure 2. Known Flycatcher and Cuckoo Detections
Yellow-billed CuckooStatus and HistoryIn 1998, a petition was filed with the Service to list the western subspecies of yellow-billed cuckoo (Coccyzus americanus occidentalis) as a threatened subspecies or a distinct population segment. In 2001, the Service noted that listing was warranted as a distinct vertebrate population segment west of the Continental Divide, but precluded the listing due to higher priority listing actions (66 FR 38611, July 25, 2001). As of the writing of this HCP, C.a. occidentalis was not Federally protected, but was considered a species of special concern by the State. DescriptionThe cuckoo is a medium-sized bird about 12 inches (30 cm) in length, and weighs about 2 ounces (60 grams). The species has a slender, long-tailed profile, with a stout and slightly down-curved bill, which is blue-black with yellow on the basal half of the lower mandible (bill). The plumage is grayish-brown above and white below, with rufus primary flight feathers. The tail feathers are boldly patterned with black and white below. The legs are short and bluish-gray, and adults have a narrow, yellow eye ring. Juveniles resemble adults, except the tail patterning is less distinct, and the lower bill may have little or no yellow. Males and females differ slightly, as males tend to have a slightly larger bill (Hughes 1999). Breeding BiologyCuckoos are very secretive birds and have unique reproductive characteristics involving a very rapid breeding cycle. Onset of breeding is apparently correlated with an abundant food supply, often coinciding with an outbreak of caterpillars or cicadas, and the average time required for egg laying to fledging is 17 days (Hughes 1999). Generally, cuckoos arrive at their breeding grounds late in the season, and both adults quickly build a stick nest in a tree or large shrub (Hughes 1999). Territory size averages 50-60 acres (20 -24 hectares) (NatureServe 2012). Cuckoos also have been known to participate in communal nesting behavior and are sometimes assisted by apparently unrelated helper males that can supply the young with up to 40 percent of their food (Hughes 1999). In general, the cuckoo nests in a variety of habitats including open woodlands, parks, and riparian woodlands (AOU 1998). The western subspecies (C.a. occidentalis) of cuckoo has a more restricted habitat requirement than its eastern counterpart (Ehrlich et al. 1992). The western subspecies is restricted to cottonwood and willow woodlands with a dense understory and large blocks of riparian habitat (Carter 1998; Franzreb and Laymon 1993). The cuckoo diet consists of mostly caterpillars, cicadas, grasshoppers, and other potential crop-destroying insects. As a result, cuckoos may exhibit irruptive behavior by moving into areas where cicada outbreaks are underway to capitalize on the available food source (Laymon 2001). The historical distribution of the western subspecies was widespread and locally common in California and Arizona. The cuckoo was locally common in a few river reaches in New Mexico; common very locally in Oregon and Washington; generally local and uncommon in scattered drainages of the arid and semiarid portions of western Colorado, western Wyoming, Idaho, Nevada, and Utah; and, probably uncommon and very local in British Columbia (Service 2001). The loss, degradation, and fragmentation of riparian habitat have been identified as the primary factors causing cuckoo declines in the western U.S. (Carter 1998; Service 2001). Estimates of riparian habitat losses were 90 to 95 percent for Arizona, 90 percent for New Mexico, 90 to 99 percent for California, and more than 70 percent nationwide (Service 2001). In Colorado, riparian habitats cover approximately 3 percent of the land area (Kittel et al. 1999), but estimates of riparian habitat loss are unavailable. Local ConditionsThere have been few confirmations of cuckoos nesting in western Colorado, and the species was probably never common and is now rare (66 FR No. 143; Carter 1998). Historical records from the Western Slope indicate that the cuckoo was found in cottonwoods along the Yampa and Uncompahgre rivers (Carter 1998). Colorado breeding bird atlas observations of cuckoos were based solely on the birds’ behavior and a single confirmed nest (Carter 1998). The National Park Service conducted cuckoo surveys in southwestern Colorado from 1988 to 1995 and found none. In addition, Park Service staff conducted surveys of the Mancos River six times over the course of 12 years and found none. There had been a few sightings of cuckoos along the Colorado River near Grand Junction, but no confirmed nesting sites (Service 2001). Cuckoos were only recently recorded in the Valley, and little is known about the specific habitat affinities or productivity of the few individuals observed along the Conejos River. Surveys to detect cuckoos on publicly owned lands in the Valley have been very limited. Cuckoos have only been documented in the Valley three times prior to 2004; one near Del Norte and two separate observations in 1980 near Monte Vista and the Great Sand Dunes. This species was observed along the Rio Grande near Del Norte in 2008 and 2011 (Ireland, pers. comm. 2010, 2011), and was observed consistently on the Conejos River with as many as four individual cuckoos detected in 2005 (Figure 2) (Lucero and Cariveau 2004). Detections of cuckoos along the Conejos River occur in mature cottonwood forests with a tall, dense, willow understory with pools of standing stagnant water (Lucero and Cariveau 2004). Breeding (active nests) in the Valley has never been confirmed, but the behavior and frequency of sightings indicate the birds are nesting (Lucero and Cariveau 2004). As of the writing of this HCP, the population trends/estimates and distribution were unknown. Cuckoos are usually found at elevations less than 6,600 feet (2,011 meters) (Service 2001), although the entire Valley is above 7,000 feet and cuckoos found near Del Norte are at about 7,900 feet. |