Conservation Assessment of the Willow Flycatcher in the Sierra Nevada

CONSERVATION ASSESSMENT OF THE WILLOW FLYCATCHER IN THE SIERRA NEVADA

Gregory A. Green Foster Wheeler Environmental Corporation Bothell, Washington

Helen L. Bombay Pioneer, California

Michael L. Morrison University of California, White Mountain Research Station Bishop, California

March 2003 CONTENTS

CHAPTER 1 INTRODUCTION ...... 1 SCOPE ...... 1 CURRENT MANAGEMENT STATUS...... 2 ACKNOWLEDGMENTS...... 2

CHAPTER 2 DISTRIBUTION AND TAXONOMY...... 3 DISTRIBUTION ...... 3 Breeding Range...... 3 Wintering Range...... 5 TAXONOMY ...... 5 POPULATION INSULARITY ...... 6

CHAPTER 3 REPRODUCTIVE BIOLOGY...... 8 PHENOLOGY...... 8 MATING SYSTEMS ...... 9 MATE FIDELITY...... 9 NEST SITE SELECTION AND BUILDING...... 9 RENESTING...... 10 EGG LAYING AND INCUBATION ...... 11 HATCHING...... 12 NESTLING STAGE ...... 12 FLEDGLING STAGE...... 13 BEHAVIORAL FACTORS INFLUENCING PRODUCTIVITY...... 13 Early vs. Late Nesting...... 13 Polygyny ...... 13

CHAPTER 4 FOOD HABITS AND PREY RELATIONSHIPS...... 16 GENERAL FORAGING ECOLOGY ...... 16 GEOGRAPHIC VARIATION IN DIETS ...... 16 PRINCIPAL PREY...... 16 HABITAT ASSOCIATIONS OF PREY ...... 17

CHAPTER 5 BREEDING HABITAT RELATIONSHIPS ...... 18 GENERAL ...... 18 HISTORY OF MEADOW HABITAT MANAGEMENT AND USE ...... 18 SUITABLE HABITAT ...... 20 SPATIAL SCALES...... 21 Nest Site ...... 21 Territory/Willow Stand ...... 22 Meadow 23 Broad-scale ...... 23 HABITAT ISOLATION ...... 23

ii K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 MEADOW HYDROLOGY...... 24

CHAPTER 6 HOME RANGE AND TERRITORIALITY...... 25

CHAPTER 7 MOVEMENTS...... 26 NATAL DISPERSAL...... 26 ADULT DISPERSAL...... 26 SURVIVAL AND RETURN RATES...... 27 PHILOPATRY...... 28

CHAPTER 8 POPULATION ECOLOGY AND RISKS...... 30 DEMOGRAPHY...... 30 Adult Survival...... 30 Juvenile Recruitment ...... 30 Fecundity ...... 30 Population Rate of Change ...... 31 ECOLOGICAL INFLUENCES ON SURVIVAL AND REPRODUCTION...... 32 Predators and Predation...... 32 Brood Parasitism ...... 33 EFFECTS OF HABITAT LOSS AND DEGRADATION ...... 34 POPULATION SIZE AND TREND ...... 35 DIRECT HUMAN EFFECTS ...... 36 Livestock Management...... 36 Water Developments ...... 37 Recreation ...... 37 Pesticides ...... 37 Roads 38 POPULATION DYNAMICS ...... 38 POPULATION GENETICS...... 39

CHAPTER 9 CONSERVATION STATUS...... 41 INTRODUCTION...... 41 Do Habitats Vary in Their Capacity to Support Willow Flycatcher Populations? ...... 41 What Are the Important Characteristics of Those Habitats?...... 41 Do Habitats Vary in Their Capacity to Support Principal Prey Species? ...... 41 If the Willow Flycatcher or Its Prey Select Particular Habitats, Are These Habitats Declining or Being Stressed by Current Management? ...... 42 Do the Life History and Ecology of the Willow Flycatcher Suggest That Populations Are Vulnerable to Habitat Change? ...... 42 What is the Current and Projected Conservation Status of the Willow Flycatcher? ...... 42

CHAPTER 10 MANAGEMENT CONSIDERATIONS AND UNCERTAINTIES...... 43

CHAPTER 11 RECOMMENDATIONS FOR MANAGEMENT...... 44 MEADOW CONDITION...... 44 MONITORING ...... 45

iii K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 HABITAT RESTORATION ...... 45 COWBIRDS...... 46

CHAPTER 12 RESEARCH NEEDS ...... 47

CHAPTER 13 LITERATURE CITED ...... 50

iv K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 TABLES Table 2-1. Number and distribution of known willow flycatcher point locations in the Sierra Nevada Forest Plan Amendment area by ownership (USDA Forest Service, unpubl. data)...... 4 Table 2-2. Number and distribution of known willow flycatcher territories (site average) in the Sierra Nevada Forest Plan Amendment area by ownership (USDA Forest Service, unpubl. data)...... 4 Table 8-1. Nest success for willow flycatchers across various studies...... 31 Table 8-2. Declines in willow flycatcher breeding sites and territories in the Sierra Nevada Forest Plan Amendment area (USDA Forest Service, unpubl. data)...... 35

FIGURES Figure 3-1. Generalized willow flycatcher breeding chronology for the Sierra Nevada, California. (Sources: Stafford and Valentine 1985, Flett and Sanders 1987, Valentine 1987, Sanders and Flett 1989, Bombay and Morrison, unpubl. data.) ...... 15 Figure 3-2. Willow flycatcher incubation onset dates for the central Sierra Nevada, California. (Sources: Stafford and Valentine 1985, Sanders and Flett 1989, Bombay and Morrison, unpubl. data.) ...... 15

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SCOPE includes data pertaining to Yosemite, Sequoia, and Kings Canyon National Parks. Populations of willow flycatchers (Empidonax Biogeographically, this administrative area traillii) have exhibited marked declines exceeds the Sierra Nevada mountain range to throughout the western United States (Sauer encompass much of the Modoc Plateau, the et al. 1997). The subspecies found in the southern Cascade Mountain Range, and the southwestern United States (E. t. extimus) western edge of the Great Basin. reached such critical levels that it was listed as Conservation assessments document all that is federally endangered in 1995 (USFWS 1995), known or unknown about a species, including while another subspecies, E. t. brewsteri, has its ecology, habitat needs, population levels, been extirpated from California’s Central and management risks. Conservation Valley (Grinnell and Miller 1944, Serena assessments also provide management 1982). Populations of brewsteri and another recommendations based on the researched subspecies, E. t. adastus, remain in the Sierra available knowledge. In turn, these Nevada, but these, too, have undergone management recommendations are substantial declines (Harris et al. 1987, incorporated into a single management Bombay et al. 2001, Stefani et al. 2001). strategy designed to benefit the species. Recognizing these population declines, the Essentially, this conservation assessment was USDA Forest Service has developed developed as a tool to guide future management strategies for conserving willow conservation strategy and recovery planning flycatcher populations in the Sierra Nevada for the Sierra Nevada populations of the under the Sierra Nevada Forest Plan willow flycatcher (Blankenship et al. 2001). Amendment. A core team of willow flycatcher experts The Regional Foresters for the Pacific (representing the USDA Forest Service, Southwest and Intermountain Regions U.S. Fish and Wildlife Service (USFWS), declared their intention in the Sierra Nevada California Department of Fish and Game, and Forest Plan Amendment (SNFPA) Record of the Southern Sierra Research Station) and the Decision (ROD) to complete a conservation authors met on 19 October 2001 to finalize assessment for the willow flycatcher and to the contents outline for the conservation make recommendations for future actions assessment and to identify information not (USDA Forest Service 2001). The readily available in the literature. The conservation assessment will be used to members of this team are Rosemary Stefani, support and further develop the willow Mary Whitfield, Teresa Benson, flycatcher conservation strategy identified in Karen Hayden, Jesse Wild, Ron Schlorff, the Record of Decision and specified in its John Robinson, Mary Flores, Helen Bombay, Standard and Guidelines (Appendix A). and Greg Green. The Sierra Nevada Forest Plan Amendment Two subspecies of willow flycatcher includes the Sequoia, Sierra, Stanislaus, predominate within the geographic area of the Eldorado, Inyo, Tahoe, Plumas, Lassen, and Sierra Nevada Forest Plan Amendment: Modoc National Forests, as well as the Lake E. t. brewsteri on the Pacific slope and Tahoe Basin Management Unit of the USDA E. t. adastus on the eastern slopes (Phillips Forest Service Pacific Southwest Region. In 1948, Unitt 1987, Browning 1993). These addition, the plan includes the portion of the subspecies are the focus of this conservation Humboldt-Toiyabe National Forest from the assessment. A third subspecies, the adjacent Intermountain Region that occurs in southwestern willow flycatcher the Sierra Nevada. This assessment also

1 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 (E. t. extimus), is currently believed to be ACKNOWLEDGMENTS limited to the extreme southern range of the The conservation assessment was produced Sierra Nevada. Because it has already under collaboration with Foster Wheeler received intense conservation focus since its Environmental Corporation and the USDA listing as federally endangered, including Forest Service, Region 5. We would like to development of conservation assessments and thank the members of the Sierra Nevada recovery plans (Finch and Stoleson 2000, Willow Flycatcher Core Team (identified USFWS 2001), coverage of E. t. extimus in above) for their support and guidance in the this assessment is limited to information initiation of this project, and especially relevant to the conservation and management Rosemary Stefani for her critical review at the of the other two subspecies. end. We are also grateful for the reviews by John C. Robinson, Jim Shackelford, Dave A. CURRENT MANAGEMENT Weixelman, Chris McCreedy, Mary Flores, STATUS Mary Whitfield, Teresa Benson, Tina Mark, and Diana Craig. Furthermore, this project All three subspecies of willow flycatcher would never have occurred without the occurring in California were listed as state support of Don Bandur, Laurie Fenwood, and endangered by the California Department of Diane Macfarlane. Fish and Game in 1990 (Steinhart 1990). The southwestern willow flycatcher Our greatest appreciation goes to John C. (E. t. extimus), found in the southwestern Robinson, the Forest Service representative United States including the Kern and Owens for this project. John was a tireless advocate River regions of southern California, was for this project, ensuring that adequate listed as federally endangered by USFWS in resources were available to meet the project 1995 (USFWS 1995). Both brewsteri and objectives, shepherding document sections to adastus are currently designated sensitive appropriate reviewers, and diplomatically species by USDA Forest Service, Region 5, resolving issues that arose from opposing or and are listed as species of concern by conflicting reviews. The claim to this USFWS, Region 1 (Williams and Craig document is as much John’s as it is ours. 1998). The willow flycatcher has been Finally, special thanks go to Judy Brown, identified as a regional “species at risk” in the Steve Flegel, Barbara Gould, Mary Jo Russell, Sierra Nevada Forest Plan Amendment. Brent Matsuda, and Mike Hall for their Activity-related standards and guidelines for assistance with the production and conserving willow flycatchers were developed organization of this project, as well as to under the Sierra Nevada Forest Plan Karen Cantillon for her tremendous editorial Amendment ROD (USDA Forest Service assistance. 2001).

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DISTRIBUTION Canyon National Parks fall within the presumed range of brewsteri, while Breeding Range populations on the Modoc, Toiyabe, and Inyo The breeding distribution of E. traillii has National Forests and the Lake Tahoe Basin been described as the conterminous United Management Unit are considered adastus. States, exclusive of the Southeast, and the The Tahoe and Sequoia National Forests southern margins of Canada (Browning 1993). straddle the Sierra Nevada crestline and, At its northern limit, E. traillii gives way to its therefore, may support both subspecies. sibling species, the alder flycatcher (E. However, the close proximity and similar alnorum), the distribution of which extends on habitat of these potentially separate into northern Canada and Alaska (Browning populations suggest that interbreeding may 1993). The exact northern limit of the willow occur (Phillips 1948, Williams and Craig flycatcher is still unclear due to difficulty in 1998). For example, Middle Fork Feather identification of E. traillii and E. alnorum River brewsteri and Little Truckee adastus are where the ranges of both species overlap. separated by only about 25 km. Because The range of E. t. extimus, the southwestern brewsteri and adastus have been separated willow flycatcher, extends into the southern based largely on subtle differences in reaches of the Sierra Nevada along the South coloration, and coloration can vary greatly Fork Kern River (near Weldon) and in the within populations, several authors have Owens Valley near Independence suggested that the two subspecies are (Unitt 1987), although recent genetic synonymous (Miller 1941, Behle 1948). investigations suggest that willow flycatcher Further, Paxton (2000) could not find genetic populations in the Owens Valley immediately separation between brewsteri and adastus and north of Bishop are extimus (Paxton 2000). attributed this to a large number of his All these sites occur within the Sierra Nevada samplings coming from a possible Forest Plan Amendment area, but only the intergradation zone (e.g., Sierra Nevada). 1,200-acre South Fork Wildlife Area on the Finally, Bombay et al. (2001) did observe a South Fork Kern River is managed by the willow flycatcher disperse approximately USDA Forest Service. Willow flycatcher 13 km (8 miles) between the Little Truckee records in the Sequoia and Inyo National River headwaters (east side) and the Yuba Forests’ interior have not yet been classified River headwaters (west side), suggesting that to subspecies and may represent intergrades the Sierra Nevada crestline is not a definitive between extimus and brewsteri, although the boundary between the two subspecies. From a inference is that west-slope Sequoia birds are conservation standpoint, it probably matters brewsteri, and east-slope Sequoia and Inyo little whether or not the Sierra Nevada birds are adastus (Unitt 1987). represents an intergradation zone, unless behavioral differences (e.g., dispersal patterns, Following the range maps of Unitt (1987) and habitat selection) between the purported Browning (1993), brewsteri can be found in subspecies call for different management the drainages flowing westward (e.g., Warner strategies. Valley), while adastus occur in the drainages flowing east (e.g., Little Truckee River). In Table 2-1 shows the number and distribution general, populations on the Lassen (including of willow flycatcher breeding sites (i.e., point Lassen Volcanic National Park), Plumas, locations) by forests and national parks within Eldorado, Stanislaus, and Sierra National Forests and the Yosemite, Sequoia, and Kings

3 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Table 2-1. Number and distribution of known willow flycatcher point locations in the Sierra Nevada Forest Plan Amendment area by ownership (USDA Forest Service, unpubl. data). Ownership National National Forest or Park* Forest Park BLM State City/County Private Total Percent Modoc 6 0 1 0 0 0 7 5% Lassen 10 0 0 1 0 8 19 14% Plumas 12 0 0 1 0 5 18 13% Tahoe 12 0 0 1 0 5 18 13% LTBMU 4 0 0 2 0 1 7 5% Eldorado 1 0 0 0 0 0 1 1% Toiyabe 5 0 0 2 0 0 7 5% Stanislaus 7 0 0 0 0 1 8 6% Inyo 8 0 1 0 4 4 17 13% Yosemite NP* 0 5 0 0 0 0 5 4% Sierra 9 0 0 0 0 4 13 10% Sequoia 8 0 0 1 0 1 10 7% Sequoia/Kings 0 5 0 0 0 0 5 4% Canyon NP* Total 82 10 2 8 4 29 135 100% Percent 61% 7% 1% 6% 3% 21% 100%

Table 2-2. Number and distribution of known willow flycatcher territories (site average) in the Sierra Nevada Forest Plan Amendment area by ownership (USDA Forest Service, unpubl. data). Ownership National National Forest or Park* Forest Park BLM State City/County Private Total Percent Modoc 10 0 1 0 0 0 11 3% Lassen 17 0 0 32 0 14 63 20% Plumas 15 0 0 2 0 8 25 8% Tahoe 35 0 0 3 0 23 61 19% LTBMU 6 0 0 2 0 4 12 4% Eldorado 1 0 0 0 0 0 1 0% Toiyabe 8 0 0 4 0 0 12 4% Stanislaus 14 0 0 0 0 1 15 5% Inyo 12 0 2 0 13 8 35 11% Yosemite NP* 0 12 0 0 0 0 12 4% Sierra 12 0 0 0 0 9 21 7% Sequoia 9 0 0 2 0 30 41 13% Sequoia/Kings 0 6 0 0 0 0 6 2% Canyon NP* Total 139 18 3 45 13 97 315 100% Percent 44% 6% 1% 14% 4% 31% 100%

4 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 the Sierra Nevada Forest Plan Amendment and subtropical areas from southern Mexico area by ownership. Most (61 percent) of the to northern South America (Gorski 1969, point locations are found on National Forest Meyer de Shauensee and Phelps 1978, System lands, but a substantial percentage Ridgely and Gwynn 1989, Stiles and Skutch (21 percent) is found in private lands. 1989, Ridgely and Tudor 1994, Howell et al. 1995, Unitt 1997); the flycatcher is thus Many of the USDA Forest Service sites termed a neotropical migrant. Significant support few willow flycatcher territories. wintering areas have recently been found in Only 44 percent of the territories (based on Costa Rica, Panama, and El Salvador where site averages) have been found on 82 National they occupy seasonal wetland habitats Forest sites, while 31 percent have been found (Koronkiewicz et al. 1998, Koronkiewicz and on only 29 private sites (Table 2-2). Exact Whitfield 1999, Lynn and Whitfield 2000, locations of all territories are not recorded, Koronkiewicz and Sogge 2000). and some meadows overlap multiple ownerships (National Forest, private, etc.); therefore, there may be a few instances where TAXONOMY some territories assigned to one ownership The willow flycatcher and its sibling species, may actually occur across boundaries on the alder flycatcher, were once recognized as another ownership. Similarly, survey efforts a single species: Traill’s flycatcher (Grinnell may not have occurred equally across all and Miller 1944). As similar as both species ownerships. Nonetheless, this dataset are in appearance, studies by Stein (1963) represents the best available information at revealed that they build different nests, sing this time. Although reported values may vary different songs, and do not interbreed where somewhat from actual values, the overall their ranges overlap. Consequently, in 1973, relative patterns of occupancy and ownership the American Ornithologists’ Union are assumed to be representative. reclassified the southern fitz-bew song type The number of territories is also skewed into the willow flycatcher and the northern towards just a few meadows. Only 6 of the fee-bee-o type (Aldrich’s [1951] nominate 135 known sites have ever been recorded to E. t. traillii) into the alder flycatcher. support 10 or more territories (USDA Forest Aldrich’s (1951) nominate E. t. campestris Service, unpubl. data). Collectively, these six then became E. t. traillii (Stein 1963, Unitt sites support a third of all territories and half 1987). Browning (1993) has since argued that of the currently active territories. Of these six E. t. campestris is a valid subspecies separate sites, two support extimus populations (South from E. t. traillii. E. t. campestris has been Fork Kern River and Owens Valley) that are described as a Midwest subspecies that has outside the scope of this Conservation extended its range eastward to western New Assessment. Only two (Perazzo Meadow and York, while E. t. traillii occurs along the Little Truckee) of the remaining four occur on eastern seaboard from Maine south to North National Forest System lands. Lacey Valley Carolina, then westward across the is private, and Warner Valley Wildlife Area is Appalachia to eastern Arkansas and Missouri owned by the California Department of Fish (Browning 1993). and Game. Three subspecies occur in California: E. t. brewsteri, adastus, and extimus. They Wintering Range have been distinguished from each other The winter range delineation for the willow based on distribution and color (Unitt 1987, flycatcher has been problematic, again due to Browning 1993). Unitt (1987) concluded that the confusion between willow flycatchers and willow flycatcher subspecies could not be alder flycatchers. However, recent defined based on measurements of size and investigations, some quite detailed, have proportions. In California, brewsteri ranges shown willow flycatchers to winter in tropical along the west slopes of Cascade/Sierra and

5 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Nevada ranges, while the adastus inhabits the concluded that there was not a gradual cline east slopes (Unitt 1987, Browning 1993). The and that many of the earlier reports suggesting southwestern willow flycatcher, extimus, intergradation were incorrect. Regardless, extends into the southern extreme of the although recent genetic research by Paxton Sierra Nevada province, with known locations (2000) concluded that extimus is genetically in the South Fork Kern River and Owens distinct from other subspecies and its northern Valley (Stefani et al. 2001), though the range (based on cytochrome-b pattern definitive range of the three subspecies in the analysis) follows closely the taxonomic area remains to be confirmed by further distributions of Unitt (1987) and Browning analysis. (1993), his data suggest an intergradation zone in southwestern Colorado. The subspecies brewsteri is darker above than other subspecies of willow flycatcher and has Interbreeding between brewsteri and extimus been described by Unitt (1987) as dark in California is also unclear. In his brownish olive. Unitt further described examination of museum collections, Unitt adastus as dark grayish green and extimus as (1987) found possible brewsteri/extimus pale grayish green. Miller (1941) and Behle intergrades from Los Angeles and San (1948) found enough color variation in Bernardino Counties. Curiously, his results eastern Oregon willow flycatchers to conclude also show a single breeding brewsteri and a that adastus and brewsteri were synonymous. single breeding extimus collected from the However, Browning (1993) reexamined the same location on the same date in 1917, eastern Oregon specimens and concluded that confounding conclusions. the darker individuals from the western edge range of adastus were actually migrant POPULATION INSULARITY brewsteri. Willow flycatcher breeding habitat in the Intergrades between adastus and brewsteri are Sierra Nevada can be described as “islands” known from Oregon and northern California, of meadows in a “sea” of forest conifers. but Browning (1993) believed that Inasmuch as these meadows (or clusters of interbreeding between the two subspecies is meadows) are geographically isolated from rather limited. However, Paxton (2000) other meadows, some level of population collected genetic samples from 232 adult insularity can be inferred. However, genetic extimus, traillii, adastus, and brewsteri at isolation, or lack of movement between 49 breeding sites and could not find populations, is much more difficult to significant genetic variation between adastus determine. Buskirk and Ruggiero (1994) and brewsteri. He attributed his results to pointed out that lack of movement between possible biased sampling of brewsteri along populations is difficult, if not impossible, to an intergradation zone with adastus prove. Further, habitat isolation is less (e.g., Sierra Nevada). Further, Paxton’s significant a factor for migratory birds than (2000) cytochrome-b sequencing data showed for any other vertebrate group for the obvious that Little Truckee River (Perazzo Meadows) reason they can circumvent long distances “adastus” were closely grouped with between isolated areas (Harris 1984). This “brewsteri” populations, including the Warner would be especially true for the willow Valley population on the Lassen National flycatcher, a neotropical migrant. Forest. Further research is necessary before Nevertheless, a significant number of genetic distinctions can be made between breeding sites in the Sierra Nevada appear no Sierra Nevada populations of brewsteri and longer to support viable breeding populations adastus. of willow flycatchers (USDA Forest Service, Although intergrades between adastus and unpubl. data). The remaining meadows, often extimus have also been reported regularly occurring in loose clusters, are now further (Behle 1985, Unitt 1987), Browning (1993) separated from the closest active populations.

6 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Implications of isolation of these patches (190 km; using extimus data from Nettor et al. depend on site fidelity and dispersal 1998), or should be twice the average capabilities and are further confounded by the dispersal distance (63.5 km; Nettor et al. presence of three subspecies, which may or 1998). Because the maximum of the closest may not interbreed. To qualify as a habitat neighbor distances in the Sierra Nevada, for isolate (Morrison et al. 1998), the distance breeding locations active since 1982, is only between a breeding location and its closest 44 km, or well below qualifying as an isolated neighbor should exceed either the maximum population, none of the breeding locations is a known willow flycatcher dispersal distance habitat isolate.

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PHENOLOGY hatch within 24 to 48 hours of each other (Bent 1942, King 1955, Walkinshaw 1966, As with other regions of the species’ range, Stafford and Valentine 1985, Flett and male willow flycatchers in the Sierra Nevada Sanders 1987, Valentine et al. 1988, Sanders generally arrive at breeding areas first, with and Flett 1989, Sogge 2000, Bombay et al. females typically arriving approximately 2001). In the Sierra Nevada, as elsewhere, 1 week later (Stafford and Valentine 1985, young willow flycatchers typically fledge at Sogge 2000, H. Bombay, pers. obs.). When 12 to 16 days of age and stay close to the nest comparing 2-year-old southwestern willow and each other for 3 to 5 days (Valentine et al. flycatchers in Arizona with older birds, 1988, Sanders and Flett 1989, Sedgwick Kenwood and Paxton (2001) reported that the 2000, Bombay et al. 2001). Recently fledged capture/resighting date (which approximates birds may repeatedly return to and leave the the arrival date) was significantly later for nest during this period (McCabe 1991, 2-year-old birds. Earliest arrival dates range Sedgwick 2000). Fledglings stay in the natal from late May to early June in the southern area a minimum of 14 to 15 days after Sierra Nevada (Grinnell and Storer 1924, fledging, possibly much longer (Walkinshaw Linsdale 1932, Stafford and Valentine 1985), 1966, Stafford and Valentine 1985, Bombay while willow flycatchers in the northern and Morrison, unpubl. data). Young typically Sierra Nevada typically begin arriving around fledge from nests from mid-July through the the first of June (Serena 1982, Sanders and end of August; later fledging dates are the Flett 1989, Bombay and Morrison, unpubl. product of renesting attempts (Stafford and data). Valentine 1985, Sanders and Flett 1989, Nest building usually begins within a week or Bombay and Morrison, unpubl. data). Adults two of pair formation, depending on the depart from breeding territories as early as arrival date and site/vegetation phenology mid-August, but may stay until mid- (Stafford and Valentine 1985, Harris 1996). September if they fledged young late in the Egg laying for first nest attempts sometimes season (Stafford and Valentine 1985, Bombay begins as early as the second week in June, 1999, Bombay and Morrison, unpubl. data). but more often begins between 25 June and Males that fail to attract or retain mates, and 5 July (Stafford and Valentine 1985, males or pairs that are subject to significant Valentine et al. 1988, Flett and Sanders 1987, disturbance (such as repeated nest predation, Sanders and Flett 1989, Bombay and etc.), may leave territories earlier (mid-July) Morrison, unpubl. data) (Figure 3-1). (Bombay et al. 2001). Renesting attempts result in laying dates Timing of fledgling departure is largely through the first week of August (Bombay unknown for the Sierra Nevada, but fledglings and Morrison, unpubl. data). Based on an have been documented foraging overlay of the incubation onset dates for independently 2 to 3 weeks after leaving the known renesting attempts compared to nest. All willow flycatchers appear to be gone presumed first nest attempts, it appears that from their territories by mid-September renesting attempts surge in numbers after (Stafford and Valentine 1985, H. Bombay, about 7 July (Figure 3-2). Nestlings are pers obs.). On 24 August 1997, a willow present in nests from early July through late flycatcher banded as a nestling was recaptured August (Sanders and Flett 1989). 29 days after fledging at a constant effort mist Incubation lasts 12 to 14 days from the date net station 350 meters from its natal territory the last egg is laid, and all eggs typically on the Tahoe National Forest (Bombay and

8 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Morrison, unpubl. data; J. Steele, unpubl. incidences of polygyny in a small population data). This suggests that fledglings may leave between 1983 and 1987 (4 of 20 nest their natal territories, but not begin long- attempts). Bombay and Morrison (unpubl. distance migration for some time (although data) found a minimum of nine polygynous sample sizes of one should be viewed males between 1997 and 2001, accounting for cautiously). This observation is supported by at least 9 percent of matings (18/204). In the fact that juvenile willow flycatchers other parts of the species’ range, polygyny is undergo their first prebasic molt before not uncommon, and polygyny rates as high as leaving the breeding grounds, while adults 15 percent have been reported in Oregon and delay their molt until reaching the wintering as high as 59 percent for southwestern willow grounds (Unitt 1987, Pyle 1997). Yong and flycatchers in California and Arizona Finch (1997) also reported that hatching year (Prescott 1986, Sedgwick and Knopf 1989, willow flycatchers tended to migrate through Sedgwick 2000, Sogge 2000, Davidson and the Rio Grande valley later than adults. Allen in press). Polygynous males usually, but not always, divide time and care between Figure 3-1 presents a generalized breeding females and nests (Sedgwick 2000). chronology for willow flycatchers in central and northern California. Assessment of data and literature available for the Sierra Nevada MATE FIDELITY suggests that, for most breeding locations Little information is available regarding mate north of Alpine County (in the vicinity of fidelity in the Sierra Nevada. On the Sierra Lake Tahoe), nest phenology is fairly uniform National Forest one female deserted her with nest initiation and fledging dates falling territory after nest failure and was replaced by within the middle of the time periods shown another female who used the remains of the in Figure 3-1 (Ingersoll 1913, Ray 1913, first nest to construct her own. The next year, Sanders and Flett 1989, Bombay et al. 2001, the first female was back on her original King and King in press, T. Ratliff, pers. territory with the same male (Stafford and comm.). Fewer data are available for the Valentine 1985). Sogge (2000) reported that portion of the Sierra occurring south of Alpine preliminary data for southwestern willow County. However, willow flycatcher nests flycatchers suggest that mate fidelity may be monitored in the 1980s in the Sierra National low and that even within-year mate shuffling Forest (South of Kings Canyon National may be common. Alternately, Sedgwick Park), as well as some historic records (2000) reported that 29.5 percent (Bennett 1934), suggest that nest initiation (n = 325 returns) of males and 36.0 percent occurs in the earlier portions of the nest stages (n = 267 returns) of females remated with a displayed in Figure 3-1 as one moves further previous mate over a 10-year period in south (Stafford and Valentine 1985, Valentine Oregon, and one pair remained together for et al. 1988). Extreme or record dates for any 5 consecutive years. stage of the breeding cycle may vary as much as a week from the dates presented. At higher elevations, for example, seasonal differences NEST SITE SELECTION AND in snow pack and timing of snowmelt may BUILDING delay starting dates for each stage by up to 2 Females select the nest site, collect the nest weeks (Valentine et al. 1988, Bombay and material, and construct the nest while the male Morrison, unpubl. data). follows her or perches nearby (McCabe 1991, Sedgwick 2000, Sogge 2000). Exact duration MATING SYSTEMS of the nest building stage is unknown for the Males are usually monogamous, but polygyny Sierra Nevada, but McCabe (1991) and Bent has been recorded in the Sierra Nevada. (1942) reported nest-building periods of 5 to Valentine et al. (1988) reported two 10 days. Holcomb (1974) reported 3.9 days for nest building in Nebraska and an

9 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 additional 1 to 6 days before the first egg was only 0.3 to 0.75 cm. Valentine et al. (1988) laid. In the Sierra Nevada, more than 10 days reported that 68 percent of stems at 22 nests have been documented between nest were less than 0.5 cm in diameter, and 96 completion and the laying of the first egg percent were less than 1.0 cm. In the north- (Bombay and Morrison, unpubl. data). central Sierra Nevada, Sanders and Flett (1989) and Bombay (1999) reported mean In the Sierra Nevada, willow flycatchers build supporting branch diameters of 0.62 cm (SD = open-cup nests approximately 9.5 cm tall and 0.54) and 0.71 cm (SD = 0.21), respectively. 8.5 cm in diameter (outside dimensions), exclusive of any dangling material at the Nest height varies considerably and may be bottom (Sanders and Flett 1989, Bombay correlated with height of nest plant, overall 1999). These dimensions suggest that willow canopy height, and/or height of the vegetation flycatchers in the Sierra Nevada build nests strata that contain small twigs and live growth that are somewhat larger than those built in suitable for nest support and concealment other parts of the species range (Sedgwick (Stein 1963, Flett and Sanders 1987, 2000, Sogge 2000). Frequently nests have a Valentine et al. 1988, Sanders and Flett 1989, bearded appearance due to additional dried Harris 1991, McCabe 1991). There are vegetation hanging up to 10 cm below the 42 nests, dated between 1898 and 1950, from base of the nest (Sanders and Flett 1989, the Sierra Nevada in the collection at the Sedgwick 2000, Sogge 2000). Western Foundation of Vertebrate Zoology. Of these, 29 document the nest height: the As elsewhere in their range, Sierra Nevada closest to the ground is from Bijou Marsh at willow flycatcher nests are typically Lake Tahoe and is recorded at 0.38 m, and the constructed using a primary base of dried highest is from Bear Valley in Mariposa grasses, sedges, forbs, and willow (Salix spp.) County in the western foothills and is bark (Sanders and Flett 1989, Valentine 1987, recorded at 5.5 m above the ground (mean = Sedgwick 2000). Nests are lined with finer 2.0 m, median = 1.8 m, SD = 1.2 m). stems, willow down, and the down or feathers Valentine et al. (1988) reported a range of from other bird species, especially waterfowl 0.77 m to 2.18 m in the south-central Sierra (Sanders and Flett 1989, Sedgwick 2000, Nevada (n = 22, mean = 1.49 m, SE = Bombay pers. obs.) When available, deer 0.78 m). On the Tahoe National Forest, hair, horsehair, and feathers can make up a Sanders and Flett (1989) reported a range in considerable portion of both the lining and nest heights of 0.70 m to 1.98 m (n = 20, outer portion of nests (Bombay pers. obs.). mean = 1.14 m, SD = 0.29 m). Bombay Manmade materials such as string, paper, and (1999) reported nest heights from 0.40 m to plastic bags are also included in some nests 2.50 m for the north-central Sierra Nevada (n (Sanders and Flett 1989, McCabe 1991, = 77, mean = 1.11 m, SD = 0.34 m). In the H. Bombay, pers. obs.) extreme northern Sierra Nevada, King and Nests are typically placed in the fork of a King (in press) reported nest heights from branch with the nest cup supported by several 0.9 m to 1.9 m (n = 10, mean = 1.3 m, small stems (Stein 1963, Flett and Sanders SD = 0.31 m). 1987, Valentine et al. 1988, Sanders and Flett 1989, Harris 1991, McCabe 1991). The main forked branch may be oriented vertically, RENESTING horizontally, or at an angle (McCabe 1991). Although occasionally reported for the Bombay (1999) reported that the mean southwestern willow flycatcher (Whitfield number of supporting stems at 70 nests was 1990, Sogge 2000, M. Whitfield, unpubl. 5.77 (SD = 1.60), and Sanders and Flett data), second clutches after a successful first (1989) reported the mean number at 9 nests nest are unknown for willow flycatchers in the was 4.7 (SD = 1.3). Stems supporting the Sierra Nevada (Stafford and Valentine 1985, nest cup are typically small with diameters of Sanders and Flett 1989, Valentine et al. 1988,

10 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Flett and Sanders 1987, Bombay and EGG LAYING AND INCUBATION Morrison, unpubl. data). Sierra Nevada Willow flycatcher eggs are buffy or creamy willow flycatchers frequently attempt a white, approximately 18 mm long and 13 mm second and even a third nest after earlier nest wide, with brown markings in a loose wreath failures (Stafford and Valentine 1985, at the blunt end (Bent 1942, Walkinshaw Bombay 1999, Morrison et al. 1999). 1966, Sedgwick 2000). Unspotted eggs (or Bombay et al. (2001) reported that renesting those that are nearly so) have been reported attempts between 1997 and 2001 accounted (Sedgwick 2000, H. Bombay, pers. obs.). for 12 to 35 percent of all nests annually Across the species range, clutch size is usually (n = 264 nests, mean = 27 percent, SE = 9). three or four eggs for first nests (Bent 1942, Nine of these were known to be third nesting King 1955, Sanders and Flett 1989, Whitfield attempts. Harris (1991) reported as many as and Enos 1996, Sedgwick and Iko 1999, six nest attempts in a single season for Sedgwick 2000, Sogge 2000), although southwestern willow flycatchers in the occasional five-egg clutches are reported in extreme southern Sierra Nevada. Substantial some bioregions (Holcomb 1974, Sedgwick declines in clutch size with subsequent 2000). Sedgwick (2000) reported mean first nesting attempts are reported for many regions clutch sizes ranging from 2.92 to 3.69 in five (Holcomb 1974, McCabe 1991, Sedgwick different study areas. In the Sierra Nevada 2000, Stoleson et al. 2000). (1997 to 2001), presumed first nest attempts Replacement nests, or new nests built for with data adequate to determine actual renesting attempts, are built in the same number of eggs laid had a mean clutch size of territory, typically within 50 m of the previous 3.52 eggs (n = 126 nests, SD = 0.68). Known nest (McCabe 1991, Bombay and Morrison, renests had a mean clutch size of 2.96 eggs unpubl. data). In the Sierra Nevada, the (n = 49 nests, SD = 0.61 (Bombay and distances of renests from previous nests range Morrison, unpubl. data). Flett and Sanders from within the same shrub to as far as 100 m (1987) reported 2.8 eggs per nest based on (Bombay and Morrison, unpubl. data). five nests with complete data. One egg is laid Although not documented in the Sierra each day until the clutch is complete, with an Nevada, renesting southwestern willow occasional day skipped (Sedgwick 2000). flycatchers have been known to reuse the Laying most frequently occurs in the morning same nest in a single year on a few occasions (Sedgwick 2000). Most authors report that (Whitfield 1990, Yard and Brown 1999). females perform all incubation activities Frequently, willow flycatchers disassemble (King 1955, McCabe 1991, Sedgwick 2000), failed nests in order to use the nesting material but Gorski (1969 in Sedgwick 2000), and to build new nests (Stafford and Valentine Yard and Brown (unpubl. data in Sogge 2000) 1985, McCabe 1991, H. Bombay, pers. obs.). reported occasional incubation by males. Many researchers report that second and third Exact timing of the onset of incubation nests are built much more quickly than first relative to egg laying is uncertain, with some attempts (McCabe 1991, Sedgwick 2000, authors reporting incubation to begin during Sogge 2000). Alternately, Holcomb (1974) laying, while others report onset to occur after reported no difference in the time involved in the last egg is laid (Sedgwick 2000, Sogge building first nests versus renests; rather, the 2000). Incubation lasts from 12 to 15 days mean time between nest completion and egg after the last egg is laid (McCabe 1991). In laying decreased from 3.1 days to 1.4 days. the Sierra Nevada, Sanders and Flett (1989) In the Sierra Nevada, replacement nest reported a 12-day incubation period. Bombay building and egg laying can occur and Morrison (unpubl. data) recorded similar (uncommonly) as late as early August incubation periods of 12 to 14 days. (Stafford and Valentine 1985, Sanders and Based on limited observations of two females Flett 1989, Bombay et al. 2001, Bombay and in Ohio, Holcomb (1972) reported that Morrison, unpubl. data).

11 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 females were at the nest 64 percent of the altricial nestlings cannot fully thermoregulate time, with attentiveness increasing later in the during this early stage of life (Welty 1962). incubation cycle. Mean attentive and The female provides most, if not all, of the inattentive bouts lasted 10.1 and 5.7 minutes, initial care of the young, although the role of respectively. Sogge (2000) reported similar the male in providing food increases with the unpublished results of 50 percent age and size of nestlings (Holcomb 1972, attentiveness during the day and constant Ettinger and King 1980, Prescott 1986). In incubating during nighttime hours for Washington, Ettinger and King (1980) southwestern willow flycatchers. reported that males visited the nest only 0.75 times as often as females. In Oregon, HATCHING Sedgwick (2000) found that the female McCabe (1991) reported that in Wisconsin all parents and male parents fed nestlings at three eggs hatch over 1 to 3 days, with 90 percent nests 59.3 percent and 3.7 percent of the time, of 160 clutches hatching in 2 days or less. respectively. A presumably unrelated adult of Females are known to remove and discard unknown gender provided the remaining eggshells away from the nests (McCabe 1991, 37 percent of feedings. Similarly, Sedgwick Sedgwick 2000). and Knopf (1989) reported that a polygynous male made 17.9 percent of all feedings at both of his mates’ nests. Both sexes remove fecal NESTLING STAGE sacs generated by nestlings, especially early in In the Sierra Nevada, the mean nestling period the nestling phase (McCabe 1991, Sedgwick appears to be slightly longer than that reported 2000). in other regions. At their Sierra Nevada study Bird blow flies (Protocalliphora) that sites, Sanders and Flett (1989) used an parasitize nestlings are common in the nests estimate of 14 days, and Bombay et al. (2001) of flycatchers, and willow flycatchers are found that most nests observed over 6 years of known hosts of Protocalliphora cuprina. study required 15 days before fledging Heavy blow fly infestations (e.g., 10 or more occurred. Extreme nestling periods of 19 to larvae per nestling) can make nestlings 20 days have been observed during extended anemic and more susceptible to starvation, periods of cool wet weather or very dry hypothermia, and other parasites like mites, conditions (Bombay and Morrison, unpubl. fleas, and lice. Severe blow fly infestations data). In Nebraska and Ohio, Holcomb may be lethal (T. Whitworth, (1972) reported a mean nestling stage of 12.5 www.birdblowfly.com), although studies of days and a range of 11 to 14 days. In the natural populations of Protocalliphora in Great Lakes region, McCabe (1991) and 48 species of birds indicate that the larval Walkinshaw (1966) reported 14 to 15 days populations are usually too small to kill or and 13.8 days, respectively. For southwestern seriously injure most nestlings (Whitworth willow flycatchers, Sogge (2000) reported a and Bennett 1992). In most areas, nestling stage that ranges from 12 to 15 days; approximately 5 to 10 percent of infested however, the nestling period used for nests are likely to have sufficient larval Mayfield calculations in Arizona is 12 days populations to make nestlings sick (Rourke et al. 1999). (T. Whitworth, www.birdblowfly.com). Brooding behavior in the form of sitting low Though blow fly parasite loads in willow over the young to protect them from cool wet flycatcher nests in the Sierra Nevada have not weather, or standing on the nest edge and been investigated, nestling parasites are not shading them with outstretched wings, occurs believed to be a significant threat to the most frequently during the first 5 days after willow flycatcher population. hatching (McCabe 1991, Sedgwick 2000). This behavior is important because these

12 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 FLEDGLING STAGE winter) than young that fledged after 15 July (n = 1,144). Likewise, Whitfield and Sogge Willow flycatcher nestlings are capable of (1999) found, over an 8-year-period, that flight 2 to 3 days prior to natural fledging and, southwestern willow flycatchers that fledged therefore, may be prompted to prematurely early were almost twice as likely to return the fledge if disturbed by predators or researchers following year. Similar results have been (Rourke et al. 1999, Sogge 2000). Once reported for white-crowned sparrows fledging occurs, young stay near the nest and (Zonotrichia leucophrys) (Morton 1992) and each other for 3 to 5 days (Walkinshaw 1966, house wrens (Troglodytes aedon) (Drilling McCabe 1991, Sedgwick 2000, Sogge 2000). and Thompson 1988). Therefore, management During this time, fledglings often huddle that results in decreased predation and together and may make repeated visits back to parasitism and protects nests from direct the nest (McCabe 1991). impact should also improve juvenile return Both adults feed the fledged young, which rates, since late fledging dates are typically beg loudly and may mob or chase the adults in the result of renesting due to earlier nest pursuit of food (Ettinger and King 1980, failure. Prescott 1986, Sanders and Flett 1989, H. Bombay, pers. obs.). In the south-central Polygyny Sierra Nevada, Stafford (1986) reported three banded adult willow flycatchers and one Polygyny has been reported for several banded dusky flycatcher feeding a single populations of willow flycatcher and may be a brood of willow flycatcher fledglings. Two of response to demographic stochasticity the adult willow flycatchers were not related (uneven sex ratios in small populations) to the young, suggesting that floaters, (Burgman et al. 1993, Sedgwick and Knopf migrants, or unsuccessful breeders may be 1989, M. Whitfield, unpubl. data) or skewed stimulated to feed begging fledglings that are nestling sex ratios at a site and insufficient not their own. As described above, Sedgwick dispersal (Paxton et al. 2002). When sex (2000) witnessed similar behavior when ratios on the breeding ground are skewed observing an unidentified adult (both parents towards males (Sogge et al. 1997, Johnson et were banded) providing 37 percent of the al. 1999 in Paxton et al. 2002, Walkinshaw feedings to a brood of nestlings. 1966, Sedgwick and Knopf 1989), perhaps as a result of lower survivorship for females Fledglings typically remain in their natal (Walkinshaw 1966, Sedgwick and Knopf territory for approximately 14 to 25 days 1989), a significant number of males go (Walkinshaw 1966, Sedgwick 2000, Bombay unmated. However, unmated females have and Morrison, unpubl. data). During this not been reported, probably because polygyny time, they become increasingly independent ensures that all females are mated where and begin foraging for themselves between female numbers exceed males (Paxton et al. feedings by adults (Bombay and Morrison, 2002, Sedgwick and Knopf 1989, unpubl. data). M. Whitfield, unpubl. data). Energetic demands of simultaneous nesting within a BEHAVIORAL FACTORS single territory are not known, but appear to INFLUENCING PRODUCTIVITY be wholly viable, especially when timing between the nests is offset (Prescott 1986). Consequently, polygyny may be an important Early vs. Late Nesting reproductive strategy to ensure maximum In a study of more than a thousand nests in productivity from females. However, this Oregon, Sedgwick and Iko (1999) found that premise still has to be viewed with some willow flycatchers that fledged on or before caution as unmated and polygynous males 15 July (n = 127) were nearly six times more have been observed simultaneously in the likely to return the following year (survive the

13 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 same breeding population (M. Whitfield, available. Hansson et al. (2000) attributed unpubl. data). Yet even this phenomenon this to varying habitat quality, especially in may indicate a strategy on the part of willow respect to predation risks. Using artificial flycatchers to maximize production. Female nests, they found predation rates were much great reed warblers (Acrocephalus higher in unmated male territories than arundinaceus) in northern Europe frequently polygynous male territories, compensating for shared territories with other females, even costs associated with sharing a male with when unmated territorial males were another female.

14 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03

| ARRIVAL |

| NEST BUILDING | | RENESTS |

| EGGS & INCUBATION |

| NESTLINGS |

| FLEDGING FROM NEST |

| DEPARTURE |

MAY JUNE JULY AUGUST SEPTEMBER Figure 3-1. Generalized willow flycatcher breeding chronology for the Sierra Nevada, California. (Sources: Stafford and Valentine 1985, Flett and Sanders 1987, Valentine 1987, Sanders and Flett 1989, Bombay and Morrison, unpubl. data.)

Nest Attempt 12 ______First ------Renest

Count

0 6/19 6/22 6/25 6/28 7/01` 7/04 7/07 7/10 7/13 7/16 7/19 7/22 7/25 7/28 7/31 8/03 Date of Incubation Onset

Figure 3-2. Willow flycatcher incubation onset dates for the central Sierra Nevada, California. (Sources: Stafford and Valentine 1985, Sanders and Flett 1989, Bombay and Morrison, unpubl. data.)

15 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 4 Food Habits and Prey Relationships

GENERAL FORAGING of E. t. extimus in Colorado and Arizona were ECOLOGY apparently similar to those reported by Beal (1912), although dragonflies (Odonata) are The general foraging strategy of willow also of importance (see Williams and Craig flycatchers is to sit and wait from a perch 1998). providing good visibility, then pursue and capture flying arthropod prey that have In the Sierra Nevada, bees, wasps, and flies ventured near (hawking) (McCabe 1991). are apparently as important to the willow Pursuit flights are short, usually less than 5 m flycatcher as elsewhere in its breeding range. (15 ft) (McCabe 1991). Via (in Dickson et al. Sumner and Dixon (1953) reported that 1979) recorded average flight distance of only willow flycatchers in the Kings Canyon and 0.9 m (3 ft) for 50 pursuit flights observed. In Sequoia National Parks consumed “wasps, the Sierra Nevada, Sanders and Flett (1989) bees, beetles, flies, caterpillars, moths, reported that most foraging willow flycatchers grasshoppers, and occasionally berries.” In flew less than 1 m (3.3 ft) in pursuit of the central Sierra Nevada, H. Bombay (pers. insects, although flight distances of up to 10 obs.) observed adult willow flycatchers m (33 ft) were observed. Willow flycatchers capturing wasps and willow sawflies (Euura), will also glean insects from vegetation (Peters deer flies (Tabanidae), moths and caterpillars and Burleigh 1951, Via in Dickson et al. (Lepidoptera), mayflies (Ephemonoptera), and 1979, McCabe 1991), but probably more damselflies (Odonata). frequently when weather is less conducive to The most important prey consumed by insect flight (Phillips et al. 1964). However, extimus at the South Fork Kern River were Koronkiewicz and Sogge (2000) found willow true bugs, flies, and small beetles, followed by flycatchers wintering in Costa Rica to dragonflies and damselflies, bees and wasps, primarily “sally glean” or pull insects from leafhoppers (Cicadellidae), and spiders vegetation surfaces while maintaining flight. (Araneae) (Drost et al. 2001). Nestlings ate significantly higher numbers of true bugs, GEOGRAPHIC VARIATION IN flies, and leafhoppers than adults, for reasons DIETS that remain unclear. Beal (1912 in Bent 1942) reported on the stomach contents of 135 willow flycatchers PRINCIPAL PREY collected in 17 states and found that The collective studies of willow flycatcher 41 percent of the captured prey were bees, diet indicate that this bird feeds on a wide wasps, and ants (Hymenoptera), followed by variety of insect and other arthropod prey and, beetles (Coleoptera; 18 percent), flies on rare occasions, fruit (berries). There are, (Diptera; 14 percent), moth and butterfly however, some prey groups that are caterpillars (Lepidoptera; 8 percent), and true universally common to all studies. Willow bugs (Hemiptera; 7 percent). McCabe (1991) flycatchers have a predilection for recorded 214 food samples delivered to hymenopterids such as bees, wasps, and willow flycatcher nestlings in Wisconsin. sawflies; dipterids such as deer flies and bee Over half the captures were from just five flies; moths and butterflies (and their groups of insects: deer flies (Tabanidae), bee caterpillars); and small flying beetles. flies (Syrphidae), common skipper Hymenopterids and deer flies are especially (Hesperiidae), spittlebug (Cercopidae), and scarab beetles (Scarabidae). Deer flies alone comprised 20 percent of the deliveries. Diets

16 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 important in the Sierra Nevada (Sumner and the vegetation found immediately adjacent to Dixon 1953, H. Bombay, pers. obs.). stream channels (Erman 1984). H. Bombay (pers. obs.) observed that fledging Wasps and sawflies, also very important to willow flycatchers capture grasshoppers by willow flycatcher diets, may not have aquatic hopping from lower branches of shrubs onto life stages, but many depend directly on the ground. Thus, grasshoppers might be very riparian vegetation. The willow sawflies important to willow flycatchers during a brief, (Euura spp.), for instance, produce galls on but critical, life stage. willow leaves to protect their larvae (Borror et al. 1976). Other sawflies and wasps have HABITAT ASSOCIATIONS OF similar relationships with riparian plants. PREY Several studies have linked insect abundance Erman (1984) examined the associations with hydrologic conditions (Gosselink and between 10 insect orders and riparian systems Turner 1978) and riparian vegetational specific to the montane meadows in the Sierra changes (Voigts 1976, Weller 1978). In turn, Nevada. Most members of Ephemenoptera increased insect abundance has been linked (mayflies), Odonata (damselflies and with increased bird abundance. Kelly and dragonflies), Hemiptera (true bugs), Wood (1996) found foraging by common Coleoptera (beetles), and Diptera (flies) found yellowthroats (Geothlypsis trichas) to here have aquatic egg or larval stages and, increase where insect abundance was greatest, therefore, are abundant in areas with extensive and this correlated with diurnal temperature water. Deer flies, mayflies, and damselflies, patterns and seasonal vegetation and insects commonly found Sierra Nevada hydrology patterns. Gray (1993) found willow flycatcher diets (H. Bombay, pers. increasing abundance of birds in the obs.), are prime examples. Even the terrestrial flycatching guild at times and locations of adults of the above insect orders depend on increasing insect abundance.

17 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 5 Breeding Habitat Relationships

GENERAL Habitat has been defined by Morrison et al. HISTORY OF MEADOW HABITAT (1998) as an area with a combination of MANAGEMENT AND USE resources (food, cover, water) and California’s riparian ecosystems, including environmental conditions (temperature, meadows, have been profoundly impacted by precipitation, presence or absence of predators human use for the last 150 years. The extent or competitors, etc.) that promotes occupancy of this impact is illustrated in the loss of and allows for survival and reproduction. riparian forest in the Central Valley alone. Appropriate breeding habitat provides the The Central Valley riparian forest in 1848 was necessary requisites of nesting cover and estimated at greater than 373,000 ha (Katibah insect food resources. As its name implies, et al. 1983, Katibah 1984), with 324,000 ha in the willow flycatcher inhabits riparian the Sacramento Valley alone (Smith 1977, deciduous shrub and small tree riparian zones, Roberts et al. 1977). By 1979, this acreage generally dominated by willow (Salix spp.). had been reduced to approximately 41,300 ha, Across its range however, there is of which 75 percent was in a degraded or considerable variability in habitat human-impacted state (Katibah et al. 1983). characteristics (Harris 1996), including use of upland thickets not close to water (King Reasons for streamside riparian loss in the 1955). Central Valley include the gold rush; agricultural needs for fencing, lumber, fuel, In California, Grinnell and Miller (1944) and irrigation; Sacramento River steamships, described the breeding habitat of farming of natural levees; construction of E. t. brewsteri as “…strikingly restricted to flood control levees; water diversions; and thickets of willows…”, generally in a riparian grazing (Katibah et al. 1983, Katibah 1984). situation. Habitat typical of willow They may also account for the extirpation of flycatchers in the central and northern Sierra the willow flycatcher from the Central Valley Nevada includes moist meadows lined with (Gaines 1977, Serena 1982). willows and alders (Alnus spp.) (Serena 1982, Gaines 1988, Harris et al. 1988). Sawyer and These impacts also spread into the Sierra Keeler-Wolf (1995) classified this meadow Nevada. For instance, the Los Angeles type as “montane wetland shrub habitat.” aqueduct project has greatly reduced or nearly However, dense thickets are generally avoided eliminated riparian vegetation along the lower in favor of more patchy willow sites providing reaches of Lee Vining and Rush Creeks considerable edge (Valentine 1987, Sanders (Stine et al. 1984) and the Owens River and Flett 1989, Harris et al. 1988). In the downstream of the intake (Brothers 1984). southern Sierra Nevada, willow flycatchers Willows are virtually absent from the Owens are more often associated with dense thickets River riparian zone from the intake to of willows and other trees along stream approximately 45 km downstream due to courses (Harris 1991). Because these thickets reduced flows (Brothers 1984). are more linear in nature and have greater Like the stream riparian zones, the meadow stand structure (taller trees), they inherently ecosystems were also impacted. Grazing provide considerable edge. began in the 1860s (Gomez-Ibanez 1967, McKelvey and Johnston 1992, Kinney 1996, Kondolf et al. 1996, Menke et al. 1996, Allen-Diaz et al. 1999). Early grazing included not only sheep and beef cattle, but

18 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 dairy cattle confined to meadows as well and culverts were constructed to reduce or (Sudworth 1900). Overstocking of livestock eliminate flooding of roadways. Such in the Sierra Nevada apparently began almost activities changed meadow hydrology and immediately (Burcham 1982), with likely led to meadow desiccation. Opening of competition between established cattle and the forest canopy through road construction nomadic sheep ensuing. By the 1890s, laws and logging also likely allowed cowbirds to were being passed to exclude sheep from gain access to meadows. forest lands as trespassing and overcrowding There is (some) evidence that the hydrology increased tensions between cattlemen and of Sierra Nevada meadows has changed since sheepherders. The USDA Forest Service the introduction of livestock. Although ended the nomadic sheep herding way of life hydrological regimes of meadows are by requiring all grazers to own base complex, and include influences from fire properties, a tenet eventually adopted by the (DeBenedetti and Parsons 1979), drought, and Taylor Grazing Act of 1934. other stochastic events, meadow desiccation The number of livestock using the Sierra as a result of gully erosion appears to be a Nevada in the nineteenth century is unknown, geologically recent phenomenon coeval with but it apparently peaked in the 1880s at the the introduction of livestock (Hagberg 1995, height of the “open-access” (uncontrolled) Dull 1999). Dull (1999), in his pollen period (Allen-Diaz et al. 1999). Dudley analysis of Sierra Nevada meadows (dating (1898) spoke disparagingly about the trampled back to 3140 BP), also observed a marked state of the meadows of the Sierra Forest decline in willows since 1850 that he Reserve in the late 1890s compared to the attributed to livestock presence. Mining, U.S. Army-protected meadows of the Sequoia water diversions, and streamside timber National Park. By 1900, Sudworth (1900) harvest are contemporaneous with intensive noted sheep bands forced to subsist on pine livestock grazing during the second half of the needles, indicating that range conditions had nineteenth century in the Sierra and could also severely declined. have contributed to meadow desiccation (McKelvey and Johnston 1992, Kattelmann In the early twentieth century, the federal and Embury 1996). Others suggest climate government began to gain control of the variation is also pertinent for determining rangelands under the Forest Reserve system. influences on changes in meadow conditions. However, World War I sparked increased Other pollen studies of Sierra Nevada demands for livestock products, and the montane meadows show willow declines from ranges were again overstocked (Rowley several hundred to thousands of years ago, 1985). From the 1920s to the 1970s, livestock which predate livestock grazing effects and grazing in the Sierra Nevada decreased indicate that willow has responded to other significantly (Menke et al. 1996), with a more conditions in the past such as climatically gradual decrease occurring since then (Forero induced changes in the water table et al. 1998). The 1900s also saw varied levels (W. Woolfenden, pers. comm.). This review of pack stock use, which also declined indicates that, while natural processes substantially in the latter half of the century (e.g., drought, climate change) certainly (McClaran 1989). determine long-term patterns in meadow Numerous other human-induced activities condition, the evidence is also strong that were co-occurring with grazing that human activities (e.g., road building, water apparently had negative impacts on meadow diversion, over-grazing) have more recently conditions. Roads were constructed to allow accelerated changes in meadow condition in access to the forest for mining, timber the context of flycatcher needs. harvesting, building construction, recreational As such, there are several interacting factors activities, and other uses. Roads were often that have led to a general decline in the placed along or through meadows, and ditches condition of meadows. As reviewed elsewhere

19 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 in this document, these human activities have reveals the characteristics important to led to both direct and indirect effects on breeding success and becomes the measuring flycatcher habitat and population parameters. stick against which change is monitored. It helps identify those sites in need of protection while implementing Forest Plan management SUITABLE HABITAT activities. Preferred habitat is important for Understanding habitat requirements of willow restoration. It is the subset of suitable habitat, flycatchers is paramount not only in defining the “best” conditions (an analog for understanding causes for population decline, preference), and is the goal responsible but in developing management strategies restoration activities are designed to reach. towards protection and restoration of Sierra Nevada populations. The concept of habitat Determining suitable habitat is one of the first use is, however, not straightforward. goals of willow flycatcher habitat Occupancy, for instance, does not necessarily conservation efforts. If a requirement of equate to suitability or preference, and suitable habitat is that the population of its potentially optimal habitat may not be occupants be stable or growing, however, then occupied if availability of such habitat long-term studies may be required to exceeds the available nesting pairs in a accurately measure the rate of population depressed population. Consequently, when change. Rate of population change or fitness assessing habitat associations, a number of (termed Lambda [λ]) is measured using a concepts must first be defined. number of functions such as fecundity, overwinter mortality, and dispersal. Each is Habitat use, or occupancy, defines the range difficult to accurately measure, and inaccuracy of tolerance a species has among the habitat of any one results in an inaccurate λ, leading choices (or habitat gradient). It reveals to an inaccurate measure of suitable habitat. nothing about suitability or preference, only Sogge and Marshall (2000) have stated that that the habitat is tolerable enough to occupy. for the southwestern willow flycatcher, at Suitable breeding habitat can, however, be least, there are not enough long-term data to defined as locations in which reproduction accurately determine population stability and, and survival result in a stable or growing therefore, suitable habitat. population (Sogge and Marshall 2000, McCallum 1994). It is habitat where the rate While recognizing the problems mentioned of population change (termed Lambda [λ]) is above, attempts have been made to develop either stable or growing. In contrast, discrete definitions of suitable habitat (Stefani unsuitable habitat is defined as occupied et al. 2001) using existing data (Serena 1982, habitat where the rate of population change is Harris et al. 1988, Flett and Sanders 1987, decreasing or is maintained by immigration Sanders and Flett 1989, Bombay 1999). (sink populations) from stable or growing These become working definitions with populations (source populations) (McCallum recognition that future refinement is needed as 1994). The concept of preferred habitat new data become available. Further, Habitat suggests that a species with a range of habitat Suitability Index (HSI) Models have been choices will seek specific habitats based on developed (KRCD 1985a, PG&E 1986, internalized standards (desirability) Fowler et al. 1991) and tested (Scully 1995) (McCallum 1994). that also attempt to define the suitable habitat range. Collectively, these studies and Each definition has its separate purpose in definition building exercises have resulted in developing management strategies. developing five components that may best Understanding the range of occupancy and define Sierra Nevada willow flycatcher habitat what constitutes unsuitable habitat is requirements. important in identifying sink habitat or sites that might be good candidates for future • Elevation: Most (88 percent or 119/135 restoration. Determining suitable habitat known sites) Sierra Nevada meadows

20 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 used by breeding willow flycatchers occur fitness, should ultimately lead to a reliable between 1,200 and 2,500 m (4,000 to definition for suitable habitat. 8,000 ft) elevation, although meadows as low as 365 m (1,200 ft) and as high as 2,900 m (9,500 ft) have been used SPATIAL SCALES (Stefani et al. 2001). Habitat use by willow flycatchers can be viewed at hierarchical scales. There is no • Wetness: Successful nesting territories single set of spatial scales ecologically are strongly associated with standing or meaningful for all wildlife species. Rather, flowing water or heavily saturated soils. scale should be based on the questions being • Meadow Size: Although use of meadows asked. For the Sierra Nevada willow less than 0.5 ha (1 ac) has been flycatchers, it is important to understand documented, more than 95 percent of the habitat use at the microhabitat scale to assess breeding meadows are greater than 4 ha site-specific conditions and at the broad scale (10 ac), and the most successful to establish regional strategies for (i.e., >1 territory fledged young) meadows conservation. are greater than 6 ha (15 ac). The smallest scale at which habitat use by • Shrub Coverage: Riparian deciduous Sierra Nevada flycatchers has been shrub coverage has generally been investigated is the nest site. Habitat use at the measured or modeled as a percentage of breeding patch level has also been meadow area; 20 to 30 percent has been investigated and is generally synonymous suggested as a minimum for suitable with willow stands. However, because several habitat. Scully (1995), however, flycatcher pairs will establish territories within measured absolute area and found sites for the same willow stand, territory is also a male willow flycatchers to average 525 useful scale on which to examine habitat use. m². In her HSI model, Scully awarded an Because of their structural similarities, willow optimal coefficient value of 1.0 for shrub stands and territory are discussed together. patches greater than 400 m². Meadow, the next hierarchy, is the level where management activities are most likely • Foliar Density: Foliar density is a to be targeted and is, therefore, the level of measure of the riparian deciduous shrub at greatest conservation importance. For the 2-m shrub height level, or the level of purposes of this assessment, breeding habitat the shrub layer where actual nesting is examined at four hierarchical scales: nest generally occurs. Based on her research, site, territory/willow stand, meadow, and Scully (1995) awarded a coefficient value broad scale. of 1.0 for foliar densities of greater than 76 percent in her HSI model. Nest Site Although research has been conducted to characterize willow flycatcher habitat, none of The nest site scale is important because it these studies was specifically designed to allows us to understand the plant species that determine discrete definitions for suitable are most important to willow flycatchers for habitat. Doing so requires further research nesting substrate. correlating habitat use with nesting success Historically, most willow flycatcher nests over a long enough time to determine accurate reported for the Sierra Nevada and other parts trends in nesting success. The HSI approach of northern California were found in willows, is a valuable tool in grading habitat suitability, with occasional references to blackberry but it does not incorporate, except by (Rubus spp.), aspen (Populus tremuloides), inference, fitness measures (λ). Continued and alder (Alnus spp.) as nest substrates research on habitat use, coupled with (Bendire and Brevet 1895, Bent 1942). Sierra demographic studies designed to measure Nevada nest records in the collection at the

21 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Western Foundation of Vertebrate Zoology (Pteridium aquilinum) (King 1955, Sedgwick dated between 1898 and 1950 include 2000). 34 records that document the nest substrate: 2 were placed in alder, 3 in aspen, 4 in wild Territory/Willow Stand rose (Rosa spp.), and 25 in willow. More recent accounts usually describe willow as the Territory is the specific area within a meadow most frequently used nest substrate. Sanders that a single male willow flycatcher defends and Flett (1989) reported that all 20 nests for breeding and foraging resources. Because found at two meadows on the Tahoe National specific resources are being defended, and Forest in 1986 and 1987 were placed in these resources may not be distributed willow (Salix lemmonii, S. geyeriana, or uniformly across the meadow, habitat use S. jepsonii). Out of more than 250 nests found within territories may vary from the general at 15 meadows in the north-central Sierra meadow habitat. To determine whether Nevada between 1997 and 2001, only three territory is a meaningful scale in relationship occurred in non-willow shrubs: two in to willow flycatcher habitat use, Bombay mountain alder (Alnus tenuifolia) and one in (1999) compared habitat use within Sierra creek dogwood (Cornus stolonifera) Nevada territories to the general meadow (Morrison et al. 2000, Bombay et al. 2001, habitat. Similarly, Sedgwick and Knopf Bombay and Morrison, unpubl. data). In most (1992) compared macroplots (roughly territories within this study area, willow is the equivalent to the size of a territory) in only available riparian shrub (Bombay 1999, Colorado between territorial and unoccupied H. Bombay, pers. obs.). Recently, however, areas. Both found the same results: willow McCreedy and Heath (in review) discovered flycatcher territories exhibited significantly (or rediscovered) a population of willow more willow cover. flycatchers in Rush Creek (Mono Lake) where In the Sierra Nevada, Bombay (1999) found all nine discovered nests were in wild rose, shrub cover (virtually all Lemmon willows despite the presence of suitable nesting [S. lemmonii]) within territories to average willows. about 48 percent, while at many of the same Valentine (1987) reported that, although sites studied by Bombay (1999), Sanders and willow was the most abundant shrub type, and Flett (1989) found shrub coverage in the most frequently used nest substrate in the territories (0.34 ha mean size) to average Sierra National Forest study area, in Poison 44 percent. Sedgwick and Knopf (1992) Meadow all four willow flycatcher nests found virtually identical results in Colorado. located there between 1984 and 1986 were Plots (0.32 ha) centered over nests averaged placed in creek dogwood. Similarly, King and 49 percent willow coverage, while plots King (in press) reported that, although willow centered over song perches averaged made up more than half (57.3 percent + 26.5 44 percent. Bombay (1999) also found that percent) of the shrubby vegetation successful territories had more shrub cover surrounding 10 nests in the extreme northern than unsuccessful ones (52 percent versus Sierra Nevada, all were placed in mountain 43 percent). At a recently discovered site near alder. Mono Lake, McCreedy and Heath (in review) found nine nests centered on monotypic Current nest records for other shrub substrates patches of wild rose. outside the Sierra Nevada, but within northern California, include mountain mahogany Bombay (1999) found that the mean coverage (Cercocarpus spp.) on the Modoc National of standing water, or highly saturated soils, Forest and blackberry along the Klamath was relatively high (44 percent) and much River (Harris 1996). In other parts of the higher than that found by Sedgwick and West, adastus and brewsteri subspecies are Knopf (1992) in Colorado (10 to 11 percent). frequently reported to nest in cow parsnip Neither study, however, indicated significant (Heracleum lanatum) and bracken fern differences in water coverage between

22 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 occupied territories and unoccupied area. Broad-scale Bombay (1999) did, however, find The broad scale enables conceptualizing about significantly greater water depths in elevational limits, nearest neighbor distances, successful (0.6 m) than unsuccessful (0.5 m) and dispersal needs. The elevational range of territories. Greater water depths may improve willow flycatchers in the Sierra Nevada nesting success by increasing food supply bioregion, which includes extimus populations (Voigts 1976, Erman 1984, Gray 1993, Kelley on the South Fork Kern River and Owens and Wood 1996) and reducing predator access Valley, is 365 to 2,900 m. However, most (Ammon and Stacey 1997, Cain 2001). In meadows used for breeding by contrast, McCreedy and Heath (in review) brewsteri/adastus are between 1,200 and found that willow flycatchers nesting along 2,500 m (4,000 to 8,000 ft) elevation (Serena Rush Creek used wild rose stands in drier 1982, Harris et al. 1988, Stafford and situations. On average, Rush Creek nests Valentine 1985, Bombay 1999, Bombay et al. were more than 130 m from water (the creek 2001). Research by Bombay (1999) suggests itself), indicating different breeding ecologies that there is an upper elevational limit to in desert riparian versus mountain meadow flycatcher use in the Sierra Nevada, which she habitats. attributed to the presence of snow and unleafed willows at the time of spring arrival. Meadow Late snowmelt at the higher elevations can The one consistency of Sierra Nevada willow delay nesting and shorten breeding seasons, flycatcher habitat use is that they nest in wet both contributing to nesting success, or even meadows with standing water and abundant nesting attempts. willows (Serena 1982; Harris et al. 1987, Willow flycatcher nest sites are distributed 1988; Fowler et al. 1991). Thus, the meadow along the length of the Sierra Nevada. scale provides insights on meadow hydrology However, multiterritory sites (excluding and distribution of willow stands. Bombay extimus) active since 1999 are clustered at five (1999) found occupied meadows to have a general locations: Lassen Peak, Truckee, significantly higher percentage of meadow Carson, Yosemite, and Mono Lake. Distances with a shrub component (60 percent versus between these clusters range from 68 to 40 percent) and standing water or saturated 323 km (42 to 60 miles) and average about soils (57 percent versus 41 percent) than 84 km (52 miles). These locations may unoccupied meadows. Bombay (1999) also represent spruce populations, or isolated found occupied meadows to contain strongholds in an ever-shrinking distribution. 22.6 percent more foliar density in the lower 2 m of shrub, 1.8 ha more shrub, 20.2 percent more grass cover, more beaver use, and more HABITAT ISOLATION small stream channels than currently Habitat isolation in the breeding populations unoccupied meadows. of Sierra Nevada willow flycatchers is inherent because of the very patchy nature of Size of meadows is also important. Meadows their breeding habitat. Grinnell and Miller used by nesting willow flycatchers in the (1944) described the range of the willow Sierra Nevada have ranged in size from 0.4 to flycatcher in California as “Roughly, the 290 ha (1 to 719 ac), with more than entire length of the State…,” but “really much 80 percent of the territories occurring in very restricted” in regard to breeding habitat. meadows greater than 8 ha (20 ac) (Serena Meadows with willow riparian basically 1982; Harris et al. 1987, 1988; Bombay represent “islands” of habitat in a “sea” of 1999). forest avoided by this bird. As the number of meadows providing suitable habitat has declined, presumably from anthropogenic factors, the remaining meadows have become

23 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 even more isolated. Whether these expanded and by reducing the pressure head to zero at distances between breeding populations are all exposed points along the gully (Reid greater than normal willow flycatcher 1989, Hagberg 1995). The result is a drop in dispersal distances remains to be determined. the water table, leading to surface desiccation (Reid 1989). Interestingly, in his study of 15 gullied meadows on the Sierra National MEADOW HYDROLOGY Forest, Hagberg (1995) used aerial The montane meadows used by willow photography to conclude that all gullies flycatchers have formed in the low-gradient formed during either a 1937 or a 1950 rain- valleys of the Sierra Nevada over the last on-snow storm event. Essentially, gullies can 10,000 years (Wood 1975). These meadows, be formed from a specific episodic (storm products of alluvial processes (low-gradient flood) event leading to a chronic condition deposits along streams), are characterized by (headcutting). Further, through a process of their high saturation of water, especially alternative hypothesis elimination and during spring snowmelt runoff. These evidence gleaned from aerial photographs, hydrological regimes, known as “wet Hagberg inferred that livestock trampling and meadows,” result in water budgets exceeding chiseling were the likely causes at 12 of the groundwater inflow and evapotranspirative meadows, and road building and mining water losses. Characteristic features are coupled with grazing were the causes at the highly saturated soils, including standing other 3. Regardless of the actual causes, many water, and a community of hydrophytic plants of these gullies remain and continue to stress able to withstand water saturation. Sawyer meadow ecology. and Keeler-Wolf (1995) have classified Sierra Nevada wet meadows, with a shrub While intensive grazing by livestock has component dominated by willows (or other damaged meadow resources in the Sierra riparian deciduous shrubs), as “montane Nevada (Ratliff 1985), and it is likely that wetland shrub habitat.” At least nine species livestock damage and road building may have of willow and two alder can be found in this resulted in gully formation leading to meadow vegetation type. desiccation, connecting grazing directly to willow flycatcher population declines remains The characteristics of shrub-dominated speculative. Nevertheless, meadow montane meadows important to willow restoration efforts and erosion mitigations flycatchers are the prevalence of willows and, leading to gully healing and an increase in during the nesting season, standing or flowing habitat components important to willow water, or highly saturated soils. As shown by flycatchers should benefit recovery of this Cain (2001; see also Cain et al., in press), species. wetness aids nesting success by inhibiting nest access of forest and edge predators and preventing establishment of lodgepole pine, which provides habitat for forest and edge predators. Wetness may also provide habitat for important willow flycatcher prey. The primary cause of meadow desiccation in the Sierra Nevada has been identified as gullying (Hagberg 1995). Gullies form in meadows when the protective sod layer has been damaged or incised, resulting in erosive processes reaching the soil layer. Gullies alter groundwater hydraulics and hydrology by intercepting surface and groundwater (thereby cutting off water supply to downstream areas)

24 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 6 Home Range and Territoriality

The breeding home range and territory are territories averaging 0.6 ha, and polygynous nearly synonymous in the willow flycatcher. males averaged 1.1 ha (Whitfield and Placer Willow flycatcher territories generally fall 1994, Whitfield and Strong 1995, Whitfield within Nice’s (1941) Type A classification and Enos 1996, Whitfield et al. 1997). where the mating, nesting, and foraging areas Information on home range use during the are all actively defended (McCabe 1991). migration and wintering period is lacking, KRCD’s (1985b) observations in the Sierra although a greater variety of habitats, Nevada confirm that most foraging and other including non-riparian vegetation, is used by activities occur within the territory. Breeding willow flycatchers during migration than willow flycatchers will, on occasion, forage during breeding (Yong and Finch 1997, Finch outside their defended territory, even crossing et al. 2000). No information on territoriality adjacent territories while doing so. Sanders during migration exists (Finch et al. 2000). and Flett (1989) found willow flycatchers on the Little Truckee River using foraging Territoriality by willow flycatchers on their perches up to 30 m outside their defended wintering ground was suspected by a number territory and conducting forage bouts to of researchers (Gorski 1969, Koronkiewicz et 100 m beyond their territory. Once young al. 1998, Koronkiewicz and Whitfield 1999), begin fledging, territory boundaries begin but was not confirmed until research breaking down, with both fledglings and conducted by Koronkiewicz and Sogge adults extending their home ranges into (2000). Koronkiewicz and Sogge (2000) adjacent territories (KRCD 1985b). monitored the behaviors of 40 wintering willow flycatchers in Costa Rica and found Territory size in willow flycatchers can vary that they not only defended specific widely depending on habitat structure, forage territories, they exhibited relatively high density, pressures from adjacent territories, within-year (85 percent) and between-year (43 and mating strategy. Sanders and Flett (1989) to 77 percent) site fidelity. Both males and found average territory size of 22 pairs of females aggressively responded to simulated willow flycatchers on the Little Truckee River intrusions into their territories by other to be 0.34 ha, or about twice the 0.18 ha flycatchers and excluded conspecifics from average KRCD (1985b) found for 6 pairs at their territories regardless of sex. Dinkey Meadows on the Sierra National Koronkiewicz and Sogge (2000) also captured Forest. E. t. extimus in the Sierra Nevada and color-banded several non-territorial Forest Plan Amendment area may defend floaters, some of which quickly occupied and even larger territories. Monogamous males defended vacant territories after the original on the South Fork Kern River defended defender had disappeared.

25 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 7 Movements

NATAL DISPERSAL by willow flycatchers (Kenwood and Paxton 2001). For comparison, a southwestern The frequency, patterns, and average distances willow flycatcher habitat patch is essentially of adult and natal dispersal for E. t. adastus synonymous with the Sierran habitat unit of a and E. t. brewsteri in the Sierra Nevada are meadow. largely unknown. Between-meadow natal dispersal data are limited to 19 resighting records collected between 1997 and 2001 ADULT DISPERSAL (Bombay et al. 2001, Bombay and Morrison, On the Tahoe National Forest, Sanders and unpubl. data). These records consist of Flett (1989) reported that an adult male between-year, between-meadow movements resettled approximately 1 km (0.6 mile) from only, and recorded distances range from his 1986 breeding territory in 1987. Among 0.8 km to 19.8 km (median = 3.6 km; mean = adult and juvenile willow flycatchers color- 6.0 km; SD = 4.9 km). Eighteen of these banded in the same study area in 1994, one dispersal events are from the eastern portion was detected 2.4 km (1.5 miles) downstream of the Tahoe National Forest, and one is from in 1997 (J. Steele unpubl. data, Bombay and an area along the boundary between the Morrison, unpubl. data). In the southern Toiyabe and Eldorado National Forests. Sierra Nevada, Stafford and Valentine (1985) Dispersal distances reported here are the reported that one female willow flycatcher straight-line distance in kilometers between (banded as an adult) moved 14.5 km (9 miles) the center of the meadow where a bird was from her 1983 territory to a new territory, banded and the territory where it was where she nested successfully in 1984. resighted. Most of these dispersal events occurred downstream within the same Data collected for southwestern willow drainage; however, four occurred upstream flycatchers in Arizona indicate that 13 to within the same drainage, and two occurred 17 percent of adults moved to new breeding between different drainages (which all have sites each year (Busch et al. 2000, Paxton ramifications for locating potential meadow 2000, Paxton and Sogge 2000). Between restoration projects). 1997 and 1998, 19 between-site movements ranging from 0.4 to 190 km were documented Similar between-patch, between-year natal for southwestern willow flycatchers (median = dispersal distances are reported for 16.0 km; mean = 31.8 km; SD = 46.6 km). E. t. extimus in Arizona (Luff et al. 2000, Four of these records represent between- Kenwood and Paxton 2001). These natal drainage movements (Netter et al. 1998). dispersal distances ranged from 0.4 to 67 km Between-patch, between-year movements by for 5 hatching year birds 1999/2000 (median = adults in Arizona ranged from 0.4 to 144 km 1.7 km, mean = 7.08 km, SD = 12.16 km) and for 1999/2000 (median = 12 km, mean = 21 hatching year birds in 2000/2001 (median 13.67 km, SD = 14.30 km) and 2000/2001 = 1.9 km, mean = 8.74 km, SD = 16.37 km) (median = 1.9 km, mean = 19.46 km, SD = (Luff et al. 2000, Kenwood and Paxton 2001). 36.74 km) (Luff et al. 2000, Kenwood and For the purpose of this document, a Paxton 2001). In 1999/2000, 1 of these southwestern willow flycatcher habitat patch 34 movements was between drainages, and 11 is defined as a distinct area of riparian of 31 movements in 2000/2001 were between vegetation supporting one or more territories, drainages. Whether the variation in dispersal and separated from other breeding areas by distances reported for adastus/brewsteri in the areas of non-riparian vegetation, or riparian Sierra Nevada and extimus in Arizona vegetation without the characteristics required represents a regional or sub-specific

26 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 difference in dispersal behavior or habitat These three factors regarding available habitat availability, or is the result of different levels may affect how far away and in what pattern of survey effort, is unknown at this time. birds disperse and, therefore, the researchers’ ability to detect all surviving young. SURVIVAL AND RETURN RATES Willow flycatcher return rates are generally Data on juvenile and adult return rates for the higher for adults. In the central Sierra willow flycatcher population in the Sierra Nevada, Bombay et al. (2001) reported that Nevada bioregion are preliminary. An the pooled adult return rate was 66.7 percent ongoing willow flycatcher demographic study from 1997 to 2001. At two of the same Tahoe in the central Sierra Nevada reported a mean National Forest study sites, Sanders and Flett juvenile return rate of 14.5 percent annually (1989) found that 4 out of 14 (29 percent) (SE = 3.1) between 1998 and 2001, based on banded adults returned the following year. In 217 banded fledglings (Bombay et al. 2001). the southern Sierra, Stafford and Valentine In Oregon, the juvenile return rate was (1985) had 4 of 12 (33 percent) adults return. 7.5 percent of 1,271 E. t. adastus nestlings Estimates of life span for willow flycatchers and fledglings banded (Sedgwick and Iko come primarily from birds followed from 1999, Sedgwick 2000), while it was 1988 to 1997 on the Malheur NWR in 1.4 percent of 147 nestlings banded in Oregon. Sedgwick and Iko (1999) reported Michigan (Walkinshaw 1966). Juvenile that willow flycatchers in this study area had a return rates for southwestern willow mean life span (not taking dispersal into flycatchers in the extreme southern Sierra account) of 1.08 years + 0.11 SE for males, Nevada and Arizona are recorded as and 0.97 years + 0.10 SE for females. At this 34 percent of 38 banded nestlings and study area, the maximum age recorded was 11 8 percent of 12 banded nestlings, respectively years (Sedgwick 2000). Reports of birds 5 to (Stoleson et al. 2000). From 1996 to 2001, 7 years of age are not uncommon in the 36 of 189 E. t. extimus nestlings banded in literature (Walkinshaw 1966, Walkinshaw Arizona were resighted from 1 to 4 years after 1971, Clapp et al. 1983). In the Sierra Nevada banding, resulting in a pooled recruitment rate a number of adults 4 to 5 years of age have of 19 percent (Luff et al. 2000, Kenwood and been reported (Bombay et al. 1999, Bombay Paxton 2001). et al. 2001). Juvenile return rates in the Sierra Nevada Adult survival for southwestern willow appear to be slightly lower than those flycatchers in the southern Sierra Nevada and currently reported for southwestern willow Arizona was estimated at roughly 52 percent flycatchers, but higher than those reported for for males and 34 percent for females based on presumably stable populations of E. t. adastus 79 returning males and 255 returning females and E. t. traillii in other parts of North (Stoleson et al. 2000). In Michigan, America. Sierran juvenile return rates are also 30 percent of 53 banded adults returned the higher than the 2 to 5 percent reported for following year (Walkinshaw 1966). most other migratory passerines (Shields Similarly, in Oregon, 45 percent of birds 1984, Blancher and Robertson 1985, Payne banded as adults returned annually over and Payne 1990, Sherry and Holmes 1992, 8 years of study (Sedgwick and Klus 1997). Roth and Johnson 1993, Lemon et al. 1996, After 10 years at the same Oregon study site, Netter et al. 1998). It is difficult to interpret Sedgwick and Iko (1999) reported how these recruitment values reflect on 53.6 percent of females (186/347) and population trends because observed 52.3 percent of males (138/264) returned to recruitment rates may depend largely on the breed in the same general area. Based on amount and distribution of available habitat somewhat limited sample sizes for Sierra close to natal areas, as well as the extent to Nevada willow flycatchers, it appears that which available habitat is fully occupied. adult survival, expressed as return rate, in the

27 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 bioregion falls within the range observed for returning to the same patch, a mean of other willow flycatcher populations in other 64 percent (SE = 10.5) returned to within bioregions. 50 m of their previous year’s territory (Luff et al. 2000, Kenwood and Paxton 2001). Between 1996 and 1998, 32 percent of adults PHILOPATRY displayed breeding site/patch philopatry in Although the previous discussion of survival Arizona (Busch et al. 2000). In extreme indicates the proportion of willow flycatchers southern Sierra Nevada, 61.6 percent of adult that survived and returned to any of a number male southwestern willow flycatchers (n = of breeding locations, it does not indicate how 138) and 51.8 percent of adult females (n = many birds return to the same breeding site in 137) returned to one of the patches within the sequential years. Philopatry, on the other study area (M. Whitfield pers. comm.). More hand, looks at how faithful willow flycatchers than half of the breeding adults captured in a are to specific meadows or even territory 1988 to 1997 study in Oregon returned to the locations. In the Sierra Nevada, little same general area to breed in subsequent information is available. On the Tahoe years (females: 186/347 [53.6 percent]; males: National Forest in 1986 and 1987, three of 138/264 [52.3 percent]) (Sedgwick and Iko four returning adult willow flycatchers 1999, Sedgwick 2000). At this same study returned to the same willow clump in which site, the median distance for returning males they bred in the previous year (Sanders and (n = 362) and females (n = 349) from the Flett 1989). Similarly, on the Sierra National previous years’ nest site was 25 and 26 m Forest in 1983 and 1984, three of four known (82 and 85 ft), respectively (males: mean = surviving adults returned to the same meadow 193 m, SE = 29 m, range = 0 to 4,662 m; used in the previous year (Stafford and females: mean = 233 m, SE = 37 m, range = Valentine 1985). Philopatry data for an 0 to 5,926 m) (Sedgwick 2000). When ongoing demography study in the central compared to willow flycatcher populations in Sierra Nevada are also limited. Of other regions, it appears that Sierra Nevada 61 resightings of known surviving “after willow flycatchers may exhibit slightly lower second year” (ASY) willow flycatchers, philopatry. 13 incidences (representing 12 individuals) of birds using the same or similar territory Within-year Movements - For the Sierra locations (within 100 m) in sequential years Nevada, no information is available relative to have been documented (J. Steele, unpubl. movements of adult willow flycatchers within data; Bombay and Morrison, unpubl. data). A a single breeding season. Bombay et al. rough estimate of philopatry based on these (2001) reported that many males annually data indicates that 20 percent of known adult disappear from what appear to be defended survivors return to use the same location. territories after only a few weeks. While the Because willow flycatchers in this study were fate of these individuals is unknown, it is not color-banded to identify individual birds assumed that at least some are settling (color-coded for year and location only), this elsewhere later in the season. Recent data value is based on the assumption that if a bird from southwestern willow flycatcher with the same cohort and natal site color populations in Arizona support this bands is detected on the same territory in assumption and suggest more mate switching sequential years it is most likely the same and within season dispersal than previously individual. assumed (Luff et al. 2000). In 2000, Luff et al. (2000) reported five incidences of adult Of the adult southwestern willow flycatchers birds moving between habitat patches during in Arizona known to survive between years, a the breeding season. Three unpaired males mean of 71 percent (SE = 4.8 percent) moved 0.4, 1.7, and 4 km to new sites where returned to the same habitat patch during the they successfully found mates. Two females 1996 through 2001 period. Of the birds moved 13 and 29 km between successive

28 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 nesting attempts. Additionally, four more of these was a female that moved 117 km unmated males moved to new territory between two within-year nesting attempts, and locations within the same habitat patch and two males moved 144 km between years. secured mates. Similarly, Kenwood and These data for southwestern willow Paxton (2001) reported that 17 flycatchers flycatchers suggest that it may not be moved more than 50 m within the same uncommon for males to move to new habitat patch; 20 moved between different locations if they cannot find a mate and that habitat patches within the same drainage, and females may move to new locations after 11 moved between different drainages. One failed nest attempts (Luff et al. 2000).

29 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 8 Population Ecology and Risks

DEMOGRAPHY Klus (1997) reported a higher return rate for females (46.9 percent) than males Demographic studies of populations are often (43.3 percent) at the same study site in conducted to determine whether populations Oregon (Malheur National Wildlife Refuge) are increasing, decreasing, or remaining as Sedgwick and Iko’s study site (1999). stable. This is done by calculating the annual rate of population change, termed Lamba (λ). A λ value of 1.0 means the population Juvenile Recruitment abundance is stable, a value lower than Bombay et al. (2001) found willow flycatcher 1.0 means it is declining, while a value greater juvenile recruitment to average 14.5 percent than 1.0 means it is increasing. For example a (range 11.6 to 18.6 percent) over 4 years of λ of 0.96 indicates that the population is banding study in the Sierra Nevada, which is annually declining by 4 percent. Three similar to the 13.2 percent return rate reported parameters define λ: adult survival, juvenile by Sedgwick and Klus (1997) from the recruitment, and fecundity. Malheur National Wildlife Refuge in eastern Oregon. However, Sedgwick and Iko (1999) Adult Survival reported juvenile return rates of exactly half (6.6 percent) that of Sedgwick and Klus Adult survival is usually estimated from (1997), even though the study sites were the banding studies to assess annual return rates same. Sedgwick and Iko (1999), however, of individual cohorts. At Malheur National questioned the credibility of their observed Wildlife Refuge in Oregon, Sedgwick and juvenile return rates because they were too Klus (1997) reported an average adult return low for the population to persist unless it is a rate of 45.1 percent, while Sedgwick and Iko sink population maintained by other sources. (1999) found adult returns rates between These rates, all from birds in the range of 48.9 and 55.6 percent, depending on sex and adastus, are similar to rates for extimus in whether nests had been parasitized by Arizona (8 percent: Paxton et al. 1997), but cowbirds. In the central Sierra Nevada, are much lower than Kern River extimus Bombay et al. (2001) reported a pooled (34 percent: Whitfield, unpubl. data) and not average survival rate of 66.7 percent over nearly as low as from Walkinshaw (1966) in 4 years of study. These rates are at or near the Michigan (1.4 percent). 50 to 70 percent adult return rates generally reported for long-distance migrants (Ricklefs Sedgwick and Iko (1999) also found 1992, Sherry and Holmes 1992, 1995). substantial differences in return rates relative to fledgling dates. Young fledged on or Survivorship may differ between sexes. In before 15 July (10 percent of total fledglings) Michigan, Walkinshaw (1966) found the were nearly six times more likely to return the return rate for male willow flycatchers to be following year than young fledged at later twice that of females in the first year after dates. they were banded (40.9 percent versus 22.6 percent). Paxton et al. (1997) reported extimus male return rates (52.0 percent) to be Fecundity much higher than that of females Fecundity is a measure of production based on (34.0 percent). Sedgwick and Iko (1999) also individual (generally female) or population found slightly higher survival rates for male performance. Fecundity is the product of the adastus in Oregon and attributed this to probability of breeding, clutch size, hatching possible higher energetic cost for breeding success, nesting success, and number of females (Nur 1988). However, Sedgwick and

30 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 nesting attempts per season (USFWS 2001). (2001) reported that 27 percent of all nesting Female willow flycatchers breed in their first over a 5-year period consisted of renests, with year, and there is no evidence of a 3 percent third nesting attempt. There is no reproductively viable females going unmated. evidence in these populations of producing If sex ratios are skewed towards females, two successful broods in the same year. females appear to choose sharing males with Bombay et al. (2001) estimated that central other females (polygyny) rather than going Sierra Nevada willow flycatcher females unmated. (n = 39) produced 1.74 fledglings on average Clutch size information was provided in detail (or 0.87 female fledglings) in 2001. They did, in Chapter 3. Of relevance here are the Sierra however, suggest that the true fledglings Nevada data from Bombay and Morrison produced per female were closer to 1.57, (unpubl. data) showing a mean clutch size of taking into account losses of some individual 3.52 eggs for first nestings and 2.96 eggs for nestlings to predation in the few days renestings. immediately before fledging. Bombay et al.’s (2001) estimate of 0.87 female produced per Reported hatching success rates for willow female in 2001 is much higher than the flycatchers have ranged from 55 percent lifetime performance of 0.5 female per female (Holcomb 1972) to 93 percent (King 1955, Williams and Craig (1998) calculated for Berger 1967). McCabe (1991) reported a Sierra Nevada populations based on data from composite average of 74 percent from five KRCD (1985b) and Sanders and Flett (1989). different studies. Reported nesting successes (number of Population Rate of Change successful nests/number of nests ratio) in the Sierra Nevada have ranged from 24.4 percent Bombay et al. (2001) calculated a range of λ (Harris 1991) to 44 percent (Bombay et al. estimates based on varied adult survival 2001). Whitfield et al. (1999) found nesting estimates (pooled versus unpooled) and success of South Fork Kern River extimus to juvenile recruitment estimates (observed increase from 23 to 41 percent after brown- versus estimate from another population headed cowbird control measures were accounting for dispersion). The three instituted. Table 8-1 provides reported estimates of annual rate of change (0.768, nesting successes from a number of locations. 0.839, and 0.869) that were calculated all indicate annual declines of between 13 and Sierra Nevada willow flycatchers frequently 23 percent, although sample sizes were small. renest if earlier attempts fail. Bombay et al. Table 8-1. Nest success for willow flycatchers across various studies. Nesting Success Sources Location 18.0% Sogge et al. 1997 Grand Canyon, AZ 24.4% Harris 1991 South Fork Kern River, CA 23.0% Whitfield et al. 1999 (pre-BHCO removal) South Fork Kern River, CA 39.0% Whitfield et al. 1999 (post-BHCO removal) South Fork Kern River, CA 40.0% Bombay 1999 Central Sierra Nevada, CA 40.7% Sedgwick and Knopf 1988 Colorado 42.0% Sanders and Flett 1989 Central Sierra Nevada, CA 44.0% Bombay et al. 2001 Central Sierra Nevada, CA 44.6% King 1955 Eastern Washington 65.6% Walkinshaw 1966 Michigan This study is ongoing, and these estimates Sedgwick and Iko (1999) did not calculate a should be considered preliminary. population rate of change for eastern Oregon willow flycatchers because they could not demonstrate a credible estimate for juvenile

31 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 mortality. They did, however, use known Nest predation is rarely directly observed. data to calculate the juvenile survival value Documented willow flycatcher nest predators needed to maintain a stable population, and include milk snake (Lampropeltis triangulum; they found this value to be much higher than McCabe 1991), common kingsnake the observed values. They concluded that (Lampropeltis getulus), red-tailed hawk their population is either in decline, or is a (Buteo jamaicensis; Whitfield and Lynn sink population. 2001), and Cooper’s hawk (Paxton et al. 1997, McCarthey et al. 1998). Other nest predators have been inferred, but not ECOLOGICAL INFLUENCES ON confirmed. They include long-tailed weasels SURVIVAL AND (Mustela frenata) and house wrens (Stafford REPRODUCTION and Valentine 1985). The most illuminating study on predation of Predators and Predation willow flycatcher nests was conducted by Adult Predators – Little information is Cain (2001) in the Sierra Nevada. First, he available in the literature regarding predators correlated predator activity with nest success of adult willow flycatchers. Presumably, and found negative correlations with Douglas avian predators specializing in hunting squirrel (Tamiasciurus douglasii), long-tailed passerines (e.g., Cooper’s hawk [Accipter weasel and short-tailed weasel (M. erminea), cooperii], northern goshawk [A. gentilis], Cooper’s hawk, and brown-headed cowbird sharp-shinned hawk [A. striatus], and presence depending on the nesting stage. American kestrel [Falco sparverius]) Douglas squirrels in particular were highly occasionally prey on willow flycatchers. negatively correlated, especially during the incubation stage. Clark’s nutcracker Nest Predators – Published willow flycatcher (Nucifraga columbiana) activity during the predation rates have ranged from 11 percent willow flycatcher incubation stage also (McCabe 1991) to 51 percent (Holcomb appeared to influence nesting success. 1972), indicating potential for high variability as well as significant influence on population Second, using sympatric yellow warbler viability. Nest predation is likely the factor (Dendroica petechia) nests baited with zebra most affecting willow flycatcher population finch (Taeniopygia guttata) eggs as viability in the Sierra Nevada (Bombay 1999, surrogates, Cain (2001) photo-documented Cain 2001). Over 9 years of study in the 14 depredation events on his study site. The South Fork Kern River, Whitfield et al. (1999) most common predators recorded were observed a loss of 36 percent of the chipmunks (Tamias spp.; five events), southwestern willow flycatcher nests to followed by Douglas squirrels (four events), predation. Sanders and Flett (1989), Bombay short-tailed weasels (three events), and a deer (1999), and Cain (2001) all conducted willow mouse (Peromyscus maniculatus; one event). flycatcher demographic studies in the Little Cain (2001) also believed that predation Truckee River drainage. Sanders and Flett pressure from squirrels and chipmunks was (1989) recorded evidence of predation at 6 of reduced for nests farthest from the forest edge 21 nests studied, but in only 1 was the entire and surrounded by standing water. Bombay brood lost. Bombay (1999) observed a loss of (1999), too, found that nest success increased 32 (36 percent) of 90 nests monitored, and as distance to the closest tree increased. Both Cain (2001) recorded 22 (45 percent) of Bombay (1999) and Cain (2001) suggested 49 nests lost to predation where the clutch that trees provide habitat, especially foraging initiation was confirmed. Morrison et al. perches, for a number of mammalian and (2000) estimated that 72 percent of the total avian predators that, otherwise, would not nest failures in the central Sierra Nevada from penetrate the meadow interior. Meadow 1997 through 2000 were a result of nest interior nesting flycatchers, therefore, may predation.

32 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 exhibit higher nesting success because they the incidence of brood parasitism is higher. are pressured only by the few predators not Whitfield and Sogge (1999) reported the discouraged by a lack of trees or presence of highest reported percentage of brood standing water (e.g., weasels) (Cain 2001; parasitism (66 percent) for E. t. extimus on the Cain et al., in press). South Fork Kern River (elevation 800 m). A meta-analysis by Lorenzana and Sealy (1999) Cain (2001) concluded that nest predation was showed that cowbirds had a very large effect the likely limiting factor controlling on flycatcher productivity based on Harris’s reproductive success of willow flycatchers in (1991) and Whitfield’s (pers. comm.) study the Sierra Nevada. The implication is that results at the South Fork Kern River. In degradation of meadows from factors such as contrast, Bombay et al. (2001) reported an past intensive grazing and water diversions annual parasitism rate of 8.3 percent (range = has led to increased habitat components 4 to 15 percent) for central Sierra Nevada (i.e., less standing water and more populations (1,700 to 2,500 m). Higher encroaching forest) used by predators of elevation forests simply may not provide a willow flycatcher nests (Bombay 1999, Cain full component of habitat requisites for 2001). Fire exclusion, too, may play a role in cowbirds, and/or most cowbirds may arrive forest encroachment. Meadow restoration (with cattle) too late in the nesting season to strategies favoring return of meadows to greatly impact breeding willow flycatchers. natural hydrological regimes, as well as Further, these values are well below the 30 mitigation of current erosive forces, and, percent parasitism rate where conservation concurrently, stemming forest encroachment concerns begin (Mayfield 1977, Laymon (especially lodgepole pine [Pinus contorta]), 1987). Nevertheless, most of the parasitism may prove the best techniques for reducing reported by Bombay et al. (2001) occurred at predation pressures and improving population three adjacent sites in the Upper Truckee viability. River drainage where the maximum parasitism rate was 47 percent between 1998 Brood Parasitism and 2001. Consequently, even at high As they did with American bison (Bison elevations, cowbirds can greatly influence bison) populations in the Midwest, brown- flycatcher productivity on a local level. headed cowbirds developed a commensal Purcell and Verner (1999) did not find relationship with domestic livestock cowbirds on their detection plots above (Friedmann 1929). As livestock grazing 2,000 m in the southern Sierra Nevada, and rapidly spread across North America, so to cowbird abundance in the ponderosa pine did the range of the cowbird (DeSante and zone (below 1,300 m) was eight times higher George 1994). Consequently, new than the mixed conifer zone (1,700 to populations of passerines became brood 2,000 m). Also, Verner and Ritter (1983) did parasitism hosts. Brood parasitism refers to not find cowbirds at remote meadows without the laying of eggs by one species in the nest cattle except when supplemental food sources of another. Cowbirds have invaded the Sierra were nearby. Telemetry studies have shown Nevada in only the last 60 to 70 years that feeding sites of individual cowbirds are (Rothstein et al. 1980). tightly linked to locations of grazing livestock In the Sierra Nevada, the prevalence of and to pack stations (or other livestock cowbirds, and the associated incidence of facilities) (Verner and Ritter 1983, Verner and brood parasitism, relates to a number of Rothstein 1988, Goguen and Mathews 1999, factors that are not mutually exclusive (Verner Halterman et al. 1999, Shapiro et al. 1999). In and Ritter 1983, Purcell and Verner 1999). At addition, the influence of supplemental lower elevations, where the environment is feeding (e.g., pack station grain spillage and more open and livestock, agriculture, and bird feeders) may not be trivial. On June 1, human disturbance areas are more prevalent, 2002, approximately a dozen brown-headed

33 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 cowbirds were observed at a sunflower seed frequently associated with meadows greater feeding station at Red Lake on the Toyaibe than 6 ha (Serena 1982, Harris et al. 1988, National Forest (G. Green, pers. obs.). Red Stefani et al. 2001). Once willow patches are Lake sits at 2,400 m (7,900 ft) elevation and degraded, possibly due to past direct grazing annually supports about five willow flycatcher by cattle or indirect meadow desiccation from nesting territories. It has not experienced natural (climate change, drought) and other brown-headed cowbird parasitism in 5 years anthropogenic causes (water diversions, (1997 to 2001) of monitoring (Bombay et al. adjacent timber harvest and fuels treatments, 2001). Cain (2001), however, did report the fire suppression, mining, roads, recreation), presence of brown-headed cowbirds and the the ability of these patches to support nesting parasitism of yellow warbler nests at Red flycatchers is lost, and the birds do not have Lake. the plasticity to nest in other habitat types. Evidence for this is the large number of The willow flycatcher is probably a poor host meadow sites that no longer support breeding for the brown-headed cowbird. Whitfield and willow flycatchers. Sogge (1999) reported that only 14 percent of the parasitized nests on the South Fork Kern Habitat degradation in the montane meadow River successfully fledged cowbirds. This is systems appears to follow a pattern beginning lower than the 18 percent McGeen (1972) with the expanded use by humans beginning reported for the yellow warbler, a in the mid- to late 1800s. As reviewed significantly smaller host (9.5 g versus 13.4 g; elsewhere in this document, grazing, mining, Dunning 1993). Bombay et al. (2001) recreation, roads, adjacent timber harvest and reported that 71 percent of the parasitized fuels treatments, fire suppression, water nests in their central Sierra Nevada study site diversion, and other factors have all combined were either abandoned by their host or to degrade meadows. It is inferred that depredated. Note, however, that nest grazing cattle can directly impact flycatchers desertion in least Bell’s vireos (Vereo bellii by removing willow cover (browsing, grazing, pusillus) does not appear to be an adequate and trampling) (Taylor 1986) and natural defense against cowbird parasitism, occasionally knocking down nests largely because subsequent nests of deserting (King 1955, Valentine et al. 1988). pairs are also parasitized (Kus 2002). Concomitantly, cattle-attending, brown- Morrison et al. (2000) and Kus (2002) headed cowbirds may arrive and parasitize a showed, however, that human removal of number of willow flycatcher nests. Further, cowbird eggs is effective in improving host some of the meadows have suffered from past nesting success. Cowbird eggs are removed as livestock damage such that the vegetation part of the willow flycatcher demography layer has been breached, followed by erosion study in the Sierra Nevada (Bombay and of underlying soils. During episodic heavy Morrison, unpubl. data). Recent work by rain events, these erosion sites form deep Kilpatrick (2002) suggests that raising gullies that alter the hydrology 1 cowbird nestling is energetically equivalent (Hagberg 1995). The water table drops and to willow flycatchers raising 2.5 of their own desiccation ensues (Reid 1989). Drier nestlings. meadows result in a reduction of hydrophytic willows and allow expansion of forest conifers, especially lodgepole pine, into EFFECTS OF HABITAT LOSS meadows. Drier meadow surfaces, expanded AND DEGRADATION forest edge, and intrusion of conifer into the Nesting willow flycatchers in the Sierra meadow proper may allow forest nest Nevada appear to occupy a narrowly defined predators, especially squirrels and chipmunks, niche. Based on available data, willow access to flycatcher nests (Cain 2001). flycatchers nest in willow patches averaging Increased predation due to meadow about 1 ha (Bombay 1999) but are more desiccation may prove to be one of the factors

34 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 most responsible for the decline of willow (Serena 1982; Harris et al. 1987, 1988; Ritter flycatchers in the Sierra Nevada. Also, the and Roche 1999). initial actions that precipitated meadow In general, the willow flycatcher has desiccation may have occurred decades earlier experienced declines throughout its North (Hagberg 1995). American range. Between 1966 and 1996, D. Cluck (Entomologist, Forest Health willow flycatchers annually declined Protection, Susanville, California) observed 1.2 percent in North America, 2.3 percent in Salix dieback, apparently caused by a fungi the western region, 5.8 percent in western (most likely Cytospora chyrsosperma, Oregon and Washington (brewsteri), and Venturia saliciperda, and Glomerella 2.5 percent in eastern Oregon and Washington miyabeana). These fungi cause dieback of (adastus) (Sauer et al. 1997). There are not willow stands through infection that is enough data to calculate current trends for the scattered on stems throughout an individual Sierra Nevada, based on surveys. However, plant. Woodboring beetles may then become Bombay et al. (2001) did calculate annual active within the dead and dying stems. In the population rates of change based on area of observed willow mortality, water demographic data from central Sierra Nevada stress may predispose the willows to indicating 13 to 23 percent annual decline infection. rates (although sample sizes were small). Another indicator of decline is that 53 of 135 POPULATION SIZE AND TREND (39 percent) breeding locations were found Current estimates of the willow flycatcher unoccupied in subsequent surveys population in the Sierra Nevada bioregion (Table 8-2), including 46 of 128 (36 percent) range from 300 to 400 individuals, with 120 known to be active since 1982. A number of to 150 individuals on National Forest lands Table 8-2. Declines in willow flycatcher breeding sites and territories in the Sierra Nevada Forest Plan Amendment area (USDA Forest Service, unpubl. data). Sites Territoriesb Forest Total Activea Change Total Activea Change Modoc 7 6 14% 11 10 9% Lassen 19 14 26% 63 52 18% Plumas 18 12 33% 25 18 28% Tahoe 18 14 22% 61 55 10% LTBMU 7 2 71% 12 4 67% Eldorado 1 0 100% 1 0 100% Toiyabe 7 4 43% 12 6 50% Stanislaus 8 3 63% 15 7 53% Inyo 17 12 29% 35 28 20% Yosemite NP 5 4 20% 12 11 8% Sierra 13 2 85% 21 4 81% Sequoia 10 5 50% 41 35 15% Sequoia/Kings Canyon NP 5 4 20% 6 4 33% Total 135 82 39% 315 234 26% a Breeding sites or territories active on the last year they were surveyed. b Total of the mean number of territories at each site.

35 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 these inactive sites, however, included only Bishop) of willow flycatcher are endangered one or two territories. Using the mean extimus. number of territories per site, the number of territories has declined from 315 to 234 (26 percent) (Table 8-2). Although these data DIRECT HUMAN EFFECTS should be viewed with caution due to the Direct human effects on willow flycatchers in variability in past survey efforts, they do the Sierra Nevada are, for the most part, those reflect a consistent decline across the Sierra that affect flycatcher habitat, resulting in Nevada. reduced breeding opportunity or success. Finch et al. (2000) listed a number of human The largest mean territory declines have activities that could directly impact willow occurred on the Sierra (81 percent), Stanislaus flycatchers, including livestock management, (53 percent), and Toyaibe (50 percent) water developments, recreation, and pesticide National Forests and the Lake Tahoe Basin use. Each is addressed below. Management Unit (67 percent) (Table 8-2). Also, the Eldorado National Forest has apparently lost its only territory. The Livestock Management Stanislaus National Forest loss may be even In their critical assessment of the management greater (93 percent) as six of its territories are recommendations and literature regarding records from the 1930s. The least decline is willow flycatcher conservation in the Sierra from Yosemite National Park at 8 percent; Nevada, Dahm and Pittroff (n.d.) concluded however, removing one old record of five that, “There is currently no sound scientific territories from 1966 brings the loss to 50 knowledge basis which justifies the assertion percent. that livestock grazing is the primary factor Relatively light losses have occurred on the driving willow flycatcher abundance in the Modoc (9 percent), Tahoe (10 percent), Sierra Nevada.” Their report, based on an Sequoia (15 percent), and Lassen (18 percent) investigation of a small subset of the literature National Forests (Table 8-2). However, 32 of used in the Sierra Nevada Forest Plan the 35 territories remaining in the Sequoia Amendment DEIS regarding livestock National Forest area are extimus nesting along impacts to willow flycatchers, indicates that the South Fork Kern River (South Fork much of the evidence they reviewed was Wildlife Area and Kern River Preserve) and at based on inference and/or circumstantial Bloomfield Ranch. Half the sites on the evidence. While they concede that livestock Sequoia National Forest thought to be may, in certain instances, based on the occupied by brewsteri/adastus are no longer literature, be detrimental to willow viable. flycatchers, none of the grazing-related findings in the 10 published and unpublished In general, sites currently supporting multiple papers reviewed in their report is statistically territories of brewsteri occur only in the robust. While concurring with Dahm and Lassen Peak region (including Warner Valley) Pittroff’s assertion of inconclusive scientific of the Lassen National Forest and in Yosemite evidence in the role of livestock grazing on National Park (e.g., Hodgdon Meadows) willow flycatcher status, the fact that meadow (USDA Forest Service, unpubl. data). resources have, in the past, been severely Relatively large numbers of adastus are found impacted by livestock (Ratliff 1985, Menke et only in the Little Truckee River drainage, al. 1996) cannot be ignored. If past livestock although a few multiple territory sites are still damage has led to chronic conditions (such as found in the Carson region (e.g., Red Lake) gullies) that continue to alter habitat and near Mammoth/Mono Lake. components important to willow flycatchers, Interestingly, two of the healthier populations then restorative actions to correct these (South Fork Kern River and Owens Valley, conditions are highly appropriate, regardless of the initial cause. Because it is impossible

36 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 to travel back in time, causes from the past streamside riparian zones. In the Owens must be inferred. Valley, riparian vegetation downstream of the intake to the Los Angeles aqueduct has Current grazing schemes that allow grazing dramatically changed to a more xeric within willow flycatcher breeding habitat may condition due to the lack of water (Brothers upset flycatcher nests (Stafford and Valentine 1984) and no longer provides habitat for 1985), alter willow habitat including shrub nesting willow flycatchers. Stine et al. (1984) vigor and spatial pattern (Taylor and documented the destruction of the riparian Littlefield 1986, Stanley and Knopf 2002), systems (e.g., Lee Vining and Rush Creeks) facilitate cowbird brood parasitism, and draining into Mono Lake due to water exacerbate chronic conditions (gullies). diversion to Los Angeles. Several hundred Preliminary results from grazing studies in the acres of willow-dominated habitat was either Sierra Nevada indicate that there are impacts inundated by impoundments or dried up from from contemporary livestock grazing diversions. Today, these riparian zones (B. Allen-Diaz, pers. comm.), though support eight territories (C. McCreedy, pers. preliminary range monitoring results from comm.), but as a result of recent restoration meadows on five National Forests in the activities. Sierra Nevada suggest a slight upward trend in ecological condition on key range sites (D. Weixelman, pers. comm.). A recently Recreation published study of historically grazed pastures Recreational activity can have varying in a high elevation floodplain of Colorado impacts to nesting birds (Knight and (Stanley and Knopf 2002) suggested that Gutzwiller 1994). Potential activities habitat for grazing-sensitive birds may be occurring at Sierra Nevada meadows include restored while still allowing late-season hiking, camping, picnicking, fishing, bird grazing, although the rate at which species are watching, mountain biking, and off-road recovered will be slower than if all cattle are vehicle use. The magnitude of these activities removed. They have strong statistical may not be high where Sierra willow evidence that bird densities of the stenotopic flycatcher are known to breed; however, given (grazing-sensitive) guild, which included the the small size of some breeding populations, willow flycatcher, increased more on any incident resulting in disturbance may be ungrazed pastures than on grazed pastures. significant. Food scraps and garbage left at The contemporary influence of managed recreational use areas can also attract jays, livestock grazing on willow flycatcher status squirrels, and other wildlife known to prey on in high-quality (i.e., good ecological willow flycatcher nests (Johnson and condition) habitat is unknown. Further Carothers 1982, Blakesley and Reese 1988, research, directed at livestock impacts on Marshall and Stoleson 2000). willow flycatchers and their habitat in the Sierra Nevada, is needed before sound conclusions can be drawn. Two issues should Pesticides be highlighted: (1) the past causes of meadow Pesticide contamination has not been raised as drying must be determined to ensure that they a major threat to Sierra Nevada willow have stopped (if they can be controlled); and flycatcher populations, probably because (2) regardless of the causes, meadow these populations are not close to agricultural condition must be improved (i.e., increase areas where pesticide use is most prevalent. meadow wetness throughout the breeding cycle).

Water Developments Water diversions have also impacted willow flycatchers, especially those populations using

37 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 However, recent research (Zabik and populations, but maintain demographic and Seiber 1993, Aston and Seiber 1997, genetic affinity with other populations. McConnell et al. 1998, Le Noir et al. 1999) Metapopulations also tend to maintain has shown that considerable pesticide loads equilibrium (Wilson 1975). are transported by prevailing summertime Population patterns of Sierra Nevada willow wind patterns to the central and southern flycatchers do not fit the metapopulation Sierra Nevada from the Central Valley, and model very well. Although little is presently such loads have been implicated in the known about willow flycatcher dispersal dramatic population declines of anurans in the patterns, as neotropical migrants, willow Sierra Nevada (Sparling et al. 2001). Further, flycatchers are wholly capable of traveling pesticide use has been documented in Central great distances over unsuitable habitat. In and South American wintering grounds particular, birds breeding in the northern (Koronkiewicz et al. 1998, Koronkiewicz and portion of their range obviously travel each Whitfield 1999, Lynn and Whitfield 2000). year past habitat used by other populations. Consequently, pesticide contamination Finally, if the Sierra Nevada population in remains a potential, but unknown, threat. general is declining, as appears to be the case, it does not meet Wilson’s (1975) equilibrium Roads criteria. There is no evidence to suggest that Roads, whether they are dirt-surfaced or Sierra Nevada populations of willow paved, provide a near impervious wall, flycatchers operate as a metapopulation(s). intercepting surface and subsurface Breeding populations of willow flycatchers in hydrological flow (Furniss et al. 1991, the Sierra Nevada are, however, patchily Kattelmann 1996). When natural meadow distributed, and in a manner perhaps hydrological flows are intercepted and explained by source/sink dynamics. Source redirected, meadow drying occurs. Runoff populations are growing populations that from road surfaces can also collect and then occupy high-quality habitat and produce discharge as erosive flows, greatly increasing emigrants (Pulliam 1988, Gutierrez and sediment yields below the roads, especially Harrison 1996). Sink populations are those during the wet season (Kattelmann 1996). occupying low-quality habitat that cannot Erman et al. (1977) found, during a study of maintain themselves without immigration logging impacts on stream invertebrates from source populations. Certain large (potential willow flycatcher prey), that meadows in the Sierra Nevada (e.g., Lacey, failures of poorly designed roads, leading to Little Truckee, and Warner Valley) are increased sediment yields, had the greatest consistently occupied by multiple territories impact to aquatic invertebrates. Roads also with apparently enough success to persist. provide access for other activities that might They may, therefore, be viewed as source impact willow flycatchers or their habitat meadows. There is also a relatively large (e.g., recreation, timber harvest) (Kattelmann number of meadows that have been occupied 1996). in the past, generally just by one territory, and might be viewed as sinks. POPULATION DYNAMICS Given the lack of consistency in willow Metapopulations are essentially populations flycatcher survey methodologies between within populations. They occur as large known sites and years, as well as unknowns in populations distributed in patches separated willow flycatcher detection probabilities and by distances farther than individuals typically site occupancy trend patterns, categorizing disperse, but not so far apart that there is no known sites as sources or sinks based upon significant demographic interchange the number of reported territory holders is (Gutierrez and Harrison 1996). premature and could be counterproductive Metapopulations function as separate (i.e., a site with one to two territory holders

38 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 could provide high quality habitat and later intercepts (Browning 1993), Barrowclough prove to be a “source”). An alternative raises a valid point. explanation is that willow flycatchers Genetic studies of willow flycatchers began currently may not be habitat-limited, but with Seutin and Simon (1988) and Winker increased mortality and decreased (1994). Both teams investigated potential productivity levels (e.g., increased nest hybridization in sympatric populations of predation, decline in prey quality or quantity, willow and alder flycatchers by using problems on the wintering ground) have electrophoretic techniques. Although both caused a general decline in the population. cautioned that further research was needed to Sites supporting few territories are more validate their results, neither group found likely to be impacted by the resulting conclusive evidence of hybridization. demographic stochasticity (localized extinction) than meadows supporting multiple Using both nuclear and mitochondrial DNA territories. Eventually, the sites occupied by analysis, the latter an improvement over multiple territories (although fewer territories) earlier electrophoretic techniques, Paxton tend to dominate. Only a third of all (2000) examined structuring of willow meadows known to be occupied since 1999 flycatcher populations based on genetics. A support a single territory. primary purpose of his study was to determine whether a molecular genetic study would If the current population declines are a result support the distinction of E. t. extimus as a of recent extrinsic factors (anthropogenic valid subspecies. The U.S. Fish and Wildlife factors), it is possible that the Sierra Nevada Service’s 1995 listing of the southwestern populations operated under source/sink willow flycatcher as an endangered species dynamics before the existence of these assumed extimus was a valid taxon, but this factors. Regardless, insufficient information assumption was based on earlier is currently available to ascertain or classify morphometric studies where subspecies willow flycatcher population dynamics. differences are often very subtle. Long-term monitoring and continued demographic study, however, should lead in After collecting genetic samples from this direction. 232 adult willow flycatchers from 49 sites across the species’ range, Paxton (2000) concluded that highly significant genetic POPULATION GENETICS variability occurred between extimus and Only very recently have the genetics of other subspecies based both on mitochondrial willow flycatchers begun to be investigated. (cytochrome-b) and nuclear (amplified Before Paxton’s (2000) genetic study, fragment length polymorphism) DNA understanding of willow flycatcher taxonomy analysis. His results also showed that the was based on song, behavior, and willow flycatcher population in the Owens morphology. While genetically determined Valley north of Bishop is extimus. Paxton song (Kroodsma 1984) and behavior were (2000), however, found no significant genetic used to separate willow flycatchers from alder difference between adastus and brewsteri flycatchers, plumage color and wing formula using either technique, lending support to have been the dominant criteria used to Miller (1941) and Behle (1948), who posited separate subspecies (Unitt 1987). However, that the two groups are not taxonomically Barrowclough (1982) has questioned whether distinct. However, Paxton (2000) did state assigning subspecies status based solely on that his sample size for brewsteri was small morphological characters is valid. Given the and perhaps biased towards brewsteri’s range controversy over the possible existence of a along an intergradation zone with adastus. Of fifth subspecies, campestris, and whether interest to this assessment were the major intergrade zones occur at subspecies cytochrome-b sequence data that indicated Perazzo Meadow (north of Lake Tahoe)

39 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 adastus were more closely related to Warner adastus and brewsteri populations in the Valley (Lassen) brewsteri than Red Lake Sierra Nevada are truly distinct is warranted, (south of Lake Tahoe) adastus, again especially if continuing declines in suggesting intergradation between the two populations necessitate conservation status subspecies. Further research on whether changes or management strategies based on taxon separation.

40 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 9 Conservation Status

INTRODUCTION Do Habitats Vary in Their Capacity to The previous chapters provide a technical Support Willow Flycatcher review of the biology and ecology of the Populations? willow flycatcher, as well as its prey and the habitats in which it is found. This technical The breeding habitat for willow flycatchers in review is the basis for assessing whether the the Sierra Nevada is quite narrowly defined as species is likely to persist within its Sierra willow patches forming meadow or Nevada range over the long term, or whether streamside riparian habitat. This habitat type management intervention may be required to provides almost all of the requisites for prevent extirpation. A number of nesting, perching, and foraging. An element conservation questions are addressed below, of standing water or wetness is also important which lead to one of three possible and may serve as both a deterrent to nest conclusions: (1) populations of willow predators and as breeding habitat for aquatic flycatchers are secure in the Sierra Nevada insect prey. The ability of these habitats to and will likely remain so, given current land support willow flycatchers is likely reduced management practices, (2) populations of under degraded conditions. Sierra Nevada willow flycatchers are in peril or are likely to be in peril in the near future What Are the Important Characteristics under current land management practices, and of Those Habitats? (3) there is insufficient evidence to determine Height and density of willow and the amount the species’ conservation status in the Sierra of standing water or meadow wetness are the Nevada. important characteristics in meadows and streamside riparian habitat. Is the Distribution and Abundance of the Willow Flycatcher Declining in the Sierra Nevada? Do Habitats Vary in Their Capacity to Both E. t. extimus and E. t. brewsteri have Support Principal Prey Species? experienced significant population declines in Willow flycatchers forage on a variety of California. E. t. brewsteri has been virtually invertebrate prey species, many of which have eliminated from its former range within the aquatic life stages (e.g., deer flies, central valley of California, and the range of damselflies, and mayflies), or larval extimus has been reduced to a very few dependence on riparian vegetation locations (e.g., South Fork Kern River, Owens (e.g., willow sawflies and certain wasps) Valley). Breeding populations of (Sumner and Dixon 1953, H. Bombay, pers. brewsteri/adastus remain in a few strongholds obs.). Desiccated meadows lack habitat for in the Sierra Nevada, but 53 of 135 known aquatic invertebrates and reduce the standing sites (Table 8-2) were found to no longer crop of riparian vegetation available for support willow flycatchers during recent willow sawflies. Consequently, degradation surveys. The distances between current sites of the meadow habitat via desiccation can are expanding, and this may have implications profoundly affect flycatcher prey, as well. regarding dispersal.

41 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 If the Willow Flycatcher or Its Prey environment, especially rodents such as Select Particular Habitats, Are These Douglas squirrels and chipmunks. Habitats Declining or Being Stressed by Current Management? What is the Current and Projected The primary breeding habitat for willow Conservation Status of the Willow flycatchers and their prey is declining and Flycatcher? stressed where past and current management The current conservation status of the willow continues to manifest long-term desiccation of flycatcher in the Sierra Nevada is that of a willow habitat. Drought or climate change population in peril. Many former breeding may create or further compound these effects. sites are no longer used, probably due to Management intervention (restoration of habitat degradation. Populations are meadow hydrology and attendant erosion experiencing high nest predation rates, likely mitigations) probably will be needed to stem caused by meadow desiccation, itself a population declines. possible result of past or current natural events and anthropogenic activities. Do the Life History and Ecology of the Populations are being impacted by a new Willow Flycatcher Suggest That threat: brood parasitism by brown-headed Populations Are Vulnerable to Habitat cowbirds. Small populations have Change? experienced stochastic environmental events Willow flycatchers are vulnerable to changes (e.g., summer snowstorm) with severe in their willow riparian habitat that lead to consequences. desiccation. Past grazing, road building, and Available demographic information suggests water diversion projects have resulted in more that the current Sierra Nevada population of mesic or xeric conditions within traditional 300 to 400 individuals (Ritter and Roche flycatcher breeding habitat. Drought, climate 1999) is declining (Bombay et al. 2001). If change, fire suppression, mining, recreation, the primary reason for population decline of roads, or current overgrazing also may create willow flycatchers in the Sierra Nevada is or exacerbate these conditions, which can meadow desiccation, then willow flycatchers result in vegetational changes away from are likely to continue to decline towards willow-dominated riparian habitat and allow extirpation unless management intervention is encroachment of conifers or sagebrush into successful in restoring the hydrological meadows. Increased conifers and sagebrush functions of, and concomitantly mitigating, and lack of standing water allow greater the erosive activities affecting these meadows. access of forest predators into the wetland

42 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 10 Management Considerations and Uncertainties

Indirect evidence brought forth in the livestock grazing pressure on shrubs. The previous chapters suggests that past livestock Aquatic Conservation Strategy Meadow grazing may have been the prime factor Study Plan, currently being developed for leading to willow flycatcher declines in the Sierra Nevada aquatic, riparian, and meadow Sierra Nevada, although there is no hard (ARM) ecosystems, is the first step leading evidence to confirm this. Livestock could towards willow flycatcher conservation and directly impact willow flycatchers by should be coordinated appropriately. knocking down nests, affecting prey base by A major uncertainty is the genetic relationship trampling and foraging, and removing nesting among the three subspecies, but most cover, as well as, indirectly, by promoting especially between brewsteri and adastus. brood parasitism from brown-headed Genetic work by Paxton (2000) suggests that cowbirds, a bird species associated with brewsteri and adastus populations in the livestock. Neither nest disruption or brood Sierra Nevada are not genetically distinct and, parasitism, however, appears to be a prevalent therefore, may be intergrades. impact in this population. Meadow desiccation, which may indirectly be caused The importance of genetic understanding to by livestock trampling (but also by roads, management relates to whether, for instance, recreation, adjacent timber harvest or fuels Little Truckee River adastus can be treatments, fire suppression, water diversions, considered a source population for recovery mining, climate changes, and drought), of Middle Fork Feather River brewsteri appears to be the single-most important populations 25 km away. Or are declining proximate factor in willow flycatcher decline populations of brewsteri in the southern half in the Sierra Nevada. Drier meadows result in of the Sierra Nevada more likely to be a reduction of willow cover and standing supplemented by Mono Lake adastus 40 km water, leading to encroachment by conifers. to the east, or Warner Valley brewsteri nearly The presence of conifers and the lack of 300 km to the north? The potential to standing water allow forest predators easier discover additional occurrences of federally access to willow flycatcher nests. The endangered extimus subspecies brings increased predation rates on these nests may additional, legally mandated, management be the primary cause most influencing willow requirements. Thus, a clearer understanding flycatcher population decline in the Sierra of the genetic distinction among the three Nevada. subspecies in the Sierra Nevada has a bearing on whether recovery efforts target subspecies Obviously, management efforts leading to differently. restoration of meadow hydrological regimes and reestablishment of healthy willow stands Another uncertainty is the possible role may prove the best options for restoring windborne pesticides from the Central Valley willow flycatcher populations. The and pesticide use on the wintering grounds magnitude of the problem is exemplified in may have on willow flycatcher immune the Feather River watershed where 98 percent response systems and egg viability. of the 100,000 ha of meadow and small Circumstantial evidence from studies of other mountain valleys are considered degraded Sierra Nevada riparian and aquatic vertebrates (Lindquist and Wilcox 2000). The impact of (Sparling et al. 2001) suggests that pesticides drought may further degrade these habitats may pose a threat to willow flycatchers, (for example by reducing willow flycatcher although significance has yet to be prey base, leading to nestling deformities determined. [H. Bombay, pers. obs.]) and also increase

43 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 11 Recommendations for Management

This Conservation Assessment has identified maintains wet conditions throughout the meadow degradation, which results in flycatcher breeding cycle. meadow drying, loss of nesting and foraging A number of grazing alternatives, proposed by substrates, increased predator access to the USDA Forest Service and outside groups, meadow interiors, and potentially cowbird were developed in the Sierra Nevada Forest parasitism as among the key factors likely Plan Amendment FEIS. They range from responsible for the decline of the willow elimination of grazing in suitable habitat flycatcher. Although few rigorous, within 5 miles of meadow and riparian quantitative, cause-effect studies are available, ecosystems occupied by willow flycatchers to the weight of evidence indicates that developing buffer zones and limiting improving meadow conditions is the most operating periods (LOPs) based on willow likely step that will enhance flycatcher flycatcher nesting phenology and habitat use. breeding success. Because each meadow is Even under the no-action alternative, some impacted by each negative factor to varying forests are adopting their own LOP standards degrees, management activities must also be to protect nesting willow flycatchers. Forest tailored on a meadow-specific basis. In this managers must make meadow-specific section desired outcomes are identified that determinations of what, if any, impact should lead to improved habitat conditions for livestock are having on willow flycatcher willow flycatchers. The primary Forest habitat and take appropriate corrective Service management activities are as follows: actions. Whatever alternative is selected, • Manage meadow hydrology so that additional research and monitoring are needed meadows remain wet throughout the to address potential livestock impacts under breeding cycle of flycatchers. current management regimes in the Sierra Nevada. • Implement a willow flycatcher monitoring program investigating nesting success and For example, if drought increases livestock habitat conditions. grazing pressure on shrubs through premature drying of herbaceous forage, livestock could • Restore degraded meadows to nesting be taken off of the grazing allotment when habitat conditions that increase shrub browse exceeds a certain percent as opportunities for willow flycatcher determined in collaboration with permit population expansion. holders. Such standards should allow • Lessen the influence of brown-headed recruitment of riparian deciduous shrubs (that cowbird brood parasitism on willow provide willow flycatcher nesting substrate) flycatcher populations. and are consistent with current management directions in the Sierra Nevada (SNFPA ROD MEADOW CONDITION 2001, p. A-59). As reviewed in this document, meadows have Roads also may have a negative influence on been negatively impacted by a variety of meadow condition, especially those that bisect factors that, together, have apparently caused meadows and have associated drainage a decline in habitat conditions for breeding structures to maintain road conditions. The and foraging flycatchers. Thus, management SNFPA ROD (P A-57) recommended road should be instituted that leads to an redesign and no new roads in flycatcher improvement in the stature (height and foliar habitat as a means of alleviating the negative cover) and recruitment of willow and effects of roads on meadow hydrology and, thus, on flycatcher habitat.

44 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 MONITORING result, of habitat change. Consequently, restoration efforts are important tools in Continued monitoring of willow flycatcher recovery of willow flycatcher populations. populations and habitat is necessary to Without a sanctioned restoration strategy for identify the factors limiting population willow flycatcher habitat, however, recovery. Protocol-based detection surveys restoration efforts might be implemented annually indicate where breeding willow without knowing whether the project will flycatchers do and do not occur. They allow contribute to willow flycatcher recovery detection of changes in numbers and (Stefani et al. 2001). distribution of breeding pairs. Demographic studies identify the elements influencing Presumably, restoration efforts should focus population change such as nest success, on restoring meadow hydrology where dispersal, and overwinter survival. activities have resulted in desiccation as well Monitoring of predation and parasitism rates as mitigating current erosion sources. should be built into the population monitoring Meadows with restored hydrological regimes and demographic studies. Nest predation by may provide greater soil saturation later in the natural predators is likely to be a significant summer season. Wetter soils may prevent factor controlling Sierra Nevada willow forest predators from accessing nest sites and flycatcher nesting success (Morrison et al. encroachment of lodgepole pines, a habitat 2000, Cain 2001). Photo-documentation of feature for forest and avian predators nest predators to help evaluate the proportion (Cain 2001, Cain et al., in press). of avian, snake, and mammalian predators Because of limited funding, a priority list of will inform strategies to mitigate willow meadows that are candidates for restoration flycatcher nest predation. Habitat monitoring should be developed. Initially, efforts should allows detection of annual changes to the be focused within willow flycatcher dispersal most significant habitat features for willow distance towards or near those meadows flycatchers, including meadow wetness and already supporting a high percentage of the willow coverage. In addition, evaluating of Sierra Nevada willow flycatcher population. the prevalence and monitoring the spread of With ramifications for locating potential recent Salix species dieback, believed to be restoration projects, most willow flycatcher caused by fungi (D. Cluck, pers. comm.), will dispersal events have occurred downstream yield valuable information. Coupled with within the same drainage; however, four have demographic information, habitat studies can occurred upstream within the same drainage, be used to define suitable habitat, quantity of and two have occurred between different value when identifying potential restoration drainages (Bombay and Morrison, unpubl. sites, define restoration targets, and determine data). desired management conditions. Restoration efforts elsewhere cannot succeed Obtain site soil profiles to determine soil without first securing the source populations characteristics, soil moisture, and site (and their habitat). Source populations capability to support desired wetness, shrub produce the birds that are expected to expand cover, and foliar density at a site. Use these data to evaluate the influence of livestock, as well as the restoration potential, at a site.

HABITAT RESTORATION Among the factors that may ultimately prove to be responsible for the decline of willow flycatcher populations (e.g., livestock grazing, increased predation rates, overwinter mortality), many are either an agent, or a

45 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 elsewhere. If flycatchers are lost at primary- be biologically harmful (Mayfield 1977, use meadows such as Perazzo, Lacey, and Laymon 1987). Nevertheless, localized high Warner Valley, sustaining populations brood parasitism rates have been observed in anywhere else in the Sierra Nevada is the central Sierra Nevada, warranting that unlikely. monitoring for parasitism should continue. The removal of cowbird eggs in parasitized Meadow restoration work should also be nests in the endangered least Bell’s vireo guided by a conservation strategy developed (V. b. pusillus) (Kus 2002) and Arizona Bell’s jointly by the USDA Forest Service and vireo (V. b. arizonae) (Morrison and Averill- U.S. Fish and Wildlife Service. The strategy Murray 2002) increased productivity and has should include site planning, action been implemented in the willow flycatcher accountability, budgeting, and implementation demography study in the Sierra Nevada and monitoring schedules. This strategy has (Bombay and Morrison, unpubl. data). to quantify minimum hydrological thresholds, or habitat components, that meadows should To reduce the incidence of cowbird brood meet once restoration is completed. parasitism, conduct a GIS analysis should be Consequently, the desired attributes of conducted to evaluate the location of all hydrology (meadow wetness) and habitat existing foraging areas throughout the Sierra (such as willow coverage and structure, Nevada and to identify vulnerable flycatcher willow patch distribution, herbaceous species sites for monitoring. A bioregional level composition, and meadow distribution) have analysis would address cumulative to be defined and incorporated into restoration effects/threats to flycatchers and ensure and management plans. Finally, to help consistent approaches across forest ensure the success of these expensive boundaries. Monitoring and mitigation could endeavors, peer-review of plans is advised. then be prioritized and scheduled. Periodic reviews, incorporating updated COWBIRDS willow flycatcher and cowbird data, are Brood parasitism by brown-headed cowbirds recommended to evaluate mitigation success does occur with Sierra Nevada willow and consider new proposals. Such analyses flycatcher populations, but does not appear to should include the influence of dispersed and be a significant problem (except with Kern developed recreation effects, cowbird use and River populations of extimus). movements relative to livestock concentrations, the use by cowbirds of Observed parasitism rates (Bombay and harvested sites, and other factors related to Morrison 2001) are below levels believed to cowbird abundance and behavior.

46 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 12 Research Needs

The following research needs are not listed in improve estimates of λ, identify suitable any order of priority. habitat criteria through linked research on 1) Continue monitoring of willow habitat use and reproductive fitness, and flycatcher sites. confirm appropriate management direction. Furthermore, these data may address whether Willow flycatcher population status in the nestling sex ratios (e.g., female; see Paxton et Sierra Nevada is precarious, especially in the al. 2002, Janota et al. 2002) and/or mating southern half. Continuous monitoring, systems (e.g., polygyny; see Paxton et al. following protocols (Bombay et al. 2000), is 2002) at a site provide clues about habitat required to ascertain the distribution and quality. In the case of polygyny, it may either abundance of willow flycatchers, track trends indicate that the particular site is outstanding in the general population and in response to or, alternatively (if available), that the other management activities (grazing, recreation), available unmated male territories are poor and evaluate mitigation or restoration quality. Additional recommendations include strategies. expanding the geographic scope of the willow 2) Using willow flycatcher protocol, flycatcher demography study to include the investigate detection probability and Warner Valley Wildlife Area population and observer bias. better understand source/sink dynamics in the Determining population trends depends on Sierra Nevada. accurate detection of nesting pairs that might 4) Investigate further role of meadow be present. Poor detection rates or variation wetness on predation rates. in an observer’s ability to detect birds can Research by Cain (2001, see also Cain et al., result in underestimating the nesting in press) has shown that predation rates, population and a subsequent exaggeration of especially from forest predators, may be the estimated population decline. By testing for most or an, important factor leading to willow detection probabilities and observer bias, flycatcher population decline in the Sierra correction factors can be developed that will Nevada. Continued investigation into the lead to more accurate estimates of population relationship of standing water and change. encroaching conifers to predation rates should 3) Continue demographic studies lead to refinement in developing meadow measuring λ. restoration strategies. In addition, the Recent demographic studies by Bombay et al. predator release hypothesis, which predicts an (2001) have helped identify which segments increase in mammalian predation pressure of the population (i.e., sex-age) are most where declines of top forest carnivores important in the observed annual rates of (e.g., fisher, marten, northern goshawk) have change. Strong correlations between nesting occurred, could be evaluated. success and recruitment suggest that future 5) Evaluate existing willow flycatcher efforts should focus on factors influencing habitat conditions and inventory nest success (e.g., nest predation). These potential restoration meadows, studies are preliminary, however, and are including meadows formerly occupied based on small sample size. In particular, by willow flycatchers. better estimates of dispersion patterns and Using a consistent protocol or monitoring overwinter survival (return rates) are needed study plan (Morrison et al., in prep.), evaluate to improve the reliability of population existing conditions and limiting factors within change estimates (λ). Continued study will

47 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 willow flycatcher habitat to establish baseline 7) Measure response of willow flycatchers data and to determine trends in meadow to meadow restoration efforts. conditions for supporting or sustaining willow Meadow restoration is costly and labor- flycatchers. intensive. Where restoration efforts are Large meadows potentially suitable for planned, measurements of willow flycatcher restoration should be inventoried and habitat requisites should be included to classified as to current hydrological regime quantify flycatcher response to revegetation (wetness). Restoring meadow wetness where and restoration efforts. it has been lost and managing or mitigating 8) Identify subspecies distributions and erosive activities (e.g., roads, mining, adjacent determine if there is a genetic timber harvest and fuels treatments, grazing, distinction between west slope brewsteri recreation) may prove to provide the greatest and east slope adastus. benefit to willow flycatcher recovery. As mentioned in Chapter 10, subspecies There are more than 50 identified sites that status, especially whether brewsteri and formerly supported breeding populations of adastus are genetically distinct, should be willow flycatcher. Those sites no longer clarified further for conservation and supporting breeding territories should be management of the species. If central Sierra examined to determine whether habitat Nevada brewsteri and adastus populations are components remain, or if options for fully intergraded and provide source/sink restoration are viable. populations for each other, then they can be There are also sites known to support managed as one population. However, if east flycatchers the last year they were surveyed slope and west slope populations are that have not been surveyed for at least genetically (or at least behaviorally) distinct, 5 years. These sites should be resurveyed to and do not intergrade, then brewsteri and determine status and condition of habitat. adastus might have to be managed separately. These considerations also apply to extimus. 6) Investigate the effects of weather At least, potential origins of source events on willow flycatcher nesting populations for recovery should be success. investigated. Reliable weather data are needed to quantify the relative contribution of habitat factors to There are four ways to define subspecies nesting success (Dahm and Pittroff n.d.). The status: ongoing demographic study (Bombay and 1) Determine whether east slope and Morrison, unpubl. data) does, however, west slope populations can be evaluate the cause of nesting failures. A differentiated using coloration single summer storm event could have a following the methods of Unitt profound influence on annual nesting success, (1987). overriding all other factors. Further, meadow 2) Conduct genetic analysis specifically wetness, already identified as an important comparing central Sierra Nevada habitat component, is directly influenced by populations (similar to work by annual snow-pack. Consequent annual Paxton [2000]). weather patterns and episodic events have to be factored in when correlating cause and 3) Conduct sonographic analyses to effects with nesting success. determine whether populations can be differentiated by vocal signatures (similar to Sedgwick 2001). 4) Intensify banding efforts and tracking dispersal.

48 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 A willow flycatcher born in one population Sierra Nevada willow flycatcher found later breeding in another provides the habitat. strongest evidence for intergradation. For example, investigate the effects of roads Quantifying dispersal can also identify which and road drainage, recreation, and livestock meadows may prove to be good candidates for grazing on vegetation (shrub and herbaceous restoration, based on known dispersal layer structure), plant species composition, distances from nearby occupied sites. predator and prey species composition and 9) Investigate pesticide burdens in willow abundance, hydrology, and brown-headed flycatchers. cowbird brood parasitism rates. Relate these Although there is no current evidence to show factors to willow flycatcher reproductive clearly that Sierra Nevada willow flycatchers success to evaluate the effects of these are threatened by pesticides, the facts that activities on willow flycatcher population 1) DDE burdens have been found in eggs productivity. (Valentine, pers. comm. in Williams and 11) Establish the relationship between Craig 1998), 2) they winter where pesticide willow flycatcher productivity and use is known, and 3) airborne pesticides from prey. the Central Valley may impact other riparian- and meadow-associated vertebrates (Sparling Explore the effects of willow flycatcher prey et al. 2001), indicate that the threat might be species composition and abundance and adult real. Further, as Dahm and Pittroff (n.d.) foraging activities across a gradient of pointed out in their critical assessment of the meadow conditions. willow flycatcher literature (e.g., Taylor and 12) Determine the impact of parasitism on Littlefield 1986), results implicating one willow flycatcher nest success and stress or stressor (e.g., grazing) may be population trends. confounded by the presence of another (e.g., pesticides). Therefore, opportunistic Quantify cowbird parasitism rates and analysis of non-viable eggs for pesticides evaluate the responses of flycatcher success to should be considered. cowbird control (i.e., egg addling and nestling removal, adult trapping). 10) Investigate the effects of major management activities that occur in

49 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Chapter 13 Literature Cited

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50 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Borror, D.J., D.M. DeLong, and C.A. of willow flycatchers and yellow warblers. Triplehorn. 1976. An Introduction to the Journal of Wildlife Management. Study of Insects. Holt, Rinehart, and Clapp, R.B., M.K. Klimkiewicz, and A.G. Winston, Chicago. 852 pp. Futcher. 1983. Longevity records of North Brothers, T.S. 1984. Historical vegetation American birds: columbidae through change in the Owens River riparian Paridae. Journal of Field Ornithology woodland. Pp. 75-84 in R.E. Warner and 54:123-137. K.M. Hendrix (eds.). California riparian Dahm, F. and W. Pittroff. n.d. Assessment of systems: Ecology, conservation, and the scientific basis of management productive management. UC Press, recommendations regarding willow Berkeley, CA. flycatcher (Empidonax traillii adastus and Browning, M.R. 1993. Comments on the E. t. brewsteri) conservation in the Sierra taxonomy of Empidonax traillii (willow Nevada Framework DEIS. Unpublished flycatcher). Western Birds 24:241-257. report. Burcham, L.T. 1982. California range land: an Davidson, R.F. and L.J. Allison. in press. historico-ecological study of the range Effects of monogamy and polygyny on resource of California (1957). University reproductive success in southwestern of California, Center for Archaeological willow flycatchers (Empidonax traillii Research at Davis, No. 7, Davis, CA. extimus) in Arizona. Studies in Avian Biology. Burgman, M.A., S. Ferson, and H.R. Akcakaya. 1993. Risk assessment in DeBenedetti, S.H. and D.J. Parsons. 1979. conservation biology. Chapman and Hall, Mountain meadow management and London. research in Sequoia and Kings Canyon National Parks: a review and update. Pp. Busch, J.D., M.P. Miller, E.H. Paxton, M.K. 1,305-1,311 in R.M. Linn (ed.). First Sogge, and P. Keim. 2000. Genetic conference on scientific research in the variation in the endangered southwestern national parks. National Park Service, willow flycatcher. Auk 117:586-595. Washington, D.C. Buskirk, S.W. and L.F. Ruggiero. 1994. DeSante, D.F. and T.L. George. 1994. American Marten. Pp. 7-37 in L.F. Population trends in the landbirds of Ruggiero, K.B. Aubry, S.W. Buskirk, L.J. western North America. Studies in Avian Lyon, and W.J. Zielinski (eds.). The Biology 15:173-190. Cooper scientific basis for conserving forest Ornithological Society, Camarillo, CA. carnivores, American martin, fisher, lynx, and wolverines, in the western United Dickson, J.G., R.N. Conner, R.R. Fleet, J.C. States. General Technical Report RM-254. Kroll, and J.A. Jackson, eds. 1979. The USDA Forest Service, Rocky Mountain role of insectivorous birds in forest Forest and Range Experiment Station, Fort ecosystems. Academic Press, New York, Collins, CO. NY. 381 pp. Cain, J.W. 2001. Nest success of yellow Drilling, N.E. and C.F. Thompson. 1988. Natal warblers (Dendroica petechia) and willow and breeding dispersal in house wrens flycatchers (Empidonax traillii) in relation (Troglodytes aedon). Auk 105:342-352. to predator activity in montane meadows Drost, C.A., E.H. Paxton, M.K. Sogge, and of the central Sierra Nevada, California. M.J. Whitfield. 2001. Food habits of the Masters thesis, California State University, endangered southwestern willow Sacramento, CA. 209 pp. flycatcher. Final report to the U.S. Bureau Cain, J.W., M.L. Morrison, and H.L. Bombay. of Reclamation, Salt Lake City, UT. 16 in press. Predator activity and nest success pp.

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57 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 changes in dispersion of the brown-headed Morrison, L.S. Hall, S.K. Robinson, S.I. cowbird in the Sierra Nevada. Auk 97:253- Rothstein, D.C. Hahn, T.D. Rich (eds.). 267. Research and management of the brown- headed cowbird in western landscapes. Rourke, J.W., T.D. McCarthey, R.F. Davidson, Studies in Avian Biology No. 18. Cooper A.M. Santaniello. 1999. Southwestern Ornithological Society, Camarillo, CA. willow flycatcher nest monitoring protocol. Nongame and Endangered Sedgwick, J.A. and R.J. Klus. 1997. Injury due Wildlife Program Technical Report 144. to leg bands in willow flycatchers. Journal Arizona Game and Fish Department, of Field Ornithology 68:622-629. Phoenix, AZ. Sedgwick, J.A. and F.L. Knopf. 1989. Rowley, W.D. 1985. USDA Forest Service Regionwide polygyny in willow grazing and rangelands: a history. Texas flycatchers. Condor 91:473-475. A&M University, College Station, Texas. Sedgwick, J.A. and F.L Knopf. 1992. Sanders, S.D. and M.A. Flett. 1989. Ecology Describing willow flycatcher habitats: of a Sierra Nevada population of willow scale and perspectives in gender flycatchers (Empidonax traillii), 1986- differences. Condor 94:720-733. 1987. California Department of Fish and Serena, M. 1982. The status and distribution of Game, Wildlife Management Division, the willow flycatcher (Empidonax traillii) Nongame Bird and Mammal Section. 27 in selected portions of the Sierra Nevada, pp. 1982. California Department of Fish and Sauer, J.R., J.E. Hines, G. Gough, I. Thomas, Game, Wildlife Management Branch and P.G. Geterjohn. 1997. The North Administrative Report No. 82-5. 28 pp. American breeding bird survey results and Seutin, G. and J-P Simon. 1988. Genetic analysis. Version 96.4. Patuxent Wildlife variation in sympatric willow flycatchers Research Center, Laurel, MD. (Empidonax traillii) and alder flycatchers (http://www.mbr.nbs.gov/bbs/bbs.html) (E. alnorum). Auk 105:235-243. Sawyer, J.O., and T. Keeler-Wolf. 1995. A Shapiro, A., S.J. Harper, and J. Westervelt. manual of California vegetation. California 1999. Modeling cowbird occurrences and Native Plant Society, Sacramento, CA. parasitism rates: statistical and individual- 471 pp. based approaches. Pp. 25-26 in Predicting Scully, M.R. 1975. Validation of a habitat species occurrences: issues of scale and suitability index (HIS) model for the accuracy. Oct. 18-22, 1999. Snowbird, willow flycatcher. Master’s thesis, UT. (abstract) California State University, Chico. 51 pp. Sherry, T.W. and R.T. Holmes. 1992. Sedgwick, J.A. 2000. Willow flycatcher Population fluctuations in a long-distance (Empidonax traillii). No. 533 in A. Poole neotropical migrant: demographic and F. Gill (eds.). The Birds of North evidence for the importance of breeding America. The Birds of North America, season events in the American redstart. Pp. Inc., Philadelphia, PA. 431-442 in J.M. Hagan, III, and D.W. Johnston (eds.). Ecology and conservation Sedgwick, J.A. 2001. Geographic variation in of neotropical migrant land birds. the song of willow flycatchers: Smithsonian Institute Press, Washington, differentiation between Empidonax traillii D.C. adastus and E. t. extimus. Auk 118:366- 379. Sherry, T.W. and R.T. Holmes. 1995. Summer versus winter limitation of populations: Sedgwick, J.A. and W.M. Iko. 1999. Costs of what are the issues and what is the brown-headed cowbird parasitism to evidence? Pp. 85-120 in T.E. Martin and willow flycatchers. Pp. 167-181 in M.L. D.M. Finch (eds.). Ecology and

58 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 management of neotropical migratory Stafford, M.D. 1986. Supernumerary adults birds: a synthesis and review of critical feeding willow flycatcher fledglings. The issues. Oxford University Press, New Wilson Bulletin 98(2): 311-312. York, NY. Stanley, T.R. and F.L. Knopf. 2002. Avian Shields, W.M. 1984. Factors affecting nest and responses to late-season grazing in a site fidelity in Adirondack Barn Swallows shrub-willow floodplain. Conservation (Hirundo rustica). Auk 101:780-789. Biology 16:225-231. Smith, R.E. 1977. A short review of the status Stefani, R.A., H.L. Bombay, and T.M. Benson. of riparian forests in California. Pages 1-2 2001. Willow Flycatcher. Pp. 143-195 in in A. Sands (ed.). Riparian forests in USDA Forest Service, Sierra Nevada California: their ecology and conservation. Forest Plan Amendment Final Institute of Ecology Publication No. 15. Environmental Impact Statement, Volume University of California, Davis, CA. 122 3, Chapter 3, Part 4.4. USDA Forest pp. Service, Pacific Southwest and Intermountain Regions, Vallejo, CA. Sogge, M.K., R.M. Marshall, S.J. Sferra, and T.J. Tibbitts. 1997. A southwestern willow Stein, R.C. 1963. Isolating mechanisms flycatcher natural history summary and between populations of Traill’s survey protocol. National Park Service flycatchers. Proceedings of the American Technical Report NPS/NAUCPRS/NRTR- Philosophy Society 107:21-50. 97/12. 37 pp. Steinhart, P. 1990. California’s Wild Sogge, M.K. 2000. Breeding season ecology. Heritage: Threatened and Endangered Pp. 57-70 in D.M. Finch and S.H. Stoleson Animals in the Golden State. California (eds.). Status, ecology, and conservation Department of Fish and Game, California of the southwestern willow flycatcher. Academy of Science, and Sierra Club USDA Forest Service, General Technical Books. 108 pp. Report RMRS-GTR-60. Rocky Mountain Stiles, F.G. and A.F. Skutch. 1989. A guide to Research Station. Ogden, UT. the birds of Costa Rica. Cornell Sogge, M.K. and R.M. Marshall. 2000. A University Press, New York, NY. survey of current breeding habitats. Pp. Stine, S., D. Gaines, and P. Vorster. 1984. 44-56 in D. Finch and S. Stoleson (eds.). Destruction of riparian systems due to Status, ecology, and conservation of the water development in the Mono Lake southwestern willow flycatcher. USDA watershed. Pp. 528-533 in R.E. Warner Forest Service, General Technical Report and K.M. Hendrix (eds.). California RMRS-GTR-60. Rocky Mountain riparian systems, ecology, conservation, Research Station, Albuquerque, NM. and productive management. University of Sparling, D.W., G.M. Fellers, and L.L. California Press, Berkeley and Los McConnell. 2001. Pesticides and Angeles, CA. amphibian population declines in Stoleson, S.H., M.J. Whitfield, and M.K. California, USA. Environmental Sogge. 2000. Demographic characteristics Toxicology and Chemistry 20:1,591- and population modeling. Pp. 83-94 in 1,595. D.M. Finch and S.H. Stoleson (eds.). Stafford, M.D. and B.E. Valentine. 1985. A Status, ecology, and conservation of the preliminary report on the biology of the southwestern willow flycatcher. USDA willow flycatcher in the central Sierra Forest Service, General Technical Report Nevada. CAL-NEVA Wildlife RMRS-GTR-60. Rocky Mountain Transactions 1985:66-77. Research Station. Ogden, UT. Sudworth, G.B. 1900. Stanislaus and Lake Tahoe Forest Reserves, California, and

59 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 adjacent territory. Pp. 505-561 in Annual Transactions of the Western Section of the Report to the Department of Interior, 21st Wildlife Society 24:105-114. Annual Report of the U.S. Geological Verner, J. and L.V. Ritter. 1983. Current status Survey, Government Printing Office, of the brown-headed cowbird in the Sierra Washington, D.C. National Forest. Auk 100:355-368. Sumner, L. and J.S. Dixon. 1953. Birds and Verner, J. and S.I. Rothstein. 1988. mammals of the Sierra Nevada. University Implications of range expansion into the of California Press, Berkeley, CA. Sierra Nevada by the parasitic brown- Taylor, D.M. 1986. Effects of cattle grazing headed cowbird. Pp. 92-98 in D. Bradley on passerine birds nesting in riparian (ed.). Proceedings, State of the Sierra habitat. Journal of Range Management Symposium, 1985-86. Pacific Publications 39:254-258. Co., San Francisco, CA. Taylor, D.M. and C.D. Littlefield. 1986. Voigts, D.K. 1976. Aquatic invertebrate Willow flycatcher and yellow warbler abundance in relation to changing marsh response to cattle grazing. American Birds vegetation. American Midland Naturalist 40:1,169-1,173. 95:313-322. U.S. Fish and Wildlife Service (USFWS). Walkinshaw, L.H. 1966. Summer biology of 1995. Final rule determining the status of Traill’s flycatcher. Wilson Bulletin 78:31- the southwestern willow flycatcher. 46. Federal Register 10,694-10,715. Walkinshaw, L.H. 1971. Additional notes on U.S. Fish and Wildlife Service (USFWS). summer biology of Traill’s flycatcher. 2001. Southwestern Willow Flycatcher Bird-Banding 42:275-278. Recovery Plan. Albuquerque, NM. 186 pp. Weller, M.W. 1978. Management of USDA Forest Service. 2001. Sierra Nevada freshwater marshes for wildlife. Pp. 267- Forest Plan Amendment Final 284 in R.E. Good, D.F. Wingham, and Environmental Impact Statement, Record R.L. Simpson (eds.). Freshwater wetlands. of Decision. USDA Forest Service, Academic Press, New York, NY. Pacific Southwest and Intermountain Welty, J.C. 1962. The life of birds. W.B. Regions, Vallejo, CA. Saunders Company, Philadelphia, PA. 546 Unitt, P. 1987. Empidonax traillii extimus: an pp. endangered subspecies. Western Birds Whitfield, M.J. 1990. Willow flycatcher 18(3):137-162. reproductive response to brown-headed Unitt, P. 1997. Progress report on the winter cowbird parasitism. Masters thesis, range of Empidonax traillii extimus. California State University, Chico. Prepared for Bureau of Reclamation, Whitfield, M.J. and K. Enos. 1996. A brown- Phoenix, AZ. Letter to Henry Messing. headed cowbird control program and Valentine, B.E. 1987. Implications of recent monitoring for the Southwestern willow research on the willow flycatcher to forest flycatcher, South Fork Kern River, management. USDA Forest Service, California, 1996. Prepared for U. S. Army Pacific Southwest Region, annual Corps of Engineers, Sacramento District, workshop, Fresno, CA. Kings River and the California Department of Fish and Conservation District, Research Report 87- Game. 002. 17 pp. Whitfield, M.J. and J. Lynn. 2001. Valentine, B.E., T.A. Roberts, S.D. Boland, Southwestern willow flycatcher and A.P. Woodman. 1988. Livestock (Empidonax traillii extimus) surveys, nest management and productivity of willow monitoring, and removal of brown-headed flycatchers in the central Sierra Nevada. cowbirds on the South Fork Kern River,

60 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 California in 2000: Final Report prepared California in 1999. Kern River Research for: U.S. Army Corps of Engineers, Center, Weldon, CA. 24 pp. Sacramento District, Environmental Whitworth, T.L., and G.F. Bennett. 1992. Resources Branch, Purchase order: Pathogenicity of larval Protocalliphora DACW05-00-P-0220 and California (Diptera: Calliphoridae) parasitizing Department of Fish and Game, Wildlife nestling birds. Canadian Journal of Management Division, Bird and Mammal Zoology 70:2184-2191. Conservation Program, CDFG contract #P9985311. Williams, P.L. and D. Craig. 1998. Willow flycatcher (Empidonax traillii). California Whitfield, M.J. and J.J. Placer. 1994. Brown- Partners in Flight Riparian Bird headed cowbird control program and Conservation Plan. October 28, 1998. monitoring for the southwestern willow 35 pp. flycatchers, South Fork Kern River,California. Report prepared for Wilson, E.O. 1975. Sociobiology. Harvard California Dept. of Fish and Game, University Press, Cambridge, MA. Wildlife Management Division, Nongame Winker, K. 1994. Divergence in Bird and Mammal Section. mitochondrial DNA of Empidonax traillii Whitfield, M.J. and M.K. Sogge. 1999. Range- and E. alnorum, with notes on wide impact of brown-headed cowbird hybridization. Auk 111:710-713. parasitism on the southwestern willow Wood, S.H. 1975. Holocene stratigraphy and flycatcher (Empidonax traillii extimus). chronology of mountain meadows, Sierra Pp.182-190 in M.L. Morrison, L.S. Hall, Nevada, California. Ph.D. Dissertation, S.K. Robinson, S.I. Rothstein, D.C. Hahn, California Institute of Technology, T.D. Rich (eds.). Research and management of the brown-headed cowbird in western landscapes. Studies in Avian Biology No. 18. Cooper Ornithological Society, Camarillo, CA. Whitfield, M.J. and C.M. Strong. 1995. A brown-headed cowbird control program and monitoring for the Southwestern willow flycatcher, South Fork Kern River, California, 1995. Prepared for California Department of Fish and Game. Whitfield, M.J., K. Enos, and S. Rowe. 1997. Reproductive response of the southwestern willow flycatcher (Empidonax traillii extimus) to the removal of brown-headed cowbirds. Draft Report prepared for the U.S. Army Corps of Engineers, Sacramento District, and California Department of Fish and Game, Wildlife Management Division, Bird and Mammal Conservation Program. Whitfield, M.J., E.B. Cohen, and C.D. Otahal. 1999. Southwestern willow flycatcher (Empidonas traillii extimus) surveys, nest monitoring, and removal of brown-headed cowbirds on the South Fork Kern River,

61 K:\EC\ADMINISTRATIVE\CONTRACTS\WILLOW_FLYCATCHER\FINAL_APPROVED_WIFL_CONSERVATION_ASSESSMENT.DOC • 3/18/03 Pasadena. USDA Forest Service, Zabik, J. and J.N. Seiber. 1993. Atmospheric Region 5, Earth Resources Monograph No. transport of organophosphate pesticides 4. 179 pp. from California’s Central Valley to the Sierra Nevada Mountains. Journal of Yard, H.K., and B.T. Brown. 1999. Willow Environmental Quality 22:80-90. flycatcher nest reuse in Arizona. Journal of Field Ornithology 70:211-213. Zeiner, D.C., W. Laudenslayer, Jr., K. Mayer, and M. White (eds.). 1990. California’s Yong, W. and D.M. Finch. 1997. Migration wildlife, Vol. 2, Birds. California of the willow flycatcher along the middle Department of Fish and Game, Rio Grande. Wilson Bulletin 109:253- Sacramento, CA. 732 pp. 268.

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