Geology topics

Scarlett L. Howell

Publications and source records attributed to Scarlett L. Howell.

23 records · Page 2Linked to original sources

USGS2021

Distribution and abundance of Southwestern Willow Flycatchers (Empidonax traillii extimus) on the upper San Luis Rey River, San Diego County, California—2020 data summary

We surveyed for Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) along the upper San Luis Rey River, near Lake Henshaw, in Santa Ysabel, California, in 2020. Surveys were completed at four locations: three downstream from Lake Henshaw, where nest monitoring occurred from 2015 to 2019 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one at VID Lake Henshaw (VLH) that was previously surveyed in 2018 and 2019. There were 62 territorial flycatchers detected at 3 locations (RRR, CNF, VLH); no flycatchers were detected at VID. Within the former nest monitoring study area, 11 flycatchers, including 5 males and 6 females, were detected at RRR and CNF. In total, seven territories were established, consisting of six pairs (two polygynous groups consisting of two males each pairing with two different females) and one male of undetermined breeding status. Upstream from the former nest monitoring study area at VLH, we detected 51 flycatchers, including 24 males and 27 females. There were 28 territories established, containing 27 pairs (23 monogamous pairings and 4 confirmed polygynous pairings consisting of 1 male and 2 females) and 1 male of undetermined breeding status. Brown-headed cowbirds ( Molothrus ater ; cowbird) were detected at all four survey locations. Flycatchers used four different habitat types in the survey area: (1) mixed willow riparian, (2) willow-oak, (3) willow-ash, and (4) willow-sycamore. Eighty percent of the flycatchers were detected in habitat characterized as mixed willow riparian, and 83 percent of the flycatchers were detected in habitat with greater than 50-percent native plant cover. Exotic vegetation was not prevalent in the survey area. There were 17 flycatcher nests incidentally located during surveys: 2 were successful, 3 were seen with nestlings on the last visit, 10 failed, and the outcome of the remaining 2 nests was unknown. Five of these nests were parasitized by cowbirds. There were 10 juveniles detected during surveys: 2 at RRR and 8 at VLH. Of the 17 banded flycatchers detected during surveys, 8 were resighted and confirmed to be adults that held territories in previous years. Seven flycatchers with a single dark blue federal band, indicating that they were banded as nestlings in the former nest monitoring study area downstream from Lake Henshaw, were resighted during surveys; 86 percent of these “natal” flycatchers held territories at VLH. In 2020, we documented both adult and natal flycatchers moving from the former nest monitoring study area downstream from Lake Henshaw upstream to the habitat surrounding Lake Henshaw. Six natal flycatchers that were originally banded as nestlings and two adults that previously held territories downstream dispersed to Lake Henshaw in 2020.

California↗

USGS2018

Distribution and abundance of Least Bell’s Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) on the Middle San Luis Rey River, San Diego County, southern California—2017 data summary

We surveyed for Least Bell’s Vireos (LBVI) ( Vireo bellii pusillus ) and Southwestern Willow Flycatchers (SWFL) ( Empidonax traillii extimus ) along the San Luis Rey River, between College Boulevard in Oceanside and Interstate 15 in Fallbrook, California (middle San Luis Rey River), in 2017. Surveys were conducted from April 13 to July 11 (LBVI) and from May 16 to July 28 (SWFL). We found 146 LBVI territories, at least 107 of which were occupied by pairs. Five additional transient LBVIs were detected. LBVIs used five different habitat types in the survey area: mixed willow, willow-cottonwood, willow-sycamore, riparian scrub, and upland scrub. Forty-four percent of the LBVIs occurred in habitat characterized as mixed willow and 89 percent of the LBVI territories occurred in areas with greater than 50 percent native plant cover. Of 16 banded LBVIs detected in the survey area, 8 had been given full color-band combinations prior to 2017. Four other LBVIs with single (natal) federal bands were recaptured and banded in 2017. Three LBVIs with single dark blue federal bands indicating that they were banded as nestlings on the lower San Luis Rey River and one LBVI with a single gold federal band indicating that it was banded as a nestling on Marine Corps Base Camp Pendleton (MCBCP) could not be recaptured for identification. One banded LBVI emigrated from the middle San Luis Rey River to the lower San Luis Rey River in 2017. One resident SWFL territory and one transient Willow Flycatcher of unknown subspecies (WIFL) were observed in the survey area in 2017. The resident SWFL territory, which was comprised of mixed willow habitat (5–50 percent native plant cover), was occupied by a single male from May 22 to June 21, 2017. No evidence of pairing or nesting activity was observed. The SWFL male was banded with a full color-combination indicating that he was originally banded as a nestling on the middle San Luis Rey River in 2014 and successfully bred in the survey area in 2016. The male SWFL left the middle San Luis Rey River after June 21, 2017 and subsequently was detected on the San Dieguito River on June 26, 2017, by USGS biologists. The transient WIFL was detected on May 30, 2017, in mixed willow habitat comprised of 50–95 percent of native plant cover.

California↗

USGS2017

Distribution and abundance of Least Bell’s Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) on the Middle San Luis Rey River, San Diego, southern California—2016 data summary

Executive Summary We surveyed for Least Bell’s Vireos (LBVI) ( Vireo bellii pusillus ) and Southwestern Willow Flycatchers (SWFL) ( Empidonax traillii extimus ) along the San Luis Rey River, between College Boulevard in Oceanside and Interstate 15 in Fallbrook, California (middle San Luis Rey River), in 2016. Surveys were done from March 30 to July 11 (LBVI) and from May 18 to July 30 (SWFL). We found 142 LBVI territories, at least 106 of which were occupied by pairs. Six additional transient LBVIs were detected. Of 20 banded LBVIs detected in the survey area, 9 had been given full color-band combinations prior to 2016, although we were unable to determine the exact color combination of 1 female LBVI. Seven other LBVIs with single (natal) federal bands were recaptured and banded in 2016. Four vireos with single dark blue federal bands indicating that they were banded as nestlings on the lower San Luis Rey River could not be recaptured for identification. Three SFWL territories were observed in the survey area in 2016. Two territories were occupied by pairs and one by a male of unknown breeding status. Both pairs attempted to nest at least once, and both pairs were successful, fledging three young each. Nesting began in early June and continued into July. Brown-Headed Cowbird ( Molothrus ater ) eggs were not observed in either nest. An additional 12 transient Willow Flycatchers of unknown subspecies were detected in 2016. Two of the five resident SWFLs were originally banded as nestlings on Marine Corps Base Camp Pendleton. One male and one female were banded as nestlings on Camp Pendleton in 2009 and 2011, respectively. One natal male of unknown breeding status, originally banded as a nestling on the middle San Luis Rey River in 2015, was recaptured and given a unique color combination in 2016. This male was later detected on Marine Corps Base Camp Pendleton.

California↗

USGS2017

Female-biased sex ratio, polygyny, and persistence in the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus)

Demographic changes in populations, such as skewed sex ratios, are of concern to conservationists, especially in small populations in which stochastic and other events can produce declines leading to extirpation. We documented a decline in one of the few remaining populations of Southwestern Willow Flycatcher ( Empidonax traillii extimus ) in southern California, USA, which dropped from 40 to 5 adults between 2000 and 2015. Declines were unequal between sexes (94% for males, 82% for females). Adult sex ratios were female-biased in 10 of 16 yr. The proportion of paired males that were polygynous ranged from 0% to 100%, depending on the ratio of females to males in the adult population. Some males paired with up to 5 females simultaneously. We investigated the role of nestling sex ratio in the female-biased adult sex ratio by using genetic techniques to determine sex from blood samples collected from 162 nestlings in 72 nests from 2002 to 2009. Both population-level and within-brood nestling sex ratios were female-biased, and were not influenced by nest order (first or subsequent), parental mating type (monogamous or polygynous), or year. Disproportionately more females than males were recruited into the breeding population, mirroring nestling and fledgling sex ratios. It thus appears that a skewed nestling sex ratio has contributed to a female-biased adult population, which in turn has influenced mating behavior. We propose that the capacity for polygyny, which generally occurs at low levels in Southwestern Willow Flycatchers, has allowed this population to persist through a decline that might otherwise have resulted in extinction.

The Condor↗

USGS2015

Habitat fragmentation in coastal southern California disrupts genetic connectivity in the cactus wren ( Campylorhynchus brunneicapillus )

Achieving long-term persistence of species in urbanized landscapes requires characterizing population genetic structure to understand and manage the effects of anthropogenic disturbance on connectivity. Urbanization over the past century in coastal southern California has caused both precipitous loss of coastal sage scrub habitat and declines in populations of the cactus wren ( Campylorhynchus brunneicapillus ). Using 22 microsatellite loci, we found that remnant cactus wren aggregations in coastal southern California comprised 20 populations based on strict exact tests for population differentiation, and 12 genetic clusters with hierarchical Bayesian clustering analyses. Genetic structure patterns largely mirrored underlying habitat availability, with cluster and population boundaries coinciding with fragmentation caused primarily by urbanization. Using a habitat model we developed, we detected stronger associations between habitat-based distances and genetic distances than Euclidean geographic distance. Within populations, we detected a positive association between available local habitat and allelic richness and a negative association with relatedness. Isolation-by-distance patterns varied over the study area, which we attribute to temporal differences in anthropogenic landscape development. We also found that genetic bottleneck signals were associated with wildfire frequency. These results indicate that habitat fragmentation and alterations have reduced genetic connectivity and diversity of cactus wren populations in coastal southern California. Management efforts focused on improving connectivity among remaining populations may help to ensure population persistence.

California↗