Santa Barbara Island Research Articles

Breeding of the Guadalupe Murrelet in Southern California

After having been observed regularly at Seal Cove, San Clemente Island, California, since 1994, the Guadalupe Murrelet (Synthliboramphus hypoleucus) was confirmed nesting successfully in an artificial nest on a rocky ledge above the cove in 2022. The incubating adults’ identity and the two chicks’ departure from the nest were confirmed by a trail camera. Another Guadalupe Murrelet nest at Santa Barbara Island in 2021 was only the second confirmed there. Though the populations of the Guadalupe Murrelet at San Clemente and Santa Barbara islands are apparently small, they are important in representing the only confirmed sites of the species’ nesting away from Guadalupe and the San Benito islands.

Network analysis reveals aggregation behaviour for an endangered predator at an offshore island.

Site fidelity and aggregation behaviour were assessed for giant sea bass Stereolepis gigas (GSB) at Santa Barbara Island, California, USA, from 2018 to 2020. Results indicate seasonal variation in GSB presence, and network analyses revealed a preferred location in a spatially constrained pattern, indicative of aggregation behaviour. Results show GSB aggregated annually during spawning months in the same location, confirming the first known aggregation of GSB at Santa Barbara Island. Identifying and monitoring aggregation sites is vital to ensuring proper protection and ultimate recovery for this protected species in a changing climate.

A statistical reanalysis of morphological differentiation among island night lizards (Xantusia riversiana) from the California Channel Islands

This study re-analyzes morphometric and meristic data among island night lizards, Xantusia riversiana, from the California Channel Islands of San Clemente, Santa Barbara, and San Nicolas in order to ascertain whether the implementation of different statistical methods can recover different results that could potentially alter biological interpretations. Our results concur with a recent previous study demonstrating that the three island populations differ morphologically from one another and that the San Nicolas Island population is the most divergent. Several important aspects, however, of the previous study depart significantly from those recovered here. Our analyses found sexual dimorphism within each population for both morphometric and meristic characters to be relatively uncommon whereas the previous study found nearly all characters to be sexually dimorphic for all island populations. The previous study also recovered significant differences among the three island populations for all morphometric characters whereas far fewer differences were recovered in the present study. Both studies found few significant inter-island differences among the meristic characters. The discordances between these two studies stem from differences in the a priori treatment of the raw character data and the different downstream statistical analyses and visualization techniques used on those data. This was particularly relevant with the use here of an allometric growth algorithm for size-correcting the morphometric data not used in the previous study and by treating all three populations as independently evolving groups. We did not conduct analyses where data from the San Clemente and Santa Barbara island populations were conflated based on their subspecific designation (X. r. reticulata) and then compared to data from the independently evolving San Nicolas Island population. This imprudent use of taxonomy violates the assumptions of statistical independence. We emphasize that explicit justification for the use of particular statistical analyses should occur in all studies—especially if the results bear on the implementation of effective and efficient resource management programs.

Exome sequencing of deer mice on two California Channel Islands identifies potential adaptation to strongly contrasting ecological conditions.

Understanding the forces that drive genotypic and phenotypic change in wild populations is a central goal of evolutionary biology. We examined exome variation in populations of deer mice from two of the California Channel Islands: Peromyscus maniculatus elusus from Santa Barbara Island and P. m. santacruzae from Santa Cruz Island exhibit significant differences in olfactory predator recognition, activity timing, aggressive behavior, morphology, prevalence of Sin Nombre virus, and population densities. We characterized variation in protein‐coding regions using exome capture and sequencing of 25 mice from Santa Barbara Island and 22 mice from Santa Cruz Island. We identified and examined 386,256 SNPs using three complementary methods (BayeScan, pcadapt, and LFMM). We found strong differences in molecular variation between the two populations and 710 outlier SNPs in protein‐coding genes that were detected by all three methods. We identified 35 candidate genes from this outlier set that were related to differences in phenotypes between island populations. Enrichment analyses demonstrated that patterns of molecular variation were associated with biological processes related to response to chemical stimuli and regulation of immune processes. Candidate genes associated with olfaction (Gfy, Tlr2, Vmn13r2, numerous olfactory receptor genes), circadian activity (Cry1), anxiety (Brca1), immunity (Cd28, Eif2ak4, Il12a, Syne1), aggression (Cyp19a, Lama2), and body size (Bc16, Syne1) exhibited non‐synonymous mutations predicted to have moderate to large effects. Variation in olfaction‐related genes, including a stop codon in the Santa Barbara Island population, suggests loss of predator‐recognition traits at the molecular level, consistent with a lack of behavioral aversion to fox feces. These findings also suggest that divergent pathogen prevalence and population density may have influenced adaptive immunity and behavioral phenotypes, such as reduced aggression. Overall, our study indicates that ecological differences between islands are associated with signatures of selection in protein‐coding genes underlying phenotypes that promote success in those environments.

California harbor dredging: History and trends

California is a major shipping point for exports and imports across the Pacific Basin, has large commercial and recreational fisheries, and an abundance of marine recreational boaters. Each of these industries or activities requires either a port or harbor. California has 26 individual coastal ports and harbors, ranging from the huge sprawling container ports of Los Angeles and Long Beach to small fishing ports like Noyo Harbor and Bodega Bay. Almost all of California’s ports and harbors were constructed without any knowledge or consideration of littoral drift directions and rates and potential future dredging issues. Rather, they were built where a need existed, where there was a history of boat anchorage, or where there was a natural feature (e.g. bay, estuary, or lagoon) that could be the basis of an improved port or harbor. California’s littoral drift rates and directions are now well known and understood, however, and have led to the need to perform annual dredging at many of these harbors as a result of their locations (e.g. Santa Cruz, Oceanside, Santa Barbara, Ventura, and Channel Islands harbors) while other harbors require little or no annual dredging (e.g. Half Moon Bay, Moss Landing, Monterey, Redondo-King and Alamitos Bay). California’s coastal harbors can be divided into three general groups based on their long-term annual dredging volumes, which range from three harbors that have never been dredged to the Channel Islands Harbor where nearly a million cubic yards is removed on average annually. There are coastal harbors where dredging rates have remained nearly constant over time, those where rates have gradually increased, and others where rates have decreased in recent years. While the causal factors for these changes are evident in a few cases, for most there are likely a combination of reasons including changes in sand supply by updrift rivers and streams related to dam construction as well as rainfall intensity and duration; lag times between when pulses of sand added to the shoreline from large discharge events actually reach downdrift harbors; variations in wave climate over time; shoreline topography and nearshore bathymetry that determine how much sand can be trapped upcoast of littoral barriers, such as jetties and breakwaters, before it enters a harbor; and timing of dredging. While there is virtually nothing that can be done to any of these harbors to significantly reduce annual dredging rates and costs, short of modifying either breakwater or jetty length and/or configuration to increase the volume of sand trapped upcoast, thereby altering dredging timing, they are clearly major economic engines, but come with associated costs.

Understanding the Dynamics of Kelp Forest Recovery from Fishing

Photo 1. Kelp forests provide numerous ecosystem services, including support for economically important fishery species. In southern California, USA, including the Channel Islands shown in the background above, kelp forests provide habitat for the spiny lobster Panulirus interruptus, which is the focus of a trap-based fishery. Photo credit: Robert Dunn. Photo 2. Herbivores can overgraze macroalgae on rocky reefs, leading to a transition from kelp forest to urchin barren. Here, a research diver surveys densities of purple and red sea urchins (Strongylocentrotus purpuratus and Mesocentrotus franciscanus, respectively) in a barren habitat at Santa Barbara Island, California, USA. In some cases, urchin barrens can form due to overharvest of kelp forest predators. Red urchins are themselves the focus of a targeted fishery, but urchins from barrens are typically not harvested due to their low gonad mass. Photo credit: Robert Dunn. Photo 3. When rocky reef fisheries are effectively managed, kelp forests can, in many instances, recover to their macroalgal-dominated state. Photo credit: Robert Dunn. These photographs illustrate the article “Transient dynamics during kelp forest recovery from fishing across multiple trophic levels” by Robert P. Dunn, Jameal F. Samhouri, and Marissa L. Baskett published in Ecological Applications. https://doi.org/10.1002/eap.2367.

Terrace formation and preservation: Santa Catalina Island and other California Channel Islands

ABSTRACT Uplifted coastal terraces are present on Santa Catalina Island, but so poorly preserved that researchers have debated for more than a century whether they even exist. Morphometric analyses of LIDAR-based topography on the California Channel Islands suggest that the poor expression of terraces on Catalina Island is due a combination of (1) geological conditions less conducive to terrace formation than on the other Channel Islands and (2) high landslide susceptibility around Catalina’s coastal margin that is erasing terrace morphology and deposits before they can reach the island's relatively un-dissected interior. Both of these factors seem to be related to the mechanical properties of the island’s predominant rock type, the Catalina Schist. Several of the other Channel Islands – such as Santa Barbara, San Clemente, Anacapa, and San Miguel Islands – have topography that is dominated by their terrace morphology, mostly by virtue of the small size of those islands. Of the large islands, Santa Rosa has the most extensive terraces, apparently driven by the prevalence of shallowly dipping sedimentary rock. Looking at terrace preservation generally, subhorizontal sedimentary units seem to represent an optimum between promoting the initial creation of wide terrace platforms and resistance to terrace erosion thereafter.

Small Islands and Marginality: Santa Barbara Island and its Role in the Prehistory of California’s Channel Islands

ABSTRACTAs the smallest of California’s Channel Islands, Santa Barbara Island has received limited attention from archaeologists. A United States National Park Service project designed to assess its 19 known sites evolved into an island-wide survey that increased the number to 63 sites that date between 4000 and 600 years ago. Most are small shell and lithic scatters, although some are larger shell middens with greater faunal and artifact diversity. Their constituents and geographic distribution indicate that the island not only served as a stopover during inter-island travel but was occupied for longer periods to target local resources such as marine mammal rookeries. Our research presents an opportunity to evaluate the significance of this island to prehistoric communities throughout the archipelago. On a broader level, it provides insights into the important roles that small islands have played in prehistoric lifeways as well as perceptions of marginality.

920. CONSTANCEA NEVINII

SummaryConstancea nevinii (A. Gray) B.G. Baldwin (Compositae: Heliantheae: Baeriinae) is described and illustrated. The distribution of the species in, and a glimpse at the history and endemic flora of, the California Channel Islands (also known as the Santa Barbara Islands), together with the conservation threats posed by feral goats, is outlined. The historically variable Conservation Status is commented on, although the species is no longer considered under threat of extinction. The position of this monotypic genus in the Heliantheae is commented on. Cultivation, propagation, and availability notes are provided. The species is rarely cultivated in the United Kingdom, but clearly widely so in the western States along the Californian coast.

Little Islands Recording Global Events: Late Quaternary Sea Level History and Paleozoogeography of Santa Barbara and Anacapa Islands, Channel Islands National Park, California

Marine terraces are common on the Pacific Coast of North America and record interglacial high-sea stands superimposed on either stable or tectonically rising crustal blocks. Despite many years of study of these landforms in southern California, little work on terraces has been conducted on the two smallest of the California Channel Islands, Santa Barbara Island (SBI) and Anacapa Island (ANA). Presented here are new field and laboratory data on the ages, paleontology, and sea level history of marine terraces of these two islands. On both islands, the lowest marine terraces have shoreline angle elevations of ∼11 m above sea level. Amino acid geochronology shows that terrace deposits on both islands host fossils of two ages, one group dating to the ∼120-ka high-sea stand and the other group likely dating to the ∼100-ka high-sea stand. A mix of fossil ages is consistent with the paleontology as well, with SBI in particular showing a faunal assemblage that includes both extralimital southern and southward-ranging species (inferred to be from the ∼120-ka high-sea stand) and extralimital northern and northward-ranging species (inferred to be from the ∼100-ka high-sea stand). Fossil mixing from these two high-sea stands supports the hypothesis that glacial isostatic adjustment (GIA) processes have left a strong imprint on the geologic record of sea level history in southern California. Nevertheless, the elevations of these terraces and that of a low terrace on Santa Cruz Island indicate that modeled GIA estimates of paleo-sea level for the peak of the last interglacial period at ∼120 ka could be too high. Future development of models of GIA effects on the Pacific Coast of North America will need to consider geologic records, such as those from SBI and ANA, in refining reconstructions of sea level history.

El Niño/Southern Oscillation-driven rainfall pulse amplifies predation by owls on seabirds via apparent competition with mice

Most approaches for assessing species vulnerability to climate change have focused on direct impacts via abiotic changes rather than indirect impacts mediated by changes in species interactions. Changes in rainfall regimes may influence species interactions from the bottom-up by increasing primary productivity in arid environments, but subsequently lead to less predictable top-down effects. Our study demonstrates how the effects of an EL Niño/Southern Oscillation (ENSO)-driven rainfall pulse ricochets along a chain of interactions between marine and terrestrial food webs, leading to enhanced predation of a vulnerable marine predator on its island breeding grounds. On Santa Barbara Island, barn owls (Tyto alba) are the main predator of a nocturnal seabird, the Scripps's murrelet (Synthliboramphus scrippsi), as well as an endemic deer mouse. We followed the links between rainfall, normalized difference vegetation index and subsequent peaks in mouse and owl abundance. After the mouse population declined steeply, there was approximately 15-fold increase in the number of murrelets killed by owls. We also simulated these dynamics with a mathematical model and demonstrate that bottom-up resource pulses can lead to subsequent declines in alternative prey. Our study highlights the need for understanding how species interactions will change with shifting rainfall patterns through the effects of ENSO under global change.

Distribution, Habitat, and Population Size of Island Night Lizards on San Nicolas Island, California

The Island Night Lizard (Xantusia riversiana) was removed from the federal list of threatened species in May 2014. This strongly differentiated species is endemic to 3 of the southern California Channel Islands—San Clemente, San Nicolas, and Santa Barbara. Suitable habitat for Island Night Lizards is extensive on San Clemente Island, and the species is abundant there. Habitat is limited and fragmented, however, on San Nicolas Island and small Santa Barbara Island. Bringing together extensive field surveys and mark-recapture sampling, we synthesize available data for Island Night Lizards on San Nicolas Island and calculate population and density estimates for the species in major habitats on the island. Island Night Lizards are widely distributed across most of the eastern half of San Nicolas Island. In contrast, they are nearly absent over the western third of the island except for isolated populations in boulder beach habitats. We combined mark-recapture population estimates with comprehensive measurements of the extent of cactus, boxthorn, and other habitat types on the island to arrive at a more accurate assessment of the status of Island Night Lizards on San Nicolas Island. High densities of Island Night Lizards on the island are found in small areas of cholla cactus (Cylindropuntia prolifera; mean of 4100 lizards/ha), boulder beach habitat (mean of 3400 lizards/ha), and prickly pear cactus (Opuntia spp.; mean of 1700 lizards/ha); low numbers are found in more extensive mixed-shrub habitat (mean of 250 lizards/ha). The U.S. Fish and Wildlife Service requires a post-delisting program for “monitoring the overall health of the Island Night Lizard” to assure the continued long-term viability of the species in its restricted distribution. The information on population size and habitat presented here will inform and guide conservation and management efforts by the U.S. Navy on San Nicolas Island over the coming years.

The Flowering Plants and Ferns of Anacapa Island, California

The 3 islets of Anacapa Island, with a combined area of 1.1 mi2 (2.9 km2), lie 13 mi (20 km) off the coast of southern California. Historically, each of Anacapa’s islets has been subjected to periodic grazing by sheep, and the eastern islet has also had a sizeable population of introduced rabbits. In spite of these past perturbations, the recovery of the island’s vegetation has been remarkable since sheep removal in 1937. Despite its small size, Anacapa Island supports a surprising diversity of vascular plants, with nearly 200 native taxa from 50 plant families. Twenty-one of these native taxa are restricted to the California Islands; one annual species of Malacothrix occurs as a narrow endemic found only on Middle Anacapa Island, while another annual subspecies of Malacothrix is known only from West and East Anacapa. The floral diversity of this island has apparently been influenced by its close proximity to the mainland and other larger islands and by its diverse topography. Anacapa Island supports a slightly larger native flora than San Miguel Island, which is about 13 times larger and is located about 50 mi (80 km) to the west. The Anacapa native flora is more than twice the size of that found on Santa Barbara Island, which has almost the same area as Anacapa Island but is located approximately 62 mi (100 km) to the southeast. Even though botanical exploration on Anacapa began in 1889, the current work represents the first complete enumeration of the island’s flora.

Cascading effects of predation risk determine how marine predators become terrestrial prey on an oceanic island.

Apex predators can suppress the foraging activity of mesopredators, which may then result in cascading benefits for the prey of those mesopredators. We studied the interactions between a top predator, the Barn Owl (Tyto alba), and their primary prey, an island endemic deer mouse (Peromyscus maniculatus elusus), which in turn consumes the eggs of seabirds nesting on Santa Barbara Island in California. Scripps's Murrelets (Synthliboramphus scrippsi), a threatened nocturnal seabird, arrive annually to breed on this island, and whose first egg is particularly vulnerable to predation by mice. We took advantage of naturally occurring extreme variations in the density of mice and owls on the island over 3 years and predicted that (1) mouse foraging would decrease with increasing predation risk from owls and moonlight and (2) these decreases in foraging would reduce predation on murrelet eggs. We measured the giving up densities of mice with experimental foraging stations and found that mice were sensitive to predation risk and foraged less when owls were more abundant and less during the full moon compared to the new moon. We also monitored the fates of 151 murrelet eggs, and found that murrelet egg predation declined as owl abundance increased, and was lower during the full moon compared to the new moon. Moreover, high owl abundance suppressed egg predation even when mice were extremely abundant. We conclude that there is a behaviorally mediated cascade such that owls on the island had a positive indirect effect on murrelet egg survival. Our study adds to the wider recognition of the strength of risk effects to structure food webs, as well as highlighting the complex ways that marine and terrestrial food webs can intersect.

Barn owls (Tyto alba) in western North America: phylogeographic structure, connectivity, and genetic diversity

The barn owl (Tyto alba) is a non-migratory species widely distributed across much of North America in areas with extensive old-field and grassland habitat and without extensive winter snow cover. We investigated the genetic diversity and phylogeographic patterns of barn owl populations in western North America, ranging from British Columbia (BC) to southern California, and one eastern population from Pennsylvania. We also determined the genetic distinctiveness of a population off the coast of southern California, Santa Barbara Island, as management plans to control the local owl population are being considered to decrease predation rate on the now threatened Scripps’s Murrelet (Synthliboramphus scrippsi). Using 8 polymorphic microsatellite markers (N = 126) and ND2 mitochondrial sequences (N = 37), we found little to no genetic structure among all sampled regions, with the exception of Santa Barbara Island. The BC mainland population, despite its northwestern geographically peripheral location and ongoing habitat degradation, is not genetically depauperate. However, individuals from Vancouver Island, likewise a peripheral population in BC, exhibited the lowest genetic diversity of all sampled locations. The low global FST value (0.028) estimated from our study suggests that old-field agricultural habitats are well connected in North America. Since the BC population has declined by about 50 % within the last three decades, it is vital to focus on preserving the remaining barn owl habitats in BC to allow successful establishment from neighbouring populations. Additionally, our microsatellite data revealed that the population on Santa Barbara Island showed genetic divergence from its continental counterpart. Mitochondrial data, however, demonstrated that this island population is not a monophyletic lineage containing unique haplotypes, and hence cannot be designated as an Evolutionarily Significant Unit.

Space Use and Home-Range Size of Barn Owls on Santa Barbara Island

Abstract. Spatial overlap between predators and prey is often a key component of predator-prey interactions. Barn Owls (Tyto alba) are important predators of some species of conservation concern on the Channel Islands in southern California; therefore, understanding patterns of owl space use on these islands could provide insights on variations in predation risk that may be useful for conservation efforts of Barn Owl prey. In this study, our objectives were to investigate home-range size and space use by individual owls on Santa Barbara Island, which at 2.6 km2 is the smallest island within the Channel Islands National Park. Specifically, we were interested in owl space use in relation to the spatial distribution of owl prey, in particular the state-listed Threatened Scripps's Murrelet (Synthliboramphus scrippsi)—a small nocturnal seabird whose largest breeding colony in California is on this island and whose nesting habitat is strictly along the island's perimeter. In contrast, the distribution of the Ba...

Importance of Early Life Stage Limitations on Recovering Populations ofLeptosyne gigantea,San Miguel Island, California

Plant communities dominated by Leptosyne gigantea (tickseed, formerly giant coreopsis) are distributed widely across the California Islands and provide critical habitat for understory plants and vertebrates, especially in landscapes where trees are absent. Leptosyne gigantea populations were severely impacted by nonnative herbivores and by grazing and ranching practices during the last century. Although these impacts have been absent from most of the islands for over 2 decades, extensive spatial heterogeneity exists both within and across the islands in relation to population growth. Many sites support very dense stands of L. gigantea that established postgrazing; whereas others, particularly on Santa Barbara Island, have experienced relatively minimal increases in L. gigantea abundance and are still dominated by alien annual grasses. To determine the factors that most affect L. gigantea establishment and survival, I conducted seed amendment experiments across populations of variable density and age structure on San Miguel Island. These experiments tested the relative effects of seed predation, seed density, microhabitat conditions, stand density, and competition on germination and seedling survival. Postdispersal seed predation by deer mice reduced germination rates only in the highest density stands. Reduced soil moisture and interspecific competition with alien annual grasses had the strongest negative effects on both germination and seedling survival. The results suggest extreme spatial variability in regulating factors for L. gigantea that include rainfall, the abundance of annual grasses, consumer abundance, and intraspecific density dependence. The presence or absence of these influences on existing site conditions will determine succession following loss of the oldest-aged stands, which will likely occur soon.

Lecanora annularis(Lecanoraceae, Lecanorales), a New Lichen Species from the Channel Islands and the Central California Coast

Abstract. Lecanora annularis, n. sp., is described from collections from Santa Cruz Island and Santa Barbara Island in Channel Islands National Park and from San Simeon and Point Lobos on the central California coast. The crystalinspersed parathecium, egranulose epihymenium, and maritime habit distinguish L. annularis from all other members of the L. dispersa group. It occurs on sandstone and decaying basalt.

Roosting Brown Pelicans at San Nicolas Island, California, 1972–2006

Abstract. To assist long-term protection of roost sites, roosting patterns of California Brown Pelicans (Pelecanus occidentalis californicus) at San Nicolas Island (SNI), California, were assessed for the 1972–2006 period. SNI was used for roosting year-round, with most birds likely from nearest primary breeding colonies (Santa Barbara and Anacapa islands) within the Southern California Bight subpopulation. Among non-El Nino years, monthly diurnal counts varied, but ranged from less than 100 birds during the breeding season to approximately 1,000 during fall. Influxes from the large Gulf of California subpopulation also occurred on occasion, best demonstrated by prolonged increased numbers during strong El Nino conditions in 1972–1973, possibly reflecting delayed or skipped breeding and increased prey availability near the outer California Channel Islands. The peak estimate of 13,500 night-roosting pelicans was on 16 November 1972 during these El Nino conditions. Most pelicans roosted diurnally on the nor...

Relationships Between Breeding Status, Social-Congregation Attendance, and Foraging Distance of Xantus’s Murrelets

At night during the breeding season, Xantus's Murrelets (Synthliboramphus hypoleucus) congregate on the water adjacent to nesting colonies. We examined relationships of attendance at these nocturnal congregations, breeding status, and daytime foraging locations of radio-marked Xantus's Murrelets from Anacapa Island (33 in 2002, 44 in 2003) and Santa Barbara Island (35 in 2002) in the California Channel Islands. Murrelets that spent more nights attending congregations were located closer to the island during the day, so regular attendance at the congregations may have constrained daytime traveling distances to foraging locations. In mid-May 2003 home-range sizes increased while congregation attendance decreased, likely indicating the end of colony attendance and declining availability of prey near Anacapa Island. In both years, incubating murrelets foraged farther from the colony than did nonbreeding murrelets, suggesting that breeding and nonbreeding murrelets use different foraging strategies to meet their energetic requirements.