Darrell L. Whitworth

Effects of radiotransmitters on the reproductive performance of Cassin’s auklets

Abstract We examined whether radiotransmitters adversely affected the reproductive performance of Cassin’s auklets (Ptychoramphus aleuticus) breeding on the California Channel Islands during 1999-2001. We attached external radiotransmitters to 1 partner in 108 Cassin’s auklet pairs after nest initiation and used 131 unmarked, but handled, pairs as controls. Compared to alpha chicks raised by radiomarked pairs, alpha chicks raised by unmarked pairs had faster mass growth rates (1.95 ± 0.30 g d-1 vs. 3.37 ± 0.53 g d-1, respectively), faster wing growth rates (2.46 ± 0.10 mm d-1 vs. 2.85 ± 0.05 mm d-1), greater peak fledging masses (118.9 ± 3.5 g vs. 148.3 ± 2.4 g), and higher fledging success (61% vs. 90%). Fledging success was reduced more when we radiomarked the male (50% fledged) rather than the female partner (77% fledged). After fledging an alpha chick, unmarked pairs were more likely to initiate a second clutch (radiomarked: 7%; unmarked: 39%) but did not hatch a second egg (radiomarked: 4%; unmarked: 25%) or fledge a second (beta) chick (radiomarked: 4%; unmarked: 18%) significantly more often than radiomarked pairs. We resighted 12 radiomarked individuals nesting during a subsequent breeding season; each bird had shed its transmitter and healed the site of attachment. We suggest caution in using telemetry to evaluate the reproductive performance of alcids, but marking only females may minimize adverse effects.

FORAGING DISTANCES OF RADIO-MARKED MARBLED MURRELETS FROM INLAND AREAS IN SOUTHEAST ALASKA

Abstract We radiotagged seven female and two male Marbled Murrelets (Brachyramphus marmoratus) of undetermined breeding status and followed their movements through the inner passages of northern southeast Alaska during the breeding season (May–July) in 1998. Six of the nine murrelets were detected inland in the early morning hours from 24 June to 17 July. Inland visits for each individual were consistent to a particular location, but short in duration, which precluded locating nest sites. We recorded 46 locations at sea up to 124 km (x̄ = 78 ± 27 km) from inland sites during the period 19 June to 16 July. We detected murrelets at inland sites and at sea on the same day on 20 occasions with a mean distance between these locations of 75 ± 42 km. The majority of murrelets were located at sea in western Icy Strait, a productive feeding area at the mouth of Glacier Bay, Alaska. This study provides the first direct evidence that Marbled Murrelets in southeast Alaska are consistently traveling considerable distances between potential nesting and foraging areas. These findings have important implications for murrelet conservation and management efforts in southeast Alaska.

Rangewide Population Genetic Structure of Xantus's Murrelet (Synthliboramphus hypoleucus)

ABSTRACT. Population genetic structure was characterized in Xantuss Murrelet (Synthliboramphus hypoleucus) by analyzing variation in the mitochondrial control region (505 samples) and 12 microsatellite loci (428 samples) in birds captured at all 13 current breeding areas in southern California and northwestern Baja California, Mexico. The two types of molecular markers were consistent in revealing strong genetic differentiation between the two currently recognized subspecies (S. h. hypoleucus and S. h. scrippsi) and little or no differentiation among breeding areas within subspecies. Estimates of gene flow were essentially zero, and no evidence for admixture was found. Gene flow among breeding locations within subspecies, on the other hand, was seemingly high. Given these genetic results, as well as clear morphological differences between the subspecies and the apparent lack of interbreeding at breeding areas where the two forms are sympatric, we suggest that two species be recognized. Both forms are genetically distinct from Craveris Murrelet (S. craveri), a closely related species whose breeding range partially overlaps that of Xantuss Murrelet. Taxonomic subdivision of Xantuss Murrelet introduces new conservation concerns, especially for S. h. hypoleucus, which urgently requires greater study and protective efforts.

Nesting ecology of Marbled Murrelets at a remote mainland fjord in southeast Alaska

ABSTRACT Studying the ecology of endangered species in portions of their range where the population remains abundant can provide fundamental information for conservation planners. We studied nesting by radio-tagged Marbled Murrelets (Brachyramphus marmoratus) during 2007 and 2008 in Port Snettisham, a relatively pristine, remote mainland fjord in southeast Alaska with high at-sea densities of Marbled Murrelets during the breeding season. Of 33 active Marbled Murrelet nest sites located during the study, we found 15 within forested habitat (tree nest sites), 16 in nonforested habitat (ground nest sites), and 2 that could not be determined. Some nests were located farther inland from the coast (range: 1–52 km) and at higher elevations (range: 42–1,100 m) than previously documented in Alaska. Nesting success to ≥20 days posthatch (0.20 ± 0.07 [SE]) was less than half of similar estimates in British Columbia and more comparable to estimates from California and Washington. A logistic regression found that nesting success did not differ between years, but nesting success was higher for tree nests than for ground nests. Conservation planners should consider that Marbled Murrelets will use certain nonforest habitat types for nesting in mainland southeast Alaska. Our reported nesting success was likely a maximum, and our results indicate that nesting success can be low even when nesting habitat is seemingly abundant and marine habitat appears excellent.

Status, Distribution, and Conservation of Scripps's Murrelet at Santa Catalina Island, California

Abstract. The small population of Scrippss Murrelets (Synthliboramphus scrippsi) at Santa Catalina Island, California, has been restricted for at least several millennia to isolated pairs nesting in cliff and shoreline habitats that are mostly inaccessible to island fox (Urocyon littoralis catalinae). Prior to 1994, the only evidence of murrelets breeding at Catalina was a single nest reportedly found on Bird Rock in 1967. In 1994–1995, a larger and more widespread population estimated at 25–75 pairs was indicated through vocal detection surveys of murrelets attending nocturnal at-sea congregations in nearshore waters near breeding areas. Murrelets were heard at 11 of 25 survey stations, with highest vocal activity between Lands End and Ribbon Rock (6–62 detections per survey). In 2004 and 2012, round-island spotlight surveys better assessed the distribution and abundance of murrelets in congregations, with 101 and 291 individuals, respectively, observed along the 82-km transect. Highest numbers in 2012 suggest a current breeding population of roughly 100–200 pairs at Catalina, the fourth largest colony in southern California. Congregations were strongly associated with coastal cliffs between (1) Isthmus Cove and Twin Rocks and (2) Iron Bound Bay and Catalina Harbor. In 2000–2013, night-lighting captures of 79 birds in congregations recorded 10 (13%) murrelets with brood patches, usually indicative of egg-laying. During captures in 2008 and spotlight surveys in 2012, three family groups (adults with small downy chicks) departing island nests were observed in nearshore waters. No nests were found during searches on offshore rocks (including Bird Rock) in 1991–1996, but 7 nests were discovered in 2012–2013 during searches of boataccessible shoreline cliffs between Isthmus Cove and Twin Rocks. Overall, 6 of 8 clutches (75%) with known fates were successful, but evidence of mammalian predators preying on murrelet eggs was also present. A long-term monitoring, research, and restoration program is needed at Catalina. Initial restoration efforts should focus on reducing predation by introduced mammals and reducing impacts from oil pollution and bright lights.

Nocturnal Spotlight Surveys for Monitoring Scripps's Murrelets in At-Sea Congregations at Anacapa Island, California

Abstract. Concealed nest sites, mostly inaccessible breeding habitats, and nocturnal colony visitation have long hindered studies of Scrippss Murrelets (Synthliboramphus scrippsi); but conspicuous and seasonally predictable at-sea congregations adjacent to nesting areas provide a valuable index for assessing murrelet colony size and population trends at all 12 breeding islands. We developed a boat-based nocturnal spotlight survey for counting murrelets in at-sea congregations at Anacapa Island, California. A high-intensity spotlight was used to count murrelets during standard surveys conducted on 2 parallel transects (1.9 km each) located 200 m (“inshore”) and 500 m (“offshore”) from shore. We conducted 130 standard surveys over 58 nights in 2001–2006. Difficulties estimating densities with strip transects and distance sampling led to use of raw counts as the best index for assessing population trends. Standard counts averaged 136 (SD 94) murrelets per survey (range 0–470). Strong correlations were noted among counts within nights, but consistent trends were not evident. We also noted a strong correlation between maximum counts on consecutive survey nights but much more variation in counts over the breeding season (annual CV range 27%–92%). Annual maximum counts occurred from 42 days before to 32 days after mean egg-laying dates. Round-island counts ranged from 29 to 564 murrelets during 12 surveys conducted along a 19.2-km transect circumnavigating Anacapa Island. Strong correlations between inshore and offshore standard counts and between standard and round-island counts indicated that major local shifts in distribution did not occur; instead, varying proportions of the murrelet population returned to the Anacapa Island congregation each night. Increases in standard counts from 2001 to 2006 and a positive correlation between standard counts and the annual number of clutches in monitored plots suggested an increase in the murrelet population after eradication of black rats (Rattus rattus) in 2002, but limited posteradication survey data were not sufficient to detect significant popu lation trends. Intensive surveys (minimum of 10 nights each year) over at least 3 consecutive years per decade are recommended to track the progress of the Scrippss Murrelet population and to validate rates of population growth observed in small nest plots on Anacapa Island.

Polymorphic microsatellite loci for the threatened Xantus’s Murrelet (Synthliboramphus hypoleucus scrippsi)

Twelve polymorphic microsatellite loci were isolated and characterized for one subspecies of the Xantus’s murrelet (Synthliboramphus hypoleucus scrippsi), a threatened seabird. Using blood samples obtained from 40 birds captured at Santa Barbara Island, California, in April–May 1996, 3–14 alleles per locus were detected, and expected heterozygosity ranged from 0.25 to 0.90. Genotype frequencies showed no departures from Hardy–Weinberg expectations. Linkage is suspected in one pair of loci.