Brachyramphus Marmoratus Research Articles

Re-Use of Nest Sites by Marbled Murrelets (Brachyramphus marmoratus) in British Columbia

Marbled Murrelets (Brachyramphus marmoratus) nest predominantly in the canopies of large old-growth conifers, and are listed as Threatened in Canada and 3 US states mainly as a consequence of reductions in this habitat due to logging. We assessed the re-use of nest sites (nest trees) by murrelets in British Columbia using 3 types of data: 1) evidence o fr eturn of adults to the same nest site; 2) evidence of multiple nests within the same tree; and 3) re-checking known nest trees in subsequent seasons for evidence of re-use. All 3 methods showed evidenc eo f re-use of nest trees in different years, but there were marked regional differences in the degree of re-use. Re-use of nest trees was most frequent in regions with extensive loss of nesting habitat due to logging (Southern Mainland Coast and East Vancouver Island), and rare in a less disturbed region (West Vancouver Island). Overall, 26 of 143 (18%) nest trees climbed showed evidence of multiple nesting in separate seasons. Management of nesting habitat should incorporate these results by providing greater protection of habitat in regions where habitat is sparse, and by minimizing predation risk where murrelets more frequently re-use nest sites. Since re-use of nest sites is infrequent, managers should aim to provide murrelets with multiple choices for nest sites, such as maintaining large tracts of old- growth forest with many large trees containing potential nest platforms.

Characterizing dispersal patterns in a threatened seabird with limited genetic structure

Genetic assignment methods provide an appealing approach for characterizing dispersal patterns on ecological time scales, but require sufficient genetic differentiation to accurately identify migrants and a large enough sample size of migrants to, for example, compare dispersal between sexes or age classes. We demonstrate that assignment methods can be rigorously used to characterize dispersal patterns in a marbled murrelet (Brachyramphus marmoratus) population from central California that numbers approximately 600 individuals and is only moderately differentiated (F(ST) approximately 0.03) from larger populations to the north. We used coalescent simulations to select a significance level that resulted in a low and approximately equal expected number of type I and II errors and then used this significance level to identify a population of origin for 589 individuals genotyped at 13 microsatellite loci. The proportion of migrants in central California was greatest during winter when 83% of individuals were classified as migrants compared to lower proportions during the breeding (6%) and post-breeding (8%) seasons. Dispersal was also biased toward young and female individuals, as is typical in birds. Migrants were rarely members of parent-offspring pairs, suggesting that they contributed few young to the central California population. A greater number of migrants than expected under equilibrium conditions, a lack of individuals with mixed ancestry, and a small number of potential source populations (two), likely allowed us to use assignment methods to rigorously characterize dispersal patterns for a population that was larger and less differentiated than typically thought required for the identification of migrants.

Genetic analyses of historic and modern marbled murrelets suggest decoupling of migration and gene flow after habitat fragmentation.

The dispersal of individuals among fragmented populations is generally thought to prevent genetic and demographic isolation, and ultimately reduce extinction risk. In this study, we show that a century of reduction in coastal old-growth forests, as well as a number of other environmental factors, has probably resulted in the genetic divergence of marbled murrelets (Brachyramphus marmoratus) in central California, despite the fact that 7 per cent of modern-sampled murrelets in this population were classified as migrants using genetic assignment tests. Genetic differentiation appears to persist because individuals dispersing from northern populations contributed relatively few young to the central California population, as indicated by the fact that migrants were much less likely to be members of parent-offspring pairs than residents (10.5% versus 45.4%). Moreover, a recent 1.4 per cent annual increase in the proportion of migrants in central California, without appreciable reproduction, may have masked an underlying decline in the resident population without resulting in demographic rescue. Our results emphasize the need to understand the behaviour of migrants and the extent to which they contribute offspring in order to determine whether dispersal results in gene flow and prevents declines in resident populations.

Concurrent declines in nestling diet quality and reproductive success of a threatened seabird over 150 years

Successful conservation of threatened species is often hindered by a lack of long-term data required to identify the vital rates contributing to population decline and the extrinsic factors influencing those rates. Museum collections can provide a valuable resource for reconstructing the historic demography and diet of otherwise elusive species. Here, we used age ratios (the relative number of hatch-year to after-hatch-year individuals) to examine the hypothesis that population declines in a threatened seabird, the marbled murrelet Brachyramphus marmoratus, are due to declines in reproductive success over the past 150 yr. We also used stable-nitrogen isotopes to exam- ine the hypothesis that variation in reproductive success over this period is related to the quality of food received by young in the nest. Age ratios from at-sea surveys conducted from 1994 to 2001 were significantly lower than museum collection age ratios for the period 1860 to 1950. Stable-nitrogen isotope values indicated that the trophic feeding level of marbled murrelet nestlings declined signif- icantly (-2.6‰) from 1854 to 2008. Our results suggest that the reproductive success of marbeled murrelets breeding in the Salish Sea has declined over the past 150 yr and that declines in nestling diet quality may be partly responsible. Overall, our results support the idea that managers should consider the quality of both nesting and marine foraging habitat as they attempt to improve repro- ductive success and population growth rate in this threatened species.

Prey-Capture by Marbled Murrelets in Southeast Alaska

Daszak P, Strieby a, Cunningham AA, Longcore JE, Brown CC, Porter D. 2004. Experimental evidence that the bullfrog (Rana catesbeiana) is a potential carrier of chytridiomycosis, an emerging fungal disease of amphibians. Herpetological Journal 14:201-207. Garner TWJ, Perkins MW, Govindarajulu P, Seglie D, Walker S, Cunningham AA, Fisher MC. 2006. The emerging pathogen Batrachochytrium dendroba tidis globally infects introduced populations of the North American bullfrog, Rana catesbeiana. Biology Letters: doi:10.1098/rsbl.2006.0494. Green DE, Converse KA, Schr?der AK. 2002. Epizootiology of sixty-four amphibian morbidity and mortality events in the USA, 1996-2001. Annals of the New York Academy of Sciences 969:323-339. Hayes MP, Rombough C, Hayes CB, and Engler JD. 2005. Rana pretiosa (Oregon spotted frog). Preda tion. Herpetological Review 36:307. Hayes MP, Engler JD, and Rombough C. 2006. Rana pretiosa (Oregon spotted frog). Predation. Herpe tological Review 37:209-210. Johnson J, Dean E, Belmont S, Darda D, Germaine S, and wagner S. 2006. Chytridiomycosis: A silent spring for Pacific Northwest amphibians? North western Naturalist 87:174. [abstract] Longcore JE, Pessier AP, Nichols DK. 1999. Batra chochytrium dendrobatidis gen. et sp. nov., a chytrid pathogenic to amphibians. Mycologia 91: 219-227. McAllister KR, Leonard WP. 1997. Washington State status report of the Oregon spotted frog. Olympia, WA: Washington Department of Fish and Wildlife. 38 p. Muths E, Corn PS, Pessier AP, Green DE. 2003. Evidence for disease-related amphibian decline in Colorado. Biological Conservation 110:357-365. Pearl C ., Bull EL, Green DE, Bowerman J, Adams MJ, Hyatt A, W nte WH. 2007. Occurrence of the amphibian pathogen Batrachochytrium dendrobatidis n the Pacific No thwest. Journal of Herpetology 41:145-149. Pessier AP, Nichols DK, Longcore JE, Fuller MS. 1999. Cutaneous chytridiomycosis in poison dart frogs (Dendrobates spp.) and White's tree frogs (Litoria caerul a). Journal of Veterinary Diagnostic Investigation 11:194-199. Pounds JA, Bustamante MR, Coloma LA, Consue gra JA, fogden MPL, foster PN, la marca E, Masters KL, Merino-Viteri A, Puschendorf R, Ron SR, Sanchez-Azofeifa GA, Still CJ, Young BE. 2006. Widespread amphibian extinctions from epidemic disease driv n by global warming. Nature 439:161-167. Wdfw [Washington Department of Fish and Wildlife]. 2009. Species of Concern, Washing ton Department of Fish and Wildlife, Olympia, Washington, (online at: http://wdfw.wa.gov/ wlm/diversity/ soc/soc.htm).

Marbled Murrelet nest predation risk in managed forest landscapes: dynamic fragmentation effects at multiple scales

The effects of forest fragmentation on bird populations have been studied primarily as static phenomena. Yet when forests are allowed to regenerate, local edge contrast and landscape matrix composition change with time, and we would expect fragmentation effects to change accordingly. Describing this process is critical for the conservation of avian species sensitive to forest fragmentation, including the Marbled Murrelet (Brachyramphus marmoratus), a seabird threatened by ongoing harvest of old-growth forest nesting habitat. We experimentally assessed potential murrelet nest predation probability in four regions of southwestern British Columbia, Canada. We compared the fates of 448 simulated murrelet nests at paired edge and interior treatments, at sites with "hard" edges (recent clearcuts), "soft" edges (regenerating forest), and natural edges (i.e., riparian areas). Motion-sensitive digital nest cameras enabled us to focus on known predators of real nests, and patterns of nest fates did not differ between real and simulated nests. Using information-theoretic model selection (AIC) with the combined data set (116 sites), we assessed effects at patch (approximately 13 ha), landscape (approximately 1700 ha), and regional (approximately 96000 ha) scales. Nest disturbance probability at hard edges was 2.5 times that of interior sites, but soft edges had less than half the disturbance probability of interiors. There was no edge effect at natural edges. At the landscape scale, overall avian disturbance risk declined by as much as 50% with increasing amounts of regenerating forest in the surrounding matrix. These results indicate that initially negative fragmentation effects decrease as forests regenerate, at both patch and landscape scales. There was no evidence that these patterns differed between regions. Predator surveys suggested that Steller's Jays drive patterns of nest predation risk at the regional scale. Assuming that corvids are the most important predators, larger reserves of habitat will lessen negative hard-edge effects. Smaller reserves should be embedded in a protective matrix of regenerating forest to reduce predation risk at both patch and landscape scales. Our results suggest that dynamic fragmentation effects are generalizable across widespread regions and can be broadly applied to both murrelet management and the conservation of old-growth forest-breeding birds in general.

Using the low-level aerial survey method to identify Marbled Murrelet nesting habitat

Identifying and managing nesting habitat for the threatened Marbled Murrelet (Brachyramphus marmoratus) is difficult because it nests secretively, high in the canopies of large, old conifers of the Pacific Northwest. In British Columbia, low-level surveying from a helicopter is now a recommended standard method of assessing forested landscapes for key microhabitat features—such as availability of potential platforms and developed moss pads for nests, foliage cover above the nest, and accessibility—that are not distinguishable on air photos, satellite images, or forest cover maps. Using a sample of 111 nest sites and 139 random sites within forests greater than 140 years old and distributed across three study areas in south coastal British Columbia, we confirmed the effectiveness of the aerial survey method for classifying overall habitat quality of murrelet nesting habitat. The minimum map units were 3-ha patches. Overall, 40% of the 111 nest sites were in patches classed as Very High, 36% were in High, 15% were in Moderate, 6% were in Low, and 3% were in Very Low. Our ranking of habitat quality was most strongly influenced by estimates of platform availability and moss development. Using an information-theoretic approach, we identified that the Resource Selection Function scores of nest patches improved as elevation decreased, slope grade increased, and the proportion of emergent and canopy trees with mossy pads increased. We also confirmed that study area location affected the strength of model application. Our findings support the potential utility of the low-level aerial survey method for identifying or confirming Marbled Murrelet nesting habitat for land-management purposes.

Relationships between habitat area, habitat quality, and populations of nesting Marbled Murrelets

We review relationships between the area and quality of apparently suitable nesting habitat (as defined by canopy structure) and the population size of Marbled Murrelets (Brachyramphus marmoratus) which such habitat might support. This information is important to manage the old seral forest nesting habitat of this threatened seabird. Studies at different spatial scales indicate that linear relationships provide good, biologically feasible fits between murrelet counts and areas of apparently suitable habitat when the effects of habitat quality are unknown. A large-scale analysis across Washington, Oregon, and California showed a strong linear relationship between murrelet numbers and area of habitat within large conservation regions. Seven separate watershed-level radar studies (six in British Columbia and one in Washington) support a linear relationship and also indicate that when logging reduces habitat, the murrelets do not aggregate in the remaining habitat at higher densities. Tree-climbing studies show similar trends at stand levels: compared to more pristine habitat, nest densities were not higher in remnant old-growth patches in depleted, highly fragmented areas. Do murrelets nest at higher densities in higher-quality habitat? The sparse information on this topic suggests a correspondence between nest locations and habitat quality as assessed by algorithms, air photo interpretation, and low-level aerial surveys. Most nests (92% and 86% in pooled data from aerial surveys or air photo interpretation, respectively) were found in habitat rated as Moderate, High, or Very High, and few (8% and 14%, respectively) in those rated Low, Very Low, or Nil. The relationship between perceived quality and the likelihood of nesting is, however, non-linear and it is premature to assume that murrelet nest densities will be significantly higher within the upper ranks of suitable habitat assessed from forest features.

Estimating seabird densities from vessel transects: distance sampling and implications for strip transects

Vessel-based transects have been a mainstay of seabird research for decades, yet there has been surprisingly little effort to evaluate the detectability of seabirds within strip transects. Dis- tance sampling methods offer an opportunity to quantify detectability and assess the proportions of birds on the water that may be missed during strip transects. Three summers of line-transect surveys were analyzed using the program Distance to model detection functions of 6 seabird taxa (marbled murrelet Brachyramphus marmoratus, rhinoceros auklet Cerorhinca monocerata, common murre Uria aalge, pigeon guillemot Cepphus columba, pelagic cormorant Phalacrocorax pelagicus, gulls Larus spp.). We tested the effects of covariates (year, observers, sea state, and cluster size) on detec- tion function estimation. Year and observer were the most important covariates for some but not all species. For a 300 m wide transect (150 m on either side), 20 to 80% of birds were detected, depend- ing on species, year, and observer. Detectability was highest for cormorants (60 to 90%) and fairly similar among other species (typically 40 to 60%). Sea state had a significant effect on encounter rate for murrelets suggesting that g(0), detection probability near the transect line, may be <1 when wave height increases. These data emphasize that a high proportion of birds on the water remain unde- tected during strip-transect surveys. It is important that surveys develop independent estimates of detection probability to account for detectability among species, years, observers, vessel types/speed, and viewing conditions. The application of distance sampling to seabird surveys can provide more accurate abundance and population estimates, which can improve conservation and management efforts.

Meeting Reproductive Demands in a Dynamic Upwelling System: Foraging Strategies of a Pursuit-Diving Seabird, the Marbled Murrelet

Abstract. Seabirds maintain plasticity in their foraging behavior to cope with energy demands and foraging constraints that vary over the reproductive cycle, but behavioral studies comparing breeding and nonbreeding individuals are rare. here we characterize how Marbled Murrelets (Brachyramphus marmoratus) adjust their foraging effort in response to changes in reproductive demands in an upwelling system in central California. we radio-marked 32 murrelets of known reproductive status (9 breeders, 12 potential breeders, and 11 nonbreeders) and estimated both foraging ranges and diving rates during the breeding season. Murrelets spent more time diving during upwelling than oceanographic relaxation, increased their foraging ranges as the duration of relaxation grew longer, and reduced their foraging ranges after transitions to upwelling. When not incubating, mur relets moved in a circadian pat ter n, spending nighttime hours resting near flyways used to reach nesting habitat and foraging during the daytime an...

Pacific Northwest Sea Bird May Lose 'Threatened' Status

The U.S. Fish and Wildlife Service agreed last week to review the protected status of the marbled murrelet, a sea bird that nests in the coastal forests of the Pacific Northwest, in response to a timber-industry-led petition claiming that the bird does not meet key provisions of the Endangered Species Act.

CHARACTERIZING SOURCE–SINK DYNAMICS WITH GENETIC PARENTAGE ASSIGNMENTS

Source-sink dynamics have been suggested to characterize the population structure of many species, but the prevalence of source-sink systems in nature is uncertain because of inherent challenges in estimating migration rates among populations. Migration rates are often difficult to estimate directly with demographic methods, and indirect genetic methods are subject to a variety of assumptions that are difficult to meet or to apply to evolutionary timescales. Furthermore, such methods cannot be rigorously applied to high-gene-flow species. Here, we employ genetic parentage assignments in conjunction with demographic simulations to infer the level of immigration into a putative sink population. We use individual-based demographic models to estimate expected distributions of parent-offspring dyads under competing sink and closed-population models. By comparing the actual number of parent-offspring dyads (identified from multilocus genetic profiles) in a random sample of individuals taken from a population to expectations under these two contrasting demographic models, it is possible to estimate the rate of immigration and test hypotheses related to the role of immigration on population processes on an ecological timescale. The difference in the expected number of parent-offspring dyads between the two population models was greatest when immigration into the sink population was high, indicating that unlike traditional population genetic inference models, the highest degree of statistical power is achieved for the approach presented here when migration rates are high. We used the proposed genetic parentage approach to demonstrate that a threatened population of Marbled Murrelets (Braclhyrarmphus marmotus) appears to be supplemented by a low level of immigration (approximately 2-6% annually) from other populations.

Limited foraging flexibility: increased foraging effort by a marine predator does not buffer against scarce prey

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 366:245-258 (2008) - DOI: https://doi.org/10.3354/meps07529 Limited foraging flexibility: increased foraging effort by a marine predator does not buffer against scarce prey Robert A. Ronconi*, Alan E. Burger Department of Biology, University of Victoria, PO Box 3020, Stn CSC, Victoria, British Columbia V8W 3N5, Canada *Email: rronconi@uvic.ca ABSTRACT: Flexibility in activity time budgets allows animals to cope with heterogeneous and changing environments. Many marine predators, such as seabirds, exhibit flexibility in their foraging behaviour to buffer reproductive success against periods of low prey availability. Over 3 years, 2004 to 2006, we studied the foraging behaviour of a threatened seabird, the marbled murrelet Brachyramphus marmoratus in southwestern Vancouver Island, British Columbia, Canada. An information–theoretic approach was used to compare among factors (temporal, spatial, environmental, and competitors) that may influence diving activity. We also quantified local prey availability by hydroacoustic surveys and regional oceanographic conditions (chlorophyll a concentrations and upwelling indices) to investigate relationships between diving activity, food supply and environmental conditions. Prey indices varied spatially, seasonally, and annually, showing reduced prey availability during incubation and chick-rearing of 2005. Upwelling indices and chlorophyll a concentrations, as an index of primary productivity, were delayed in 2005. Year and breeding phase had the greatest impact on diving activity, with additional variation among sites. Murrelets increased diving activity in years and seasons with scarce prey and poor oceanographic conditions (incubation and chick-rearing 2005) and decreased diving activity at sites with high prey availability. There was a linear relationship between diving activity and food availability, suggesting no clear thresholds in response to decreases in prey. Despite their flexible activity budgets, increased foraging effort by murrelets in 2005 was inadequate to ensure average levels of reproductive success. Thus, flexible foraging behaviour by murrelets may be ineffective to buffer reproductive success when environmental conditions are extremely poor. KEY WORDS: Activity budgets · Prey availability · Foraging ecology · Thresholds · Seabirds · Brachyramphus marmoratus Full text in pdf format PreviousNextCite this article as: Ronconi RA, Burger AE (2008) Limited foraging flexibility: increased foraging effort by a marine predator does not buffer against scarce prey. Mar Ecol Prog Ser 366:245-258. https://doi.org/10.3354/meps07529 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 366. Online publication date: August 29, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Predictive Model of Habitat Suitability for the Marbled Murrelet in Western Washington

Abstract: The marbled murrelet (Brachyramphus marmoratus) is a small Pacific seabird with a breeding range that extends from the Aleutian Islands to central California. Throughout most of its breeding range, it uses mature and old‐growth coniferous forests as nesting habitat. Although most murrelets seem to nest within 60 km of the coast, occupied nesting habitat has been identified as far as 84 km from the ocean in Washington state. Due to the extensive inland distances within which birds are known to breed, the area requiring surveys to identify breeding sites can be enormous. Therefore, the standard 2‐year survey protocol can be expensive and time‐consuming for forest management agencies and companies to administer. We developed a logistic regression model to determine whether a suite of forest structural characteristics could be used to reliably predict occupancy of a forest patch by marbled murrelets. We tested the performance of the final model using cross‐validation procedures and a sample of independent sites. We used 50 sites surveyed for marbled murrelets to estimate the model, and 48 independent sites were available to test model performance. All 50 sites were on private forestland owned by Rayonier located in the western lowlands of Olympic Peninsula within the Sitka spruce and western hemlock transition zones. We sampled forest habitat at each site, and we collected information on 15 explanatory variables. The best‐fitting logistic regression model contained variables that measured number of canopy layers (P&lt;0.001, approx. F test) and mistletoe (Arceuthobium sp.) abundance (P = 0.031, approx. F test). The model misclassified 2 of 33 (94% correct) unoccupied sites as occupied using a classification cut‐off (c) of c=0.25. In the other direction, under cross‐validation the final model misclassified 2 of 17 (88% correct) occupied sites as unoccupied. On a test of the model against an independent sample, using a classification cut‐off value of c = 0.25, the final model correctly classified 36 of 48 sites (75% correct). The final model misclassified 3 of 31 occupied sites as unoccupied (90% correct). Use of predictive models could greatly reduce the amount of forest that requires surveys by screening out those sites with little probability of use and by focusing remaining effort on higher probability sites, resulting in a higher likelihood of identifying occupied sites and thereby more efficiently conserving marbled murrelet nesting habitat.

MARINE DISTRIBUTION AND BEHAVIOR OF JUVENILE AND ADULT MARBLED MURRELETS OFF SOUTHWEST VANCOUVER ISLAND, BRITISH COLUMBIA: APPLICATIONS FOR MONITORING

Abstract We examined the marine distribution and behavior of newly fledged juvenile (hatching year; HY) and adult (after hatching year; AHY) Marbled Murrelets (Brachyramphus marmoratus) off southwest Vancouver Island, British Columbia, to test whether assumptions associated with estimating productivity are met in this area. Productivity estimates for murrelets use HY:AHY ratios from marine surveys, which assume limited emigration and that juvenile and adult birds are similarly distributed. We examined observations from June–August, 1994–2005. Behavioral data were collected from land-based surveys via instantaneous scan sampling. Locations of murrelets at sea were mapped from cliff-top vantage points using a theodolite; Geographic Information Systems (GIS) was then used to compare the distances from shore of juveniles and adults. Data from boat surveys were analyzed using GIS kernel density analysis to compare adult and juvenile murrelet distributions at sea. At fine scales (1–100 m), juveniles were associ...

Using air photos to interpret quality of Marbled Murrelet nesting habitat in south coastal British Columbia

Reliable habitat assessment methods are needed to ensure the adequate management of Marbled Murrelet (Brachyramphus marmoratus) habitat in British Columbia. In two south coastal study regions, the Sunshine Coast and Clayoquot Sound, we evaluated the effectiveness of a qualitative habitat classification that uses air photo-interpreted forest structural characteristics for identifying and ranking habitat quality. Using a sample of 118 nest sites and 157 random sites within forests greater than 140 years old, we found that murrelets selected nest patches non-randomly with respect to forest characteristics. While selectivity varied between study regions, generally nest patches had taller and larger trees, exhibited more complex forest structure, and were located at lower meso-slope positions near large gaps or nearby edges. In addition, these patches were more often ranked higher in terms of habitat quality. However, we found that probable breeding success was greater in habitats classified as lower quality. Thus, further research is needed to understand our findings relative to other influences on breeding productivity, such as predators and hierarchal habitat selection. In summary, while our study supports the use of the current air photo habitat classification standards to improve identification and selection of murrelet nesting habitat for management, some modifications to these standards may be needed.

The impact of recreational boat traffic on Marbled Murrelets ( Brachyramphus marmoratus)

This study evaluated the impact of small boat traffic on reaction distances of Marbled Murrelets ( Brachyramphus marmoratus), in the marine waters of Pacific Rim National Park Reserve, British Columbia, Canada. Observers on moving boats recorded the minimum distance the boat came to murrelets on the water, and any disturbance reaction (fly, dive, no reaction). Out of the 7500 interactions 11.7% flew, 30.8% dove and 58.1% exhibited no flushing reaction. Using a product-limit analysis, we developed curves for the proportion of Marbled Murrelets flushing (dive or flight) as a function of reaction distance. Overall, the majority of Marbled Murrelets waited until boats were within 40 m before reacting, with 25% of the population reacting at 29.2 m. A stepwise Cox regression indicated that age, boat speed, and boat density (loaded in that order), significantly affected flushing response. More juveniles flushed than adults (70.1 versus 51.7%), but at closer distances. Faster boats caused a greater proportion of birds to flush, and at further distances (25% of birds flushed at 40 m at speeds >29 kph versus 28 m at speeds <12 kph). A stepwise logistic regression on diving and flight responses indicated that birds tended to fly completely out of feeding areas at the approach of boats travelling >28.8 kph and later in the season (July and August). Other secondary variables included; boat density and time of day. Discussion focused on possible management actions such as the application of speed limits, set back distances, and exclusion of boat traffic to protect Marbled Murrelets.

COEXISTENCE AND SPATIAL DISTRIBUTIONS OF MARBLED MURRELETS (BRACHYRAMPHUS MARMORATUS) AND OTHER ALCIDS OFF SOUTHWEST VANCOUVER ISLAND, BRITISH COLUMBIA

Abstract Niche overlap and resource partitioning have seldom been investigated in the marine habitats of seabirds but are obvious determinants of community and population status. We investigated interspecific differences in densities and spatial aggregations of seabirds during summer (June–August) off southwest Vancouver Island, British Columbia. Two 300-m-wide parallel transects were sampled along 66.6 km of shoreline in 1993–1996, centered 200 m and 600 m from shore. Analysis focused on the threatened Marbled Murrelet (Brachyramphus marmoratus) and three other fish-eating alcids. Densities of Marbled Murrelets were among the highest reported at sea in the species' range; they were concentrated close to shore (>75% within 0.6 km and virtually all within 2.0 km of shore), usually in water <20 m deep, and showed strong fidelity to certain sectors along the coast from year to year. Common Murres (Uria aalge) and Rhinoceros Auklets (Cerorhinca monocerata) were not as closely associated with nearshore habitat...

EFFECTS OF RAPID FLIGHT-FEATHER MOLT ON POSTBREEDING DISPERSAL IN A PURSUIT-DIVING SEABIRD

Abstract Breeding seabirds have been well studied but seabird ecology during the nonbreeding season is poorly understood because many species disperse far from breeding colonies to molt at sea. We characterized the timing of prebasic molt and postbreeding dispersal, described postbreeding dispersal movements, and estimated changes in body mass during molt for Marbled Murrelets (Brachyramphus marmoratus; Alcidae) in central California, 1999–2004. According to mark–recapture and at-sea surveys, 248–315 of 496–637 individuals (43–50%) used Ano Nuevo Bay, located immediately adjacent to nesting areas, for their prebasic molt in August–October. Long-distance dispersal (≥ 100 km) from Ano Nuevo Bay by radiomarked Marbled Murrelets was low during breeding (9–13%, n = 46), but was greater for individuals radiomarked at the end of the breeding season (69–90%, n = 20). The mean dispersal dates were 18 May and 21 October for the breeding and postbreeding samples, respectively, and postbreeding dispersal occurred an ...

Capture Methods for Migrating, Wintering and Molting Sea Ducks

Abstract Sea ducks have been captured with mist nets set across breeding streams and in drive traps at sea during the flightless period, but capture of flying birds on staging and wintering coastal areas presents a challenge. Here, we describe a highly successful technique for capturing Harlequin Ducks (Histrionicus histrionicus) at sea, modified from a mistnet set developed to capture Marbled Murrelets (Brachyramphus marmoratus) at sea. While the original method was passive, decoys were added to attract birds and occasionally birds were driven toward the nets using small boats. The capture technique proved to be safe and effective. Three hundred and seventy-eight birds were captured during 28 d of effort and no birds died in the nets or during handling. The technique has been further modified to capture molting Harlequin Ducks. The technique and its modified version could be easily used to capture other sea ducks on their staging, wintering and molting areas.