Marbled Murrelet Brachyramphus Marmoratus Research Articles

Aerial hearing thresholds and ecoacoustics of a threatened pursuit-diving seabird, the marbled murrelet Brachyramphus marmoratus

As humans increasingly utilize sensitive coastal areas, diving seabirds like the marbled murrelet Brachyramphus marmoratus face a unique combination of exposure to pervasive anthropogenic sound and acoustically mediated disturbances in terrestrial and marine environments. Despite its threatened status, the sound sensitivities and sensory ecology of this species are unknown, limiting any predictions of the frequencies or sound levels that may induce acoustic impacts. In this study, we measured electrophysiological aerial hearing thresholds for 10 wild individuals captured, sedated, examined inside a field-deployed anechoic chamber and subsequently released. Auditory responses were detected across a 0.5 to 6 kHz frequency range. The median auditory threshold was lowest at 2 kHz (33 dB), while hearing was generally sensitive between 0.75 and 3.8 kHz. B. marmoratus thresholds were elevated compared to other studied alcid species. In-air sensitivities were used to provide an initial prediction of underwater hearing thresholds. To further explore the auditory sensory ecology of this solitary-nesting species, hearing data were also compared to short-term recordings (5 d) of the aerial soundscape of a marbled murrelet nesting habitat. The soundscape contained both abiotic and biotic sounds that contributed to broadband sound levels of 46-55 dB re: 20 µPa rms (0.2-10 kHz). This comparatively quiet habitat enabled relatively frequent detection of anthropogenic sounds within the soundscape. Energy from this acoustic pollution consistently overlapped marbled murrelet sound sensitivities, indicating that the species is susceptible to disturbance from a range of noise types.

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.

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.

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.

Diet reconstruction and historic population dynamics in a threatened seabird

Summary For the overwhelming majority of species, we lack long‐term information on the dynamics of populations. As a consequence, we face considerable uncertainty about how to discriminate among competing hypotheses of population decline and design conservation plans. The marbled murrelet Brachyramphus marmoratus is a small seabird that nests in coastal old‐growth forest but feeds year‐round in near‐shore waters of the north‐eastern Pacific. Although a decline in nesting habitat is the primary reason why marbled murrelets are listed as threatened in Canada, nest predation and food availability may also influence population abundance. To examine the hypothesis that murrelet populations are influenced by variation in diet quality, we analysed stable‐carbon and ‐nitrogen isotopes in feathers of museum specimens collected in the Georgia Basin, British Columbia. Between 1889 and 1996, we found a decline in stable isotopic signatures that was approximately equal to a 62% drop in trophic feeding level. We also found that the estimated proportion of fish in murrelet diet was related closely to murrelet abundance over the past 40 years, as estimated from volunteer surveys. Using these isotopic data, we modelled population size as a function of variation in reproductive rate due to changes in diet quality and found that our model matched closely the 40‐year field estimates. We then applied our 107‐year isotopic record to the model to back‐cast estimates of population growth rate to 1889. Our results suggest that, up to the 1950s, murrelet populations in the Georgia Basin were capable of growing and were probably limited by factors other than diet quality. After this period, however, our results imply that murrelets were often, but not solely, limited by diet quality. Synthesis and applications. Protecting nesting habitat may not be sufficient to rebuild populations of this highly secretive and threatened seabird and recovery might also require the restoration of marine habitat quality, as well as a better understanding of how ocean climate affects prey abundance and reproductive rate. Combined with contemporary demographic data, stable isotope analysis of historic samples provides a unique opportunity to reconstruct population histories for species where we lack long‐term information.

Influence of landscape pattern on breeding distribution and success in a threatened Alcid, the marbled murrelet: model transferability and management implications

Summary The marbled murrelet Brachyramphus marmoratus is a threatened Alcid nesting in old‐growth coastal forests from central California to Alaska. Logging has greatly reduced the amount and altered the pattern of the species’ nesting habitat. Landscape fragmentation effects on the breeding ecology of the species are poorly understood because of the inaccessibility of nest sites. Using radio‐telemetry, 157 marbled murrelet nests were located in two old‐growth areas in British Columbia, Canada, with different logging histories. Probable breeding success was estimated from nest attendance patterns by radio‐tagged parents. Information‐theoretic and hypothesis‐testing methods were used to model breeding distribution (used vs. random unknown sites) and success (successful vs. failed nests) within c. 50‐km radius extents at a scale of 2·3‐km radius landscapes. Intersite transferability of distribution models was tested. Breeding distribution was positively related with old‐growth patch proximity, edge density (natural and artificial) and contrast, proportion of landscape under old‐growth or core habitat, and interspersion of old‐growth patches; it was negatively related with coastal zone proximity and mean old‐growth patch size. Breeding success was negatively affected by the edge contrast, coast proximity and proportion of young forest, probably reflecting the distribution of nest predators. All distribution models discriminated well between used and random landscapes within the training area. Intersite model transferability was good for 50% of the models. The models less predictive of the training site (area under the curve 0·676–0·738) were more transferable, probably because at the training site, which had considerably less old‐growth nesting habitat (18% of extent) than the testing site (55%), breeding distribution was driven by a different subset of predictors. Synthesis and applications. Geographic information system (GIS) data were helpful in discriminating between landscapes known to be used by nesting marbled murrelets and those with unknown breeding status. Previous indirect inferences about landscape‐level effects on breeding distribution in the birds were shown to correspond with their true nesting distribution. Our results suggest that habitat fragmentation per se need not have a negative effect on the birds beyond that as a result of habitat loss, unless associated with an increased abundance of predators. Our results fine‐tune the existing habitat conservation guidelines by suggesting that protection of old‐growth forest adjacent to clearcuts is important. We provide a means for desktop classification of marbled murrelet landscapes. We advise the application of several different models, depending on the amount of remaining old‐growth forest, to evaluate the consistency of predictions.

Comparison of Coastal Fringe and Interior Forests as Reserves for Marbled Murrelets on Vancouver Island

Abstract Much of the protected habitat available to the threatened Marbled Murrelet Brachyramphus marmoratus and other old-growth associated species in the Pacific Northwest is in narrow strips along the coast (e.g., parks and scenic fringes). Using data over two years from three watersheds on southwest Vancouver Island, we show that such shoreline strip forests represent suboptimal habitat for murrelets. Murrelet detections, including circling and subcanopy behaviors, were significantly lower at 30 coastal stations (20–250 m from the shoreline edge) than at 30 interior stations (1.5–21.0 km inland). Densities of predators were significantly higher at the coastal stations. The coastal trees were of similar mean height and diameter, but they had lower structural diversity and provided fewer and less suitable (thinner epiphyte cover on large boughs) nesting platforms than trees in the interior. When possible, reserves for Marbled Murrelets should be placed in interior and not shoreline forests.

COMPARISON OF COASTAL FRINGE AND INTERIOR FORESTS AS RESERVES FOR MARBLED MURRELETS ON VANCOUVER ISLAND

Abstract Much of the protected habitat available to the threatened Marbled Murrelet Brachyramphus marmoratus and other old-growth associated species in the Pacific Northwest is in narrow strips along the coast (e.g., parks and scenic fringes). Using data over two years from three watersheds on southwest Vancouver Island, we show that such shoreline strip forests represent suboptimal habitat for murrelets. Murrelet detections, including circling and subcanopy behaviors, were significantly lower at 30 coastal stations (20–250 m from the shoreline edge) than at 30 interior stations (1.5–21.0 km inland). Densities of predators were significantly higher at the coastal stations. The coastal trees were of similar mean height and diameter, but they had lower structural diversity and provided fewer and less suitable (thinner epiphyte cover on large boughs) nesting platforms than trees in the interior. When possible, reserves for Marbled Murrelets should be placed in interior and not shoreline forests.