Long-term surveys at stopover sites provide measures of abundance (counts) that are commonly used to assess the status of shorebird populations. We analyzed a 29-year time series of counts of Western Sandpiper (Calidris mauri) and Least Sandpiper (C. minutilla) conducted during southward migration from 1990 to 2018 at a small stopover site on Sidney Island, British Columbia, Canada, and examined correlations between counts and conditions local to the site, on the breeding grounds, and large-scale climatic indices. Annual counts varied from 0 to similar to 4,000 birds, and did not show strong long-term trends over the study period. Counts were most strongly associated with conditions on breeding grounds or large-scale climatic indices, rather than local weather variables, suggesting counts of juvenile shorebirds could serve as an index of reproductive success. Further, counts of juveniles and adults were positively correlated in the same year for both Western and Least sandpipers, indicating a common underlying process determining the abundances of the two age classes at this site. Across the 29-year study period, Sidney Island has remained a consistently used and locally important stopover site for both adults and juveniles of both shorebird species.

The Rhinoceros Auklet Cerorhinca monocerata is an abundant and widely distributed North Pacific seabird. We describe noteworthy longevity records derived from banding operations (1984-1985 and 2008-2018) on several large breeding colonies in British Columbia, Canada. Of note was an individual banded as a nestling on the Lucy Islands in 1985 and recaptured as a breeding adult in 2016, 31 years later. Several other individuals banded in the mid 1980s survived into at least their late 20s. These longevity records for the Rhinoceros Auklet are close to the value predicted by the linear relationship between longevity and log body mass for the 15 species of Alcidae for which data are available.

Long-distant migrants timing their arrival on the breeding grounds face a tradeoff between optimal timing for breeding and optimal timing for survival. For many shorebird species, the flyway northward spans thousands of kilometers, and both conditions encountered en route and priorities of individuals can affect the timing of migration. We used data from spring migration surveys of Western Sandpipers (Calidris mauri) and Pacific Dunlins (Calidris alpina pacifica) along the Pacific Flyway of North America to determine whether the timing of their northward migration changed from 1985 to 2016. We compiled survey data for both species from 6 sites of varying size along the northern portion of the flyway from Washington, USA, through British Columbia, Canada, to Alaska, USA, and estimated interannual trends in the timing of passage through each site. Peak passage dates at the sites closest to the species' breeding grounds in Alaska became later by 1-2 days over the study period, while dates of peak passage at sites farther south became similar to 3 days earlier. A post hoc analysis suggested that local temperatures affected peak passage dates at most sites, with warmer temperatures related to earlier passage. Discerning patterns of movement by Dunlins at southern sites was complicated by the presence of winter residents. Simulation analyses of sandpiper movement through a stopover site highlighted both length of stay and timing of arrival as important factors shaping peak passage estimates. We suggest that Western Sandpipers appear to be arriving earlier at southern sites and staying longer at larger stopover sites, such as Alaska's Copper River delta. Our methodology generated specific predictions of peak passage dates on northward migration that may be useful in other systems for which historical count data are available.

We modelled how nestling growth rates of Cassin’s Auklet (Ptychoramphus aleuticus (Pallas, 1811)) varied with timing of peak copepod prey availability at two breeding colonies in British Columbia: on Triangle Island, in the California Current Ecosystem, and Frederick Island, in the Gulf of Alaska Ecosystem. We used time series of nestling growth rates and estimated the seasonal timing of peak biomass of the copepod Neocalanus cristatus (Krøyer, 1848) using a temperature-dependent phenology equation. We developed a single model to examine intercolony differences in the effect of the timing of regional peak prey biomass on seabird nestling growth rates. This model indicated nestling growth rates on Triangle Island varied widely and were positively associated with timing of peak zooplankton biomass, such that higher growth rates were observed when the peak biomass occurred later in the breeding season. In contrast, nestling growth rates were consistently high at Frederick Island, where peak copepod biomass always occurred relatively late. If ocean climate warming results in a poleward shift of Neocalanus abundance and induces earlier and more narrow timing of availability, then episodes of poor nestling growth will increase in frequency on Triangle Island and could eventually affect auklets on more northerly colonies.

We present a species distribution model (SDM) for prediction of Black Oystercatcher (Haematopus bachmani) breeding pair occurrence in Haida Gwaii, British Columbia. Boosted regression trees, a machine learning algorithm, was used to fit the model. In total, 14 predictors were selected a priori through development of a conceptual model. Breeding pair occurrence data were compiled from two available surveys conducted in 2005 and 2010 (545 km of shoreline surveyed in total). All data were aggregated to common model units (vector polyline shoreline segments approximately 100 m in length), which approximate breeding territory size. The final model, which included eight predictors (distance to treeline, island area, wave exposure, shoreline type, intertidal area within 50 m, segment length, rat occurrence, and intertidal area within 1000 m), had excellent predictive ability assessed by 10- fold cross- validation (AUC = 0.89). Predictive ability was reduced when the model was trained and tested on spatially (AUC = 0.86) and temporally (AUC = 0.83) independent data. Distance to treeline and island area had greatest influence on the model (RI = 41.5% and RI = 36.7%, respectively); we hypothesized that these predictors are related to avoidance of predators. Partial dependence plots revealed that breeding pairs tended to occur: further from the treeline, on small islands, at high wave exposures, at moderate intertidal area, on bedrock or gravel shoreline types, and on islands without rats. However, breeding pairs tended not to occur on very small islands and at very high wave exposures, which we hypothesize to reflect avoidance of nest washout. Results may inform local conservation and management efforts, i.e., from predictive maps, and eventual development of a high- resolution (similar to 100 m) model for prediction of Black Oystercatcher breeding pairs at a regional scale. Further, methods and GIS data sets developed may be used to model distribution of other coastal species in the region.

RODWAY, M.S., WILSON, L.K., LEMON, M.J.F. & MILLIKIN, R.L. 2017. The ups and downs of ecosystem engineering by burrownesting seabirds on Triangle Island, British Columbia. Marine Ornithology 45: 47–55. Some plant communities develop as a result of chemical and physical perturbations by burrowing seabirds and are affected when those activities are reduced. Declines in burrow density and population size of Cassin’s Auklets Ptychoramphus aleuticus at their largest breeding colony on Triangle Island, British Columbia, from 1989 to 2009, have been associated with decreases in tufted hairgrass Deschampsia cespitosa and increases in salmonberry Rubus spectabilis cover. These habitat changes may inhibit population recovery because Cassin’s Auklets prefer tufted hairgrass and tend to avoid tall salmonberry for nesting. Surveys conducted in 2014 suggested a reversal in the population trend and provided an opportunity to compare vegetation changes during periods of increasing and decreasing burrow density. We hypothesized that decreased burrowing by seabirds allows salmonberry to invade and outcompete grass as the dominant cover and that increased burrowing reverses those trends. We related changes in vegetation composition to trends in burrow numbers within permanent plots established to monitor Cassin’s and Rhinoceros Cerorhinca monocerata auklets on Triangle Island over a 25-year period. Trends in salmonberry cover and burrow numbers were negatively related. Decreases in salmonberry cover were directly correlated to increases in burrow numbers within plots, but, as found previously, increases in salmonberry cover were not directly correlated with decreasing numbers of burrows. There was no corresponding increase in grass cover with increasing burrow numbers. Vegetation damage and reduction due to seabird activities is probably more immediately apparent than establishment, spread or recovery of vegetation following seabird impacts. Our results confirm that biopedturbation by burrow-nesting seabirds negatively affects and reduces percent cover of woody shrubs, but only when burrow densities are increasing or high. At lower or declining burrow densities, seabird activities are inadequate to halt what may be the natural succession to mainly salmonberry cover on this non-forested island.

The Tofino Wah-nah-jus Hilth-hoo-is Mudflats on Vancouver Island, British Columbia, Canada, include both pristine areas and sites with residential and resort development. Shorebird counts were conducted at six sites around these mudflats in 2011 and compared with historical counts from 1988, 1989, and 1995. Temporal trends of counts did not vary among sites with different levels of disturbance. Over the entire mudflats, counts of Dunlin (Calidris alpina) moving northward had a negative trend over time (beta(yr) = -0.04), as did counts of Western Sandpiper (Calidris mauri; (beta(yr) = -0.04), Least Sandpiper (Calidris minutilla; beta(yr) = -0.03) and Short-billed Dowitcher (Limnodromus griseus; beta(yr)= -0.04) moving southward. In contrast, counts of Black-bellied Plover (Pluvialis squatarola; ( beta(yr) = 0.03) and Semipalmated Plover (Charadrius semipalmatus, (beta(yr) = 0.02) moving northward increased over time. Counts of Dunlin and Short-billed Dowitcher were lower at disturbed sites relative to non-disturbed sites, indicating that disturbance may be displacing birds away from some sites. Further, counts of northward migrating shorebirds were negatively correlated with the presence of people and dogs at the most disturbed site (Chesterman Beach). Monitoring and precautionary actions to address effects of disturbance at this important stopover site are warranted.

The Fraser River Delta in British Columbia, Canada, is a globally significant stopover site for shorebirds, but the population status and trends of many species that use the site remain uncertain. We describe an ongoing program to monitor population trends of the two most abundant species, Western Sandpipers (Calidris mauri) and Dunlins (Calidris alpina), during northward migration. Counts of these species were conducted at a mudflat where large flocks assembled at mid-tide from 15 April to 15 May, 1991-2013, and we estimated species-specific counts as the product of daily total flock counts and species proportions obtained during supplementary sampling. The median peak count of both species combined was 177,000 birds, and occurred between 24 April and 3 May. Ratios (proportions) of the two species followed a predictable pattern during the migration period, with a low proportion of Western Sandpipers (3%-20%) in flocks before 20 April, followed by a rapid increase to 80%-100% between 25 April and 10 May and a variable decrease to 30%-80% by 15 May. Mean counts of Western Sandpipers showed no significant trend over the study period. Mean counts of Dunlins showed a non-linear trend, decreasing until 2001 and then increasing to 2013. Bias and random error in field counts were quantified by comparing field counts to counts made from photographs taken during surveys, and analysis revealed that field counts had a downward, but predictable, bias, accounting for >90% of birds present, with a stochastic error rate of 28.0%. Uncertainty in total population estimates was high after accounting for the effect of length of stay and sampling error. Population estimates suggested that 600,000 Western Sandpipers and 200,000 Dunlins typically passed through the site during northward migration. Our estimates indicate the usefulness of daily counts at major stopover sites during northward migration as an effective tool for monitoring shorebird populations, and underscore the need for conserving such sites.

Estimating breeding populations at colony, regional and global scales, and detecting trends in those populations over time, are prerequisites to informed management and conservation of seabird species. Accurate population estimates are often laborious and expensive to obtain. This is especially so for burrow-nesting species, which are inconspicuous and often nocturnal on their breeding grounds and for which populations cannot be counted directly but must be estimated from derived parameters (Nettleship 1976, Evans 1980). Repeated counts of nests or birds within permanently established monitoring plots have been used as an expedient alternative to full-scale population surveys to provide indicators of population trends (Walsh et al. 1995, AnkerNilssen et al. 1996, Byrd & Dragoo 1997, Barrett 2001). Such counts rarely provide estimates of population size because plots are usually distributed subjectively and are not representative of entire colonies, but trends in the counts are thought to reflect trends in population size. Here we describe the use of permanent monitoring plots in British Columbia (BC), test the assumption that trends in plot counts mirror trends in overall population size, and discuss some of the problems we have encountered in repeating and interpreting counts.

We asked whether the lack of a population response by ancient murrelets (Synthliboramphus antiquus) to eradication of rats (Rattus spp.) at Langara Island could be due to a change in vegetative cover. We quantified ancient murrelet habitat associations on 12 islands and assessed changes in vegetation at Langara Island between 1981 and 2007. We found that ancient murrelets exhibit a high degree of flexibility in their use of available breeding habitats, and we noted no changes over time. Thus, recovery of ancient murrelets at Langara Island is unlikely to be limited by habitat quality. We propose artificial social attraction as a method to speed recovery. 2011 The Wildlife Society.

SummaryThe Scott Islands, British Columbia, Canada, support the largest aggregation of breeding seabirds in the eastern Pacific Ocean south of Alaska. However, large seabird populations were eradicated by American MinkNeovison visonand RaccoonsProcyon lotorintroduced to Lanz and Cox islands in the 1930s, while the ecological consequences of the introduction of European RabbitsOryctolagus cuniculusto Triangle Island in the 1920s are unknown. We have seen dramatic changes in the vegetation on Triangle Island in recent decades, chiefly a decrease in Tufted HairgrassDeschampsia cespitosacover and a concomitant increase in SalmonberryRubus spectabiliscover. We carried out vegetation surveys at Triangle Island (1989 and 2004) and its nearest neighbour, rabbit-free Sartine Island (1987 and 2006), to test the hypothesis that rabbits have caused these changes. We found, however, that similar changes have occurred at Sartine Island as at Triangle Island over the same time period. Because these two islands support the bulk of the world's breeding population of Cassin's AukletPtychoramphus aleuticus, a small seabird that selects grass-covered habitat but avoids tall Salmonberry for nesting, the vegetation changes raise serious concerns for a species that has experienced dramatic population declines in recent years. Restoration of seabird nesting habitat by removing American Mink and Raccoons from Lanz and Cox islands will be vital for long-term seabird conservation in the Scott Islands.

Systematic monitoring of seabird populations in Canada has been ongoing since the 1920s and the monitoring of diets and other biological indicators of ecosystem change started in the 1970s. Long-term monitoring of population parameters began in the 1980s. These studies originally were conducted mainly by the Canadian Wildlife Service, but subsequently have involved several universities and nongovernment organization groups. We review the results of this monitoring from the 1970s onwards for six oceanographic regions to assess population trends among Canadian seabirds and correlated trends in diets, phenology, and other breeding biology variables. Within regions, trends in most variables studied have been broadly congruent, but there was often variation among regions. In particular, seabird populations in the Pacific coast zone affected by the California Current upwelling system have shown generally negative trends since the 1980s, whereas trends for populations of the same species to the north of this zone have been mainly positive. Likewise, on the east coast, trends at Arctic colonies have been decoupled from those at colonies around Newfoundland and in the Gulf of St. Lawrence, especially since the major cold water event of the early 1990s. Several long-term studies have shown an association between population events and diet and phenology changes. Diet and indicators of condition (chick growth, reproductive success) sometimes responded very rapidly to oceanic changes, making them excellent signals of ecosystem perturbations. The review highlights the effects of decadal-scale regime shifts on Canadian seabirds, confirms the value of long-term studies and supports the applicability of single-site observations to regional populations.

Introduced predators pose grave threats to colonial seabirds, and their removal can be an effective seabird conservation action (Burger & Gochfeld 1994, Boersma et al. 2002, Jouventin et al. 2003). Langara Island, in the Haida Gwaii archipelago, British Columbia, formerly supported an estimated 200 000 breeding pairs of Ancient Murrelets Synthliboramphus antiquus, and large populations of Fork-tailed Oceanodroma furcata and Leach’s O. leucorhoa StormPetrels, Cassin’s Auklet Ptychoramphus aleuticus, Rhinoceros Auklet Cerorhinca monocerata and Tufted Puffin Fratercula cirrhata (Rodway 1991, Gaston 1992). Seabird population declines were observed following the introduction of rats to the island. Black Rats Rattus rattus were introduced to the Queen Charlotte Islands early in the 20th century. They were first identified on Langara Island in 1946 and were replaced more recently by Norway Rats R. norvegicus, first identified in 1981 (Bertram & Nagorsen 1995). By 1988, five burrow-nesting seabird species had been extirpated from Langara Island, apparently as a result of rat infestation, and only 24 000 pairs of Ancient Murrelets remained (Rodway 1991, Bertram 1995, Bertram & Nagorsen 1995). This remnant population was further reduced to fewer than 20 000 pairs by 1993 (Harfenist 1994). Following success in eradicating rats from islands in New Zealand (Towns & Broome 2003), Langara Island was targeted for rat eradication. Langara Island was a good candidate because of its historical importance as a seabird colony, because a remnant colony of Ancient Murrelets and nearby colonies of other species could facilitate recovery, and because the breeding habitat is ideal (Kaiser et al. 1997). Rat eradication took place in 1995 and was considered complete in January 1996 (Kaiser et al. 1997, Taylor et al. 2000). In 2004, nine years after the eradication of rats, we surveyed burrow-nesting seabirds on Langara Island to assess the current status and prognosis of this historically important Ancient Murrelet colony and to assess whether other seabird species had recolonized the island. Specifically, we compared colony characteristics (colony area, burrow density, number of burrows, burrow occupancy, breeding population) before (1981, 1988, 1993) and after (1999, 2004) rat eradication (1995). We also compiled population trend data on nearby colonies to control for potential regional population fluctuations that might provide alternative explanations for changes observed on Langara Island.

Western sandpipers Calidris mauri on southward migration fly over the Gulf of Alaska to the Strait of Georgia, British Columbia, where they stop for a few days to replenish reserves before continuing. In the Strait, individuals captured on the extensive tidal mudflats of the Fraser estuary (∼25000 ha) are significantly heavier (2.71 g, or >10% of lean body mass) than those captured on the small (<100 ha) mudflat of nearby Sidney Island. Previous work has shown that the difference cannot be attributed to seasonal timing, size, age or gender effects, and here we compare predictions made by six hypotheses about a diverse set of data to explain why, partway through a migratory journey of ∼10000 km, birds have such different body masses at two stopover sites within 40 km of each other. The ‘trade‐off’ hypothesis – that the large Fraser estuary offers safety from predators, but a lower fattening rate, while the small Sidney Island site is more dangerous, but offers a higher fattening rate – made six successful predictions, all of which were upheld by the data. All other hypotheses failed at least one prediction. We infer that calidrid sandpipers arriving in the Strait of Georgia with little fat remaining (and therefore low body mass) choose to take advantage of the high feeding rate at small sites like Sidney Island because they are less vulnerable to avian predators than are individuals with higher fat reserves, who instead elect to feed at large open sites like the Fraser estuary mudflats.

We surveyed marbled murrelets (Brachyramphus marmoratus) at Long Inlet and Shields Bay in the Queen Charlotte Islands, British Columbia, from May through July during the 1990 breeding season. Abundance varied daily and through the season. Maximum counts at sea were recorded prior to the egg-laying period in early May, and numbers were lowest in mid-June, during incubation, at both Long Inlet and Shields Bay. Mean numbers peaked in July during the latter part of the nestling period at Long Inlet but remained low at Shields Bay. The distribution of birds in Long Inlet changed over the season with a greater proportion of birds gathering at the head of the inlet as the season progressed. More birds were observed on morn- ing surveys, 2-5 hr after sunrise, than on afternoon and evening surveys in Long Inlet. In Shields Bay, birds were more abundant in the evening. Numbers of detections in the forest peaked in late July at both sites and were positively correlated with abundance of murrelets in Long Inlet but not in Shields Bay. Contrasting patterns of abundance in Long Inlet and Shields Bay pose complications for survey design, and indicate that at-sea distribution does not dependably re- flect breeding distribution.

The nest distribution and habitats of Ancient Murrelets (Synthlibo- ramphus antiguus) and Cassin's Auklets (Ptychoramphus aleuticus) were compared in the Queen Charlotte Islands. Ancient Murrelets (about 254,000 breeding pairs) and Cas- sin's Auklets (about 236,000 pairs) nested on forested (often the same) islands. Cassin's Auklets nested in burrows in grass or moss-covered ground along island peripheries. Ancient Murrelets nested in moss habitat farther inland or along the periphery when Cassin's Auklets nested diffusely or were absent. We suggest that nesting differences are related to different chick-rearing strategies. The Queen Charlotte Island breeding population of Ancient Murrelets comprises one-half, and that of Cassin's Auklets one-quarter, of the overall population of the two species in the northeastern Pacific. The importance of the Queen Charlotte Islands to those alcids apparently relates to their preference for open nesting habitat beneath mature forest on offshore islands. A combination of a cool, moist climate and over- browsing of tree seedlings and shrubs by coastal Black-tailed Deer (Odocoileus hemionus sitkensis) is conducive to the maintenance of the open forest habitat preferred by