Egg production in a coastal seabird, the glaucous-winged gull (Larus glaucescens), declines during the last century.
TL;DR: It is demonstrated that glaucous-winged gull investment in egg production has declined significantly over the past ∼50–100 y, with such changes potentially contributing to recent population declines and the incremental long-term impoverishment of a coastal marine ecosystem bordering one of North America's rapidly growing urban areas.
Abstract: Seabirds integrate information about oceanic ecosystems across time and space, and are considered sensitive indicators of marine conditions. To assess whether hypothesized long-term foodweb changes such as forage fish declines may be reflected in a consumer's life history traits over time, I used meta-regression to evaluate multi-decadal changes in aspects of egg production in the glaucous-winged gull (Larus glaucescens), a common coastal bird. Study data were derived from literature searches of published papers and unpublished historical accounts, museum egg collections, and modern field studies, with inclusion criteria based on data quality and geographic area of the original study. Combined historical and modern data showed that gull egg size declined at an average of 0.04 cc y−1 from 1902 (108 y), equivalent to a decline of 5% of mean egg volume, while clutch size decreased over 48 y from a mean of 2.82 eggs per clutch in 1962 to 2.25 in 2009. There was a negative relationship between lay date and mean clutch size in a given year, with smaller clutches occurring in years where egg laying commenced later. Lay date itself advanced over time, with commencement of laying presently (2008–2010) 7 d later than in previous studies (1959–1986). This study demonstrates that glaucous-winged gull investment in egg production has declined significantly over the past ∼50–100 y, with such changes potentially contributing to recent population declines. Though gulls are generalist feeders that should readily be able to buffer themselves against food web changes, they are likely nutritionally constrained during the early breeding period, when egg production requirements are ideally met by consumption of high-quality prey such as forage fish. This study's results suggest a possible decline in the availability of such prey, and the incremental long-term impoverishment of a coastal marine ecosystem bordering one of North America's rapidly growing urban areas.
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01 Jan 2014
TL;DR: The authors used stable isotope (δ(13)C, δ(15)N) analysis of feathers from glaucouswinged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long-term trends in gull abundance.
Abstract: The world's oceans have undergone significant ecological changes following European colonial expansion and associated industrialization. Seabirds are useful indicators of marine food web structure and can be used to track multidecadal environmental change, potentially reflecting long-term human impacts. We used stable isotope (δ(13)C, δ(15)N) analysis of feathers from glaucous-winged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long-term trends in gull abundance. Sampled feathers came from birds collected between 1860 and 2009 at nesting colonies in the Salish Sea, a transboundary marine system adjacent to Washington, USA and British Columbia, Canada. To determine whether temporal trends in stable isotope ratios might simply reflect changes to baseline environmental values, we also analysed muscle tissue from forage fishes collected in the same region over a multidecadal timeframe. Values of δ(13)C and δ(15)N declined since 1860 in both subadult and adult gulls (δ(13)C, ~ 2-6‰; δ(15)N, ~4-5‰), indicating that their diet has become less marine over time, and that birds now feed at a lower trophic level than previously. Conversely, forage fish δ(13)C and δ(15)N values showed no trends, supporting our conclusion that gull feather values were indicative of declines in marine food availability rather than of baseline environmental change. Gradual declines in feather isotope values are consistent with trends predicted had gulls consumed less fish over time, but were equivocal with respect to whether gulls had switched to a more garbage-based diet, or one comprising marine invertebrates. Nevertheless, our results suggest a long-term decrease in diet quality linked to declining fish abundance or other anthropogenic influences, and may help to explain regional population declines in this species and other piscivores.
57 citations
TL;DR: Stable isotope analysis of feathers from glaucous-winged gulls in a heavily disturbed region of the northeast Pacific suggests a long-term decrease in diet quality linked to declining fish abundance or other anthropogenic influences, and may help to explain regional population declines in this species and other piscivores.
Abstract: The world's oceans have undergone significant ecological changes following European colonial expansion and associated industrialization. Seabirds are useful indicators of marine food web structure and can be used to track multidecadal environmental change, potentially reflecting long-term human impacts. We used stable isotope (δ(13)C, δ(15)N) analysis of feathers from glaucous-winged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long-term trends in gull abundance. Sampled feathers came from birds collected between 1860 and 2009 at nesting colonies in the Salish Sea, a transboundary marine system adjacent to Washington, USA and British Columbia, Canada. To determine whether temporal trends in stable isotope ratios might simply reflect changes to baseline environmental values, we also analysed muscle tissue from forage fishes collected in the same region over a multidecadal timeframe. Values of δ(13)C and δ(15)N declined since 1860 in both subadult and adult gulls (δ(13)C, ~ 2-6‰; δ(15)N, ~4-5‰), indicating that their diet has become less marine over time, and that birds now feed at a lower trophic level than previously. Conversely, forage fish δ(13)C and δ(15)N values showed no trends, supporting our conclusion that gull feather values were indicative of declines in marine food availability rather than of baseline environmental change. Gradual declines in feather isotope values are consistent with trends predicted had gulls consumed less fish over time, but were equivocal with respect to whether gulls had switched to a more garbage-based diet, or one comprising marine invertebrates. Nevertheless, our results suggest a long-term decrease in diet quality linked to declining fish abundance or other anthropogenic influences, and may help to explain regional population declines in this species and other piscivores.
56 citations
Cites background or methods from "Egg production in a coastal seabird..."
...2–4 weeks before the lay date of first eggs (mid- to late May; Verbeek, 1986; Blight, 2011)....
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...Glaucous-winged gulls in the region also exhibit a long-term decline in clutch and egg size consistent with a hypothesis of declining food quality (Blight, 2011)....
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...…diet of breeding adults, we used a section (~1 9 2 cm) cut from the tip of the innermost primary feathers as the first of these (P1) are generally moulted from mid-April to early May (Verbeek, 1979), ca. 2–4 weeks before the lay date of first eggs (mid- to late May; Verbeek, 1986; Blight, 2011)....
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...Glaucous-winged gulls in the region also exhibit a long-term decline in clutch and egg size con- sistent with a hypothesis of declining food quality (Blight, 2011)....
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...Indeed, Blight (2011) showed that glaucous-winged gulls in the Salish Sea have experienced a long-term decline in egg volume and clutch size, consistent with the hypothesis that die- tary declines in high-quality fish and an increase in ter- restrial sources of food reduces fecundity in this…...
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TL;DR: Food-stressing surface feeders such as gulls, diminishing energy intake and lengthening foraging bouts, and increasing levels of cannibalism could lead to declining populations in the absence of compensatory adaptive modifications or range shifts are tested.
Abstract: Cannibalism occurs regularly across a broad range of taxa with a variety of ecological and evolutionary consequences. Rises in sea surface temperature (SST) have been linked to increased cannibalism in some species, including polar bears (Ursus maritimus), Peruvian anchovy (Engraulis ringens), and Peruvian hake (Merluccius gayi peruanus), and might be expected in birds that depend on marine food webs for sustenance. Increased SSTs are associated with lowered ocean thermoclines and weakened upwellings. These changes, in turn, lead to decreased productivity in surface water and movement of surviving forage fish to deeper water, thereby food-stressing surface feeders such as gulls, diminishing energy intake and lengthening foraging bouts. While controlling for a suite of other environmental factors, we tested whether egg cannibalism and hatching success were independent of rises in local SST at a colony of Glaucous-winged Gulls (Larus glaucescens) and Glaucous-winged × Western Gull (L. glaucescens ×...
39 citations
TL;DR: It is suggested that egg levels as low as 10 ng/g BDE‐99 may affect reproduction in small passerines by reducing clutch size and no evidence of effects over the longer term and in successive generations is found.
Abstract: Based on a literature review of avian data for polybrominated diphenyl ethers (PBDEs), ecologically relevant doses, low (10 ng/egg), medium (100 ng/egg), and high (1,000 ng/egg) of the 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99) congener along with dimethylsulfoxide (DMSO) control were injected into the yolk sac of un-incubated eggs of zebra finch, Taeniopygia guttata. Offspring development and adult phenotype were followed over three generations. No effects of in ovo PBDE exposure on hatching success, chick growth, thyroid hormone levels, or hematological traits were measured at sexual maturity (90 d posthatching). However, the authors did detect significant effects of BDE-99 treatment on adult phenotype of in ovo–exposed birds by breeding observations, in which clutch size was significantly smaller in all PBDE-dosed birds (low, medium, and high) compared with controls. A trend was also seen for longer laying intervals in PBDE-dosed birds (13–14 d) compared with control birds (8 d). In addition, a significant effect of PBDE was found on growth of the second-generation offspring of in ovo–treated females; body mass was significantly lower in the high-PBDE dosed birds compared with controls from hatch through to fledging (day 30). The authors found no evidence of effects over the longer term and in successive generations, whether in adult, reproductive phenotype of the second-generation offspring of in ovo–treated birds, or in the growth of their (third-generation) offspring. Their results suggest that egg levels as low as 10 ng/g BDE-99 may affect reproduction in small passerines by reducing clutch size. Environ. Toxicol. Chem. 2013;32:562–568. © 2012 SETAC
38 citations
References
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Book•
27 Apr 200910,518 citations
State Street Corporation1, University of California, Santa Barbara2, University of Hawaii at Manoa3, Stanford University4, Arizona State University5, Wildlife Conservation Society6, University of North Carolina at Chapel Hill7, National Oceanic and Atmospheric Administration8, Environmental Defense Fund9, Ocean Conservancy10, The Nature Conservancy11, University of Maine12, University of British Columbia13
TL;DR: This article developed an ecosystem-specific, multiscale spatial model to synthesize 17 global data sets of anthropogenic drivers of ecological change for 20 marine ecosystems and found that no area is unaffected by human influence and that a large fraction (41%) is strongly affected by multiple drivers.
Abstract: The management and conservation of the world's oceans require synthesis of spatial data on the distribution and intensity of human activities and the overlap of their impacts on marine ecosystems. We developed an ecosystem-specific, multiscale spatial model to synthesize 17 global data sets of anthropogenic drivers of ecological change for 20 marine ecosystems. Our analysis indicates that no area is unaffected by human influence and that a large fraction (41%) is strongly affected by multiple drivers. However, large areas of relatively little human impact remain, particularly near the poles. The analytical process and resulting maps provide flexible tools for regional and global efforts to allocate conservation resources; to implement ecosystem-based management; and to inform marine spatial planning, education, and basic research.
5,365 citations
TL;DR: This paper reviews the use ofMeta-Analysis as a data pooling technique in a non-technical manner and illustrates the type of information that can be obtained from a Meta-Analysis, that is not conventionally available from individual trials.
3,787 citations
"Egg production in a coastal seabird..." refers methods in this paper
...I used metaregression, with fit assessed using Q-tests [45,46], to analyse trends in glaucous-winged gull egg and clutch size over time and to examine the relationship between clutch size and first egg date....
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...I used meta-analysis rather than a standard statistical approach because disparate datasets derived from a group of primary studies must be properly weighted to yield correct standard errors and pvalues and meta-analysis has been developed specifically to perform these weightings correctly, increasing the power of significance tests while retaining robustness [45,46]....
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...I used random-effects meta-analytical models as these assume that component studies differ not only by within-study sampling error (as fixed-effects models do), but also by a genuine difference in effect sizes among studies [45,46]....
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TL;DR: Evidence for food limitation in the context of life history theory is reviewed because it provides a fundamental framework from which to interpret.
Abstract: Food limitation is an important issue in ecology because it can influence life history traits, population sizes, and community structure (through effects of competition). Work at the level of populations and communities has led to arguments that food limitation and competition are more important in winter than during the breeding season (e.g. 1, 2, 7, 8, 83, 85, 211, 234). In fact, it is commonly argued that food is superabundant during the breeding season (7, 8, 161, 213, 246, 250, 251, 308-311). However, such arguments are based on indirect rather than direct evidence of the effects of food on reproduction and survival (fitness) (149). Direct evidence for food limitation and competition in winter exists when survival is affected, and some experimental evidence suggests such effects (e.g. 75, 113, 122, 132). However, if current or future reproductive success is limited by food, then food limitation will also exist during the breeding season. Reproductive ecologists historically have argued that food limits reproductive success (e.g. 13, 297). Yet, even this school has included recent arguments against food limitation. For instance, Ettinger & King (77) think that perching time of birds commonly reflects loafing time because birds set their clutch and brood sizes based on years and periods of stringent (low food) conditions. However, perching time may not reflect loafing but rather an important time commitment to reproductive success (T. Martin, unpublished ms.) Thus, the status of food limitation in breeding birds is not clear. Here, I review evidence for food limitation in the context of life history theory because it provides a fundamental framework from which to interpret
1,453 citations
"Egg production in a coastal seabird..." refers background in this paper
...The most important effect of increased egg size in birds overall seems to be improved survival in the days posthatching, allowing young chicks to weather temporary food shortages [5,7,69,70]....
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...These concurrent egg and clutch size declines are noteworthy because although gulls lack an obligate clutch size, a mode of three is a well-known feature of most Larus gulls’ biology, and egg size reduction is a flexible mechanism that allows birds to accommodate limited decreases in energy availability while maintaining offspring number [5]....
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TL;DR: There is a strong tendency for those young which are hatched earliest in the season to have the greatest chance of surviving to breed, and not all species are likely to be prevented, by food shortage, from breeding at the best time for raising young.
Abstract: Summary
Examination of survival rdtes of nestlings and fledglings of some species show that there is a strong tendency for those young which are hatched earliest in the season to have the greatest chance of surviving to breed. Since natural selection so strongly favours parents who leave many surviving young, the question arises as to why other birds breed later than the date at which they could most successfully raise their young.
It is suggested that the food supply for the breeding females immediately prior to the breeding season may limit their ability to form eggs and the females may thus not be able to lay at the time which would result in young being in the nest at the best time for raising them, but as soon after this time as the female is able to produce her eggs. Not all species are likely to be prevented, by food shortage, from breeding at the best time for raising young and the groups of birds most likely to be affected are discussed.
1,364 citations