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

Abstract

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 examine 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 significantly (-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 reproductive success and population growth rate in this threatened species.KEY WORDS: Marbled murrelet · Stable isotopes · Age ratios · Diet reconstruction · Museum specimens · Brachyramphus marmoratus · Salish Sea Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Forensic methods in conservation research' OPEN PEN ACCESS CCESS

Low breeding propensity and wide‐ranging movements by marbled murrelets in Washington

“…Poor marine conditions may also enable adults to survive but with insufficient energy reserves to attempt or succeed at breeding, as was found by Peery et al () in some years in central California. For the region encompassing our study area in Washington, such conclusions are supported by stable isotope analyses by Norris et al () and Gutowsky et al (), which show murrelet diet and productivity have declined in the last 100 years throughout the Salish Sea.…”

“…Losses in nesting habitat over the last century may have contributed to or caused low breeding propensity. Although long‐term survival data are lacking, murrelets are considered long‐lived birds (Peery et al , Gutowsky et al ). Therefore, individuals hatched many years ago may have lost nesting habitat for breeding, but are still persisting in the population.…”

Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore

“…Like bone, both feather and fur keratins retain the isotopic signatures from the time of growth and remain chemically inert in museum collections, however they have the advantage of being easily sampled from living specimens as well (Mizutani et al, 1990;Hobson, 1999). Indeed, timeseries of feathers including samples from both living birds and museum collections have been used to link population declines in an endangered alcid, Marbled Murrelet (Brachyramphus marmoratus) to reductions in the relative quantity of high trophic-level fish in their diet over the twentieth century (Becker and Beissinger, 2006;Norris et al, 2007;Gutowsky et al, 2009).…”

Site-specific reproductive failure and decline of a population of the Endangered yellow-eyed penguin: a case for foraging habitat quality

“…In other marine bird species, degradation of foraging habitat appears to have caused substantial recorded long-term population declines through chronic poor reproductive success tied to low-quality diet for nestlings (Gutowsky et al 2009). Northern Stewart Island penguins forage in Foveaux Strait, which differs from other Stewart Island coastal waters both physically and in terms of human activity.…”