Geology topics

Andrew C. Doll

Publications and source records attributed to Andrew C. Doll.

5 recordsLinked to original sources

USGS2018

Effects of leg flags on nest survival of four species of Arctic‐breeding shorebirds

Marking wild birds is an integral part of many field studies. However, if marks affect the vital rates or behavior of marked individuals, any conclusions reached by a study might be biased relative to the general population. Leg bands have rarely been found to have negative effects on birds and are frequently used to mark individuals. Leg flags, which are larger, heavier, and might produce more drag than bands, are commonly used on shorebirds and can help improve resighting rates. However, no one to date has assessed the possible effects of leg flags on the demographic performance of shorebirds. At seven sites in Arctic Alaska and western Canada, we marked individuals and monitored nest survival of four species of Arctic‐breeding shorebirds, including Semipalmated Sandpipers ( Calidris pusilla ), Western Sandpipers ( C. mauri ), Red‐necked Phalaropes ( Phalaropus lobatus ), and Red Phalaropes ( P. fulicarius ). We used a daily nest survival model in a Bayesian framework to test for effects of leg flags, relative to birds with only bands, on daily survival rates of 1952 nests. We found no evidence of a difference in nest survival between birds with flags and those with only bands. Our results suggest, therefore, that leg flags have little effect on the nest success of Arctic‐breeding sandpipers and phalaropes. Additional studies are needed, however, to evaluate the possible effects of flags on shorebirds that use other habitats and on survival rates of adults and chicks.

Journal of Field Ornithology↗

USGS2018

Temporal records of diet diversity dynamics in individual adult female Steller sea lion (Eumetopias jubatus) vibrissae

Detailed information on the nutrition of free-ranging mammals contributes to the understanding of life history requirements, yet is often quite limited temporally for most species. Reliable dietary inferences can be made by analyzing the stable carbon (C) and nitrogen (N) isotopic values ( δ 13 C and δ 15 N) of some consumer tissues; exactly which tissue is utilized dictates the inferential scope. Steller sea lion (SSL) vibrissae are grown continuously without shedding and thus provide a continuous multi-year record of dietary consumption. We applied a novel kernel density approach to compare the δ 13 C and δ 15 N values along the length of SSL vibrissae with δ 13 C and δ 15 N distributions of potential prey species. This resulted in time-series of proportion estimates of dietary consumption for individual SSL. Substantial overlap in δ 13 C and δ 15 N distributions for prey species prevented a discrete species-scale assessment of SSL diets; however, a post hoc correlational analysis of diet proportion estimates revealed grouping by trophic level. Our findings suggest that adult female SSL diets in the western and central Aleutian Islands shift significantly according to season: diets contain a higher proportion of lower trophic level species (Pacific Ocean perch, northern rockfish, Atka mackerel and walleye pollock) in the summer, whereas in the winter SSL consume a much more diverse diet which includes a greater proportion of higher trophic level species (arrowtooth flounder, Kamchatka flounder, darkfin sculpin, Pacific cod, Pacific octopus, rock sole, snailfish, and yellow Irish lord).

Oecologia↗

USGS2015

Improved arrival-date estimates of Arctic-breeding Dunlin ( Calidris alpina arcticola )

The use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. The prevailing assumption that laboratory-derived isotopic parameters apply to free-living animals is largely untested. We used stable carbon isotopes (δ 13 C) in whole blood from migratory Dunlin ( Calidris alpina arcticola ) to estimate an in situ turnover rate and individual diet-switch dates. Our in situ results indicated that turnover rates were higher in free-living birds, in comparison to the results of an experimental study on captive Dunlin and estimates derived from a theoretical allometric model. Diet-switch dates from all 3 methods were then used to estimate arrival dates to the Arctic; arrival dates calculated with the in situ turnover rate were later than those with the other turnover-rate estimates, substantially so in some cases. These later arrival dates matched dates when local snow conditions would have allowed Dunlin to settle, and agreed with anticipated arrival dates of Dunlin tracked with light-level geolocators. Our study presents a novel method for accurately estimating arrival dates for individuals of migratory species in which return dates are difficult to document. This may be particularly appropriate for species in which extrinsic tracking devices cannot easily be employed because of cost, body size, or behavioral constraints, and in habitats that do not allow individuals to be detected easily upon first arrival. Thus, this isotopic method offers an exciting alternative approach to better understand how species may be altering their arrival dates in response to changing climatic conditions.

The Auk↗

USGS2015

Stable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets

Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion Eumetopias jubatus in some regions of the North Pacific. Isotopic analysis of vibrissae (whiskers) is a potentially useful approach to resolving the nutritional ecology of this species because long-term (up to 8 yr) dietary information is sequentially recorded and metabolically inert once formed. Additionally, vibrissae are grown in utero , potentially offering indirect inference on maternal diet. However, diet reconstruction using isotopic techniques requires a priori knowledge of trophic enrichment factors (TEFs), which can vary relative to diet quality and among animal species. In this study, we provide new TEF estimates for (1) maternal relative to pup vibrissae during both gestation and nursing and (2) adult vibrissae relative to a complex diet. Further, we refine vibrissa-milk TEFs based on an additional 76 animals with an age distribution ranging from 1 to 20 mo. Mother-pup vibrissae TEF values during gestation and nursing were near zero for δ 13 C and averaged 0.8 and 1.6&permil;, respectively, for δ 15 N. In contrast, vibrissa-fish/invertebrate TEFs averaged 3.3 (± 0.3 SD) and 3.7&permil; (±0.3) for lipid-free δ 13 C and δ 15 N, respectively. Average lipid-free δ 13 C and δ 15 N vibrissa-milk TEFs were 2.5 (±0.9) and 1.8&permil; (±0.8), respectively, and did not differ among metapopulations. Empirically determined TEFs are critical for accurate retrospective diet modeling, particularly for evaluating the hypothesis of nutritional deficiency contributing to the lack of Steller sea lion population recovery in some regions of Alaska.

Marine Ecology Progress Series↗

USGS2015

Stable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus

Multiple factors, including limitation in food resources, have been proposed as possible causes for the lack of recovery of the endangered western segment of the Steller sea lion population in the United States. Because maternal body condition has important consequences on fetal development and neonatal survival, the diets of pregnant females may be particularly important in regulating population sizes. We used the stable carbon and nitrogen isotope values of vibrissae from Steller sea lion pups as an indirect indicator of maternal diets during gestation. Combining these data with isotope data from potential prey species in a Bayesian mixing model, we generated proportional estimates of dietary consumption for key prey. Our analysis indicated that females in the most westerly metapopulations relied heavily on Atka mackerel and squid, whereas females inhabiting the Gulf of Alaska region had a fairly mixed diet, and the metapopulation of Southeast Alaska showed a strong reliance on forage fish. These results are similar to previous data from scat collections; however, they indicate a possible under-representation of soft-bodied prey (squid) or prey with fragile skeletons (forage fish) from analyses of data from scats. This study supports the utility of stable isotope modeling in predicting diet composition in gestating adult female Steller sea lions during winter, using pup vibrissae.

Alaska↗