Browsing by Author "del Rio, Carlos Martinez"

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    Dietary and isotopic specialization: the isotopic niche of three Cinclodes ovenbirds
    (2009) del Rio, Carlos Martinez; Sabat, Pablo; Anderson-Sprecher, Richard; Gonzalez, Sandra P.
    By comparing the isotopic composition of tissues deposited at different times, we can identify individuals that shift diets over time and individuals with constant diets. We define an individual as an isotopic specialist if tissues deposited at different times have similar isotopic composition. If tissues deposited at different times differ in isotopic composition we define an individual as an isotopic generalist. Individuals can be dietary generalists but isotopic specialists if they feed on the same resource mixture at all times. We assessed the degree of isotopic and dietary specialization in three related Chilean bird species that occupy coastal and/or freshwater environments: Cinclodes oustaleti, Cinclodes patagonicus, and Cinclodes nigrofumosus. C. oustaleti individuals were both isotopic and dietary generalists. Tissues deposited in winter (liver and muscle) had distinct stable C (delta C-13) and stable N isotope ratio (delta N-15) values from tissues deposited in the summer (wing feathers) suggesting that birds changed the resources that they used seasonally from freshwater habitats in the summer to coastal habitats in the winter. Although the magnitude of seasonal isotopic change was high, the direction of isotopic change varied little among individuals. C. patagonicus included both isotopic specialists and generalists, as well as dietary specialists and generalists. The isotopic composition of the feathers and liver of some C. patagonicus individuals was similar, whereas that of others differed. In C. patagonicus, there were large inter-individual differences in the magnitude and the direction of seasonal isotopic change. All individuals of C. nigrofumosus were both isotopic and dietary specialists. The distribution of delta C-13 and delta N-15 values overlapped broadly among tissues and clustered in a small, and distinctly intertidal, region of delta space. Assessing individual specialization and unraveling the factors that influence it, have been key questions in animal ecology for decades. Stable isotope analyses of several tissues in appropriate study systems provide an unparalleled opportunity to answer them.
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    Multi-tissue δ2H analysis reveals altitudinal migration and tissue-specific discrimination patterns in Cinclodes
    (2015) Newsome, Seth D.; Sabat, Pablo; Wolf, Nathan; Rader, Jonathan A.; del Rio, Carlos Martinez
    One of the fastest growing uses of stable isotope analysis in ecology is using hydrogen isotope (delta H-2) values to characterize animal movement and migration strategies. Most studies measure delta H-2 values in metabolically inert tissues such as feathers, which are typically grown during or just after the summer breeding season and provide a limited snapshot of an individual's annual life history. In contrast, isotopic analysis of metabolically active tissues can provide ecological information integrated over weeks to months prior to sampling. Here we characterize delta H-2 patterns among multiple metabolically inert and active tissues in Cinclodes, a genus of South American songbirds noted for variation in altitudinal movement and foraging strategies. We also coupled delta H-2 with carbon (delta C-13) and nitrogen (delta N-15) isotope data to combine information on movement with marine versus terrestrial resource use at the individual level. We find that a combination of physiological and ecological factors control delta H-2 patterns among tissues, which mirrors results of feeding experiments on captive birds. For example, in the coastal resident C. nigrofumosus, metabolically active muscle collected during the winter has higher delta H-2 values than feathers grown the previous summer, a tissue-specific discrimination pattern previously observed in captive birds. This pattern is reversed to various degrees for altitudinal migrants such as C. fuscus and C. oustaleti that spend winters foraging in marine intertidal habitats but migrate to high elevation and forage in stream habitats during the summer. We also find that among altitudinal migrants, individuals that forage sympatrically in intertidal habitats during the winter appeared to summer at a wide range of elevations, as evidenced by large differences of >50 parts per thousand in delta H-2(muscle-feather) offsets. Lastly, a positive correlation between feather delta H-2 and delta N-15 values in Cinclodes that consume a mixed marine-freshwater diet confirms that delta H-2 is a useful proxy for quantifying marine resource use. We anticipate that comparison of delta H-2 values in metabolically active and inert tissues may allow for the reconstruction of animal movement and foraging strategies within the annual life cycle; however, more work is required to better understand the physiological mechanisms responsible for the observed delta H-2 patterns among tissues.
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    Osmoregulatory capacity and the ability to use marine food sources in two coastal songbirds (Cinclodes
    (2006) Sabat, Pablo; Maldonado, Karin; Farina, Jose Miguel; del Rio, Carlos Martinez
    Cinclodes nigrofumosus and C. oustaleti are two closely related songbirds that inhabit the northern Chilean coast during the austral fall and winter. This stretch spans a dramatic north to south latitudinal gradient in rainfall and temperature. Whereas C. nigrofumosus lives exclusively on coastal environments, C. oustaleti shifts seasonally from coastal environments to inland freshwater ones. We used the delta C-13 of these two species' tissues to investigate whether the reliance on marine versus terrestrial sources varied from the hyperarid north to the wet south. We also investigated latitudinal variation in the renal traits that mediate how these birds cope with dehydration and a salty marine diet. Both species increased the incorporation of terrestrial carbon, as measured by 613 C, as terrestrial productivity increased southwards. However, C. nigrofumosus had consistently more positive (i.e. more marine) and less variable delta C-13 values than C. oustaleti. The osmoregulatory traits of both species varied with latitude as well. Urine osmolality decreased from extremely high values in the north to moderate values in the south, while C. nigrofumosus produced more concentrated urine than C. oustaleti. In both species, the proportion of kidney devoted to medullary tissue decreased from north to south, and kidney size increased significantly with latitude. Cinclodes nigrofumosus had larger kidneys with larger proportions of medullary tissue than C. oustaleti. C. nigrofumosus and C. oustaleti are terrestrial organisms subsidized by a rich marine environment where it is adjacent to an unproductive terrestrial. Variation in the reliance on marine food sources seems to be accompanied by adjustments in the osmoregulatory mechanisms used by these birds to cope with salt and dehydration.