Mesoscale patterns of altitudinal tenancy in migratory wood warblers inferred from stable carbon isotopes

Abstract

Abstract. We analyzed carbon isotope ratios (d 13 C) of liver and pectoral muscle of Blackthroated Blue Warblers (Dendroica caerulescens) to provide a mesoscale perspective on altitudinal tenancy in the Appalachian Mountains, North Carolina, USA. Movements of males are poorly understood, particularly the degree to which yearlings (first breeding season) and older males (second or later breeding season) wander altitudinally during the breeding season. Liver and muscle d13 C values of warblers exhibited significant year and altitude effects, but yearling and older males were isotopically indistinguishable. Liver d13 C values increased with altitude at the rate of ;0.5ø per 1000 m. The altitudinal lapse rate of muscle d 13 C (;1.1ø per 1000 m) was nearly identical to the average rate of increase reported in several groups of C 3 plants (;1.1ø per 1000 m). This suggests that the majority of males foraged within relatively narrow altitudinal zones during the breeding season. We caution, however, that the discrimination of altitudinal trends in carbon isotope ratios depends on relatively large multiyear samples. Given the scatter in data, it is unlikely that individuals can be accurately assigned to a particular altitude from carbon isotope values. Rapid adjustment of liver and muscle d13 C values to local altitudinal environments is consistent with the results of experimental dietary studies that show carbon turnover rates are relatively rapid in small migratory passerines. In a broader context, carbon isotope data have been increasingly used as proxies for wintering habitat use of Nearctic-Neotropical migratory passerines. However, tissues with high metabolic rates are unlikely to retain much isotopic signal of wintering habitat use by the time migrants reach their breeding territories.

Abiotic, Biotic, and Evolutionary Control of the Distribution of C and N Isotopes in Food Webs

“…Variation of carbon isotope ratios with elevation in birds was similar to that described in Dendroica warblers in the Appalachian Mountains (Graves and Romanek 2009), hummingbirds in the Ecuadorean Andes , and passerines in Taiwan (Chang et al 2011), thus pointing to a general pattern in mountain birds similar to that observed in plants. In the study grasshoppers, d 13 C also increased with elevation but not at the interspecific level, possibly because of the bias introduced by a few species (Calliptamus barbarus, Chorthippus binotatus) that occasionally feed on tree or shrub matter, which greatly differs from herbs in composition (Picaud et al 2002;Benzara et al 2003).…”

Stable hydrogen isotope variability within and among plumage tracts (δ2HF) of a migratory wood warbler

“…The δ 2 H F profile of the black-throated blue warbler ( Setophaga caerulescens ) is among the best studied of North American songbirds [ 1 , 5 , 8 , 42 – 44 ]. This small insectivorous warbler (body mass, 9–10 g) breeds in mixed deciduous-coniferous forests in eastern North America and winters primarily in the Greater Antilles [ 45 – 47 ].…”

“…The influence of altitude on δ 2 H F has not been systematically studied [ 1 , 5 , 8 ]. In the southern Appalachian Mountains, ASY males are believed to forage within a restricted altitudinal zone centered on breeding territories not only during the early part of the breeding season [ 42 ] but also during molting period [ 43 ] as inferred from the altitudinal lapse rates (the rate at which isotope values vary with altitude) of δ 13 C values observed in liver, pectoral muscle, and feather keratin.…”

Stable-hydrogen isotope turnover in red blood cells of two migratory thrushes: application to studies of connectivity and carry-over effects

“…In some species, migration may be too long and half‐life too short for metabolically active tissues, such as blood, to reflect anything other than migration (Mazerolle and Hobson 2005, Graves and Romanek 2009). However, Stutchbury et al (2009) found that spring migration by Wood Thrushes ( Hylocichla mustelina ) can be as short as two weeks.…”