Variation in Hydrogen Stable-Isotope Ratios Between Adult and Nestling Cooper's Hawks

Abstract

Hydrogen stable-isotope analysis of feathers is an increasingly popular method for estimating the origins of migrating and wintering birds. Use of this method requires that investigators know which feathers are grown on breeding grounds and how the hydrogen stable-isotope ratios of feathers (δDf) relate to those of local precipitation (δDp). In this study, we measured δDf of adult (primaries 1, 3, and 10) and nestling Cooper's Hawks (Accipiter cooperii) in Wisconsin, North Dakota, and British Columbia, Canada. As previously shown, δDf of nestling feathers were related to δDp. In contrast, the δDf of adult feathers grown on the breeding grounds were substantially greater than those of their nestlings, and varied significantly across primary feathers and study areas. Our findings suggest that it is not possible to use hydrogen stable-isotope analysis of feathers to learn the origins of migrating adult Cooper's Hawks (or possibly adults of other large-bodied species with extended molting periods) until more is learned about the physiological or ecological mechanisms underlying these isotopic discrepancies.Variación en las Proporciones de Isótopos Estables de Hidrógeno entre Adultos y Polluelos de Accipiter cooperiiResumen. El análisis de isótopos estables de hidrógeno en las plumas es un método cada vez más popular para determinar el origen de aves migratorias e invernantes. El uso de esta técnica requiere que el investigador conozca qué plumas crecen en los lugares de nidificación y cómo las proporciones de isótopos estables de hidrógeno de las plumas (δDf) se relacionan con aquellas de la precipitación local (δDp). En este estudio, medimos las δDf en adultos (primarias 1, 3 y 10) y en polluelos de Accipiter cooperii en Wisconsin, North Dakota y British Columbia, Canadá. Como se ha mostrado previamente, las δDf de plumas de polluelos se encontraban relacionadas con las δDp. Por el contrario, las δDf de plumas de adultos que crecieron en los lugares de nidificación fueron substancialmente mayores que aquellas de sus polluelos, y variaron significativamente entre plumas primarias y áreas de estudio. Nuestros resultados sugieren que no es posible utilizar el análisis de isótopos estables de hidrógeno de plumas para determinar el origen de adultos migratorios de A. cooperii (o de adultos de otras especies de aves con tamaños corporales grandes y con períodos de muda extendidos) hasta que los mecanismos ecológicos y fisiológicos que subyacen a estas discrepancias isotópicas sean mejor entendidos.

Variation in Stable Hydrogen Isotope Values in a Wetland-Associated Songbird

“…Similar to several other studies, we found that SY individuals had more depleted δ 2 H f values compared to ASY individuals (Meehan et al 2003;Langin et al 2007;Gow et al 2012;Haché et al 2012). Explanations for this variation include differences in physiology and diet between the age classes (Hobson et al 1999;Meehan et al 2003).…”

“…Similar to several other studies, we found that SY individuals had more depleted δ 2 H f values compared to ASY individuals (Meehan et al 2003;Langin et al 2007;Gow et al 2012;Haché et al 2012). Explanations for this variation include differences in physiology and diet between the age classes (Hobson et al 1999;Meehan et al 2003). Differences in δ 2 H values of prey items and drinking water and/or differences in the proportion of those items consumed among age classes may lead to systematic variation in δ 2 H f values between younger and older individuals (Langin et al 2007;Betini et al 2009).…”

“…However, previous studies have found that δ 2 H f can vary within a site (Table 1). Specifically, δ 2 H f can vary among individuals of different ages (Meehan et al 2003;Langin et al 2007;Gow et al 2012;Haché et al 2012), and between years at the same site (Haché et al 2012;Van Dijk et al 2014;Tonra et al 2015). An interaction between year and other sources of variation has been found in some studies, with species-specific (Nordell et al 2016) and age (Gow et al 2012;Haché et al 2012) effects being different among years.…”

“…Most studies have not investigated differences between sexes, but those that did have been inconclusive (Langin et al 2007) or found no effect (Nordell et al 2016). A further assumption is that δ 2 H f values should not vary between feather types in the same individual, but small differences have been found between primary and rectrix feathers in a songbird (Haché et al 2012) and large differences were seen between various primary feathers in a raptor (Meehan et al 2003). δ 2 H f values can also vary seasonally Table 1.…”

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

“…Factors other than precipitation may also exert an influence on δ 2 H values of bird blood at breeding sites. High temperatures can increase evaporative water loss, thus increasing δ 2 H tissue values of nestlings, as suggested in studies of Cooper's Hawks ( Accipiter cooperi ; Meehan et al 2003) and nestling Tree Swallows ( Tachycineta bicolor; Betini et al 2009). If present, these effects are unlikely to have had large influence on the δ 2 H blood values of Bicknell's and Swainson's thrushes at their breeding sites.…”