Nutritional stress and body condition in the Great Gray Owl (Strix nebulosa) during winter irruptive migrations

Abstract

<jats:p>The largest irruptive migration of the Great Gray Owl ( Strix nebulosa Forster, 1772) recorded since 1831 occurred in Minnesota, USA, during the winter of 2004–2005. We tested the hypothesis that morphometric indicators of nutritional stress covary with stable isotope signatures in a sample of 265 owls killed by vehicle collisions. The ratio of carbon to nitrogen in muscle (C/N<jats:sub>muscle</jats:sub>) was shown to be a reliable proxy of nutritional stress. δ<jats:sup>13</jats:sup>C values for liver and muscle were significantly higher in owls in poor condition, reflecting the depletion of lipid reserves in fasting individuals. On the other hand, δ<jats:sup>15</jats:sup>N values for liver and muscle were marginally lower or unchanged in owls in poor condition. Stomachs of emaciated owls were less likely to contain prey, implying that many nutritionally stressed individuals were too weak to hunt and were near the tipping point of irreversible fasts. In a broader context, sexual differences in the correlative relationships between stable isotope signatures, C/N, and body condition suggest that the consequences of reversed sexual size dimorphism extend to physiological processes during the nonbreeding season.</jats:p>

Immune state is associated with natural dietary variation in wild mice Mus musculus domesticus

“…Similarly to stable isotope studies in other species (e.g. Graves et al, ; Robertson, McDonald, Delahay, Kelly, & Bearhop, ; Mangipane et al, ), we found an association between isotope values and nutritional status, measured in our case by concentration of circulating leptin. However, it is often observed that different biomarkers of nutritional status yield conflicting results (Graves et al, ; Mangipane et al, ).…”

Stable isotopic signatures in modern wood bison (Bison bison athabascae) hairs as telltale biomarkers of nutritional stress

“…Instead, ␦ 13 C values of plants at high latitudes can be related to different environmental conditions, including plant water-use efficiency (Wooller et al 2007) and vegetation coverage (Drucker et al 2008). The ␦ 13 C values of a consumer can also decrease as a result of using fat reserves, which have relatively low ␦ 13 C values compared with other tissues (Graves et al 2012;Wolf et al 2015;Rode et al 2016Rode et al , 2018.…”

Age composition of winter irruptive Snowy Owls in North America

“…Indeed, 3% and 1% of juveniles have been detected in Manitoba (4 of 126 juveniles during winter 1995–1996, Nero & Copland ) and Minnesota (2 of 265 juveniles during winter 2005–2006, Graves et al . ), respectively. Such a low proportion of juveniles was detected on a few occasions in the present study, but only in the regular wintering areas.…”

“…For instance, winter irruptions of some boreal owl species such as the Great Grey Owl Strix nebulosa seem to coincide with periods of low densities of small mammals on the owls’ regular distribution range (Nero & Copland , Graves et al . ). The consequences of such a scenario would be that non‐juvenile birds should compose the bulk of the overall population during winter irruptions because the lack of food should have reduced reproductive output during the preceding breeding season and/or fledgling survival.…”