Isotopic Evaluation of Interrupted Molt in Northern Breeding Populations of the Loggerhead Shrike

Abstract

AbstractAbstractThe Loggerhead Shrike (Laniusludovicianus) breedsthroughout North America and various populationsapparently exhibit diverse molt strategies.However, molt in this species and how it may varygeographically is generally poorly known. Weinvestigated molt sequence in 27 breedingLoggerhead Shrikes using stable hydrogen(δD) isotope analysis of flightfeathers. Because feather δD varies with thelatitude at which feathers are grown in NorthAmerica, it is relatively straightforward toidentify those feathers grown south of anindividual's breeding location. We sampled 11feathers per individual to evaluate locations offeather molt between breeding and wintering groundsin North America. Sampling took place in centralSaskatchewan, Canada (n = 18 individuals) andin the southern region of the Saskatchewan-Manitobaborder (n = 9). We found evidencethat shrikes initiated flight feather molt on theirbreeding grounds (P1 and P3) but thenlargely suspended molt until reaching theirwintering areas. The isotopic evidence suggeststhat the first primary (P1, most depleted indeuterium, mean = −103‰) provides information onshrike breeding latitudes while the innermosttertial (S9, most enriched in deuterium, mean = −49‰)provides information on shrike wintering orsouthernmost molting latitudes.