Stressed by Maternity: Changes of Cortisol Level in Lactating Domestic Cats.

Lactation is the most energetically expensive component of maternal care in mammals. Increased reproductive investment can lead to physiological stress for the mothers, based on the exhaustion of energy resources and increase in glucocorticoids level. This study aimed to estimate the changes in cortisol concentrations during lactation in domestic cats and compared the differences among litter sizes. Eleven females gave birth to 27 litters, which were divided in two groups-small (1-3 kittens) and large (4-7 kittens) litters. Blood samples were collected from each female before mating, after parturition, at 4 and 8 weeks of lactation. We showed that the cortisol level in females changed significantly during lactation-the highest concentrations were observed at the peak of lactation at 4 weeks. Cortisol levels varied significantly among females but did not depend on their maternal experience. We also revealed that there were no differences in cortisol levels between females with small and large litters, but at 4 weeks of lactation, the hormone concentrations were higher in females with small litters. It is likely that these females initially invested less in reproduction, giving birth to fewer offspring.

Year-round spatiotemporal distribution pattern of a threatened sea duck species breeding on Kolguev Island, south-eastern Barents Sea.

BACKGROUND: The long-tailed duck (Clangula hyemalis) was categorized as ´Vulnerable` by the IUCN after a study revealed a rapid wintering population decline of 65% between 1992-1993 and 2007-2009 in the Baltic Sea. As knowledge about the European long-tailed duck's life cycle and movement ecology is limited, we investigate its year-round spatiotemporal distribution patterns. Specifically, we aimed to identify the wintering grounds, timing of migration and staging of this population via light-level geolocation. RESULTS: Of the 48 female long-tailed ducks tagged on Kolguev Island (western Russian Arctic), 19 were recaptured to obtain data. After breeding and moulting at freshwater lakes, ducks went out to sea around Kolguev Island and to marine waters ranging from the White Sea to Novaya Zemlya Archipelago for 33 ± 10 days. After a rapid autumn migration, 18 of 19 birds spent their winter in the Baltic Sea and one bird in the White Sea, where they stayed for 212 ± 3 days. There, they used areas known to host long-tailed ducks, but areas differed among individuals. After a rapid spring migration in mid-May, the birds spent 23 ± 3 days at sea in coastal areas between the White Sea and Kolguev Island, before returning to their freshwater breeding habitats in June. CONCLUSIONS: The Baltic Sea represents the most important wintering area for female long-tailed ducks from Kolguev Island. Important spring and autumn staging areas include the Barents Sea and the White Sea. Climate change will render these habitats more exposed to human impacts in the form of fisheries, marine traffic and oil exploitation in near future. Threats that now operate in the wintering areas may thus spread to the higher latitude staging areas and further increase the pressure on long-tailed ducks.

Baseline and stress-induced corticosterone levels are higher during spring than autumn migration in European robins.

During spring and autumn migrations, birds undergo a suite of physiological and behavioral adaptations known as migratory disposition. The position of migratory seasons within the annual cycle and specifics of environmental conditions in each season could lead to formation of specific regulatory mechanisms of spring and autumn migratory disposition. However, this topic remains largely unstudied. Here we compared corticosterone (CORT) concentration (baseline and stress-induced) in European robins (Erithacus rubecula) captured during seven consecutive migratory seasons on the Courish Spit in the Baltic Sea; >650 plasma samples were analyzed in total. We found that baseline and stress-induced CORT concentrations in free-living robins during spring migration were nearly twice as high comparing to autumn passage. Moreover, the strength of relationship between these two parameters differed between the seasons. In autumn, individuals with elevated baseline CORT level invariably expressed high stress response; in spring, the stress response was more variable. These facts are in line with the hypothesis that spring and autumn migrations are separate life history stages characterized by similar physiological and behavioral adaptations but somewhat different regulatory mechanisms. Further work is needed to understand effects of seasonal differences in CORT concentrations in regulation of migratory disposition in birds.