Body mass and timing of the active season in European Ground Squirrels (Spermophilus citellus) at high and low population density [Tělesná hmotnost a načasování období aktivity sysla obecného (Spermophilus citellus) při vysoké a nízké populační hustotě]
|Citation||HOFFMANN, Ilse E. a Eva, MILLESI. Body mass and timing of the active season in European Ground Squirrels (Spermophilus citellus) at high and low population density [Tělesná hmotnost a načasování období aktivity sysla obecného (Spermophilus citellus) při vysoké a nízké populační hustotě]. Lynx, new series. Prague: National Museum, 2008, 39(2), 305–315. DOI: https://doi.org/. ISSN 0024-7774 (print), 1804-6460 (online). Also available from: https://publikace.nm.cz/en/periodicals/lns/39-2/body-mass-and-timing-of-the-active-season-in-european-ground-squirrels-spermophilus-citellus-at-high-and-low-population-density-telesna-hmotnost-a-nacasovani-obdobi-aktivity-sysla-obecneho-spermophilus-citellus-pri-vysoke-a-nizke-populacni-hustote|
In this study we compared timing of the active season and body mass in a colony of European ground squirrels (Spermophilus citellus) in years with high and low population density. Data were collected in a suburban area near Vienna, Austria, over a decade. Ground squirrels were live-trapped and censused to determine vernal emergence, immergence into hibernation and body mass in different age and sex cohorts. Among reproductive males, yearlings were generally lighter than older males, but emerged with a slightly lower body mass at high than at low density. Including nonreproductive individuals, yearling males were significantly heavier at emergence in the low compared to the high-density years. Similar to males, yearling females were significantly lighter at emergence at high than at low density. Emergence dates of reproductive females in the high-density period preceded those at low density. Both male and female immergence dates did not differ between the two periods. In juveniles, body mass at natal emergence was similar in both density situations. However, at low density, both male and female juveniles were heavier at immergence than at high density. Juvenile survival rates were lower at low density and most of the yearlings emerging in spring had been born in the study area in the previous year. This was in contrast to the high-density period, in which more than a half of the individuals that were captured after their first hibernation were juvenile immigrants of the previous season. Hence, lower body mass at high density shortly before hibernation may partly reflect the costs of dispersal. In addition, better access to resources and lower social stress at low density could lead to faster growth rates, particularly in juveniles. This may result in a high proportion of reproductive yearlings in the low-density period.