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- Kärvemo, Simon
(författare)
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Gender differences in seasonal movements of dice snakes in Histria, southeastern Romania
- 2011
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Ingår i: Mertensiella. - 0934-6643. ; 18, s. 245-254
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Tidskriftsartikel (refereegranskat)abstract
- An archaeological excavation site among ancient ruins in Histria, south-eastern Romania, that harbours several thousand dice snakes (Natrix tessellata), is the focus of various ongoing studies. The current work evaluates seasonal variation of gender specific movements. Seasonal movements were estimated from captures of adult snakes over four years. Visible abundance of snakes among the ruins was largest in early spring and autumn. Summed over one entire season, the capture rates were similar for both sexes. During April males were more frequently captured than females. However, the proportion of males decreased later during the mating period in spring and until the end of June, only to rise again in August. Capture rates of gravid females continued to remain high in the vicinity of the ruins throughout vitellogenesis until ovulation, for which they mainly stayed near the hibernation area, which is also favoured for ovipositing. At the onset of hibernation in October, the ratio of males to females was consistently 0.4 across all years of study. We suggest that the skewed sex ratio among captures is due to gender-specific behaviours rather than to a naturally uneven sex ratio or capture artefacts. Males generally emerge earlier from hibernation in order to maximize their chances to reproduce. Consistent with our data, we suggest that in autumn males may be entering hibernation dens over a longer period than do females. Arguably, males do not have the same energy requirements as females, which could be expected to exploit the feeding season maximally, due to their higher-energy reproductive investment
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| 2. |
- Kärvemo, Simon
(författare)
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Monitoring a large population of dice snakes at lake Sinoe in Dobrogea, Romania
- 2011
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Ingår i: Mertensiella. - 0934-6643. ; , s. 237-244
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Tidskriftsartikel (refereegranskat)abstract
- Dice snakes (Natrix tessellata) can reach exceptionally large population densities where local conditions permit. Here we report on a study of one large population from Histria, the southern-most area of the Danube Delta in Romania. There the dice snakes forage in the brackish waters of Lake Sinoe. Many snakes are visibly infected by parasitic nematodes, which have piscivorous birds as definitive hosts. The nematode, Eustrongylides excisus, can be fatal to its snake host. In 2005, we began to study the dice snake population at Histria. In 2006 we initiated a monitoring study based on capture-mark-recapture methodology using PIT tag markers. This paper presents general aspects of this population and analyses the results to date in relation to fieldwork effort. We also discuss how external factors may affect the dynamics of the population. Even though it is generally considered that the population was larger in the past, we have not found evidence of a population decline. We estimate that the population has remained at or above 10,000 adult individuals during the three years of PIT tagging
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