Hundred-ninety dead grass snakes Natrix natrix (L. 1758) were collected over 10 months in two years on an 1800-meter stretch of a local road in the outskirts of Wroclaw, a major city in SW Poland. The mortality rate reached a record high value of 204 snakes km⁻¹ year⁻¹ (1.16 snakes km⁻¹ day⁻¹). Two peaks of road mortality, one from the end of May through the beginning of June, and the other, at the beginning of August, contributed 80% of records. The majority (89%) of 110 measured specimens were juveniles with the total length below 30 cm, and around 30% of those collected in the spring and the summer were hatchlings with the total length up to 20 cm. This suggests a significant extension of the hatching period, which may be related to the local mild climate and/or climate warming. The road kill numbers correlated significantly with maximum daily temperatures through the cool (for May) to average (for June) spring of 2004 but not through the hot spring of 2003, which suggests that under average or cool weather conditions the mobility of grass snakes is limited by maximum daily temperatures. No significant correlation with daily rainfall could be established.
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