The Sciuridae family is generally referred to as herbivorous and occasionally omnivorous. Although sciurids are known to opportunistically feed on carcasses of other vertebrates (including cannibalism), the active predation on vertebrates is presumably rare. Here, we present a case of a European ground squirrel (Spermophilus citellus) catching and eating a young Eurasian tree sparrow (Passer montanus) accompanied by photographic evidence. This is the first documented observation of bird-killing behavior in this endangered rodent. The incident happened at the end of spring (beginning of June) when the plant proteins are still scarce. At this time of the season, the ground squirrels are exhausted by reproduction efforts and need highly energetic food in order to recover.