A negative relationship, or trade-off, between egg size (egg volumeor egg mass) and clutch size is a central component of life-history theory. This paper presents evidence for a relationship between clutch size and egg volume (egg size) of the Magpie (Pica pica). Magpies are common and sedentary birds in study area. Egg characteristics were recorded in Mokrice rural area (46°00’N, 15°55’E), northwestern Croatia; carried out during the breeding season (April–May) in the year 2012. I have not detected any negative correlation (trade-off) between mean estimated egg volume (egg size) and clutch size in the Magpie. The results indicate that, in researched Magpie population, in northwestern Croatia, there is a positively significant correlation between clutch size and egg volume. It can probably be explained by good environmental conditions and/or good quality females, which other authors offer as a plausible explanation. In conclusion, these results do not seem to support the prediction based on the theory of optimal egg/clutch size concerning the inverse relationship between egg size and clutch size.
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