Magpies and Jays, like most of their cousins in the Crow (Corvid) family, will take the eggs and young of small birds. Both have been around the garden while the 5 fledglings in the Great Tit nest box have been reduced to 3. The Magpie was trying to get it’s beak into the nest hole so I suspected it in the first disappearance, and protected the entrance hole but the second died in the box, of no visible cause. The RSPB commissioned a study which shows that the huge decline in small song birds is the same in areas with few Magpies as in areas where they have increased. Food and nest site loss is much more likely to be the cause of the worrying decline. Conditions: Dry and still, with some sun. Temperature:Max 18- Min 10c.