Calcium availability affects bone growth in nestlings of free-living great tits (Parus Major), as detected by plasma alkaline phosphatase

Published source details Tilgar V., Mand R., Ots L., Magi M., Kilgas P. & Reynolds S.J. (2004) Calcium availability affects bone growth in nestlings of free-living great tits (Parus Major), as detected by plasma alkaline phosphatase. Journal of Zoology, 263, 269-274.
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This study is summarised as evidence for the following.

	Action	Category
	Provide calcium supplements to increase survival or reproductive success Action Link

Provide calcium supplements to increase survival or reproductive success

A replicated, controlled trial in mixed forest site in Estonia in 2000-1 (Tilgar et al. 2004) found that hatching success of great tit Parus major chicks did not differ between calcium-supplemented and control nests, but that a higher proportion of supplemented chicks fledged in 2000 (93% of hatched eggs from 14 supplemented nests vs. 78% from 19 controls), but not 2001 (78% of hatched eggs from 25 supplemented nests vs. 70% from 17 controls). At 15 days old, supplemented chicks were no larger or heavier than controls, but showed significantly lower levels of bone calcification activity. This suggests that supplemented nestlings already had fully developed bones by the time measurements were taken. The consequences for fitness and future reproduction may include decreased predation or parasitism in chicks and a lower reproductive costs for parents (because of shorter nestling periods), but these are not investigated in this study. This difference was only apparent in 2000, possibly because 2001 was a very poor year for reproduction, lowering growth rates and fledging success for all broods. Supplementation consisted of chicken eggshell provided in excess in small feeders on the outside of nest boxes.