The Kakapo, a large nocturnal, forest dwelling and flightless parrot native to New Zealand, is under severe threat of extinction.
The birds breed only in years when the native rimu trees are fruiting heavily, with the fruit being the preferred food both for breeding females and for growing chicks. The birds will climb 20-meter high trees to eat the berries during breeding season.
For unknown reasons, the birds will usually not breed in captivity, even when fed a high calcium diet. A group from down-under may have discovered why.
Von Hurst PR, Moorhouse RJ, Raubenheimer D.Preferred natural food of breeding Kakapo is a high value source of calcium and vitamin D. J Steroid Biochem Mol Biol. 2015 Oct 26. pii: S0960-0760(15)30119-9. doi: 10.1016/j.jsbmb.2015.10.017. Review.
Dr. Pamela Von Hurst and colleagues had the brilliant idea of analyzing these rimu berries for vitamin D content. The berries are loaded with vitamin D. Also, it is not all plant based vitamin D (D2); the berries have significant amounts of vitamin D3 as well, about 15% of the total was D3.
They were able to measure the vitamin D levels of some parrots in captivity and found their vitamin D levels were almost undetectable. Mean vitamin D status of the 10 adult birds was 2 ng/ml (5 nmol/L). Given the importance of vitamin D in fertility, this finding offered a plausible explanation as to why parrots in captivity do not breed.
What was really amazing was the amount of vitamin D these chicks get from eating rimu berries. The authors report growing chicks will consume 550 g of rimu fruit per day and given their analysis of the vitamin D content of the berries, the rapidly growing chicks appear to be getting about 18,000 IU of vitamin D daily!