The causal reason is that carotenoi

The causal reason is that carotenoid pigments, which the boobies get through their diet, are concentrated in their feet, making them appear blue in colour. ... During courtship, a male booby conducts a foot-flaunting dance to try to impress the females

Results (Chinese) 1:

因果原因是类胡萝卜素，它的鲣鸟通过他们的饮食中获得，都集中在他们的脚，使它们看起来呈蓝色。......在求爱，男性诱杀进行一次脚炫耀的舞蹈，试图打动女性

Results (Chinese) 2:

其因果是类胡萝卜素色素，通过他们的饮食，集中在他们的脚，使他们看起来蓝色的颜色。...在求爱期间，一个雄性诱饵进行脚飞舞，试图打动女性

Results (Chinese) 3:

究其原因，是胸部通过饮食摄取的类胡萝卜素色素集中在足部，使足部呈现蓝色。... 在求爱的过程中，一只雄性鲣鸟会跳起炫耀脚的舞蹈，试图给雌性留下深刻的印象