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 16 overwintering monarchs DHJanzen100179.jpg high resolution
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| Close view of one of the trees in the previous image (DHJanzen100178.jpg). The ground below these aggregations of torpid monarchs is littered with wings and body parts. Many of these parts are the remains following feeding by local birds that have learned to dissect the monarch and eat just the body parts that have little or no cardiac glycosides (these might well be, for example, the large thoracic flight muscles). Apparently some species of small rodent does the same. This brings to mind the question of why birds in the northern breeding grounds do not do the same. I suspect that if monarchs occurred in huge numbers sitting around waiting to be eaten, some northern birds would also learn this trick. On warm days in the overwintering sites, many of the monarchs do fly locally among the trees and are sensitive to disturbance - presumably burning up fat reserves needed for survival there and for the flight back to the breeding grounds in the north (see next image DHJanzen100180.jpg). It is striking that global warming will warm these refrigerated (cloud forest) mountain tops and could well destroy the entire monarch life cycle. | ||
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