1.
Science
; 204(4395): 847-51, 1979 May 25.
Article
in English
| MEDLINE
| ID: mdl-17730529
ABSTRACT
Analyses of predated butterflies on the forest floor at five monarch overwintering sites in Mexico and observations of birds foraging in mixed flocks indicate that individual birds of several species have learned to penetrate the monarch's cardenolide-based chemical defense. Predation is inversely proportional to colony size and appears to be one evolutionary explanation of the dense aggregations.