Blue jays

Some insects can protect themselves against the toxins present in their food plants by storing them. One example is the monarch butterfly, the caterpillars of which store potentially toxic cardiac glycosides obtained from a food plant, the milkweed (see Harborne 1993). Subsequently, the stored glycosides have a deterrent effect upon blue jays that feed upon them. 

Adult Utetheisa tend to be rejected also by birds (blue jays, Cyanocitta cristata scrub jays, Apkelocoma coemlescens T.E., unpublished observations), as might be expected, given their aposematism, but there is no definitive evidence that the unacceptability is due specifically to the PAs. 

Dixon, M. D., Johnson, W. C., and Adkisson, C. S. (1997). Effects of caching on acorn tannin levels and Blue Jay dietary performance. Condor 99,756-764. 

Remains of acorns of red oak, Quercus rubra, after gray squirrels, Sciurus carolinensis) have been feeding on them. Top row. cross section of acorn, with radicle barely visible at apical pole at the bottom. Middle row. Parts of acorns left behind by squirrels. They discard apical pole (with radicle visible). Such pieces are later consumed by birds such as blue jays (Cyanocitta cristata). Bottom row. pieces of acorn shells. Photo D. MiiUer-Schwarze... 

Irruptive migration occurs in species which do not migrate at all during some years, but may do so during other years, when the winter is particularly cold or food particularly scarce. For example, some populations of blue jays Cyanocitta cristata) are believed to migrate only when their winter food of acorns is scarce. 

Discrimination and generalization of leaf damage by blue jays (Cyanocitta cristata), Anim. Learn. Behav., 12 202. 

Fig. 10.1 (a) Naive blue jay eating a monarch butterfly. If the monarch contains cardiac glycosides, emesis (b) soon follows. After drinking water it vomits again (c). The bird recovers, but rejects (d) subsequent monarchs on sight (from Brower, 1969, with permission). 

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