Abstract:
The paradox of secondary metabolites, toxic defence compounds produced by plants, in nectar and fruits is well
known. Deterrence of feeding by nectarivorous and frugivorous birds is better understood than the effect of these
chemicals on the digestive performance of birds. Digestive parameters such as transit time and sugar assimilation
are important in assessing nutrient utilization and deterrence may be related to post-ingestive effects involving
these parameters. Nectar andmany fruits contain mainly sugars andwater, and avian consumers compensate for
lowsugar content in their diet by increasing food intake: thismay also increase their intake of secondary metabolites.
We investigated howthe alkaloid nicotine, naturally present in nectar of Nicotiana species, influences compensatory
feeding and digestive performance of nectar-feeding birds. High nicotine concentration negatively
affected compensatory feeding and apparent assimilation efficiency of white-bellied sunbirds Cinnyris talatala
and Cape white-eyes Zosterops virens; but nicotine slowed gut transit time only in the latter species. In contrast,
food intake and digestive performance of dark-capped bulbuls Pycnonotus tricolor was unaffected by nicotine up
to a concentration of 50 μM. Bulbuls are primarily frugivorous; hence, they are more exposed to secondary metabolites
than sunbirds and possibly white-eyes. Because their diet is richer in toxins, frugivorous birds may have
evolved more efficient detoxification strategies than those of specialist nectar-feeding birds.
