Limited ability of Palestine Sunbirds Nectarinia osea to cope with pyridine alkaloids in nectar of Tree Tobacco Nicotiana glauca

1. Secondary compounds are common in floral nectar but their relative effects on nectar consumption and utilization in nectarivorous birds are unclear. 2. We studied the effect of two pyridine alkaloids, nicotine and anabasine, present in Tree Tobacco (Nicotiana glauca) nectar, on food consumption, gut transit time and sugar assimilation efficiency of the Palestine Sunbird (Nectarinia osea), a pollinator of N. glauca in east Mediterranean ecosystems. 3. Sunbirds demonstrated dose-dependent deterrence; they were not deterred by the lowest natural concentrations of these alkaloids in nectar (0.1 ppm nicotine and 0.6 ppm anabasine) but they were significantly deterred by the average concentrations detected in nectar (0.5 ppm nicotine and 5 ppm anabasine). 4. The two pyridine alkaloids reduced gut transit time (by 30-42%) and sugar assimilation efficiency (by 9-17%) compared with the control alkaloid-free diet. 5. Sunbirds are able to cope with low, but not average, concentrations of nicotine and anabasine in N. glauca nectar. If sunbirds are efficient pollinators of N. glauca they may induce selection on it to reduce pyridine alkaloid production in the nectar. Alternatively, high concentrations in some N. glauca plants may lead the birds to visit more plants with lower alkaloid concentrations. Hence, they will be more efficient pollinators, especially if other nectar-producing plants are scarce.