Seasonal change of flower use by the Slaty Flowerpiercer (Diglossa plumbea)

I observed a pair of Slaty Flowerpiercers (Diglossa plumbea) in highland Costa Rica during 1996 and quantified their flower use in three distinct months. The total number of open flowers in the territory declined from dry to wet season, and the composition of flower species changed. The pair changed their flower use from dry to wet season, exploiting more abundant flower species in each season. Previous studies have shown that the change of flower abundance and composition affected hummingbird abundance in this area because they leave the area when their favorite flower species become scarcer. The Slaty Flowerpiercers, in contrast, maintained the same territory, shifting flower use in response to seasonal changes in flower abundance and composition. My observations suggest that the unique feeding method of flowerpiercers as 'nectar thieves' allows them to use flowers more flexibly and to remain resident on the same territory throughout the year.