Birds are among the most studied animal groups and are most likely the one that attracts more general public attention. These winged animals, are known throughout the world for their interactions and coevolution with plants. They are known to be very important for several plant groups, providing seed dispersal and promoting sexual reproduction through pollination.
When anyone hears about birds pollinating plants, their first thoughts go to hummingbirds, which are very specialized bird pollinators that are able to hover. However, there are other bird groups that are not considered so specialized in pollination (and unable to hover), but well known to pollinate plants, as the honeyeaters. This bird group, somewhat specialized in taking nectar and consequentially pollinate flowers, are present in almost all over the world, except in Antarctica and Europe. If in Antarctica that is not unexpected, in Europe (and actually in almost all the Western Palearctic) that seems a little odd, that how such ubiquitous and abundant food source is not recognized to be regularly exploited by any bird species. With this, insects are often considered the only ecologically relevant pollinators in Europe. Nevertheless, generalist birds are also known to visit flowers and in some cases to successfully pollinate plant species around the world.
In Europe there are several scattered publish records of flower visitation by birds. We carried out a fine literature search and compiled our own observations to estimate the extent, richness and ecological relevance of this mutualistic interaction. These interactions were not only of direct feeding observation, but also from pollen found attached to feathers, in faeces and stomach contents. We found that 46 bird species visited flowers of at least 95 plant species, 26 of these being exotic to Europe, yielding almost 250 specific interactions inside Europe. Additionally, we registered four more European bird species interacting with 12 different plant species outside Europe. Despite these numbers, only six plants species, both native and exotic, were confirmed to be efficiently pollinated by birds in Europe. We argue that the ecological importance of bird-flower visitation in Europe is still largely unknown, particularly in terms of plant reproductive output. We suggest that nectar and likely pollen are important food resources for several bird species, mainly during winter and spring, especially for tits (mainly Cyanistes), Sylvia and Phylloscopus warblers. The prevalence of bird flower-visitation, and thus potential bird pollination, is slightly more common in the Mediterranean basin, which is a stopover for many migrant bird species, which might actually increase their rule as potential pollinators by promoting long-distance pollen flow. We argue that research on bird pollination in Europe deserves further attention to explore its ecological and evolutionary relevance.