Hummingbirds and Food Plants

 Hummingbirds and their food-plants rely to a large extent on each other for food supply and pollination service, respectively. This mutual relationship has co-evolved for millions of years and across the Americas involving over 330 hummingbird species and an estimated nearly 8000 plant species relying on hummingbirds as their principle pollinators.

Although birds other than hummingbirds also act as pollinators, hummingbird plant interactions are one of the most striking examples of bird-plant co-evolution, and the associated morphological adaptations have been studied intensively e.g, Snow.

 These studies have found that plants adapted to hummingbird pollination typically are odorless, have a long and narrow conspicuous orange-red tubular corolla, and produce extensive dilute nectar - broadly matching the sensory capabilities, morphology and energetic demands of hummingbirds. Similarly, hummingbirds show an array of features considered nectar-feeding adaptations, such as the capability to hover, a specialized tongue, highly specialized and variable bill morphologies, as well as a minute body size.

The smallest of all birds is the Bee Hummingbird (Mellisuga helenae) endemic to the Cuban archipelago, including the main island of Cuba and Isle of Youth (formerly Isle of Pines), in the West Indies. Of the 15 hummingbird species endemic to the West Indies, the Bee Hummingbird is the only species considered threatened on the IUCN red list.

Although the Bee Hummingbird is the smallest bird in the World, is categorized as Near Threatened and its population size is clearly declining, only very basic information regarding its distribution and reproduction has previously been reported. Almost nothing is known about its feeding ecology. For instance, apart from the record of some 15 food plants, nothing is reported about its preferred food plants or the overlap in flower use with the larger-sized Cuban Emerald (Chlorostilbon ricordii) - the only other resident Cuban hummingbird.

We here: 1) identify and describe the floral traits of several food plants the Bee Hummingbird uses; 2) report to what extent the Cuban Emerald uses the same flowers as the Bee Hummingbird; and 3) compare our data on flower use with those previously reported, and discuss how our results could direct future studies beneficial for the conservation of the Bee Hummingbird.

Each of the identified ten plant species visited by the Bee Hummingbird belongs to different plant families, of which one species (Antigonon leptopus) was introduced to Cuba. The remaining nine plant species are either native or endemic to Cuba (Table 1). Most of the ten flowers visited by the Bee Hummingbird - of which nine were also visited by the Cuban Emerald, as well as insects, such as bees and butterflies - have floral traits that fall outside the traditional ornithophilous syndrome, noticeably most flowers had little nectar and a short, white corolla, although some had more vivid colors.

This indicates that the Bee Hummingbird uses plants with generalized pollination systems as has also been reported for plants visited by small hummingbirds on Trinidad, Tobago, and other islands in the West Indies.

Conclusions. A total of 15 plant species from 15 different genera had previously been reported to be visited by the Bee Hummingbird, but no study had described their floral traits. Of the herein-reported ten food plants, only one species (Hamelia patens) occurs in the 15 genera previously listed as being visited by the Bee hummingbird. Many of the previously reported food plants in the Zapata Swamp were observed in March–June during the breeding season of the Bee Hummingbird, whereas the food plants we here report bloom in the latter part of July, outside the breeding season of the Bee Hummingbird.

In Cuba, the dry season extends from November to April, whereas the wettest months are from June to October (Garrido & Kirkconnell 2000). Therefore, it seems likely that the flower community largely changes between the dry and the rainy season, roughly coinciding with the termination of the Bee Hummingbirds breeding season.

This is the first step in identifying the floral niche of the Bee Hummingbird. We recommend that a quantitative field study be undertaken to evaluate the floral overlap in the context of floral use and availability, and behavioral interactions with the Cuban Emerald (Vaurie 1957) and insect-pollinators, such as the potential negative impact of the non-native honeybee (Apis mellifera). Comparing the herein reported food plants of the Bee Hummingbird with the plant species indicates that it would be essential to examine both dry season and rainy season floral overlap and behavior.

It would also be interesting to study the effect of introduced plants, forest loss, and degradation on the feeding behavior of the Bee Hummingbird. Finally, we recommend that field studies are also conducted in other areas than the Zapata Swamp, e.g., in the Bee Hummingbirds strongholds in the low-lying Guanahacabibes peninsula in western Cuba and in the eastern mountains of Cuchillas del Toa and Sierra Cristal. This should prove valuable for the conservation of the Bee hummingbird, an endemic and threatened species of the Cuban archipelago, West Indies.