New dietary observations on Melanerpes flavifrons (Aves, Picidae): nectar consumption and possible pollination of two inflorescences

Despite the predominant insectivorous habits of woodpeckers, the Yellow-fronted Woodpecker (Melanerpes flavifrons) stands out for its primarily frugivorous diet. In this study, we report two observations made in the Atlantic Forest of Goiás regarding nectar consumption by M. flavifrons. These are the first documented records of this habit in Brazil for the flowers of Inga ingoides and Combretum fruticosum. This behavior suggests that pollination might be involved in the process and there is possibly a greater demand for nectar by birds in the interior of the country during the driest period of the year.

The Yellow-fronted Woodpecker (Melanerpes flavifrons) is one of the most attractive, colorful, and strepitous representatives of the family and exhibits noteworthy social habits (SICK, 1997;SIGRIST, 2014;WINKLER et al., 2020). It is endemic to the Atlantic Forest (VALE et al., 2018) and occurs from southern Bahia to Rio Grande do Sul, as well as in Paraguay, Argentina, and locally in central Brazil (SICK, 1997;WINKLER et al., 2020). It includes a variety of items in its diet, such as arthropods, fruits, seeds, and even sugary water (WINKLER et al., 2020). Examples of fruits it consumes are those of Cecropia pachystachya (MARCONDES-MACHADO; ARGEL-DE-OLIVEIRA, 1988;MIKITCH, 2002) and Cabralea canjerana (PIZO, 1997), and it is one of the most frugivorous woodpeckers in southeastern Brazil (PARRINI, 2015).
Despite copious previous records of vegetable matter in the diet of this species, apparently M. flavifrons has still not been documented feeding on nectar of native flowers; although, there are a few comments of nectar ingestion in the literature (e.g., SICK, 1997;PARRINI, 2015). Contrastingly, other species of the genus (e.g., Gila Woodpecker, M. uropygialis) are known to seek nectar (WINKLER; CHRISTIE, 2002). Here, we present the first documented records of M. flavifrons feeding on the flower nectar of two species native to Brazil, as well as the possibility that pollination is involved in this activity.
We recorded Yellow-fronted Woodpeckers visiting the flowers of two species of canopy plants native to central Brazil, Inga ingoides (Rich.) Willd., a relatively tall arboreous legume, and Combretum fruticosum (Loefl.) Stuntz., a large liana that is widespread in the Neotropical region. The flowers of Inga are hermaphroditic with white stamens and a green corolla (KOPTUR, 1983;NETO et al., 2007). In Goiás, I. ingoides blooms for two to four months at the end of the dry season (between July and October). Combretum fruticosum has erect flowers in elongated inflorescences, which vary in color from green to yellow and orange (SCHEMSKE, 1980;GRYJ et al., 1990). It blooms from April to July in the study region.
In Area 1, a pair of M. flavifrons was observed foraging on an I. ingoides tree for about 4-5 minutes while it climbed up the trunk and insistently vocalized. Once, the female jumped to a horizontal branch in the periphery of the tree and landed immediately next to some flowers. The individual penetrated its acuminate bill amidst the stamens and appeared to reach the corolla and obtain nectar with its long tongue. This movement was repeated several times within a couple minutes, and two other flowers were visited before the pair flew away.
In Area 2, a group of five individuals of M. flavifrons (three males and two females) was fortuitously observed and spent almost 2 h around the flowers of C. fruticosum in the canopy of seasonal semideciduous forest (ca. 15 m high). All five individuals sought nectar, perching beside or on the inflorescences and using both the bill and the tongue to reach the nectaries (Figures  1 and 2). One female chased a Variable Oriole (Icterus pyrrhopterus) to visit a flower and one male scared away a Sayaca Tanager (Thraupis sayaca) from the treetop. All the individuals seem to have contacted the reproductive organs of the flowers. At the end of the process, they had their forehead, throat, and bill covered in reddish pollen.
It is not clear if the female Yellow-fronted Woodpecker observed feeding on nectar of I. ingoides in Area 1 was also pollinating flowers, since the individual was not observed carrying pollen. However, it touched the nectaries and visited more than a single flower in a row, so it might have acted as a pollen vector. Inga is more regularly pollinated by bats and moths (KOPTUR, 1983), but this does not exclude other activities, including pollination by diurnal visitors, such as hummingbirds (KOPTUR, 1984;AMORIM et al., 2012), tanagers and icterids (pers. obs.). Gryj et al. (1990) attested that perching birds are the main pollinators of C. fruticosum flowers, since they carry abundant pollen during usually long visits. As mentioned above, we observed all the individuals of M.  Indeed, other species of woodpeckers, including other Melanerpes, have also been observed feeding on the nectar of Combretum species. Gryj et al. (1990) listed M. chrysogenis as a visitor of C. fruticosum in Costa Rica, and Silva and Rubio (2007) observed M. candidus visiting C. lanceolatum in the Brazilian Pantanal. Thus, these observations suggest that the nectivorous habits of Melanerpes are likely much more common, including in other plant species with a perching-bird pollination syndrome. Rocca et al. (2006) suggested that moving from sipping fruit juice to feeding on nectar is a relatively simple step for woodpeckers, due to their morphological attributes. Furthermore, we postulate that the certain demand for nectar among woodpeckers and other birds, at least in the region, perhaps involves seasonality. Both of our observations were made during dry periods of the year (May and July), when fleshy fruits are generally scarce. Considering the frugivorous habits of M. flavifrons, we assume that this resource scarcity in the winter favors a more regular search for nectar, which could also increase the obtainment of nutrients during periods of food deficiency. Such patterned behavior has also been postulated for events of flower consumption by insectivorous bird species, which may increase their search for this resource during the dry season when food is scarce (see GONSIOROSKI et al., 2021).
We suggest making more observations in Brazil of avian floral visitors, especially perching birds, for both species of plants. Systematic observations will provide a better understanding of the benefits of these visits to the birds and the reproductive and phenological systems of the plants. Ultimately, this data would contribute to increasing our knowledge of the natural history of these species and could contribute to habitat conservation and restoration. Since many woodpeckers are fond of "plant juice" additional observations could corroborate the importance of this resource for the group, especially during periods of food scarcity.