4.7 Reproduction and feeding behavior
Given the number of feeding visits to the Llano Grande Gumbo Limbo by both male and female Scarlet-rumped Tanagers, I am certain they had a nest nearby and were feeding the fruits to their young. I also once saw either a female or young Scarlet-rumped Tanager sitting hidden underneath a bush right next to this tree. [After reading Skutch’s account of fledged Scarlet-rumped Tanager behavior, I now wonder if what I saw was indeed their fledgling (Skutch 1980)]. This was also the only Gumbo Limbo where I observed Scarlet-rumped Tanager. Scarlet-rumped Tanagers are very common birds, so their absence in other trees indicates Gumbo Limbo fruits are not a major food resource for them. Their presence in only this tree is further indication that they were feeding young. Either they took advantage of a convenient food source to feed their chicks, or perhaps the high sugar and lipid-poor content of Gumbo Limbo may have met the nutritional needs of its young, but not have been needed by the adults.
McDiarmid et al. (1977) surmised that the arils of Huevos de Caballo may not be a suitable food for young birds. The basis of their assumption was that in only five of ninety-six observations of Hoffmann’s Woodpeckers feeding their young had the young been fed the arils of that fruit. Unlike theirs, my observations suggest that the lipid-rich arils of Huevos de Caballo may be an important nutritional need of several species of newly-hatched birds, specifically Hoffmann’s Woodpecker, Yellow-green Vireo, and Rufous-naped Wren.
I made fifty observations of feeding done by Hoffmann’s Woodpecker with forty-four done at Willy’s Huevos de Caballo . As previously noted, there was at least one nest hole of Hoffmann’s Woodpecker close by. I observed both males and females fly in, grab one of the “fruits” (arils) and immediately fly off. On 11 April 2021, adults flew in and grabbed fruit eight times in an hour, and on 15 April 2021, they did this nine times within a half-hour. Several of those times I followed the bird to its nest hole and observed the young being fed, and I assume it was also being fed on those occasions when I did not follow the bird.
I also saw fifty-one instances of feeding being done by Yellow-green Vireos, with forty done in Willy’s Huevos de Caballo . From 11 April to 15 April I observed 23 different feedings in this tree. Birds arrived to feed both singly and in pairs, and like the Hoffmann’s Woodpecker, the birds flew in and out grabbing fruits constantly. Although I did not see a Yellow-green Vireo nest near this tree, given this concentration of feeding behavior, I suspect there was a nest nearby.
Finally, I observed twenty-nine similar instances of feeding by Rufous-naped Wren in Willy’s Huevos de Caballo. As Rufous-naped Wren is a very common species that nests in gardens, it is likely there were many nests and young nearby. Again, the frantic feeding behavior of the adults was similar to that of Hoffmann’s Woodpeckers, which led me to believe they too were feeding young.
What might account for the differences between my observations and those made by McDiarmid, especially with respect to Hoffmann’s Woodpeckers? My observations of Hoffmann’s Woodpecker feeding on Willy’s Huevos de Caballo were made over a period of over a month (25 March to 29 April) with the greatest number of feedings from 11-15 April. In contrast, Mc Diarmid’s observations at the Hoffmann’s Woodpeckers’ nest site were done on one day, 25 April. Could it be that the young they observed being fed were at a stage where insect protein was a more important food source for them? It may be that earlier in their development the young are more in need of lipid-rich nutrients. Alternatively, perhaps there were insufficient quantities of insects during the earlier period of my observations, and the Hoffmann’s Woodpecker were substituting a readily available food resource.
In conclusion both Gumbo Limbo and Huevos de Caballo are important food resources in the neotropics for both frugivorous and insectivorous species of birds. Gumbo Limbo fruits are high in sugar content, and consumed by many normally insectivorous birds and migrants, and as my 2022 study shows, the tree is especially important as an energy source toward the end of the dry season when other trees are not in fruit. In contrast, Huevos de Caballo provides fruits high in lipids which many larger and mostly resident birds consume. Both trees also seem to be important sources of nutrition for young birds during their development and help to maintain bird diversity in populated areas. The continued use of Gumbo Limbo as living fences and cultivation of Huevos de Caballo should both be encouraged to maintain bird diversity in areas of human habitation.