1. INTRODUCTION
Frugivory is an important means of nutritional intake, and is practiced
by many birds in the tropics. Since different fruits are available
virtually year-round whereas insects may not be, it can often supplement
and sometimes become the dominant diet of normally insectivorous as well
as normally frugivorous species. It is important for both migrants and
resident birds and engaged in by many different families of birds (Snow
1981, Jordano 1987, Albrecht et al. 2018).
A number of frugivory studies have been done previously in Costa Rica (
e.g., Levy 1987, Loiselle and Blake 1990, Wilms and Kappelle 2006, and
Thornton et al. 2015). Most had either been undertaken in tropical
lowlands and/or on the Caribbean side of the country. They had also been
conducted in relatively uninhabited areas. None of them, however, seems
to have been conducted in Tropical Moist Forest of Pacific “middle
elevations.”
A detailed study of birds feeding on Huevos de Caballo had also
been done by McDiarmid et al. in 1977. This study was done in Tropical
Dry Forest at lower elevation in the Costa Rican province of Guanacaste.
In this part of the country the vegetation and bird life are also
significantly different than the Pacific side of the Central Valley.
Several studies of trees in the family Burseracae have also been
done. In a study done in Panama (Griscom et al. 2007), Gumbo Limbo was
fed on by 21 different species of birds. Two other studies were cited by
them (Trainer & Will 1984 , Greenberg et al. 1995) which had shown
Gumbo Limbo to be a major food resource in Mexico and Central America.
The family of Gumbo Limbo, Burseracae, had also been previously
cited as one of the three most important plant families for specialized
frugivores (Snow 1981). Another study of birds feeding on a close
relative of Gumbo Limbo, Bursara longipes, was done in Mexico
(Almazan-Nuñez 2016). In this study twenty species of birds fed on its
fruits. Observations were made at three different stages of succession
of the trees. Species of the family Tyrannidae (Flycatchers) were
the most frequent visitors in all three stages of succession, and except
for the stage of mature succession they also consumed the most fruit.
After having seen a presentation by Tomás Carlo on frugivory in the
tropics (2021), several questions had arisen in my mind. Since
medium-sized flycatchers had been the most frequent frugivores, I
wondered whether size had played a part. Additionally, he had stated
that certain bird families preferred fruits high in lipids, while others
preferred fruits that were low in lipids. I wondered which types of
fruits were being eaten in my town, Desamparaditos de Puriscal, and if I
could show a similar preference. I had emailed him for further
information and he had sent me a copy of the paper by Pizo et al. (2020)
which showed the lipid contents of different plant families.
Since both Gumbo Limbo (low in lipids) and Huevos de Caballo(lipid-rich) were both fruiting at the time, I conducted a study of
birds visiting and/or feeding on them while I was in Costa Rica in 2021.
The study further sought to determine if these trees were also an
important food resource for birds on the Pacific side of the Central
Valley of Costa Rica, and how they helped to maintain a greater
diversity of birds in a more inhabited area of the country.