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.