Abstract

A survey of wild vertebrates was conducted during two years in a semi-abandoned oil palm plot in Tabasco. Twenty-six species were identified: birds (14), mammals (5), reptiles (5) and amphibious (2). Several of these species may be of some importance in the biological control of common pests of the crop, and twelve of them are considered in danger of extinction in the area. The negative effects on these species that some agronomic practices may have are discussed.

Introduction

An integrated pest management program needs knowledge of the organisms present in an agro-ecosystem, since some of them may be important regulators of pests and may be adversely affected by the different pesticides used (Hilje and Hanson 1998). In general, most of vertebrates associated with oil palm can be harmful to the crop, but some species may be important as biological control agents (Wood 1976). Furthermore, an oil palm plantation may be an alternative environment where some endangered species may find refuge as their natural habitat is further deteriorated. 

An important oil palm development project is under way in the state of Tabasco, where near 3000 hectares are expected to be planted by the year 2000 (Astengo 1999). This work had the objective to register the wild vertebrates observed in a semi abandoned oil palm plot located within the campus of the Postgraduate College in Tabasco. 

This experimental plantation of about 12 ha was planted in 1970 (Pastor 1972). During the period of study the place was occupied by grazing cattle and no herbicides or pesticides were used. Grasses formed the dominant ground cover. Nearby areas are covered by pastures, coconut groves and secondary vegetation along roads and drainage canals. 

Monthly visits were done during 1997 and 1998, when vertebrates species were determined following the work by Casas and Clarence (1979), Aranda (1981), Aranda and March (1987), Esparza et al . (1988), and Peterson and Chalif (1989).

Results

Twenty-six vertebrate species were identified, including birds (14), mammals (5), reptiles (5) and amphibians (2) ( Table 1 ). All these species are residents and were observed all year around. Some species could not be identified including birds, bats, rats, snakes, frogs and lizards.

Coragyps atratus feeds on ripe oil palm fruits and is considered a pest in Tabasco (Sanchez and Ortiz 1998). Some rats (unidentified species) were abundant and some of them could be important pests, particularly in young plantings (Wood 1976), but are also eaten by some of the predators registered in this study. Rats damaged about 50% of the plants during the early years of this plantation (Pastor 1972). 

The bird Quiscalus mexicanus is known to be an important predator of larvae and adults of the oil palm defoliator, Opsiphanes cassina (Lepidoptera: Brassolidae) in Central America (Chinchilla 1997). This pest is also present in Tabasco (Sanchez and Ortiz 1998).

In Malaysia, the owl Tyto alba is used as an important predator of rats in oil palm plantations (Duckett 1984), and Cyanocorax morio has been observed predating adults of Rhynchophorus palmarum vector of Bursaphelenchus cocophilus causal agent of the red ring-little leaf disease (Ortiz Garcia, 1999. CP-CT, personal communication).

Several of the birds observed are considered endangered in Tabasco, such as Buteo magnirostris , C. morio , Q. mexicanus , Melanerpes aurifrons , and T. alba , and so the mammals Felix yagouaroundi , Tamandua mexicana and Procyon lotor , and the reptiles Boa constrictor , Bassiliscus vittatus and Iguana iguana (Garcia et al . 1996, Fraire 1997, Perez 1998). F.yagouaroundi is in danger of extenuation in all Mexico (Hernandez 1994).

The agronomic management given to an oil palm plantation will determine to a great extend the suitability of the environment to provide to many animals places for nesting, refuge, feeding, resting or bridges to reach other more suitable places. Important aspects to consider are weed control practices and the use of pesticides. For example, in Malaysia the use of the rodenticide brodifacoun is associated with the death of predatory birds that eat a poisoned animal (Duckett 1984). In a similar way, when traps contain poisonous substances may affect nontargeted organisms. Traps for R. palmarum (plastic containers with pineapple and metomil) when not properly used may also attract and cause the death of D.marsupialis , rats, and even bats.

Some other vertebrates may have a more precarious habitat within an intensively managed plantation, such as the woodpecker ( M.aurifrons ) that looks for refuge in old leaf bases

These considerations call the attention on several aspects that are important to consider when a commercial oil palm is managed if beneficial wild life is to be conserved. On the other hand, species such as Bothrops asper are always a threat to field workers.

Conclusions

An oil palm plantation could be managed in such a way to become an attractive environment where several vertebrate species may live. In this manner, several species, including important biological control agents may survive and help to regulate not only harmful species to the crop,but also for other neibourg more-inten-sively managed crops that do not offer many opportunities for survival of such species. 

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