The geographical distribution of the black howler monkey, Alouatta pigra, is restricted to the south of Mexico (in the state of Tabasco, the north of Chiapas, and the Yucatán peninsula), Guatemala (Petén), and Belize (Horwich and Johnson, 1986; Horwich and Lyon, 1990; Rowe, 1996; Estrada and Mandujano, 2003). The only monkey reported as native to El Salvador is the black-handed spider monkey, Ateles geoffroyi, which is found mainly in the forests of the Jiquilisco Bay in the Department of Usulután, in the southeast of the country (Morales Hernández, 2002).

The park guards of the San Diego Forest have been reporting the presence of two monkeys there since 2004. The San Diego Forest (SDF) is a dry tropical forest in the department of Santa Ana (northern El Salvador) on the border with Guatemala. It covers 1,842 ha, with altitudes ranging from 440 to 780 m above sea level (CEPRODEFIAES, 2000). SDF is outside the known range of spider monkeys in the country (Morales Hernández, 2002), and it was first thought that they were spider monkeys that had been released there. I visited this area three times to verify their presence.

The guards described these monkeys as “all black.” Drawings and pictures of different Mesoamerican monkeys were shown to them in order to correctly identify the animals, but they never recognised them as “spider monkeys” (Ateles geoffroyi). The monkeys were eventually found during my third visit to SDF, on 16 February 2005, and I was able to verify that they were in fact two female howler monkeys, Alouatta pigra.

According to the information I have to date, their presence is a result of the pet trade, but their origin remains unknown. The authorities received recommendations from expert primatologists who have studied howler monkeys in the wild that they would best be left in the San Diego Forest and monitored. Their relocation would be expensive, traumatic for the animals, and pointless. They are both females and so will not reproduce. They are surviving well there, eating leaves and fruits of vegetation such as Brosimum alicastrum, B. terrabanum and Ficus spp. (CEPRODE-FIAES, 2000). Howler monkeys are adaptable (Eisenberg, 1979), although both A. palliata and A. pigra are seriously threatened, because of forest destruction within their small geographic distributions (Crockett and Eisenberg, 1987). It is important for us to know how these animals got there, and why their presence has been ignored for so long. It is urgent that national and international authorities along the borders and within the countries reinforce their efforts to protect endangered primates such as Alouatta pigra, as well as other wildlife, from the pet trade.