Introduction

Urban growth affects ecosystems in several ways, leaving them more vulnerable (Alberti and Marzluff, 2004). In Porto Alegre, the combined effects of human presence including deforestation, hunting and other indirect effects are reducing howler's area distribution with consequences still unknown (Lokschin et al., 2005). Human density within a primates' geographical area should be considered by the World Conservation Union (IUCN) in the evaluation of species status (Harcourt and Parks, 2003). The southern brown howler monkey (Alouatta guariba clamitans, Cabrera 1940) is considered an endangered species in Rio Grande do Sul (Marques, 2003); in Brazil and globally it is considered near threatened (Machado et al., 2005; Rylands et al., 2006).

There are many species of Neotropical primates living close to urban areas, including: Alouatta clamitans (Buss, 1996), Alouatta caraya (Codenotti et al., 2002), Callicebus nigrifrons (Oliveira et al., 2003), Saguinus leucopus (Poveda and Sánchez-Palomino, 2004) and Saguinus bicolor (Vasconcelos et al., 2005). Problems and threats linked to urbanization, such as danger from vehicles when crossing roads, predation by dogs and electric hazard, are already documented for A. clamitans (Printes, 1999; Alonso et al., 2005), C. jacchus (Menezes, 2005) and S. bicolor (Vasconcelos et al., 2005). Ecosystems close to urban areas are important for wildlife (Dickman, 1987) and measures must be taken to guarantee their existence. Howler monkeys (A. g. clamitans) utilize areas of forests close to urban developments and are suffering from contact with several electric hazards. Here we describe a way to mitigate the occurrence of such accidents around Porto Alegre.

Methods

Porto Alegre is the capital city of the state of Rio Grande do Sul, Brazil (Fig. 1), with a population of 1.4 million (IBGE, 2006). Approximately 10% of the municipal area is natural semi-deciduous seasonal forest, influenced by Atlantic rainforest (Brack et al., 1998; Velez et al., 1998). The southernmost area of the municipality (Fig. 2) is a rural landscape containing a number of small villages. The most important natural areas are also in this zone, which is also the most important area for howler monkeys (Alouatta guariba clamitans) (Romanowski et al., 1998; Lokschin et al., 2005). Lami Biological Reserve, the only biological reserve of the city, is located in this region (30°14′13,2″S, 51°05′43,4″W). In its buffer zone there are some forest fragments and a district named Lami, which is an urban area holding around 2,700 people (Porto Alegre, 2006), with many native trees still remaining around the houses. Most of the power lines in Brazil are aerial. Since 1999, the ‘Programa Macacos Urbanos’ (Urban Monkeys Program) has been documenting howler monkey mutilations and deaths caused by electric hazards in Lami (Printes, 1999). We conducted a survey to identify the critical areas where electric cables, responsible for the majority of accidents, should be insulated. These areas were identified based on previously documented howler distribution (Romanowski, 1998), the presence of vegetation, known accidents and reports from local people. Areas where electric cables pass through tree branches (especially those of Ficus organensis), and riparian forests were prioritized for cable insulation. Areas where howlers died or were mutilated were plotted on a Global Positioning System (GPS) and photographed. String bridges were also installed on three critical points, based on assessment of risk of animals being electrocuted (Figure 2, a, b and c).

Results and Discussion

From 2000 to 2006 eight howlers were electrocuted and three of them died as a result of injuries sustained. This number is lower than that found by Printes (1999) who recorded three cases in one year in the same locality. But our results may have underestimated the total number of deaths and mutilations caused by electric discharge since not all accidents are reported or recorded. When animals attempt to use cables as a bridge or as a base (Fig. 3), they support two of their limbs on two different cables causing a short circuit. Electric current, passing through the animals' body, may cause burns, hemorrhage and cardiac arrest, which can eventually kill them. Low tension cables (127–380 v) are the main cause of accidents, due to their frequent use by howlers as bridges between forest fragments. Howlers are not the only victims of such accidents in the region. Birds with large wing spans are also susceptible; these include the southern screamer (Chauna torquata Oken, 1816) and striped owl (Rhinoptynx clamator Vieillot, 1807).

Figure 1.

Porto Alegre, RS, Brazil. (30°S, 51°W)

The first step to reduce electric hazards was the installation of a bridge in 1999. It consisted of two parallel vertical strings. This model of bridge had no success and was replaced by another one, similar to a ‘ship ladder’ but in a horizontal orientation (Figures 4 and 5). The ‘steps of the ladder’ are used by howlers in a horizontal plane (the same way ladders are used by humans vertically). We reported accidents to the relevant authorities every time we became aware of their occurrence and requested the insulation of the cables, at least in critical areas. As nothing was done by 2003 a legal strategy was adopted; in March 2003, a legal case was presented based on National Legislation for Environmental Crimes (n° 9605/98), citing known cases. This resulted in Civil Inquiry n° 21/03 and the legal authorities judged that the Electric Energy State Company (CEEE) should insulate cables in critical areas. The insulation work started in 2004 costing approximately US$30,000. The ‘Programa Macacos Urbanos’ was ordered by the court to designate priority areas, identifying those in which cables presented a higher risk of accidents. We decided that close collaboration with local communities was vital for the successful implementation of any conservation activities. The first step taken to engage with local communities was to use about 10 local residents to monitor the occurrence of howler electrocutions pre-installation and use of bridges post-installation. Thus, the presence of houses and people's availability to collaborate was a decisive point in choosing areas for new bridges. Two other bridges were installed in critical areas in 2003 and 2004, with local people reporting occasional use by howlers. In March 5, 2006, we saw a group of howlers crossing one of these bridges (Fig. 2c and Fig. 5). There seems to be a seasonal pattern to the use of bridges by howlers, probably linked to the availability of food resources.

We suggest that bridges should be considered a complementary activity to the insulation of electric cables. In addition to insulation, the three low tension cables must be braided forming only one cable, thereafter reducing the possibility of animal use. Since the first bridge was installed and critical areas were isolated accidents have become rare. One accident was recorded in 2005 in an already insulated area, which had its terminal poles exposed. Since then, the CEEE arranged to insulate all terminals. In 2006, another howler was hurt on high tension cables, in an area already requested to be insolated. The CEEE does not have a way to isolate this type of cables, so pruning was requested. These two last cases suggest that prioritized areas are actually being used by howlers and that they are exposed to danger. If cables are not insulated, they offer potential risks to the animals. Nowadays, to reduce accidents, CEEE has taken the responsibility for keeping cables insulated and trees cut. This legal decision in favor of wild animals was the first one in the country and might set a precedent in Environmental Justice. The ‘Programa Macacos Urbanos’ will keep supervising selected areas around Porto Alegre, monitoring risks to howler monkeys from power lines and installing bridges in critical points. In 2006, a howler died from electrocution crossing low tension cables at Itapuã Village (30°17′00″S, 51°01′19″W), in the neighboring municipality of Viamão, 20 km from Lami (Fig. 2). This resulted in a preliminary study of other cases at Itapuã Village that revealed at least five other deaths caused by contact with electric cables. The first one was in 1995. At present, we are mapping critical points where cables must be insulated at Itapuã.

Figure 2.

Southernmost area of Porto Alegre, and the neighboring city of Viamão, Itapuã district, a, b and c are critical points where bridges for howler monkeys were installed in Lami, Porto Alegre, RS, Brazil.

Figure 3.

Howler monkeys (Alouatta guariba clamitans) using cables as a bridge, at Lami, Porto Alegre. (Photo by L. X. Lokschin).

Figure 4.

String bridge, ‘ship ladder’ model, before being installed in Lami, Porto Alegre. (Photo by L. X. Lokschin).

Figure 5.

String bridge where howlers were seen crossing between forest fragments at Lami, Porto Alegre. (Photo by G. Buss).

Conservation Consequences

In 2002, a Municipal Law (N° 9.971) was created regulating the use of ‘ecological’ power lines in Porto Alegre. These lines can be either underground or aerial, with an insulating or semi-insulating cover, and built in a compact form. With appropriate monitoring and community participation the enforcement of this law (Decree n° 14.196/03) should guarantee a lower impact of cables on wild howler populations. However, the application of this law is not retroactive; areas where cables were installed before 2003 are still dangerous and should be monitored. Other municipalities should create laws concerning power lines and their impact on flora and fauna; we suggest that researchers should collaborate in this long process. Brazilian researchers should meet in a forum to discuss primates in urban areas. The aim of this forum should be getting to know common problems and standardizing proposals and actions to be taken.