Introduction

The American black bear (Ursus americanus, Pallas, 1780) is the largest carnivorous mammal in Mexican territory. There is incomplete information regarding its geographical distribution in Mexico, partly because this species has disappeared from many areas of its original range (^{Deflín-Alfonso et al. 2011}; ^{Juárez-Casillas and Varas 2013}; ^{Scheick and McCown, 2014}; ^{Monroy-Vilchis et al. 2016}). It should be noted that ecological information is even more scarce for black bear populations inhabiting Sierra Madre Occidental, which, according to ^{Hall (1981)}, belong to two subspecies: U. a. machetes and U. a. amblyceps.

In Mexico, black bear have withstood a number of anthropogenic pressures, the most significant being the decline of wild populations by the end of the decade of 1950s as a result of campaigns aiming to the extermination of carnivores promoted by the Federal Government (^{Villa 1960}; ^{Baker and Greer 1962}). Other factors made the situation worse, such as hunting, habitat loss, and fragmentation caused by the promotion of livestock and agriculture from 1950 across the country (^{Leopold 1959}; ^{Moctezuma and Doan-Crider 2005}). Likewise, the social perception of rural communities about large predators, sometimes coupled with the lack of environmental legislation and poor law enforcement, among others, have historically contributed to the few records and lack of robust scientific information about large carnivorous mammals, including the black bear (^{Delfín-Alfonso et al. 2012}; ^{Juárez-Casillas and Varas 2013}, ^{Servín 2013}). In recent years, the incorporation of new technologies to the study of wildlife, including camera traps, genetic analysis and telemetry, has started to yield reliable data on these mammals, whose unique biological characteristics of large-scale movements and nocturnal habits, as well as low population densities, make them hard to spot, so they frequently go unnoticed in the wild (^{Delfín-Alonso et al. 2011}; ^{Juárez-Casillas and Varas 2013}; ^{Monroy-Vilchis et al. 2016}; ^{Camargo-Aguilera et al. 2017}).

Recently, historical and current records on the presence of black bear in Mexico have been reviewed (^{Deflín-Alfonso et al. 2011}; ^{Juárez-Casillas and Varas 2013}; ^{Monroy-Vilchis et al. 2016}). These reviews found seven records of black bear for the State of Durango, distributed in four municipalities. One record corresponds to the municipality of Canatlan, evidenced by a skin in 1989; four records, to the municipality of Mezquital, through the recovery of one skull and one partial skeleton in 1956 (MSU 817), one stool sample and two cubs captured in 1957; a direct sighting in 2005; one specimen was recorded in the municipality of Ocampo, from a skull in 1903; and, finally, one record was obtained from the municipality of Tepehuanes through direct sighting in 2004 (^{Baker and Greer 1962}; ^{Deflín-Alfonso et al. 2011}).

Materials and Methods

During the winter (22 December to 20 March) of 2009, intensive field surveys were conducted in Sierra Madre Occidental ranging from southwestern Chihuahua to northwestern Durango, in regions covered by well-preserved temperate forests, through camera traps (Wildview^® Xtreme4 model). These were distributed at a distance of approximately one kilometer between stations across the study areas, along old roads used for timber extraction, bridle paths, and trails. Each area surveyed included 40 fixed monitoring stations equipped with one camera trap (placed at a height of approximately 50 cm, depending on the characteristics of the land) plus an scent station; bait consisted of sardines in tomato sauce, vanilla extract, and apple. Cameras were operating 24-hours a day for 30 days, capturing 3 images per motion detection event. Sampling effort was calculated by multiplying total number of monitoring stations by total number of sampling days (^{Chavez et al. 2013}).

Results

A total sampling effort of 2400 days/trap resulted in one record of an American black bear (Ursus americanus) standing upright on its two hind legs; based on body size, it corresponds to a juvenile individual. The animal was photographed at 08:40 hrs on 2 February 2009 (Figure 1), at 25° 09’ 45.14” N and 105° 57’ 15.90” W, in pasture land of Ejido “Lobos y Pescaderos”, municipality of Tepehuanes, Durango (Figure 2). The record was obtained at 2,436 meters above sea level, representing the second reliable report of the presence of American black bear at these altitudes in the Western Sierra Madre, as the altitudinal distribution of this species ranges between 1,015 and 2,809 masl (^{Deflín-Alfonso et al. 2011}). The full identification of the American black bear individual involved an exchange of opinions of specialists, where six observers determined that the images correspond to a black bear.

Figura 1 Individuo de oso negro americano (Ursus americanus) fotografiado en los terrenos de agostadero del Ejido “Lobos y Pescaderos”, en el Municipio de Tepehuanes, Durango, México 

Figura 2 Mapa mostrando el área de estudio en donde se efectuaron las prospecciones en el año 2009, en el Ejido de Lobos y Pescaderos, municipio de Tepehuanes y donde se obtuvo el registro de Oso negro americano (Ursus americanus). Ubicación de la fotocolecta (triangulo rojo). Municipio de Tepehuanes (achurado en gris). División del estado (línea oscura). Sierra madre Occidental (achurado verde). 

Based on this record, and given that the specimen photographed is a juvenile, is could not be determined whether this individual belongs to an established population inhabiting the municipality of Tepehuanes or whether it is a juvenile individual in a dispersal process. The same camera trap station also recorded the presence of other wildlife species, such as coyote (Canis latrans), white-tailed deer (Odocoileus virginianus), rabbit (Sylvilagus spp.), hare (Lepus californicus), and even creole cattle. There were no further records of U. americanus over the course of the survey.

The area where the record was obtained is characterized by pine and pine-oak forest, at an altitude of 2,436 masl. The local climate is temperate, semi-cold with cool and long summer, Cb (w2), with summer rainfall; precipitation ranges between 873 and 1,200 mm. The maximum temperatures recorded in the area vary between 24 °C and 34 °C, and the minimum from -8 °C to -16 °C (^{INEGI, 2016}; ^{Medina et al. 2005}). The local topography is mountainous, with areas of gullies to the northwest of the ejido, with elevations ranging from 1,900 to 2,800 masl. in mountainous zones (^{INEGI, 2016}). The study area comprises a broad extension of perennial and intermittent runoff, the latter primarily during the rainy season.

Discussion

Except for two records, one involving direct sighting in 2004 in Sierra de la Candela, municipality of Tepehuanes, Durango, at 2,809 meters a.s.l. in a pine forest (pers. comm., Jorge I. Servin in ^{Deflín-Alfonso et al. 2011}), and one capture in 2014 in the town of Felipe Carrillo Puerto, municipality of Guadalupe Victoria, where it was determined that this individual was dispersing from Sierra Madre Oriental (^{Camargo-Aguilera et al. 2017}), no other recent study had formally reported the presence of American black bear in the State of Durango.

In Mexico, the historical range of the species covered forested regions of northwestern and northeastern States (^{Leopold 1959}; ^{Baker and Greer 1962}; ^{Hall 1981}). It is currently acknowledged that not all areas within its historical distribution range in Mexico has been properly explored, so that there is a geographic gap regarding its current distribution, mainly in the States of Durango, Aguascalientes and Zacatecas. These gaps, together with insufficient field work aimed at the monitoring of the species, have led to consider U. americanus as locally absent or extirpated from these regions (^{Delfín-Alonso et al. 2011}; ^{Monroy-Vilchis et al. 2016}).

The present photographic record have determined its presence and underscores the need to implement and intensify field surveys spanning at least one full year, or better still, develop mid- and long-term projects contributing to monitor the presence and even the habitat use and activity patterns of the American black bear in the northwestern regions of Mexico, particularly in the State of Durango on Sierra Madre Occidental. These surveys should be conducted in areas that have been identified as having suitable habitat conditions that favor the presence of this bear as in the municipalities of Guanacevi, Tepehuanes, Topia, Tamazula, Otaez, Santiago Papasquiaro, Durango, Canelas, Pueblo Nuevo, Mezquital and Suchil, just to mention a few.