Habitat fragmentation is often considered a major threat to biodiversity; however, our understanding of how fragmentation impacts populations is poor. Identifying appropriate models for such studies is difficult. Tree squirrels are dependent on mature forests for food, cover and nests; these are habitats that are being fragmented rapidly and that are easily defined by humans. Squirrels represent excellent models for study of fragmentation. The literature on tree squirrels was reviewed to glean data on density and home‐range size in forest fragments. Sufficient data were available on four species (Sciurus carolinensis, S. niger, S. vulgaris, Tamiasciurus hudsonicus). Density was negatively related to fragment size for S. carolinensis and S. niger and marginally so for T. hudsonicus. Sciurus vulgaris did not exhibit this relationship. Home‐range size was analysed for three species of Sciurus and was positively related to forest fragment size for S. carolinensis and S. niger. Again, only S. vulgaris did not to show this relationship. Sciurus vulgaris is rarely found in small forest fragments and is believed to be especially sensitive to fragmentation; other tree squirrels appear to be sensitive to fragmentation in more subtle ways. Home range compaction provides a mechanism by which densities may increase in small fragments. The demographic consequences resultant from the high densities of squirrels found in small woodlots are not known but may explain the forest damage, avian nest predation and reduced diversity often cited to occur in woodland fragments.

Spermophilus citellus (Linnaeus, 1766) is a medium-sized sciurid commonly called the European ground squirrel. The species inhabits grasslands in cen

Direct mortality of forest wildlife due to fire is rarely documented. In June and July 2004, the Nuttall Complex Fire burned 11,898 ha in the Pinaleño Mountains, southeastern Arizona. Portions of these mountains serve as the only habitat of endangered Mount Graham red squirrels (Tamiasciurus hudsonicus grahamensis). Survival of radio-collared red squirrels over a period that included the fire was lower in areas that were burned than on unburned areas; however, the majority of squirrels on our study areas survived the fire. Distance of nests from middens did not differ between pre-fire and post-fire periods for animals in burned or unburned areas, indicating that squirrels did not abandon middens immediately after surviving the effects of fire. Resumen La mortandad directa de la fauna silvestre de los bosques a causa del fuego raramente se docúmenta. En junio y julio del 2004, el Nuttall Complex Fire quemó 11,898 ha en las Pinaleño Mountains, al sureste de Arizona. Porciones de estas montañas sirven como el único hábitat de las ardillas rojas en peligro de extinción, Tamiasciurus hudsonicus grahamensis. La supervivencia de las ardillas rojas con radiocollares en un período que incluyóal fuego fue más baja en áreas que fueron quemadas que en las no quemadas; sin embargo, la mayoría de las ardillas en nuestras áreas de estudio sobrevivieron al fuego. La distancia de los nidos desde los muladares no difirióentre los periodos de pre-fuego post-fuego para los animales en áreas quemadas o no quemadas, indicando que las ardillas no abandonaron los muladares inmediatamente después de haber sobrevivido a los efectos del fuego.

Microtus californicus (Peale, 1848) is a cricetid commonly called the California vole or California meadow mouse. A sexually dimorphic, medium-sized

Tremarctos ornatus (F.G. Cuvier, 1825) is a tremarctine bear commonly known as the Andean bear. It is a medium-sized bear with black to dark red-brown pelage with dense, long, coarse fur; creamy white marks occur on the chin, neck, and chest, and often white to creamy marks occur on the face, around the muzzle, and eyes. It is distributed in the tropical Andes of Venezuela, Colombia, Ecuador, Perú, Bolivia, and northern Argentina in South America. T. ornatus is catalogued as “Vulnerable” (VU) by the International Union for Conservation of Nature and Natural Resources and is included in CITES Appendix I. Main threats include habitat loss and fragmentation, illegal killing, human–bear conflicts, and most likely climate change.