Abstract: 1. Carnivores can have critical impacts on ecosystems, provide economic value through tourism and are often important flagships. However, their biological traits (e.g. low density, cryptic colouration and behaviour) make them difficult to monitor and hence wildlife managers rarely have access to reliable information on population trends, and long-term information at the community level is almost completely lacking. 2. We use data from transect counts in the Serengeti ecosystem in Tanzania to examine trends in abundance for seven co-existing carnivore species. Distance-based transect counts between 2002 and 2005 are compared with adjusted data from fixed-width transect counts across the same area in 1977 and 1986. 3. Distance-based methods provided density indices for the seven most commonly seen carnivores: lion Panthera leo, spotted hyaena Crocuta crocuta, golden jackal Canis aureus, black-backed jackal Canis mesomelas, cheetah Acinonyx jubatus, side-striped jackal Canis audustis and bat-eared fox Otocyon megalotis. Detection curves were used to correct estimates fromearlier fixed-width transect counts. 4. Trend analyses detected significant declines in densities of golden and blackbacked jackal and bat-eared fox, but found no significant changes in spotted hyaena, lion, cheetah and side-striped jackal. 5. Overall, despite wide confidence intervals, we show that distance-based data can be used effectively to detect long-term trends and provide critical information for conservation managers. Power analysis demonstrated that for the most frequently seen species, spotted hyaena, golden jackal and lion, abrupt declines of up to 20% may be detectable through long-term monitoring; however, for the remaining species, declines of 50%may only be detected half the time. 6. Synthesis and applications. Distance methods provide a tool for rapid counts and monitoring of several species of carnivores simultaneously in suitable habitats and can be combined with historical fixed-width transect counts to test for changes in density. The method can provide key information to managers on long-term population trends and sudden abrupt changes in population size across a carnivore community. Long-term trends in carnivore abundance using distance sampling in Serengeti National Park, Tanzania 1. Carnivores can have critical impacts on ecosystems, provide economic value through tourism and are often important flagships. However, their biological traits (e.g. low density, cryptic colouration and behaviour) make them difficult to monitor and hence wildlife managers rarely have access to reliable information on population trends, and long-term information at the community level is almost completely lacking. 2. We use data from transect counts in the Serengeti ecosystem in Tanzania to examine trends in abundance for seven co-existing carnivore species. Distance-based transect counts between 2002 and 2005 are compared with adjusted data from fixed-width transect counts across the same area in 1977 and 1986. 3. Distance-based methods provided density indices for the seven most commonly seen carnivores: lion Panthera leo, spotted hyaena Crocuta crocuta, golden jackal Canis aureus, black-backed jackal Canis mesomelas, cheetah Acinonyx jubatus, side-striped jackal Canis audustis and bat-eared fox Otocyon megalotis. Detection curves were used to correct estimates from earlier fixed-width transect counts. 4. Trend analyses detected significant declines in densities of golden and black-backed jackal and bat-eared fox, but found no significant changes in spotted hyaena, lion, cheetah and side-striped jackal. 5. Overall, despite wide confidence intervals, we show that distance-based data can be used effectively to detect long-term trends and provide critical information for conservation managers. Power analysis demonstrated that for the most frequently seen species, spotted hyaena, golden jackal and lion, abrupt declines of up to 20% may be detectable through long-term monitoring; however, for the remaining species, declines of 50% may only be detected half the time. 6. Synthesis and applications. Distance methods provide a tool for rapid counts and monitoring of several species of carnivores simultaneously in suitable habitats and can be combined with historical fixed-width transect counts to test for changes in density. The method can provide key information to managers on long-term population trends and sudden abrupt changes in population size across a carnivore community
