Estimating the distribution and abundance of species is an important part of biodiversity conservation. Automatic camera traps have emerged as one of the most promising methods for making such estimates. Despite many advantages of these cameras, there are also disadvantages, such as problems of getting animals to stay in front of the camera long enough to get identifiable images. One method to reduce this problem is to apply odor-based bait in front of the cameras. Although previous studies have shown that baits can improve detection rates for some species, there is a limited knowledge of how baits influence detection rates of many other species. The aim of this study is to evaluate how the odor of rotted fish affects the effectiveness of camera traps, and whether a possible effect differs among mammal species. The study was conducted in the province of Cantabria, northern Spain in five regions with varying habitat types. The experiment consisted of 20 camera traps; 10 with bait and 10 without bait. The mammals included in the analysis had at least 10 observations: badger, red deer, marten, roe deer, fox and wild boar. The use of bait did not increase the number of observations, but the effect of baiting may vary between species. Badgers were observed more frequently at cameras without bait than at cameras with bait. Limitations of the study such as the time of data collection may have affected the results, and therefore a longer data collection period would have been of interest in future studies. Different kinds of bait could also have been included. More studies are needed to gain a better understanding of how baiting can be used to optimize data collection with camera traps in ecology and conservation biology.