Sampling bias is a key issue to consider when designing studies to address biological questions and its importance has been widely discussed in the literature. However, some forms of bias remain underestimated. We investigated the roosting decisions of free-living great tits utilizing nest-boxes in response to the installation of a novel object (a miniature video camera) inside their nest-boxes. We show that birds that score highly on a widely used exploration test (i.e., fast explorers) are more likely to accept and approach novel objects used in a seemingly unobtrusive sampling technique; thus, the sample collected overrepresents fast explorers. This form of behavior-related bias, sensitivity to novel objects, has largely been overlooked in sampling design. We demonstrate potential pitfalls of neglecting this behavior-related sampling bias in biological studies.