Elusive species are challenging to study and conserve because basic elements of their biology may be unknown. Specimens of opportunity provide a means of collecting information on these species and may be critical for elusive species’ conservation. We used snowball sampling to identify Sowerby’s beaked whale (Mesoplodon bidens) specimens in museums and research institutions. Snowball sampling proved highly effective: we located 180 specimens from 24 institutions in North America and Europe, 62 of which were not listed in online collections databases, resulting in the largest collated dataset for this species. Analysis of these data resulted in several new findings for this species, including significant morphological variation between specimens from different collection regions, suggesting the presence of previously unidentified population structuring in this species. These data provide critical information regarding this species and demonstrate the effectiveness of specimens of opportunity for elusive species research and conservation. We recommend other researchers consider snowball sampling when designing research projects utilizing specimens of opportunity. Our results demonstrate the usefulness of snowball sampling and specimens of opportunity to elusive species research and conservation, and the methods of our study can be readily adapted for other species.

Research in psychiatry could speeden its progress by taking the manifest heterogenity and variability of symptom expression within diagnostic groups more fully into account. Since Kraepelin symptom variation has been recognized to have both biological and environmental roots. If investigated systematically, such variations in illness experience will yield new subtypes that will provide greater insight into the onset, course and vulnerability of mental disorders. Studies ranging from population surveys to the laboratory have demonstrated that psychopathology is not randomly distributed in a population, nor is it constantly present in the lives of individuals. At both the population and the person levels, psychopathology varies with time and place. At the population level, illness processes localize in risk groups, who often reside in specific neighbourhoods or social settings. The individual experience of psychopathology also fluctuates with time, place and culture. This variability requires methods for case detection and treatment planning that take this into account.

A contact process first posed as a random mapping problem is discussed together with a model for the spread of a rumour through an archaic telephone system. Snowball sampling and the well-known Reed–Frost chain binomial model are also commented on. Our main interest and emphasis is on distributional properties of discrete-time models. Simple combinatorial arguments are used along with a class of discrete distributions originally proposed for catch–recapture sampling.