The paper does say this: "While I closely and respectfully examined the genitals of slightly fewer than ten thousand dogs, being careful not to cause alarm and

The paper does say this: "While I closely and respectfully examined the genitals of slightly fewer than ten thousand dogs, being careful not to cause alarm and moving away if any dog appeared uncomfortable...". The term "I" implies it was a single person doing all that. Elsewhere, it specifies that the total time spent observing dogs was 1000 hours. Elsewhere: "From 10 June 2016, to 10 June 2017, I stationed myself on benches that were in central observational locations at three dog parks in Southeast Portland, Oregon. Observation sessions varied widely according to the day of the week and time of day. These, however, lasted a minimum of two and no more than 7 h and concluded by 7:30 pm (due to visibility)." It'd be an average of nearly 3 hours per day, every day.