Abstract:
Ecologists increasingly rely on camera-trap data to estimate biological parameters such as population abundance. Because
of the huge amount of data camera trap can generate, the assistance of non-scientists is often sought after, but an assessment
of the data quality is necessary. We tested whether volunteers data from one of the largest citizen science projects – Snapshot Serengeti – could be used to study breeding phenology. We tested whether the presence of juveniles (less than one
or 12 months old) of species of large herbivores in the Serengeti: topi, kongoni, Grant’s gazelle, could be reliably detected
by the ‘naive’ volunteers versus trained observers. We expected a positive correlation between the proportion of volunteers
identifying juveniles and their effective presence within photographs, assessed by the trained observers. The agreement
between the trained observers was good (Fleiss’ κ > 0.61 for juveniles of less than one and 12 month(s) old), suggesting that
morphological criteria can be used to determine age of juveniles. The relationship between the proportion of volunteers
detecting juveniles less than a month old and their actual presence plateaued at 0.45 for Grant’s gazelle, reached 0.70 for
topi and 0.56 for kongoni. The same relationships were much stronger for juveniles younger than 12 months, reaching 1
for topi and kongoni. The absence of individuals < one month and the presence of juveniles < 12 months could be reliably
assumed, respectively, when no volunteer and when all volunteers reported a presence of a young. In contrast, the presence
of very young individuals and the absence of juveniles appeared more difficult to ascertain from volunteers’ classification,
given how the classification task was presented to them. Volunteers’ classification allows a moderately accurate but quick
sorting of photograph with/without juveniles. We discuss the limitations of using citizen science camera-traps data to study
breeding phenology, and the options to improve the detection of juveniles.
