Data from: Comparing diel activity patterns of wildlife across latitudes and seasons: time transformations using day length

(1) Camera trapping allows scientists to study activity patterns of
animals under natural conditions. However, comparisons of activity
patterns across seasons or latitudes can be biased, because activity is
often attuned to sunrise and sunset, the timing of which varies with
latitude and season. Existing transformation methods to solve this problem
have limitations. (2) Here, we explore whether and how activity patterns
can be transformed more accurately using two alternative ‘double
anchoring’ transformations – equinoctial and average anchoring – that
anchor activity time to two chosen anchor points during the study period.
(3) Using simulated noisy datasets mimicking species with either
crepuscular, diurnal or cathemeral activity patterns, we compared the
ability of different transformation methods to extract the latent pattern
and activity levels under different study conditions. We found that
average anchoring best retrieved the original diel activity pattern and
yielded accurate estimates of activity level. Two alternative
transformation methods – single anchoring and equinoctial anchoring –
performed less well. Bias in estimates from using untransformed clock
times was most marked (up to 2.5-fold over-estimation) for longer studies
covering 4-5 months either side of an equinox at high latitude, and
focusing on crepuscular species. (4) We applied the average anchoring
method to 9 months of data on Red deer (Cervus elaphus), Wild boar (Sus
scrofa) and Mouflon (Ovis amon musimon) activity as captured by camera
traps in National Park Hoge Veluwe, the Netherlands. Average anchoring
revealed more pronounced peaks of activity after sunset than was apparent
from untransformed data in red deer and wild boar, but not for mouflon, a
cathemeral species. Similarly, activity level was lower when calculated
using average-anchored time for red deer and wild boar, but no difference
was observed for mouflon. (5) We conclude that transformation of time
might not be necessary at latitudes below 20°, or in studies with a
duration of less than a month (below 40° latitude). For longer study
periods and/or higher latitudes, average-anchoring resolves the problem of
variable day length. Code is provided. The transformation functions are
incorporated in the R-package ‘activity’.