Discussion
Our results demonstrate that community photography, including old and
recent images, has potential for investigating phenological differences
across wide spatial areas. In particular, we have shown that statistical
analyses can be informative even when a significant fraction of the
photographs are missing information (e.g., animal states), which is
often inevitable with community science data. We were able to
incorporate nearly all of the community science photographs that were
associated with uncertainty into the statistical analysis by building
missingness explicitly into the statistical model expectations.
Conclusions drawn from the community science analysis are supported by
similar conclusions drawn from the analysis of our Yukon Wildlife
Preserve data that included complete data and repeated observations of
individuals.
Our findings (using both crowd-sourced and field-sourced data) on sex
differences and effects of new (current year’s) kids are also consistent
with earlier published results from Caw Ridge, west-central Alberta
(Déry et al., 2019) as well as with the recorded knowledge of a Tlingit
weaver (Rofkar, 2014) who observed that nannies finish moulting only
after weaning their kids. The stage of hair moult has also been used to
make assumptions about sex and reproductive status in the field
(Chadwick, 2002).
Community-sourcing of photos was generally successful; every naturalist
with existing mountain goat photos already uploaded on iNaturalist
granted us permission to have their photos included in our analysis and
some people uploaded additional photographs after learning about our
study. More than 100 people submitted photos via our designated CitSci
platform. That we detected sex and kid effects using photos
crowd-sourced over approximately one year demonstrates that community
science can be leveraged to boost research scope, scale and speed
especially if it can be validated against long-term and/or carefully
field-sourced data.
While our sample had broad spatial coverage (Figure 1) directly
inferring the effects of latitude and elevation on moult was difficult
due to their negative correlation. Where mountain goats have access to a
range of elevations (e.g., in the southern Rocky Mountains) there are
presumably advantages as the climate warms as average temperature drops
by approximately six degrees Celsius for every 1000-meter increase in
elevation. However, as observed in cashmere goats (Capra hircus )
wool is also thicker at higher elevation, so presumably there is also
more to shed if animals shift higher up, a pattern noted by British
military officer Cecil Rawlins when above 4000m in Tibet in 1905
(Berger, 2018). We found later and slower rates of moult in mountain
goats where they were photographed in high mountains / higher
elevations, although we acknowledge this does not account for their
vertical movements as photographs are mere snapshots of locations and
not indicative of long-term responses or behaviour (Beever et al.,
2017), for example shade-seeking or timing of activity.
We found later moult at higher latitudes in contrast to findings in
muskoxen where earlier shedding occurred in animals at 69 degrees N than
at 57 degrees N (Wilkinson, 1974). Whereas photoperiod is considered to
be a primary cue for moult (Lincoln and Ebling, 1985; Zimova et al.,
2018), temperature also plays a role; for example, cattle populations at
the same latitude but different temperatures show earlier moult where
lower and warmer (Murray, 1965). In northern mountain goats, delayed
moult may be warranted if a warm coat is still needed for the late
spring cold. Rate of moult was faster at the lower elevation, higher
latitude sites, which might also be explained by northern mountain
goats’ need to put winter coats on more quickly in time for winter.
We found no clear long-term climate signal, however, consistent with our
hypothesis that moult may occur earlier in the year in recent years
because of climate warming, we detected some evidence of earlier moult
in 2015-2018 (Figure 5A). Our inability to tease apart long-term change
with random but recent shifts to earlier shedding may be partly due to a
limited sample of historical photographs. Specifically, more than 90%
of our 650 photos were from the year 2000 and later. Further outreach
and time would be required to meet the objectives of boosting sample
sizes and reducing bias, especially for the acquisition of historical
images. However, such data are necessary to enable a more rigorous
assessment of the extent to which climate is driving shedding schedules.
Analyzing shed extent from photographs by hand is slow, thus as data
accumulate an important research focus will be how best to employ
automated processing of photographs (e.g., Artificial Intelligence,
machine learning).
One further caveat, and an indirect effect of climate change, was the
prevalence of ticks (Dermacentor andersoni ) and their effect on
moult patterns. We noted visible hair loss in mountain goats’ shoulder
areas associated with active rubbing, especially at Glacier National
Park (the locale of most crowd-sourced photographs) and where others,
notably Douglas Chadwick and Sumio Harada observed these tick-affected
bare patches (personal communication, 2018). As moult starts at the
face, loss of hair and irritated skin at the shoulder area when the face
and neck are not yet shed can most likely be attributed to ticks and not
to moult onset. However, we did not attempt to distinguish tick-related
loss of hair from regular moult. Our Yukon data offer a tick-free
baseline for the far north; while ticks were first detected in the Yukon
in the early 1990s and have also been found on ungulates in the NWT,
these ticks are cervid-specific and it is highly unlikely that they have
reached mountain goat range in the Yukon. Future moult research would
still more carefully distinguish between regular moult and tick-affected
hair loss resulting from rubbing.
Our future work will explore the potential to reduce analysis effort and
time by linking the CitSci platform with Zooniverse, where community
scientists engage with image classification tasks. From a community
science theory perspective, such a linkage offers opportunities to study
cross-over motivations between volunteers submitting photos and those
classifying images. Given opportunity for additional field research, it
would be valuable to compare the captive herds of the YWP with adjacent
wild mountain goats (at the same latitude) to explore the roles played
by nutrition and relative safety from predators in moulting.