Seasonal variation in daily activity patterns of snow leopards and their prey

Abstract

The daily and seasonal activity patterns of snow leopards (Panthera uncia) are poorly understood, limiting our ecological understanding and hampering our ability to mitigate threats such as climate change and retaliatory killing in response to livestock predation. We fitted GPS-collars with activity loggers to snow leopards, Siberian ibex (Capra sibirica: their main prey), and domestic goats (Capra hircus: common livestock prey) in Mongolia between 2009 and 2020. Snow leopards were facultatively nocturnal with season-specific crepuscular activity peaks: seasonal activity shifted towards night-sunrise during summer, and day-sunset in winter. Snow leopard activity was in contrast to their prey, which were consistently diurnal. We interpret these results in relation to: (1) darkness as concealment for snow leopards when stalking in an open landscape (nocturnal activity), (2) low-intermediate light preferred for predatory ambush in steep rocky terrain (dawn and dusk activity), and (3) seasonal activity adjustments to facilitate thermoregulation in an extreme environment. These patterns suggest that to minimise human-wildlife conflict, livestock should be corralled at night and dawn in summer, and dusk in winter. It is likely that climate change will intensify seasonal effects on the snow leopard's daily temporal niche for thermoregulation in the future.

Figure 1

Summary of GPS-movement data: (a) mean 5-hourly movement distance (in meters) for each calendar month for snow leopards (adult males = blue, subadults = green, adult females = red, females-with-young-cubs = grey) and for ibex (orange). The monthly estimates were generated from a random-effects GLMM with the joined points representing the mean and the shaded area the 95% CI of the mean. Ibex estimates were from hourly data and were therefore rescaled to be made comparable to the 5-hourly snow leopard estimates. (b) Histogram of the log-transformed snow leopard GPS-movement data (male and female adults combined) showing the frequency of observed snow leopard movements related to the distance they moved from one GPS position to the next (5 h later). For separate histograms of males and females see Supplementary Figure S2.

Figure 2

The relative proportion of snow leopard activity across the 24-h cycle for adult males and females during winter (blue) and summer (red) for two types of activity data collected from the GPS-collars (a = GPS movement data; b = accelerometer activity data). The activity densities on the y-axis have no absolute meaning, but rather are relative measures of probability density calculated from the raw movement data. The time of all observations has been standardised along the x-axis using ‘sun-times’; where the time of observation on each day is calibrated to sunrise, solar-noon (midday) and sunset. These overlap plots show the activity overlap between winter and summer activity (grey) and highlight periods when activity was greater in winter or summer (blue or red shaded polygons, respectively).

Figure 3

The relative proportion of activity across the 24-h cycle based on GPS movement data for: (a) adult snow leopards (green) versus adult ibex (orange), and (b) adult ibex during winter (blue) and summer (red). The activity density values have no absolute meaning, but rather are relative measures of probability density calculated from the raw movement data. The time of all observations has been standardised along the x-axis using ‘sun-times’; where the time of observation on each day is calibrated to sunrise, solar-noon (midday) and sunset. These overlap plots show the activity overlap (in grey) between: (a) snow leopards and ibex: for periods when snow leopards use more of their activity budget relative to ibex this is shaded (cross-hatched) green, for periods when ibex use more of their activity budget relative to snow leopards is coloured orange. (b) Ibex winter and summer activity: for periods when ibex are more active during winter (shaded blue) or during summer (shaded red).

Figure 4

The relative proportion of activity across the 24-h cycle based on GPS movement data for adult snow leopards (green) versus domestic goats (brown). The activity density values have no absolute meaning, but rather are relative measures of probability density calculated from the raw movement data. The time of all observations has been standardised along the x-axis using ‘sun-times’; where the time of observation on each day is calibrated to sunrise, solar-noon (midday) and sunset. These overlap plots show the activity overlap (in grey) between snow leopards and goats: for periods when snow leopards use more of their activity budget relative to ibex this is shaded (cross-hatched) green, for periods when goats use more of their activity budget relative to snow leopards is shaded brown.

Figure 5

Prediction plots from GAMMs examining variation in snow leopard accelerometer (motion) activity relative to the calendar month for four specific periods during the 24-h cycle: night (black), dawn (yellow), day (blue) and dusk (red). The top two panels show the proportion of total time spent active, and the lower two panels show the activity rate when active. Plots show means (lines) ± SE (shaded areas) generated from the individual models.