Information transfer among widely spaced individuals: latrines as a basis for communication networks in the swift fox?

1. What they did

Swift foxes are small foxes of the North American short-grass prairie. Pairs live in large home ranges (about 8 km² in this study area), so neighbours rarely meet or hear each other. The authors asked whether latrines, places where foxes leave collections of scats, urine and possibly other secretions, could let several foxes pass information to each other over time, even when they are never in the same place at once. They predicted that latrines would be concentrated where the home ranges of neighbouring pairs overlap.

• Mapping home ranges. They live-trapped 22 adult foxes from 12 mated pairs, fitted them with very high frequency (VHF) radio collars and located each fox at night by triangulation, aiming for 40 locations per fox per season, from January to March 2005 and 2006. From these they mapped each pair’s home range (99% contour) and core area (50% contour), and the areas where neighbouring pairs overlapped.
• Searching for scats (February and March 2005). Observers walked transects, each only once, along landscape features such as tracks and fence-lines, where pilot work showed latrines were likely, and across open prairie. They recorded every swift fox scat with a Global Positioning System (GPS) unit and noted where it lay. Two or more swift fox scats from at least two deposition events counted as a latrine. Scats were scored as NEW (current season, intact surface) or OLD (previous season, surface missing), and any coyote scats in a latrine were counted.
• Checking the counts. Each latrine was photographed. A second observer recounted 15% of latrines from the photos, and all observers searched the same 1 km strip to check that they found scats equally well.
• Measuring use and reuse. Latrines were revisited at the end of March 2005 to estimate how many scats were added per day, and again in January and March 2006 to see which latrines were in use the next breeding season.
• Watching visits (February and March 2006). Motion-triggered infrared video cameras watched 10 latrines in overlap areas, recording what foxes did there.

2. What they found

Scats and latrines

• On 212 km of transect they found 580 latrines and 1630 single scats. On average, each pair had 13.7 km of transect, 89.2 single scats and 48.6 latrines in its home range.
• A latrine held on average 5.9 new scats (7.8 in total). Latrine size was not affected by location in the home range or by coyote scats.
• The two observers’ scat counts from photos agreed closely (correlation 0.91, average difference 1.7 scats per latrine), and observers were equally likely to find latrines and single scats.

Where latrines were

• Latrines were closer together, and denser along transects, inside a pair’s core area (0.65 latrines per 100 m) than outside it (0.33 per 100 m).
• Latrines were also closer together in areas where neighbouring pairs’ home ranges overlapped.
• Latrines containing coyote scats tended to be farther from the next latrine, though this was not quite significant.
• Single scats were also denser inside core areas (1.11 versus 0.85 per 100 m), but, unlike latrines, were not more common in overlap areas.

How latrines were used

• Scats were added fastest at latrines in two places: inside the core area where it was not shared with neighbours, and outside the core where it overlapped with neighbours.
• The next breeding season, latrines were more likely to still be in use if they were in an overlap area, and less likely if they were outside the core. Latrines in non-overlap areas outside the core were the least likely to be reused.

Behaviour at latrines

• In 270 camera nights, 56 video clips showed foxes. In 19 the fox did not approach the latrine.
• In the other 37, the fox sniffed the latrine, and 75.7% of these visits ended with the fox leaving a mark. Urination (67.6% of all visits) was much more common than defecation (21.6%). Foxes rubbed on the latrine only twice.

3. What they concluded

• Swift foxes do not leave their scats at random in their home ranges.
• Latrines probably have a dual function. In the exclusive part of a pair’s core area they probably help maintain the territory. In outer areas shared with neighbours they probably act as information centres where neighbouring foxes exchange information.
• Latrines may be an economical way to mark: many marks in one small place make a stronger, easier-to-find signal, and give both senders and receivers a predictable place to exchange information.
• Because urination was the most common mark, scats may not be the most important information at a latrine, but they may be the long-lasting part because they persist in the landscape.
• During the mating season, latrines may carry information on who a fox is, their sex and reproductive state, and on interactions between foxes. Females may advertise their presence and fertility, and males may advertise their presence or defend paternity. Swift fox populations can have high rates of extrapair paternity.
• Within a pair, information is probably exchanged through sharing daytime dens rather than at latrines.
• Neighbouring foxes, and any transient foxes, may form a communication network around a pair’s edge latrines. Future studies should record when resident and non-resident foxes visit latrines and what they do there, and include other marking media such as urine.

4. How tracking was or was not used

The study rests on finding and identifying signs. Observers walked transects and recorded every swift fox scat, told swift fox scats from coyote scats, and judged each scat’s age from its surface: intact for the current season, missing for a previous season. Latrines were defined from scats of at least two deposition events. Pilot observations showed that latrines tended to lie along tracks and fence-lines. No following of tracks was reported. The foxes themselves were located by radio telemetry, and their behaviour at latrines was recorded with video cameras.

5. Tracker or observer certification

Not reported. Nothing is said about the observers’ experience in identifying scats. The authors did test observers in two ways: all transect observers searched the same 1 km strip and were equally likely to find latrines and single scats, and a second observer recounted 15% of latrines from photos with close agreement. How swift fox scats were told apart from coyote scats, and how reliable the new versus old scoring was, is not described.

6. Other technologies, skills or innovations

• VHF radio collars (45 g, with mortality sensor) and triangulation from a vehicle.
• Box traps with a custom fine mesh to avoid broken teeth or jaws, and a single-person handling method in a fabric bag, without anaesthesia. One fox chipped a canine tooth; no other injuries were reported.
• Handheld GPS unit (Garmin GPS 72) to map scats.
• Digital photographs of each latrine, so scat counts could be checked in the lab.
• Motion-detector infrared video cameras (Leaf River IR-3BU) recording 90-second clips at latrines.