Vigilance in badgers
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human persecution of badgers in Wytham has been minimal during this century and non-existent
during recent decades.
In Nibley, infra-red video recordings were made outside main setts of 2 social groups every night
during July–August in 1995 (Quarry and Waterley) and 1996 (Nuclear and Waterley). In September
1995, the government removed 6 social groups in North Nibley (see Tuyttens et al. 2000). Because
access to Quarry was difficult in 1996, filming took place at Nuclear instead. Nuclear was chosen
because it resembled Quarry most in position and environment. In Wytham, various social groups of
badgers have been filmed since 1994 as part of a long-term study (Stewart 1997). We used recordings
made at 4 setts (Sundays Hill Outlier, Pasticks Main, Pasticks Outlier and Pasticks 3) in 1995, and at
3 setts (Pasticks Main, Pasticks 2 and Pasticks 3) in 1996.
The video-surveillance system has been described in detail by Stewart et al. (1997). It consists of a
camera and microphone linked to a remote time-lapse video-recorder. The video-recorder was
programmed to record at fixed times (before dusk till after dawn) and switched from slow-mode to
real-time mode by alarm triggers connected to motion detectors. Infra-red light sources were used and
power was supplied using rechargeable car batteries. Stewart et al. (1997) report that badgers quickly
habituate to the video equipment. Badgers that had been live-trapped prior to the video-recording
periods were given a fur-clip to allow individual identification (Stewart and Macdonald 1997).
Emergence times in Nibley versus Wytham
The average time the first individual emerged from a sett at dusk was compared between Nibley
and Wytham during July–August 1995 and 1996. We used a generalised linear model to test for an
effect of location, year, and year by location on emergence times. The latter analysis investigates
whether the variation in emergence time between 1995 and 1996 differed between badgers that had
been subjected to culling operations in the meantime (Nibley) as compared to badgers that had been
left undisturbed (Wytham). More specifically, this analysis aims to test whether emergence times had
been delayed by the most recent badger culling operation in Nibley (September 1995).
Effect of aggregate group size on vigilance
Focal sampling was used to measure duration and frequency of bouts of vigilant behaviour for each
identifiable individual in view of the camera for different group sizes. A bout of vigilant behaviour was
deemed to have occurred when the badger interrupted its activity, its body stiffening and its head
facing in a fixed direction or scanning from side to side. Pilo-erection may sometimes occur. Aggregate
group size was determined as the number of badgers in view of the camera. Camera positions were
fixed on activity platforms above the sett. These analyses were restricted to recordings made at an
annexe sett of Sundays Hill social group in Wytham Woods between 24–27 May 1995 (annexe defined
as per Kruuk 1978). There were ca 21 adults (of which 18 identifiable) and 4 cubs (of which 2
identifiable) in this social group.
Vigilant behaviour was quantified in 2 contexts: (a) when badgers first emerged from the sett at
dusk (‘emergence vigilant behaviour’), and (b) later in the night after all badgers had already spent
some time above ground (‘post-emergence vigilant behaviour’). Time during emergence was defined to
start when the head of a badger appeared from the sett for the first time in a night until 2 minutes had
passed or until another badger appeared that had not been in view of the camera when the focal animal
started to emerge. The proportion of time spent being vigilant during and post emergence was
calculated. Observations for all individuals were averaged to obtain total time spent being vigilant for
each group size (range: 1–8). We tested the effect of aggregate group size on vigilance with a linear
model using the proportion of time spent being vigilant as the dependent variable with badger identity
and group size as the independent variables. For each combination of badger and aggregate group size,
the observation was weighted according to the total amount of observation time contributing to it.
Corporate vigilance, ie the time for which at least 1 badger in the group was vigilant, was also
calculated for different group sizes.