Kenneth W Fink; Photo Researchers 
Snuggling in their afternoon bed- 
ground, two peccaries typify the 
close contact maintained by these 
animals. The herd to which these 
peccaries belong will use another 
site for its nighttime bed-ground. 
ing around the head of a canyon rather 
than crossing directly by going down 
and then up). Obviously, the animals 
know, in some sense, their destination 
(whether a bed-ground or a feeding 
ground) and they take the most ef- 
ficient, but usually not the most direct, 
route to get there. 
Herds also seem to know when they 
are near the borders of their home 
ranges. At these times, the peccaries 
increase the rate of deposition or se- 
cretion from their large dorsal gland, 
a scent organ present in both sexes 
that lies on the midline of the back, 
just anterior to the tail. Tyson made 
much of the dorsal gland in his 1683 
article and, after examining in a with- 
ering fashion the hypotheses of his 
contemporaries that the structure was 
a second navel, a mammary gland, 
a urinary orifice, an intestinal orifice, 
or a spiracle for breathing, he cor- 
rectly identified it as a scent gland. 
But what is most particular in our Hog , 
and makes the greatest wonder; and dif- 
ferences it, from any other Animal I know 
of in the World; is the Teat or Navill 
or Foramen rather on the hinder part 
of the back. All who mention this Animal ; 
look on this, as a thing so extraordinary, 
and uncommon; that I know not how their 
amazement has so far clouded their rea- 
son, as to betray them into most extrava- 
gant Conjectures, and opinions concern- 
ing it. 
Scent marking is probably the way 
in which adjacent herds define the 
boundary between their home ranges. 
This seems plausible because the rate 
of actual interactions between herds 
is extremely low; in a year of field 
observations I saw herds come to- 
gether only twice. In one of these in- 
stances, there was a flurry of short 
chases back and forth, then both herds 
drifted apart and bedded down within 
1,000 feet of each other. In the other, 
the same two herds were together, 
feeding peacefully along the border 
between their home ranges when I 
found them; they slowly fed and am- 
bled in separate directions. 
I tested the idea that scent marking 
might be important in boundary defi- 
nition by erecting fence posts at quar- 
ter-mile intervals along a ridge where 
the home ranges of three herds met. 
Peccaries investigated the posts but 
did not mark them. I then collected 
dorsal gland secretions from a cap- 
tured member of a herd five miles 
away and placed it on the posts. Res- 
idents responded to this new odor by 
marking on top of it, often with such 
vigor that I could smell the posts from 
some distance and could see dorsal 
gland secretion dripping from them. 
This result suggested that peccaries 
recognized an unfamiliar dorsal gland 
scent and re-marked it to indicate that 
the area was occupied. 
The dorsal gland, besides being used 
in scent marking, figures prominently 
in a cooperative social action I call 
the “mutual rub”: two animals ap- 
proach each other and stand side by 
side so that each rests its head against 
the other’s rump; each then vigorously 
rubs the side of its head up and down 
over the other’s rump and dorsal 
gland. This activity lasts about five 
seconds, and no doubt smears the oily 
secretion of each partner’s dorsal 
gland onto the head and back of the 
other. Peccaries also spend much time 
nuzzling each other and lying in close 
contact — two activities that further 
promote the transfer of the secretion. 
The overall result is that each animal 
becomes an effective broadcaster of 
the dorsal gland scent, so much so 
that when herds were directly upwind 
from me, I could sometimes detect 
them by smell. This suggested to me 
that peccaries, with their keen sense 
62 
