Wolf Howling and Its Role in Territory Maintenance

1. What they did

Wolves keep their pack territories with very little overlap, and fights between packs can kill. Scent marks tell neighbours who has been there, but not where the pack is right now. Howls carry that news instantly over long distances, so the authors asked whether howling helps wolves keep their territories.

In Minnesota’s Superior National Forest they worked with radio-collared wolves from eight packs, plus ten lone wolves:

• Finding the wolves. Collared wolves were located from the air about twice a week, and from the ground at night with an antenna on a truck. The researchers stopped within hearing range (200 to 1,600 m) and stayed by the truck.
• Howling to them. A person imitated a wolf: three to five howls of 5 to 6 seconds each, kept as similar as possible from trial to trial. Earlier work had shown that wild wolves answer people as well as or better than recordings, and treat the human howler as a strange wolf. About 80% of the roughly 1,900 trials were by Harrington.
• Recording the replies. They taped the answers and made about 4,000 sound pictures (sonagrams) to count how many wolves replied and whether pups or adults howled. They followed the radio signals to see whether wolves stayed, came closer or moved away.
• Comparing situations. They compared reply rates at pup-rearing “rendezvous sites”, at kills, in different seasons, for groups of different size and makeup, for wolves alone, and for lone wolves with no territory.

2. What they found

How often wolves replied

• Pack wolves replied to 494 of 1,783 trials (27.7%). There was no sign that wolves got used to the howling.
• Away from rendezvous sites, packs replied in about 30% of sessions, with peaks in March and from August.
• At rendezvous sites, they replied in 77% of sessions.
• Near kills, they replied in 73% of sessions, against 35% elsewhere in the same months. Replies dropped as a kill was eaten. Two packs replied at moose kills but not at deer kills.
• Groups with alpha animals replied in 7% of sessions before the breeding season and 40% during and after it.

Who replied

• Away from rendezvous sites, adults began almost every group reply. At rendezvous sites in 1973, pups began 94% of them.
• Wolves alone rarely replied. Among adults, only the alpha males ever replied alone, and the Harris Lake alpha male once howled at least 66 times in a 2-hour session.
• Pups alone replied more often than yearlings alone.
• Bigger packs replied more often, sooner (30 to 40 seconds after the howl) and for longer (at least a minute).
• Lone wolves never replied when alone (26 sessions). The only two replies came from two or three loners at a kill.

What wolves did

• Most movement was away from the howler. Wolves that replied stayed at or near their spot 89% of the time; wolves that stayed silent, 69%. Single wolves often moved off even after replying.
• Adult pack wolves approached at least seven times, usually after repeated howling, and whenever the wolf could be identified it was an alpha, usually the alpha male. No other collared adult was ever known to approach. One alpha male came onto a snowy road near the howling site, leaving fresh tracks, a scat and a raised-leg urination.
• Young pups (under 4 months) sometimes approached, looking curious. After September, pups moved away instead.
• Three times, wolves at rendezvous sites 9.4 to 10.8 km away howled within a minute of the researchers’ howls, suggesting wolves can hear howling from at least 9 km. People heard wolves at up to 5 km.
• Packs that replied more also scent-marked more: the ranking of three packs was the same for howling and raised-leg urination.

3. What they concluded

• Wolves treated the human howler as a stranger, not as a lost pack member. Their responses were part of contests between packs.
• Three factors that raised reply rates (pack size, social role and the breeding season) are the same ones that raise aggression toward strange wolves. The other two, kills and pups, are valuable resources that a pack has to keep to itself. This is strong circumstantial evidence that howling helps keep territories.
• Howling seems mainly to help packs avoid each other. Packs rarely approached (under 3% of sessions).
• Replying has a cost: it tells others where the pack is. So a pack with a kill or young pups stays and replies, while a pack with nothing to defend tends to leave quietly.
• Wolves were within hearing of at least one neighbouring pack about 78% of the time, and conditions allowed howling exchanges on about 40% of nights in the nomadic season.
• Scent marking and howling work together: scent marks are long-lasting and tied to a place; howling is immediate and long-range.
• Lone wolves, with no territory to advertise, keep a low profile.

4. How tracking was or was not used

The main method was radio tracking and howling, not tracks and signs. Tracks and signs were used along the way:

• Tracks helped the researchers work out which wolves were in a group, or whether a collared wolf was alone.
• After one approach, fresh wolf tracks on a snow-covered road showed where a wolf had come out of the woods, walked past the howling site and gone back in. A scat and a raised-leg urination there were taken as a sign of an alpha male.
• After another approach, fresh tracks and much scent marking along the road the next morning centred on the first howling site.

The authors note that it was impossible to tell by ground radio tracking whether wolves were at a kill or just near it.

5. Tracker or observer certification

Not reported. The track and sign observations were made by the research team; no tracking skill or experience is described. They are supporting details, not central to the findings.

6. Other technologies, skills or innovations

• Radio collars, aerial and ground radio tracking from an antenna-equipped truck.
• Human imitation of wolf howls, checked against recorded wild wolf howls for length and pitch.
• Nagra IV-D tape recorder with Sennheiser parabolic and directional microphones; sonagrams on a Kay Vibralyser, used to estimate the number and age class of wolves replying.
• Automatic monitors recording howling at rendezvous sites.