Den checks and counting wolf pups:
updates from our spring pup research
By Tom Gable
Project Lead
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Every spring, we visit active wolf dens to count the number of pups in the den and to tag the pups. The tagging process entails briefly removing the pups from the den so that we can sex and weigh the pups, collect a genetic sample, and insert a microchip, which then allows us (or other researchers) to readily identify that pup if it is ever studied as an adult.
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The most valuable piece of information from these ‘den checks’ is counting the number of pups because we need this crucial piece of data to estimate pup survival for each pack. If we do not know how many pups are born in a given pack, we cannot determine what percent survive. Estimating pup survival in forested ecosystems has been a challenge for researchers for decades given how difficult it is to find wolf dens and then keep track of the pups as they grow up. As such, we have made a concerted effort to not only understand pup survival rates but to also understand what drives monthly and annual changes in pup survival.
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We recently finished our ‘den checks’ this spring and we wanted to share updates on what we learned at each den. In total, we visited active dens from 7 packs, counted pups from 5 litters, and tagged 16 of those pups. We were unable to count or tag pups from 2 packs (see below). All-in-all, we were very pleased with how our pup research went this spring and we look forward to studying these pups as they continue to mature and grow.
Arrowhead Ridge Pack
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The Arrowhead Ridge Pack took over the Half-Moon Pack territory late last summer. We do not know where the wolves in the Arrowhead Ridge Pack came from, and we did not have a GPS-collar on any pack members as of early May. However, we knew of dens that the previous packs that occupied this territory (Ash River Pack: 2013-2025, Bowman Bay Pack: 2016-2029, and Half-Moon Pack: 2020-2024) had used. In early May, we hiked out to these old dens in hopes that the Arrowhead Ridge Pack might re-use one. ​
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To our delight, we found the Arrowhead Ridge pups. The pups were in a den below a large boulder that rested on the slope of a substantial ridge. The space beneath this boulder has been used periodically for a den by packs in this area as far back as 2014.
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The pack had a small litter at 2 pups (average litter size is 5 pups in our area). This den is very difficult for people to get in because the den is very narrow toward the back and a person cannot easily fit in. As a result, we were only able to reach one of the two pups to weigh, sex, and tag it. But fortunately, we did get a genetic sample from that pup which might help us understand if the wolves from the Arrowhead Ridge Pack are related to other packs in the Greater Voyageurs Ecosystem.
A pup from the Arrowhead Ridge Pack's litter.
Sophie Heny guiding an Arrowhead Ridge pup back in the boulder den.
Biondich Pack
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We were able to locate the Biondich den via data from a GPS-collar on a 2 year old wolf in the pack. Turns out, the pack had their pups in a burrow created by beavers on the edge of a beaver pond that drained over winter, leaving this burrow nice and dry.
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A pup from the Arrowhead Ridge Pack's litter.
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Inside the burrow, we found 3 pups huddled together. Getting into this den was quite difficult as the tunnel into the chamber where the pups were at was very narrow and quite long (~5 ft long). Nonetheless, we reached all 3 pups and were able to tag all 3 of them. The pups were about 3 weeks old when we tagged them and all appeared to be in good shape.
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This marked the first time we have tagged pups from the Biondich Pack. We wanted to tag pups from the pack last year (May 2024) but for whatever reason, the pack did not produce pups last spring.
A pup from the Biondich Pack litter.
Austin Homkes guiding a pup back in to the excavated burrow den.
Bug Creek Pack
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The Bug Creek Pack seems to have our number! For the 3rd year in a row, we have known where the den is at and yet the pack and their pups have eluded us.
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In 2023, we showed up to their den just 24 hours after the breeding male had spent time at the den—an indication that the den was still being used by the pack—and found that sometime in the last 24 hours the pups had been moved. Thus, the den was empty on our arrival, and unfortunately, the breeding male’s collar quit working the next day due to technological failures. As a result, we could not determine where the new den was.
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Last year, we again showed up to their den as a GPS-collared yearling female had been returning to it for several days. We hiked in and quickly found the den. It was empty. Like in 2023, this GPS-collared wolf had been at the den the previous night. Nonetheless, the pups had once again just been moved to another den.
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We waited a week for the GPS-collared female to return to the new den. After a bit, we determined where the new den was and hiked in, thinking we would find the pups. We showed up to this new den and it was empty as well. At that point (mid-May), the pups were getting fairly old (likely ~5 weeks) meaning they were fairly mobile and could move surprisingly quick.
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Thus, we do not know if the pack had moved the pups just before we arrived or if the pups had simply run-off in the woods with an adult pack member as we approached. Either way, we realized any subsequent attempts to tag the pups was futile.
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That brings us to this spring. We collared a yearling male wolf in the Bug Creek Pack on May 10 and this male subsequently went to and from the den several times over the first week he was collared. Again, we put on our hiking boots and walked in, hopeful we would finally find the pups. Yet, we showed up to the den, which was a very well-worn area around a large upturned white-pine, but the pups were gone. The pups had been moved sometime the night or day before! And so, we did not tag any Bug Creek Pups this year yet again.
Laphroaig Pack
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The Laphroaig Pack occupies the southwestern corner of the Greater Voyageurs Ecosystem. Last fall, a GPS-collared subordinate male from the Stub-tail Pack left the pack and became the breeding male of the Laphroaig Pack. The pack gave birth to a litter of pups in mid-April this year.
The Laphroaig den was a super-long excavated tunnel in the side of a conifer-covered ridge right along a creek. Even after crawling 5 feet into the den, we could not see the end of the den, or view all the nooks and crannies that appeared to fork off of the chamber in the back of the den. This kind of den is all but impossible to count all the pups in because there are so many places for the pups to hide out of sight. Additionally, even if we could see all the pups, we would never be able reach them because of how long and narrow the tunnel into the chamber is.
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Fortunately, a pup was outside of the den when we arrived so were able to tag that little guy. However, we did not see or tag any other pups. But, we installed trail cameras at the den after we tagged this pup, which revealed that the pack had two pups—the one pup we tagged and another one we did not tag.
Mithrandir Pack
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The Mithrandir Pack occupies the central portion of the remote Kabetogama Peninsula in the middle of Voyageurs National Park—a spot we are rarely able to study wolves because of the difficulty of GPS-collaring wolves in such an area. But, fortunately, a GPS-collared wolf from south of the Voyageurs National Park settled down in this territory last winter. This spring, this wolf and his mate produced a litter of pups.
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When we showed up to this den, we found 5 pups milling about in a den underneath the branches of some downed trees. Luckily, counting and subsequently tagging the pups was very easy and straightforward in such an open den. The only complication we faced was that one of the pups in this litter was very feisty. This little pup was growling at us well before we ever reached the den and certainly did not appreciate being picked up.
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One of the fascinating aspects of tagging pups, like in this instance, is seeing the variability in the behavior of pups within the same litter. Most pups are very docile but every once in a while, we find some seemingly dominant pups who are quite feisty and put up a fight. Although difficult to determine, we think it would be fascinating to see if such a difference in temperament influences a pup’s eventual survival.
Three pups hunkerdowned nearby the Mithrandir den. The pup to the left was the feisty one!
Paradise Pack
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The Paradise Pack had the largest litter of any of the packs we visited dens for this spring. The pack had 8 pups, just one shy of the largest litter we have ever observed (9 pups). The pack’s den was primarily in a rocky overhang near the top of a pine-covered ridge. However, there were many large boulders and other crevices in the vicinity of the den that the pups could hide in.
A pup from the Paradise Pack litter.
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​Although we saw all 8 pups, we were only able to get our hands on 6 of the pups—2 pups were hunkered down at the far end of a thin, long cavity underneath a huge boulder and we could not squeeze into the space to reach them. Such an occurrence is not uncommon for us. Pups are experts at wedging themselves into inaccessible places, a strategy that likely is beneficial when predators such as bears visit dens.
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We tagged the 6 pups we could reach and all were very docile. Afterwards, we put them back in the den, and then set-up a few trail cameras to observe the pups after we left. We have not collected the trail cameras yet but hopefully we will capture some neat footage to share soon.
The Paradise Pack's den under the large, rocky overhang.
The Paradise Pack's den under the rocky overhang.
Stub-tail Pack
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We learned about the location of the Stub-tail den around mid-May—a time when pups are getting large and very mobile—when we collared a yearling male in the pack. We promptly hiked into the den hoping the pups were still small enough that we might be able to count and tag them.
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However, we an unexpected surprise. The Stub-tail den was without a doubt the deepest den we have ever observed. More specifically, the den started was along the bank of an old abandoned gravel pit, with the main tunnel of the den burrowing back 15-20 feet or longer (we couldn’t see the end). And notably, this tunnel was very narrow.
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Further, about ~12-14 feet into the den, we could see there was another chamber or tunnel that dog-legged to the left. Even after crawling 4-5 feet into the den, we could not see any pups. We realized crawling in any further would be futile because we would never be able to safely reach the back of the den even if we could see pups in it.
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The den was an expansive labyrinth it seemed. Although it was disappointing we did not get the data we wanted, we could not help but be amazed at how deep the pack had excavated this den.
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Near the den entrance, we saw several pup scats that were fairly large for this time of year. Given the size of the scats, we concluded that the pups were already at least 5-6 weeks old and future efforts to tag the pups would likely be unsuccessful because the pups would be too mobile. So, the Stub-tail pups evaded us this spring!