Researchers working in the Greater Voyageurs Ecosystem in northern Minnesota picked up five fresh wolf scats packed with digested fruit, dried them for three to four weeks and froze them. Months later they teased the blueberry seeds out by hand and set them on wet filter paper in a growth chamber. Separate batches of seeds taken straight from wild blueberry bushes were grown as controls, under the same chamber conditions. The seeds that had been through a wolf did better on both counts the team was measuring.
Of the 802 scat-passed seeds sown, 96 percent germinated, with a 95 percent confidence interval of 94 to 97 percent. Of the 484 control seeds, 69 percent germinated, confidence interval 65 to 73 percent. Half of the wolf-passed seeds had sprouted by day 19; the controls took until day 26.
The result was published on 26 August in Biology Letters by Alex Gross, Thomas Gable, Austin Homkes, Kathy Winnett-Murray, Ryan Woodside, Joseph Bump and K. Greg Murray, and it makes the grey wolf the largest canid known to improve the germination of seeds from fruit it has eaten.
Why is an apex predator eating fruit?
Wolves are mostly ungulate hunters, and the image of a wolf as a pure carnivore is close enough to true for most of the year. In midsummer in the southern boreal forest it stops being true. Wild blueberries, mainly Vaccinium angustifolium, come ripe in the Voyageurs country from early to mid-July until the middle of August, growing thickly on rock outcrops, hilltops, open conifer stands and logged or burned black spruce bogs.
Earlier work led by one of this paper’s authors found that during those peak weeks berries made up as much as 83 percent of the weekly diet biomass of a wolf pack in northeastern Minnesota. The new paper cites that literature as putting berries above 30 percent of a pup’s diet. In August 2017 an adult wolf was observed regurgitating wild blueberries for pups at a rendezvous site in this ecosystem. Its authors described it as the only known observation of wolves provisioning pups with wild berries, and said it suggests berries may matter more to wolves than had been appreciated. A 2024 camera-trap study concluded that berry foraging is widespread here and likely in similar southern boreal ecosystems.
The open question was what the wolf does to the seed on the way through. Passage through an animal gut can help a seed, harm it or do nothing, and among the dog family the answer has come out differently for different species. Red foxes and coyotes have been found to improve germination in several studies. Domestic dogs, gray foxes, crab-eating foxes and coyotes again have been found to reduce it or leave it unchanged in others.
If a seed’s germination rate can jump this much just from passing through a wolf, imagine what else shifted when wolves returned to Yellowstone after seventy years of being gone — the riverbanks, the willows, the beavers, the whole shape of the park. A video on This Is Earth, “The Wolf That Rebuilt Yellowstone,” walks through that entire chain reaction, and it’s worth watching if you want to see how one animal coming back changed a whole ecosystem:
How do you test what a wolf does to a seed?
The scats were collected opportunistically over two summers, three in 2017 and two in 2018, all judged one to two days old and all filled primarily or entirely with digested fruit. Control seeds came from intact berries picked from ten wild plants a year, in 2017, 2018 and 2019.
Immature seeds and empty seed coats were floated off in water and the remainder checked by eye. Randomly chosen subsets were then laid on Whatman no. 2 filter paper in 90 by 15 millimetre Petri dishes. The seeds used from any one scat were grown together as a single trial, so the treatment group is five trials and the controls are three, one per collection year. The eight trials were not run concurrently, which matters later.
The dishes sat in a Conviron growth chamber on 16 hours of light and eight of dark, at 60 percent humidity, cycling between 21.5 degrees Celsius in the light and 9.5 in the dark. Full-spectrum lamps delivered about 500 micromoles per square metre per second. The seeds were watered daily for 60 days, and one counted as germinated once its radicle pushed about half a millimetre clear of the coat.
The team had intended to model germination speed with a Cox proportional hazards regression and abandoned it when the data failed the test for proportional hazards, the hazard ratio between the two groups not staying constant over time. They fell back on Kaplan-Meier curves and log-rank tests, which make no such assumption.
What happened in the dishes?
Pooled, the gap is wide. Fisher’s exact test on germination success returned a p value below 0.001 and an odds ratio of 9.45, and the log-rank test on the cumulative curves returned a p value below 0.0001 with a chi-squared of 276.
The five wolf trials varied somewhat but all landed between 91 and 100 percent, on similar curves. The three control trials did not hold together. The 2017 batch germinated at 42 percent, the 2018 batch at 91 percent and the 2019 batch at 81 percent. The last of those was cut off at 40 days rather than 60 by a COVID-19 shutdown, with its curve at or near its plateau. The researchers say plainly that they do not know why the 2017 seeds did so badly, though they suspect the extraction and the storage.
That suspicion has some ground under it. The scats were dried for three to four weeks and then held at minus 15 degrees for 134 and 127 days. The 2017 controls were frozen inside the whole fruit for 43 days, dehydrated, shipped at room temperature for 11 days, then frozen again for 144. The 2018 controls spent 98 days at room temperature before 97 days frozen; the 2019 controls spent 120 days warm and then 265 frozen. Treatment and control seeds were not handled the same way, and no two control years were handled the same way either.
Is the gap as big as it looks?
Pool all three control trials and wolf passage raises germination success by 27 percentage points, from 69 to 96. Set the same 802 seeds against the best control trial alone, the 2018 batch, as the paper does because of how much the controls varied, and the advantage falls to five percentage points, 96 against 91. Both comparisons clear significance, the second with an odds ratio of 2.10 instead of 9.45. Which figure belongs in a headline turns largely on whether the 42 percent batch belongs in the calculation.
The paper does not choose, and says why: its results clearly indicate an increase in speed and success, while the extent of that increase is less certain. Even five points could be considerable, the authors argue, given how numerous and widespread blueberry-filled wolf scats are in this landscape through the summer months.
Speed holds up better under the stricter test than size does. Against the 2018 controls, wolf-passed seeds still reached their halfway point four days sooner, 19 days against 23, and among only the seeds that did germinate the median was 18 days against 23, which the paper reports as 22 percent shorter.
One more thing the arithmetic hides. The 27 and the 5 are percentage points, the plain difference between two success rates, and not proportional increases; expressed proportionally the same two comparisons come to about 39 percent and about 5.5 percent. The paper’s own phrasing, “increased germination success by 27%”, invites the second reading.
And every one of those numbers came out of Petri dishes on filter paper in a chamber. No germination in this study was measured on a forest floor, which the authors point to as the next test. The seeds a wolf actually leaves behind arrive clumped in one parcel, in whatever microhabitat the animal happened to be standing in, and both of those likely influence what happens. The seeds also came from five scats produced by an unknown number of wolves, which could be five animals or one animal five times.
How far could a seed ride?
How long a blueberry seed stays inside a wolf has not been measured. That one missing number sits between this germination result and the claim the paper builds on it in its abstract, that wolves are likely effective long-distance dispersers of blueberry seeds. Any distance anyone quotes is an assumption about retention time wearing a number’s clothes.
What the paper offers instead is a bracket. Wolves cover ground at around 8.7 kilometres an hour in regular travel, a figure measured in arctic wolves, so the authors note that even one or two hours of retention could carry a seed a long way from the bush it came from. They also point to work published last year in a southern boreal Minnesota system. As this paper reports it, that study estimated that wolves held fungal spores in their guts for 16.1 hours after eating spore-carrying small mammals, and dispersed them an estimated 3.5 kilometres on average. Whether berry seeds behave like spores in a wolf gut has not been tested.
The wolves themselves make the geometry plausible. GPS collar data from three animals in one pack, tracked from 10 July to 16 August 2024, show them working repeatedly between separate known berry patches inside a single territory. That is the movement pattern that could carry seed from an established patch into a new one, which is what the authors suggest may happen in recently burned or clear-cut ground.
Why did nobody ask this sooner?
The percentages here would move if anyone repeated the experiment with matched storage and a larger set of scats. The more durable finding is that a question this basic, about an animal this closely studied, stayed open until 2026.
The authors offer three likely reasons. Wolves are apex predators that mostly kill larger-bodied prey, and the questions asked about them have accordingly been questions about killing: what they take, how much, and what happens to the prey population. Wolves also have a narrower dietary breadth than most of the canids already known to help seeds along. And their seasonal frugivorous tendencies, as the paper puts it, were not well documented until recently, which the summer diet work of the past few years changed.
This is not a case for the wolf as a gardener, and the paper makes no such case. Its wider suggestion is that an animal can be thoroughly described by one relationship and still be doing something else that matters. Sometimes the something else is sitting in a pile of scat on a logging road in August, waiting for somebody to think it worth picking up.