A moose browsing on birch on the Kenai National Wildlife Refuge. (Photo by Colin Canterbury/FWS)

A moose browsing on birch on the Kenai National Wildlife Refuge. (Photo by Colin Canterbury/FWS)

Refuge Notebook: Moose and pizza: A matter of taste?

Special note from Kris Inman, refuge supervisory wildlife biologist: From time to time, we look back at previous articles, and this article stood out at first by its title. It struck an unusual chord with me because I had heard moose and pizza in the same sentence twice in the last week — not something that one would typically connect!

The first reference to this unlikely combo came from good friends visiting from Montana suggesting we eat at Moose’s Tooth Pub and Pizzeria in Anchorage. So why was I hearing it again?

My hand hovered over the archived link, and with one mouse click, I saw the second reference to moose and pizza unfold. I was compelled to read based on the title, then the information, and the homage to past researchers on the Kenai refuge, as we continue to celebrate our 80th anniversary.

So, I felt it fitting to share Ed Berg’s July 16, 1999, article on moose and pizza.

In a previous notebook article, I told of those strange green “roses” growing on willow bushes. The willow roses, the reader may recall, are actually growth deformities called “galls,” which are induced by a small fly (midge) larva. The midge larva eats the stem’s growing center and prevents the stem from elongating, so the leaves emerge on top of each other to form a “rose.”

Now here is the puzzle: Why do moose dislike eating willow roses? Observant moose watchers will notice that about midwinter, there are still a lot of willow roses (now dry brown leaves) on the willow bushes, whereas the ungalled branches are heavily browsed.

My attention was first drawn to this phenomenon when I discovered an old 1982 report in the Kenai Peninsula Wildlife Refuge files by former refuge biologist Ed Bangs. (Ed had moved into the public eye as the director of wolf reintroduction in Yellowstone Park and later as the U.S. Fish and Wildlife Service wolf recovery coordinator for the northwestern U.S.)

Ed tagged stems on 15 willow bushes and found that the moose ate about three times as many ungalled as galled branches. This choice is probably about the same degree of preference that one would find in teenagers for, say, pepperoni pizza over plain cheese pizza.

To convince myself that this browsing preference was real, I repeated Ed’s study in more detail in the winter of 1994-95. I tagged 65 Barclay’s willow bushes along the roads near my place in Funny River and carefully matched the tagged branches (with galls and without galls), so they were about the same height above ground and the same stem diameter.

In the fall, I labeled the branches with twine (which would be harmless if eaten) — one turn of twine if ungalled and two turns if galled. When I checked the bushes in April, I found that the moose had eaten 78% of the ungalled stems and only 52% of the galled stems. This preference wasn’t as strong as Ed found, but it looked real enough.

During this same winter (1994-95), Nikiski High School senior Ethan Ford came into our office searching for a science project. We hatched the idea of doing some feeding experiments with live moose at the Moose Research Center.

We soon enlisted the assistance of Curt Shuey, the MRC caretaker, refuge biologist Richard “Mac” McAvinchey, and former Alaska Department of Fish and Game moose biologist Chuck Schwartz. (Chuck, too, moved on to grander experiments and worked as the U.S. Geological Survey Interagency Grizzly Bear Study Team leader in Montana).

We did two experiments with “tame” moose at the MRC. In the first experiment, we offered the moose 5-gallon buckets with willow branches frozen in snow: some buckets had only galled stems, and others had only ungalled stems.

Then, we provided each (of five) moose a pair of buckets (galled and ungalled) for 10 minutes, and we computed the amount eaten by weighing the buckets before and after the feeding. Ten minutes was plenty of time because these moose were hungry, and willow is like candy to a moose.

The preference was clear: they ate almost three times as much ungalled as galled stem (by weight). This result confirmed with tame moose what we had seen along the roadsides with wild moose, and it wasn’t too surprising.

The second experiment was more interesting to my way of thinking. When teenagers prefer pepperoni over plain cheese pizza, the preference is based primarily on taste and not texture. So, do galled stems taste bad to moose?

One extreme possibility is that the tiny (4 millimeters long) midge larva has a powerful bad taste. Unfortunately, we couldn’t see any easy way to test this, although we could have collected a bunch of larvae and spiked the moose pellet rations with them. But the larva seemed so small that we decided to assume that it was flavorless.

A more interesting possibility is that the larva stimulates the plant to produce a bad-tasting chemical that would help protect the insect and the plant from being eaten. Many plants have an elaborate chemical defenses that poison their would-be consumers or significantly reduce palatability.

Have you ever noticed the powdery white scale on birch bushes around here? These scales are papyrific acid, which the plant secretes when it has been damaged by browsing. These scales make birch very unpalatable to hares and moose to a lesser extent, and hares will starve rather than eat heavily scaled birch.

To test for a taste effect, we prepared more buckets of galled and ungalled willows, but this time we clipped off the galls from the galled branches and also clipped off the current year’s growth on the ungalled branches.

The branches in each bucket now looked exactly the same and had the same texture. So if the moose preferred one bucket over another, it would have to be a matter of taste, we reasoned. (This is like taking the pepperoni off a cooked pizza and telling someone that this is just a plain cheese pizza. Can they tell the difference?)

The moment of truth came we presented each moose with the two identical-looking buckets, and lo! they ate the same amount from each bucket. Hypothesis rejected! Taste was irrelevant! It appears that texture is crucial: The moose simply don’t like eating a mouthful of dry leaves.

In any case, the larva has evolved a pretty good defense against being eaten by moose. We observed that the tame moose would sometimes bite off the willow rose and drop it before continuing to eat the rest of the branch.

In this case, the larva still has its winter home in the rose and maybe some extra snow overhead for added protection. The texture seems a pretty good defense for the larva, and a bad taste might not add that much more. Ethan Ford wrote an excellent paper on this study and won a prize at the Alaska Statewide High School Science Symposium in Fairbanks.

Ed Berg is a retired ecologist from the Kenai National Wildlife Refuge. He lives with his wife, Sara, in Homer, where he is an instructor in Geology at the Kenai Peninsula College and continues to impact our understanding and conservation of the Kenai positively. This article appeared originally in the Refuge Notebook of July 16, 1999. Find out more about refuge events, recreation, and more at kenai.fws.gov or Facebook: https://www.facebook.com/kenainationalwildliferefuge. To find more Refuge Notebook Articles go to https://www.fws.gov/kenai-refuge-notebook.

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