Category: Education

By Matt Bowser, Entomologist at Kenai National Wildlife Refuge

In early June, I received multiple accounts of abundant black caterpillars stripping foliage along the Marsh Lake Trail on Kenai National Wildlife Refuge. Dark caterpillars were subsequently reported from Cooper Landing to Sterling to Kasilof. These larvae consumed leaves of aspen, highbush cranberry, birch, willows, roses, soapberry, and almost any other broad-leaved plant.  Steve Swenson of the USDA Forest Service tentatively identified them as caterpillars of the battered sallow moth (Sunira verberata). This identification was confirmed when caterpillars my kids and I raised in canning jars eventually emerged as adults in July.

Battered sallow moth caterpillars finish off a leaf on Marsh Lake Trail on Kenai National Wildlife Refuge. Multiple years of defoliation can lead to tree and shrub mortality. Credit: Cynthia Detrow

We periodically see outbreaks of these caterpillars in southern Alaska. The last event was in 2017, when  they were seen in numbers along the Richardson Highway and in the Mat-Su, Anchorage, and Kenai Peninsula.  The largest recorded outbreak of battered sallow moth caterpillars happened during 2003–2006 on the Alaska Peninsula, when up to 20,000 acres of alders and willows were damaged annually.  That outbreak, which may have included speckled green fruitworm moths, killed alders on mountain slopes over large areas. Deciduous trees and shrubs like alders and willows can usually withstand multiple years of their leaves being consumed without suffering lasting damage, so the severity of that event was notable.

Although the battered sallow moth naturally occurs from Alaska to central Canada and south to Colorado, there is no record of outbreaks of this species outside our state.  I wonder why battered sallow moths become so abundant in Alaska but nowhere else.  As with other forest caterpillars with periodic cycles of abundance, declines are likely caused mainly by diseases and parasites that pass through the populations.  At least one other sallow moth species is attacked by short-tailed ichneumon wasps.  The female wasp deposits an egg into a mature caterpillar, and the developing wasp larva will eventually kill its host during the moth’s pupa stage.

A Forest Service report links the 2003–2006 outbreak to higher than normal temperatures, but there’s not enough information yet to explain why higher temperatures might lead to increased populations. In related moths, outbreaks are often terminated by “zombie viruses” that rapidly sweep through dense caterpillar populations. The virus alters the caterpillars’ behavior, causing them to stop feeding and climb to the tops of trees. There the caterpillars die and disintegrate, spreading virus particles over the foliage below, where they can be eaten by other caterpillars. In some species the infected cadavers become attractive to other caterpillars, which cannibalize them and then become “zombie caterpillars” themselves.

An adult battered sallow moth that emerged from caterpillars raised by Matt Bowser (Kenai Refuge entomologist) and his kids this summer.  The caterpillars were provided by Dan Thompson (ADF&G biologist)

Adult battered sallow moths began emerging in late July, continuing into this fall when they presumably lay eggs. The life history of this species has not been worked out, so we do not know when the eggs hatch and larvae begin feeding. The larvae may hatch in the fall, feed and grow some, then overwinter as small caterpillars. Alternatively, the eggs may hatch in early spring. We do know that the caterpillars are out by the beginning of June.

I will pay attention to what happens on the Kenai Refuge this year and next. In general, we would expect trees and shrubs to recover quite well from this year’s damage unless there are high numbers of battered sallow moth caterpillars consuming leaves for multiple years. It’s also possible that other defoliators, like the recently introduced green alder sawfly, may have additive effects on mortality events, an increasing problem as nonnative insects and a warming climate collide.

Want to “Live Your Wild” in a refuge cabin?  Kodiak, Kenai and Tetlin all have public use cabins and Kodiak just added a new one.   There are now nine public use cabins scattered across the Kodiak National Wildlife Refuge.  The most recent addition to the cabin system came “online” in September, and graces a serene site along the Chief Cove shoreline. 

Since all of Kodiak’s cabins are remotely located, the logistics were a bit more involved to get construction crew and materials on-site.  Success was enhanced by all of the pre-planning and preparations that took place prior to leaving the refuge headquarters.  In most years, support could also be provided by refuge pilots, but this year because of COVID-19 concerns, gear and personnel transportation depended entirely on using the refuge vessel Ursa Major II.

We have maintenance workers Danny Hernandez, Darrel Fox, and Kyle Coleman to thank for their efforts and expertise in building the Chief Cove cabin over two weeks in early September.  The construction crew is happy that their work will allow increased access to and appreciation of refuge lands. 

The previously established cabins are in Blue Fox, Deadman, and Viekoda bays, North Frazer, South Frazer, and Uganik lakes, Uganik Island, and Little River.  Each cabin allows visitors to spend extended time exploring the beautiful and breath-taking Kodiak NWR lands and wildlife.  While the cabins are sturdy, nicely appointed, and comfortable, they will, no doubt, also serve as safe shelters from the elements.  All are priced at $45/night, and all have bunk beds to accommodate 4 people (except the Deadman Bay cabin that accommodates 8).

To browse refuge public use cabins and what they have to offer or reserve a cabin follow these links for Kenai and Kodiak on recreation.gov and this link to the refuge website for information on Tetlin’s.  All refuge cabins are very popular so plan ahead.

By Mark Bertram, Supervisory Wildlife Biologist, Yukon Flats National Wildlife Refuge

In recent years, you may have seen a Canada lynx, heard of a lynx sighting from a friend or read about one in your local newspaper.  Lynx populations have been high in much of Alaska, so they have been out and about.  That population high is fueled by snowshoe hares, the primary prey for lynx.  Every decade or so, hare populations skyrocket and then crash.  Lynx populations follow the same cycle as hares but lag by one or two years.  Interestingly, this predator-prey cycle occurs in sync across boreal Alaska.

Dr. Knut Kielland, with the University of Alaska-Fairbanks, has studied this intimate predator-prey relationship since the 1990s.  In 2014, he teamed up with Tetlin National Wildlife Refuge to examine a long-standing scientific theory that the peak of the 10-year hare cycle acts in a synchronous “traveling wave” across the Alaskan and Canadian boreal forest, similar to a rippling wave in a pond. 

But just what is it that sets the wave in motion and carries it over thousands of miles through the boreal biome?  Weather patterns have been suggested, perhaps related to cyclical sunspot activity, but these patterns are inconsistent.  The most likely explanation is long distance movements by predators.  Both lynx and great horned owls disperse over 700 miles in search of food.  Predators moving great distances from food-poor to food-rich areas could explain these 10-year patterns across the landscape.

Photo by Lisa Hupp, FWS

Kanuti, Koyukuk, and Yukon Flats Refuges and Gates of the Arctic National Park and Preserve have since partnered with Dr. Kielland and Tetlin Refuge to collectively examine lynx movements across the northwestern reaches of North America’s expansive boreal forest.  Our goal is to identify which habitat characteristics are critical as dispersal corridors so land managers can maintain viable lynx populations across Alaska conservation units.  To follow lynx movement, we capture lynx in walk-in live traps and attach a radio collar that records location every 4 hours.  Every few days, the collars upload stored locations to a satellite, from which we can subsequently download data. 

In the past four years, 163 lynx were captured and fitted with radio collars near Tok, Fort Yukon, Bettles, Galena and Wiseman, providing hundreds of thousands of locations.  Some lynx stay close to home while others disperse in all directions over great distances (Figure 1).  For instance, Tetlin Refuge biologists collared an adult male near Tok in 2017 that took a year-long sojourn through the Yukon and Northwest Territories, eventually settling west of Great Slave Lake, 2,100 miles away!  In February 2019, another adult male was collared near Bettles.  That April, he headed northwest 550 miles through the Brooks Range to the Chukchi Sea coast near Icy Cape.  In May, he beachcombed south for 200 miles, double-backed along the North Slope for 500 miles to the Dalton Highway at the Sagavanirktok River, and then meandered southwest through the Brooks Range.  Since October 2019, he has taken a respite in a secluded stretch of the Killik River headwaters.

Movements of 163 telemetered Canada lynx across Alaska and northwestern Canada, 2018-2020

We have recorded long distance dispersals for both young and old, male and female, with daily travel averaging 10 miles and up to 27 miles per day!  There appear to be no natural barriers to movement as lynx have trekked across the Brooks and Alaska ranges, and the Wrangell, Cassier and Mackenzie mountains while crossing the formidable waters of the Yukon, Tanana, Porcupine, Copper, Kuskokwim and Mackenzie rivers.  Collectively, this collared sample of Alaska lynx from four refuges and one park have traveled from the Chukchi Sea to British Columbia to the North Slope to the Yukon Delta, traversing through 20 conservation areas thus far. 

Hare populations are now decreasing across Alaska.  In response, we expect more collared lynx will disperse in search of food across the landscape.  As more than 1,000 lynx locations are downloaded daily, university, refuge and park biologists will look closely at these dispersal movement patterns in search of terrain that dispersing lynx prefer.  Identifying landscape corridors that link conservation units in Alaska and Canada will prove valuable in future land use planning.

Want to learn more and see more stunning lynx photos?  Author Mark Bertram will be our speaker at our October membership meeting, October 20 at 5 p.m. on zoom.  Put it on your calendar and watch next month’s newsletter and our web site meetings page for the zoom link.