Crossbill Puzzles

We crossed back into the U.S. on Sept. 3, in Montana, with one month before we were due in Albuquerque, New Mexico. We first visited Glacier National Park (NP), an old favorite, but it was disappointing as Manyglacier had far fewer mammals than last time we were there (October, 2001), and was much more crowded, with all camping booked. We did see some Mountain Goats perched on lofty cliffs, and these became the last additions to a tally of mammals of the north country, begun when we crossed into Canada in early May. The list is rather long to include here, but following are those species seen in double or triple digits: Caribou, 483; Snowshoe Hare, 312; Arctic Ground Squirrel, 222; Muskox, 214; Red Squirrel, 135; Sea Otter, 134; Wood Bison, 91; Mountain Goat, 64; Moose, 46; Black Bear, 39; Dall Sheep, 34; Harbor Seal, 31; Steller’s Sea Lion, 25; Grizzly Bear, 18; Collared Pika, 16; Beaver, 13; and Red Fox, 12.

We next visited Red Rock Lakes National Wildlife Refuge, about an hour west of Yellowstone NP. Sand dunes on the north side of the refuge, also protected on land owned by The Nature Conservancy (TNC), contain several rare plants. We were too late in the year to search for these, but enjoyed driving through the habitat, where we surprised a Badger. A long drive brought us to southern Idaho, where our first stop was Formation Springs Preserve, located northeast of Soda Springs, and managed by TNC. The crystal-clear spring water fed small streamlets and ponds, and the preserve had interesting geology and a nice assemblage of plants. We camped nearby at the Blackfoot Reservoir Campground, administered by the Bureau of Land Management. By choosing one of the highest sites, we got a lovely panoramic view and our booster was just barely able to pull in a Verizon signal. It was so pleasant, and we were in such need of catching up on activities requiring a signal, that we stayed four nights.

Our next destination was City of Rocks National Preserve, southwest of Pocatello, ID. This is a climbing destination and has nice campsites and trails. It is noted for its small mammals, including a number of bats, but we had no luck recording bats nor hiking around at night with the thermal scope, perhaps because of the cold weather at this time of year. City of Rocks is at the south end of the Albion Mountains, which, with the next chain to the west, the South Hills, comprise the entire world range of Cassia Crossbill, which was just accepted as a new species by the American Ornithological Society in 2017. It is a very interesting case from an evolutionary and taxonomic standpoint. Crossbills have upper and lower mandibles that are curved sideways in opposite directions, so that they cross and act something like a pair of scissors, allowing them to dismantle conifer cones to eat the seeds. Different populations of Red Crossbills have slightly differently shaped and sized bills, which have evolved to optimize foraging efficiency for different types of cones. Some of these populations wander quite widely around the continent, breeding in different areas in different years, depending on where their preferred food species are heavily fruiting. In recent decades, correlation has been found between bill size/shape, preferred food, and details of the flight calls. About 10 populations have been distinguished in the U.S. and Canada, and it was one of these that became Cassia Crossbill.

Cassia Crossbill feeds almost exclusively on Lodgepole Pine (Pinus contorta), the cone crop of which is so consistently favorable that this crossbill is not known to occur outside its core range. When Red Crossbill populations wander through the Albion Mountains or South Hills, they are presumed to move on quickly, because the local Lodgepole Pines in these two mountain ranges have cone structure differing from that found elsewhere in North America, and the Red Crossbill populations are thought unable to forage on them effectively. This causes Cassia Crossbills to be reproductively isolated from other Red Crossbill populations, the key justification for their being reclassified as a new species. Perhaps the most remarkable aspect of this situation is the reason why the local Lodgepole Pine cones differ from those elsewhere – it is attributed to the absence of Red Squirrels in these isolated mountain ranges! Everywhere else, Red Squirrels feed heavily on Lodgepole Pines, which has caused the trees to evolve different cone shapes to reduce predation by the squirrels. So, the absence of Red Squirrels in these mountains freed the Lodgepole Pines from the necessity of an evolutionary arms race, allowing them to evolve differently, and the local population of Red Crossbills to also evolve differently, leading to a new species, Cassia Crossbill.

When we left City of Rocks, we headed to the north end of the Albion Mountains, which are high enough to contain Lodgepole Pine. We were enchanted by the alpine area around Mount Harrison, with its interesting botany, but the Lodgepole Pines were somewhat sparse, so we headed west to the South Hills. After some exploration, we decided to camp at Diamondview Jack Campground, as it was on the edge of an especially large and heavily fruiting stand of Lodgepole Pine. This strategy worked well; we had Cassia Crossbills right from our campsite each evening and morning during the two days we stayed there! We saw them well, photographed them, watched them forage on Lodgepole Pine cones, and recorded the calls, which I was able to identify independently based on their spectral signature.

A long and scenic drive south took us to Great Basin NP, near Ely, NV. This was our penultimate national park in the U.S. of those that are accessible by road; we also lack only one such national park in Canada. This is a remote and beautiful park with two primary draws: Lehman Caves and Great Basin Bristlecone Pines (Pinus longaeva), the longest-lived species known to science (excluding some that form clonal colonies). We enjoyed our tour of the caves, though the longer of the two tours was booked well out into the future; reserving far ahead is advisable. Another day we took a lovely 5-mile hike starting around 9800 feet elevation, on the Bristlecone and Alpine Lakes Loop Trails. This hike visited one of three Bristlecone groves in the park, though it is not a pure grove, being mixed in with Limber Pine (Pinus flexilis), another timberline species. This grove is very unusual because it occurs on quartzite, a slightly acidic metamorphic rock derived from sandstone. Nearly all other occurrences of this species are on alkaline carbonate-bearing rocks such as limestone and dolostone. One individual tree along a short nature trail loop trail is nearly 5000 years old. During that hike we recorded Red Crossbills flying overhead; these were “Call Type 5”, complementing our recent Cassia Crossbills!

Next time: 2019 Wander Wrap-up