August: Legacy Effects

Emily Dickinson wrote a lovely poem using a brook as a metaphor for one’s interior life. The poem includes the lines: . . . And later, in August it may be, When the meadows parching lie, Beware lest this little brook of life Some burning noon go dry! . . . No chance of the little brook going dry if it runs through a beaver meadow. The movement of water across and through the North St. Vrain beaver meadow has slowed perceptibly by August. Some of the secondary channels barely flow and the main channel is easily crossed on foot. The water remains high in the main beaver pond, but few of the small dams winding across the meadow have water spilling over them. My feet are less likely to sink into wet black muck as I wander through the meadow, and even the moose tracks leave less of an imprint in the drying soil. Plenty of water remains, however, and the meadow is a much brighter shade of green than the adjacent, drier hill slopes. Many flowers remain in bloom across the meadow. Stalks bristling with the elaborate, richly pink blossoms of elephant’s head rise above standing water. Dusky purple monkshood flowers in slightly drier soil, as do the showy blue and white columbines. The blue bell-shaped flowers of harebell mark the driest sites. The late-summer flowers are joined now by the spreading tan or scarlet caps of fungi, as well as green berries on the ground juniper and kinnikinnick growing on the drier terrace beside the beaver meadow. Songbirds born this summer are fully feathered and capable fliers, and some of the birds have already left the meadow for the year. Early morning temperatures carry a hint of the coming autumn. The beaver kits grow steadily more capable, too, and by now they are used to foraging on their own. Presumably, this frees the breeding adult female for more time spent in dam and lodge repair or starting the food cache for the coming winter.

Colonization of the Beaufort Coastal Plain by Beaver (Castor canadensis): A Response to Shrubification of the Tundra?

A consequence of rapid global warming has been the shrubification (increase in shrub abundance, cover, and biomass) of arctic and alpine tundra ecosystems. Shrubification is likely a key driver of predicted and observed changes in the biodiversity of the Arctic. The American Beaver (Castor canadensis) has a vast distributional range, covering most of north America below the tree line; however, it has not been recorded in tundra habitat of the Beaufort Coastal Plain of Yukon and Alaska. in 2015, we observed a beaver dam, lodge, and winter food cache on the Babbage River in Ivvavik National Park, Yukon, Canada. Local Inuvialuit hunters first observed beavers on two rivers immediately east of the Babbage River in 2008 and 2009. Together, these are the first observations of beavers on the Beaufort Coastal Plain and indicate initial attempts at colonization. Colonization of the Beaufort Coastal Plain by beavers may have been facilitated by shrubification of river valleys on the tundra of northern Yukon and adjacent Alaska, which is a consequence of rapid climate warming in the western Arctic.

Food cache recovery by Northwestern Crows (Corvus caurinus)

This field study examined experimentally whether Northwestern Crows (Corvus caurinus) used random search or memory to relocate food caches. The crows cached food items in the ground, one per cache, and covered the cache before leaving the site. Most caches were recovered within 24 h. The crows found caches made by me 1 m from their own caches significantly less often than they found their own caches. Replacing the covering of the cache with material other than the crows used did not significantly affect recovery success, but the crows found significantly fewer of their caches when the latter were experimentally moved 15 cm. Adding a 25 cm long stick to the site 15 cm from the cache significantly decreased a crow's ability to relocate its cache, but not when it was placed 30 cm away. A 50 cm long stick placed 15 or 30 cm away had the same negative effect on a crow's ability to relocate its cache, but not when it was placed 45 cm away. When memory is used, recovery success can be as high as 99%; when random search is used, it can be as low as 6%.

Daily energy requirements of beaver (Castor canadensis) in a simulated winter microhabitat

Daily energy expenditure, food consumption, and aquatic activity were investigated in beavers housed in a microhabitat designed to simulate winter field conditions. Beavers consumed an average of 0.52 kg/day of woody forage, representing an estimated gross energy intake of 6547 kJ/day. Animals exhibited a distinct daily rhythm in metabolic rate, which averaged 2.87 W/kg, or 1.7 times the basal rate previously reported for beaver. Beavers spent an average of 140.5 min, or about 10%, of each 24-h measurement period in water. Mean daily energy expenditure was 3880 kJ/day, and was independent of both the cumulative immersion time and the frequency of aquatic excursions per day (P > 0.05). Based on previous estimates of the energy content and digestibility of forage cached prior to freeze-up, it is unlikely that the winter energy requirements of this species can be met solely from the submerged food cache.