An Observation of Inter- and Intra-Specific Aggression Involving Brown Bear, Black Bear, and Moose in Southcentral Alaska

An observation of interactions between brown bear (Ursus arctos), black bear (Ursus americanus), and moose (Alces alces) revealed the following: 1) A cow moose successfully protected her calves by holding a black bear at bay, but lost her calves to a brown bear; 2) aggression between female brown bears; 3) a fight between a female brown bear and a female black bear that ended with the retreat of the larger brown bear; and 4) expropriation of a calf moose kill by a male brown bear from an estrus female brown bear. These observations were made in the Talkeetna Mountain Range 56 km SSE of Cantwell, Alaska on 28 and 29 May 1984. I watched the bears from a Piper Supercub (PA-18) aircraft circling at about 220 m above the animals. Habitat in this area was upland shrubs (Alnus sinuata, Betula nana, Salix spp.). I observed a black bear (Bl) with two yearlings being chased by a cow moose with two calves (3-4 days old) on 28 May at 1906 h AST. The bear retreated to a knoll that was about 40 m distant and 20 m higher elevation and watched the cow and her calves (at about 1,080 m elevation). The cow remained alert to the presence of the bear, never looking away from the bear and standing between it and her calves. These animals were seen in the same locations and postures in the morning and evening of the following day. At 2237 h on 29 May, I located a radio-collared 13-year-old female brown bear (G313) at the foot of this same ridge (820 m elevation). The bear was chasing, at full run, an unmarked brown bear (GI) that was accompanied by three yearlings. When first seen Gl and her yearlings were running fast about 100 m ahead of G313. G313, in turn, was being followed at a slow walk by a radio-collared 13-year-old male (G279). G279 had joined up with G313 in the morning of that day and would remain with her until 5 June; I presume G313 was in estrus. G1 and her yearlings fled up the ridgeline until they encountered Bl with her litter; G313 was then about 400 m behind Gl. At this encounter, the black bears fled along the ridgeline about 30 m ahead of Gl. Gl was right behind Bi and definitely appeared to be chasing Bi. Gl's offspring ran in a direction about 30? away from that followed by Gl and Bl. After fleeing about 200 m, the smaller Bl turned and charged G1. The adult bears fought for about 15 s during which time Bl's yearlings watched from a distance of about 20 m and Gl's yearlings continued to run on their divergent path. Gl broke off the fight and ran to her offspring with Bi chasing after her for about 100 m. Bl and GI then both rejoined their offspring and left the area of the encounter. Gl may have quit the fight more to protect her young from the pursuing G313 than because of the resistance offered by Bl. I estimated the weight of GI at 113 kg and of Bl at 59 kg. G313 was not observed during the interaction between Bl and Gl. About 1 min after the fight, however, I saw G313 lying down facing the cow moose with calves that were formerly under observation by Bl. At this point, G313 was about 2 km from where she was first seen chasing GI and was about 100 m downhill from the cow moose. I thought the moose and G313 were in visual contact, but the hillside was bushy so they may just have been in olfactory contact. G313 alternately looked uphill at the moose and downhill at the approaching G279. About 5 min later G279 joined G313. The two bears engaged in about 5 min of apparently amorous play (chasing each other around for short distances), during which they appeared to be oblivious of the moose. Following this, G313 moved around and uphill of the moose, while G279 slowly moved straight upridge towards the moose. G313 then charged to within 1 m of the moose twice, but was driven back by the cow who remained between her calves and the bear. On the third charge it appeared that the bear made contact with the cow following which the cow trotted off about 20 m and G313 swept through the calves effortlessly killing them both. I did not precisely observe the method of kill as it happened very quickly with no indication that G313 even broke her stride. It appeared that she ran over the calves, but she probably trampled or swiped one with her paw and grabbed the other in her jaws. Without breaking her momentum, G313 ran off with one dead calf in her mouth. About 30 m from the kill site, she stopped and began eating the calf. Within a few seconds G279 arrived and started to consume the remaining calf. In most cases where black and brown bears have been studied, considerable overlap between the home November 1985 805