On The Trails: Animal friendships and a surprise on the trail

A great egret strayed to Juneau recently. (Photo by Gus van Vliet)

By Mary F. Willson

Animals often form friendships with each other (and even with other species). Horses have favorite equine companions in the pasture, and cows and goats have similar associations. Dogs have canine buddies, cats have feline chums, and both birds and fish are known to form favored associations with other individuals.

I recently read an account of friendships among vampire bats. Vampires roost in groups and sally forth to get blood meals from mammals or birds. A long-term study of vampires in Panama involved a team of investigators. The team marked individual bats, often with electronic sensors, and could tell what each bat was doing. They also spent some time lying on the ground under a colony in a hollow tree, making direct observations.

Over many years of study, the team learned that blood meals are often shared among relatives in the roost, although that was far less important than other interactions. Feeding interactions sometimes developed from mutual grooming, but that was just a beginning.

A very hungry bat, no doubt with urgent begging, was more likely to get fed than one that was not so hungry. A bat was much more likely to share a meal with another who had previously fed it, and a very hungry bat that won a shared meal was more likely to reciprocate later on. Reciprocity worked even after several years. Individuals that shared when in the roost also met up while out foraging and shared meals there too. Bats that had more sharing friends were better fed than those with few.

A vampire bat feeding on a pig. (By Sandstein — own work, CC BY 3.0)

At the beginning of a walk, I’m always expectant that there will be something of interest, and I’m seldom disappointed. Sometimes there’s even a surprise or two, for extra fun.

One day in early November, I went with a friend to Kingfisher Pond, which usually has something to offer the curious onlooker. But not that day! No action on the pond at all (except a few midges). However, the adjacent big quarry pond was a different story. There were several distant ducks that remained unidentified. Near the trail we saw a solitary coot that nervously moved away. I don’t see coots very often, but they do occur here in various seasons moderately frequently.

A little farther offshore, we saw a pied-billed grebe, a species that visits us occasionally. The nearest breeding area occurs in extreme southern B.C. and far-eastern B. C., so this one had strayed some distance, giving us a small surprise. Territorial in the breeding season, they sometimes forage in groups in the off-season. These grebes feed on fish, frogs, and various invertebrates, by diving and searching underwater. Sometimes, instead of diving forward and down, they simply sink straight down and submerge (the one we saw did this). That is done by pressing air out of the air sacs and from the spaces between feathers and body.  Other grebes do that too, including the horned grebes we often see on our waters.

A pied-billed grebe visits Juneau and finds a fish to eat. (Photo by Bob Armstrong)

And then, a big surprise. With the help of a Real Birder, we spotted a tall white bird poking around in the shallows on the far side of the big pond, occasionally disappearing in the shrubbery. A great egret!!! It had been recently reported from other ponds, so the Real Birder was ready for it and happy to share. They eat opportunistically on fish, small vertebrates, and invertebrates. Great egrets don’t show up in Juneau very often, although it has happen occasionally. They normally range well to the south in the coterminous states (and the tropics around the world). They nest colonially, sometimes with other species, and commonly forage in groups. So finding a solitary one so far from its normal range is quite unusual. 

The question is what causes the solitary grebes and egrets to stray so far from their normal ranges occasionally? 

As we strolled around the pond, we also noticed some recent beaver chewings, but there was no sign of a cache in front of the old lodge along the shore of the big pond. Have they moved house??

• Mary F. Willson is a retired professor of ecology. "On The Trails" appears periodically in the Juneau Independent.