Subject: Re: Stashing behavior of Corvids?
Date: Aug 22 09:41:37 1994
From: Michael Smith - whimbrel at u.washington.edu


>
> According to _The Birder's Handbook_ (Ehrlich, Dobkin and Wheye, 1988):
>
> "...recent experiments with (Clark's) Nutcrackers in aviaries, done by Stephen
> Vander Waal of Utah State University, have shown clearly that individuals are
> able to recall where they have cached seeds. The birds remember where seeds
> are in relation to certain landmarks, such as rocks. If the landmarks are
> moved, the areas the birds search are displaced by an equivalent amount."

A series of papers given at the June AOU/COS/WOS meetings in Missoula
addressed this issue, with some fascinating results. Two that I remember
most are as follows:

First, Nutcrackers cache food in several different types of
microhabitats. There seems to be a relationship with them being able to
locate caches next to landmarks better, as suggested above. However, the
caches located away from landmarks actually fared better in surviving.
So there is a tradeoff involved here. The birds can cache near a tree
and remember where they left it, or put it away from the tree and risk
forgetting the exact location (or a rock, downed log, etc.). The cost of
locating them close to trees is significantly higher predation (perhaps
the wrong term?) of caches by rodents which use rocks, trees, and downed
logs as runways. Another benefit of placing caches near these objects
(especially live trees), is that they are the first areas to become
snow-free in the spring, and the first place Nutcrackers can look for
food. The result is that the smart Nutcracker hedges his bets and places
caches in many locales, some near markers which will become snow-free and
are easier to find, and others in areas which are less likely to be
discovered by hungry squirrels, mice, or voles. The smart
Nutcracker will also place many more caches than he needs near these
spots that are succeptible (sp. ?) to losses by rodents to offset
the known losses. There is another tie-in to elevational gradients as
well, as discussed below.

Nutcrackers also cache differently at different elevations. At lower
elevations they are more likely to cache near trees and logs, and at
higher elevations they are more likely to cache anywhere. The reason
again is related to snow cover and rodent predation of caches. They have
to cache near trees at lower elevations if they expect to have food when
spring thaws arrive, but later in the summer can rely on higher elevation
caches which have not been plundered by their fuzzy counterparts. The
caching also seems to have a rather interesting impact on the location of
timberline in mountains, and if our planet is indeed warming up a bit
(whether it's our doing or not), they could play a large role in the
colonization of trees at higher elevations as they 'plant' trees while
storing caches. It's neat to think about that, the fact that Nutcrackers
are having a large impact on their environment (so you see, we're not the
only ones who do this - but of course they haven't figured out how to
make nuclear waste yet).

Anyway, they were pretty neat discussions which seemed relevant to the
topic on Tweeters. Unfortunately, I can't remember the researcher's
names, but if somebody really wants to know, I can look them up.

Mike Smith
University of Washington
whimbrel at u.washington.edu