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From: Marian Fricano <MFRICANO at SCU.BITNET>
Subject: Jay predation

This is Marian, from San Jose, and I have witnessed Scrub Jays actively
chasing down Brown Towhee fledgings and killing them, but they do not
eat them. They chase the fledglings of other birds too, and kill them
if they get the chance, without eating them, but their most active prey
(for killing) seems to be both the Brown and Rufous-sided Towhee fledgings.
If someone could offer an explanation I would appreciate it, as these birds
do not necessarily eat the same things, for the most part, and there seems
to be plenty of nesting sites available...
============================================

From: Michael Smith <whimbrel at U.WASHINGTON.EDU>

This is an interesting topic, why would jays kill other fledgelings,
without eating them? I have often seen or heard accounts of jays
destroying other nests, maybe they don't eat those eggs either.

Without any evidence to back it up, here's a 10-cent hypothesis:
Maybe they're doing it to reduce competition for food by other parents
nearby? Or to reduce the amount of prey for a predator in the vicinity
of the nest (hoping the predator will not try hunting there anymore)?

To further mess this up, I offer the following contribution: When I was
in the Davis Mts. (Texas) a few years ago, I saw a Scrub Jay flying
around with a dead mouse in its beak. It landed but didn't eat it
(didn't toss it, either), just sat there. I don't know if it killed it
or found it, and whether it ate it or not.

Let's have some more speculation...

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

From: William Barnard <BARNARD at NORWICH.bitnet>

For 8 years I have been studying the Gray Jay in Vermont where it
exists in small numbers in a single portion of the state. Most of my work
has been to color band the birds in order to get a handle on their numbers
and mortality rates. Several years ago, I happened to spot a juvenile Gray
Jay in mid July. I saw no adults around so I presumed that it had recently
achieved independence (or, now, as I understand, been forced from the natal
territory). I decided to take advantage of the relatively open area and
follow the bird for as long as I could.

While watching the perched bird, it suddenly flew in a direct and
rapid path and overtook a small bird, knocking it to the ground, killing it
with repeated pecks and then carried the bird to a perch and proceeded to
begin eating the bird. After a few minutes I approached in order to see
better and, with that, the bird flew off with part of the carcass in its
mouth. I retrieved the other part and later identified it as a fledgling
Magnolia Warbler. I never saw either adult Gray Jays or Magnolia warblers.

I was impressed with two things 1. the efficiency with which the
predation took place. The young prey was seen trying to avoid capture and
it was not the labored flight of a really young fledgling. 2) To see this
behavior in a young bird suggests that predation in this species of Jay
might be a regular or learned response.

There are many instances in the literature of Gray Jays killing and
seen carrying mammalian and bird carcasses but no documentation of its
killing and eating prey.

Bill
____________________________________________________________
| William Barnard Phone: 802-485-4691 |
| Biology Department FAX: 802-485-2580 |
| Norwich University E-MAIL:barnard at norwich.bitnet |
| Northfield, Vermont USA |
| 05663 |
------------------------------------------------------------
=================================

From: William Micha Klein <klein at CHOPIN.UDEL.EDU>

Just to add my 2 cents to why Jays would kill other birds. Perhaps
the birds are seeking extra protein, amino-acids, etc. that are relatively
scarce but necessary for proper development(especially in young birds).
Several of the previous posters stated that the bird was only seen killing
the birds or carrying the bodies but never actually eating them. Others
have seen the Jays kill then eat the prey. If I may take a stab at this, I
think that the non-consumption witnesses may have just missed the bird eating
the prey item. That is to say, perhaps the Jays never fully consume the prey
item but merely pick at it. Perhaps they selectively eat certain parts(eyes,
liver, brain, etc.)and leave the rest. From far away it may appear that the
bird is not eating the prey. I found the post noting the increased killing
in Jays around nesting time to be interesting. Instead of eliminating the
competition, I again propose that the Jays may be going after extra protein
or trying to fulfill nutritional requirements.

While this is only a guess on my part, there is some evidence that
may support my idea. There have been some studies showing that birds will
switch nearly identical diets to obtain certain(added)amino acids during
high demand periods(during molt)(I think Murphey and King). How the birds
could distinguish between diets was not fully understood, they just did.
I also bring into play how some birds switch from mostly seed diets to a
diet composed mostly of insects when rearing young. Sometimes the young
never even eat the "normal" seed diet until near the end of their first
summer. While none of this supports my theory of Jay predation, I think
that it may help explain the Jays' behavior. I've even heard stories
about deer/caribou stomping on voles(apparently intentionally)then eating
the little "protein packets" to supplement their herbivorous diet, especially
during tough times. I don't know how true this story is, but it may be
similar to the Jays. Hope this helps or at least gives you something to
think about while daydreaming at work :)

Is it just me or do you have
a craving for a burger,
William Klein
U. of Del.
klein at bach.udel.edu
===============================


From: Bill Glenn <bglenn at NMSU.EDU>
Subject: Re: avivory?
Las Cruces, NM USA

The GREATER ROADRUNNER (Geococcyx californianus) in another species which
dines on other birds. We have watched many roadrunners wipe out nests of
mockingbirds, barn swallows,and house finches. I suspect they will eat
whatever they come across. For those of you who have visited the Spofford
Ranch in the Chiricahuas, you may recall the roadrunner that comes in to
sit below the many hummingbird feeders, and jumps straight up to grab the
hummers. Mrs. Spofford brings the roadrunner hamburger to try to dissuade
it from getting the hummers. I was always afraid it would nab a Lucifer's
or Berylline, but have not heard of this happening.

BTW, have any of you heard of the large preying mantises grabbing and
eating hummers?
===================================

From: Marian Fricano <MFRICANO at SCU.bitnet>
Subject: Re: avivory?

Marian in San Jose, I've heard that both preying mantises and large
spiders are known to grab hummers, but have not actually seen this. On
the subject of preying mantises--I'm adamantly opposed to spreading this
species throughout the U.S. via selling their egg cases--the type usually
sold are larger than the U.S. variety and could out-compete with them, etc.,
etc. Plus, I don't want to personally witness a large mantis eating a
hummingbird!
===========================

From: "Anthony L. Lang" <tony at ZOO.TORONTO.EDU>
Subject: Re: Jay predation

The latest Wilson Bulletin contains a note about a "KILLER GRACKLE"
preying on migrant passerines trapped among 70 storey office buildings in
downtown Toronto. The grackle (COMMON GRACKLE) is back (it is
identifiable by an aluminum band on the left leg) and I saw it
vigourously pursuing an OVENBIRD and later a WHITE-THROATED
SPARROW. I didn't see it kill anything during that visit, but its
intent was clear. It was chasing birds for 5 minutes straight. The
author of the Wilson Bulletin note saw the grackle kill and eat several
birds.

====================================================================
Anthony Lang, Dept. of Zoology | "Always keep your
Univ. Toronto, Ontario, Canada, M5S 1A1 | stick on the ice."
tony at zoo.toronto.edu | RED GREEN
===============================

From: "Henry M. Brodkin" <hankb at KAIWAN.COM>
Subject: Re: avivory?

There is apparently a bird eating tarantula native to the Amazon Basin.
We should not be surprised that other species besides us eat meat. It is
infinitely more "natural" for a jay to eat a nestling then for us to
raise and eat veal!

Hank Brodkin "It is not necessary
Marina Del Rey, CA to understand
hankb at kaiwan.com the opening of the door
to feel the wind" (Michael Ventura Sr.)
===================================

From: "WHITLOCK. PETER L." <WHIT0522 at VARNEY.IDBSU.EDU>
Subject: Re: Jay speculation

Marian Fricano began an interesting thread with her observation
of a jay killing a young bird but not eating it. This has been well
backed up by sightings from other chatters and information from the
literature. As my old friend and fellow hawkwatcher Bill Klein points
out, there may be several good dietary reasons why jays sometimes may
need to add small birds to their diet.

Bill goes on to speculate that perhaps the jays did eat a few
choice morsels unseen to the observers. I have fed many jays and
other birds by hand, and I agree that this certainly could be the
case. The beak is quicker than the eye. Another possibility is that
the jays return to the prey at some point. When given small mice to
eat in captivity, Blue Jays will often drag them out of the bowl,
leave them on the floor of the cage, and then return to them several
hours later (personal observation). But I am unhappy with the sheer
number of similar observations in many other species of predators
killing but not eating prey. Probably most Birdchatters have seen
cats do this. I have also heard several reports with Great Horned
Owls. Migrating hawks have been observed killing birds that were
harassing them; some of the killed birds were eaten on the wing while
others were dropped immediately. And several years ago, I worked on a
study of Nuctenea cornuta, a garden furrow spider endemic to upstate
New York which occasionally tosses prey items out of the web without
eating them - even prey which it painstakingly killed and wrapped
hours before.

The only easy explanation that comes to mind for a
predator abandoning recently killed prey is that the predator has
suddenly noticed some apparent threat unseen by the observer. But I
don't much care for this explanation either. Has anyone heard any
good evolutionary explanation with any predator for why they would
kill apparently healthy and tasty animals (unlike Monarch butterflies
for example) and then toss them aside without eating any?

One final speculation: perhaps some individual predators are
"super-endowed" with the killing instinct and kill prey even when they
have no need to eat. Such "aberrant" behavior would even be expected
in some young animals (like Dr. Barnard's young Gray Jay) that have
limited experience in making cost-benefit energetics decisions.

Unlike Bill K's need for a burger, I
suddenly have lost my appetite,

Peter L. Whitlock
Boise State University
e-mail: whit0522 at varney.idbsu.edu