Kathy:

What you describe could be the result of sibling aggression. I've observed
this many times in my monitoring Great Blue Herons at Kiwanis Ravine.
Sometimes the older chicks very aggressively attack the youngest, and
although sometimes this does result in death (either by pecking or being
pushed off the nest), I have observed the victim often surviving to fledge.
One strategy the victim takes is to "play possum" and remain perfectly
still, which usually discourages the attacker from active pecking. After the
attacker loses interest, the victim will move away. Of course, if this
occurs too often around the time of a feeding, the loss of feedings could
have serious consequences. I've never seen the adults intervene during
sibling aggression behavior.

Pam Cahn
Seattle

-----Original Message-----

Message: 4
Date: Sat, 17 May 2008 14:43:29 -0700 (PDT)
From: Kathy Andrich <chukarbird at yahoo.com>
Subject: [Tweeters] Medina Herons
To: tweet <tweeters at u.washington.edu>
Message-ID: <540016.5671.qm at web52907.mail.re2.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

Hi Tweeters,

I haven't posted about the Medina Park Great Blue
Herons in awhile. All of the nests but one or two has
chicks in them. The three cottonwood nests have two
chicks on the top level, three in the middle level
nest and four in the lowest. There are 6 nests at
least in the tallest fir tree. I was only able to
count three of those nests. Looking from the back
side, walking around the second larger pond and
looking at the nests the lowest nest on the right that
is out a ways on the branch has three, the one above
it and closer to the trunk has four and one on the
left slightly above this one has three. The lower
right nest has a chick in poor condition.

I thought for sure the weak chick was probably dying
but it stirred some before I left. Being a licensed
veterinary technician for soon to be 15 years (where
does the time go...) I feel like I can be fairly
objective when it comes to assessing whether an animal
is moribund (near death) or not and this weak chick
really looked like it was giving up the ghost,
completely draped over the edge of the nest, wing
splayed out, head down, not moving, then it started to
come around some before I left. This is the worst I
have seen one and it will be interesting to see if it
really turns around, if experience is a guide it
probably will.

Over the several years I have watched the nests at
Medina I have seen weaklings before and how they
survive amazes me. All of them have fledged. Only
one chick in that colony has disappeared that I noted
and it wasn't from a nest with a weakling.

The cottonwood tree with four chicks had a weakling
too but it looks fine now two weeks later. "The Great
Blue Heron" book by Robert Butler, my heron bible,
talks about chick mortality but not at all about weak
ones that survive and go on to fledge.

To find Medina Park go to this church website,
directionas about 3/4 way down on the left hand side,
the park is right across the street from the church:

http://www.stthomasmedina.org/

Kathy
Roosting in Kent, near Lake Meridian
(chukarbird at yahoo dot com)