Subject: Re: Marbled Murrelet Fledging
Date: Jan 13 18:33:22 1998
From: wings at olympus.net - wings at olympus.net


OK, Tweets -- here goes. Albeit out of the current "loop" of Marbled
Murrelet research, I think I make a stab at answering some of the questions
that have been posed.

Michael Price commented and queried:

"...even those nesting far inland are still only an hour or two at most
from the ocean, and if they head even vaguely west they'll still hit ocean.

"So, then, another question arises: are the birds which are on the ocean
directly offshore from their nests, that is, are the water territories at
the shortest straight-flight distance from the nest?"

Answer: Don't know. Don't think so, necessarily.

Paul Moorehead asked:

"Could the birds just be headed downstream? Is there telemetry that
indicates that they cross ridges on their flight to the sea?"

Answer: Think so. Don't know for sure about the telemetry.

And Kelly Cassidy suggested:

"Maybe they go the same direction Mom and Dad fly everyday?"

Answer: Maybe, but I doubt it.

These answers are strictly my own, based on observations, musings with
other researchers, and minimal literature. It *is* known that murrelets
occur with greater density offshore of appropriate inland forest habitat.
Whether that also corresponds with specific nest sites is unknown, nor is
the influence of shifting prey locations and the changing influence of
marine conditions on prey the parents need to find and take back to the
chick. As for whether the adults (and later the fledging chick) take a
direct line to the water, crossing mountainous ridges if need be, I don't
think that's been shown as yet with telemetry. Radiotelemetry has been
extremely problematic with this species, though I gather that techniques
are improving and results are more encouraging, particularly in B.C.
Murrelets definitely seem to prefer following stream corridors, but have
been detected on occasion crossing ridges.

In reflecting on these questions my mind keeps returning to a nest I helped
monitor along a river in the Coast Range of Oregon. The river at the site
ran north/south, perpendicular to the direct-line flight one would assume
to be most desirable for reaching the ocean. Yet in approaching the nest
tree, the adults zoomed up the river and seemed to follow it pretty
religiously as they came and went. But in reference to Kelly's question,
murrelets don't always follow the same route in and out of the tree. They
tend to follow the same flight corridor through the canopy, but will switch
their route on occasion. Most likely their choice of routes is limited by
the configuration of tree crowns and branches, but it is thought this is a
predator-avoidance measure -- along with their tendency to circle through
and above the canopy, and to choose nest branches with overhead cover. The
specific nest I have in mind was 20-some miles inland, and when I looked at
a map and remembered the adults' flight behaviour, it was obvious that they
would have to cross a ridge or two in getting to and from the ocean, even
if they tried to follow stream corridors most of the way. Keeping in mind
the fact that: these are heavy-bodied little birds that fly 50-some mph in
direct flight; each parent can make 2-3 visits to the nest each day,
carrying a fish crosswise in its bill (not very aerodynamic!); and they
have to go God-really-only-knows-how-far to and from the nest by whatever
route -- this is one amazing energetic puzzle!

As for Roger Hoffman's comment:

"... marbled murrelet's first flight ... that once they do so, they manage
to link up with their parents who are already out there bobbing around!"

Hmmm. Unless there has been some more recent data, preferably with chick
and adults marked at a nest and subsequently observed together at sea, I
would tend to doubt this. The adults often stop feeding the chick just
before it fledges, and are thought to abandon it from there on. I will end
with a quote from a reference I would recommend to Tweeters interested in
more in-depth information:

"Once juveniles reach the ocean they are thought to be independent and not
attended [by] either parent contrary to the suggestion of Ydenberg (1989)."

This is from Nelson and Hamer, "Nesting Biology and Behavior of the Marbled
Murrelet," Chapter 5 in: _Ecology and Conservation of the Marbled
Murrelet_, published February 1995 by the Pacific Southwest Research
Station of the US Forest Service, General Technical Report PSW-GTR-152. If
your local library doesn't have it, you can request a copy by phoning (510)
559-6300. Or write to: Pacific Southwest Research Station, P.O. Box 245,
Berkeley, CA 94701-0245

Personally, I have always guessed that the birds use some sort of magnetic
sense in making their first flight to the ocean.

Hope this is helpful. ->Sigh<- -- now you've made me more anxious to go to
the Pacific Seabird Group conference Scott Richardson mentioned...

Cheers,

Janet Hardin
Port Townsend, WA
wings at olympus.net