That sounds very interesting, even though I quite don’t
understand it. Is it that the resistance against the substrate: ground or water
is greater, against than it is in air, from the downbeat of wings. That makes
sense although surely this only applies within a very small distance from the
surface (no more that a metre or two). Or is it the same as saying air density
reduces at higher altitude? But for a pelican that travels largely by thermal
soaring, I would have thought there is not much rising thermal air mass less
than a metre above a cold water surface like a river.
Philip
From: Isobel Crawford
[
Sent: Monday, 18 May 2015 3:09 PM
To: Philip Veerman
Cc:
Subject: Re: [canberrabirds] pelicans and uplift
The lower birds fly, the more uplift they obtain (i.e. the
less energy required to move horizontally), simply because soil and water are
denser than air. There are of course contra-indications which encourage them to
take other factors into account!
Australian Botanical Surveys,
POB 6031,
O'Connor ACT 2602.
02 6257 1860
0429 798 887
On 18/05/2015, at 2:29 PM, "Philip Veerman" <> wrote:
I’m unsure as to the intention of the question –
location, date, frequency, flying low or over a river and is “Eur”
Uriarra? Obviously Pelicans will be flying low when arriving or leaving the
water, yes they also fly low some distance over rivers and lakes. I have seen
this sometimes at Kambah Pool one flying for several hundred metres (till out
of sight) along the river only a metre or two above it. Over places away from
water they will usually fly high but that varies, probably according to how
much warm air there is. I have an obs from my home on last year’s GBS
chart of 3 flying very low over my home.
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