birding-aus
wrote:
>
> birding-aus
>
> G'day all
>
> I've been mulling over a theory for a while now and thought I would
> ask
> for other opinions.
>
> Riding to work along the same rural roads south of Hamilton each
> morning I
> get to know the local birds quite well. Last spring I was used to
> seeing
> and hearing a range of species (Stubble Quail, Shining and
> Horsefield's
> Bronze-Cuckoos, Golden-headed Cisticolas, Richard's Pipit, Skylark,
> Brown
> Songlark, Clamorous Reed-warbler). This was the case until 21 Dec
> when I
> went to Melbourne for Christmas. Back on the bike again on the 29th
> the
> scene was completely different. None of the listed species were
> calling
> and very few can still be seen. Looking back over past years' bird
> lists
> seems to support my theory that all calling and display flight
> activity
> ceases around Christmas.
>
> An exception to this was our Koel which continued calling for a couple
> of
> weeks into the new year. This bird is obviously not reliable as it
> shouldn't be here at all.
>
> I don't think Christmas is an important event for birds (geese,
> turkeys
> excepted) but it occured to me that Dec 22nd is the summer solstice -
> the
> day when daylength is greatest and the beginning of shortening days.
> Is
> this the trigger for many species to stop breeding activity (calling
> and
> display flights)? I know daylength (or nightlength) is important for
> many
> plants and I'm sure that I've read where it is a probable trigger for
> migrating birds but the daily change around the solstice is so small
> (seconds) that I find it hard to believe birds could detect it as
> precisely as my theory suggests.
>
> I welcome any discussion on this but please - not too technical.
>
> Cheers
>
> Steve
>
> ------------------------------------------------
> Stephen Clark
> Agriculture Victoria, Pastoral & Veterinary Institute
> Private Bag 105 HAMILTON 3300 Australia
> Phone 0355 730 977 Fax 0355 711 523
>
> ------------------------------------------------
>
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>
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> quotes)
Re Daylength:
Hullo Steve. When I started trying to study birds in early 1970s, most
books agreed that most breeding and migration was triggered by
daylength. Probably because most research was done in northern Europe
and America, where it does seem important. However it seems clear now
that there is much more to it than just that for many species.
I have often noticed that almost immediately after winter solstice
domestic hens start to lay again. Commercial growers fiddle with the
lights for this purpose.
Australian birds seem much more flexible in their approach -
particularly waterbirds with mainly inland distribution, ptc Grey Teal.
Once after a severe drought broke c.Feb/March, Purple Swamphens were
feeding babies here in Melbourne in April after no breeding at all while
billabongs were dry. Redbrowed Finches were also breeding then.
I am certain that most inland Eyrean species are opportunists and nest
whanever they think they can, after rain or some other good season, eg
rat plagues for raptors.
Spotted Doves (yes,exotic N.Hemisphere types) had 3 nests in our
courtyard. First lost young, probably to Raven, 2nd and 3rd attempts in
the same nest (2 ft from first site) successful. Clutch 3 left nest in
New Year. No subsequent attempts - this may be illustration of your
point or had they just had enough?
Anthea Fleming
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