At 14:27 6/11/98 +1000, Chris Dahlberg wrote:
>Hello everybody
> I have been watching the posts on Tawny Frogmouths with
>interest, particularly which sex carries out the incubation and brooding
>during the day. It has been the experience of John Young that the female
>carries out these duties and not the male. I am sure that Lloyd Nielsen is
>of the same opinion but I cannot contact him easily at present.
Hi Chris and others,
I am aware that John Young is of the opinion that females carry out the
incubation and brooding. This is infact the common view. I disagree. I
looked at several hundred sexed skins of frogmouths in Australian museums
and searched the literature last year looking for criteria to identify sex,
age, subspecies, and two forms of individual variation, morphs and (the
left over) plain individual variation. This work has been written up,
edited, refereed and is in press in HANZAB. John is an extremely talented
observer and I have a lot of respect for him. However, how do you sex birds
in the field? Behaviour, copulation, morphological criteria established
from museum studies. Now if birds have sexualy reversed roles in nesting
behaviour there's a good chance that you could develop the wrong sexing
criteria. Museum skins are sexed by the morphology of their gonads and so
independantly of the birds behaviour.
Having developed reliable criteira for sexing frogmouths (included below) I
then turned to photos, just to polish descriptions and check points. There
are plenty of close photos of nesting frogmouths (See especially David
Holland's "Birds of the Night" and the NPIAW "Cuckoos, Nightbirds and
Kingfishers of Australia". I was surprised to notice that all the brooding
and incubating birds of all three species that could be identified to sex
were male. Gordon Beruldson showed me video footage of a brooding and
incubating Marbled frogmouth he was observing over an extended period. Day
and night, who was at the nest, the male. Gordon rarely saw the female. But
take a look for your self. Most (if not all) photos of Marbled and Papuans
sitting on nests are grey with marbled bellies and not rufous. Males. Most
if not all photos of Tawnys on nests are grey morph (all males and most
females are grey morph), have marbled bellies, big eyebrows behind the eye,
lack chestnut shoulders and tawny marks around the throat are reduced
compared with their partner's. Males.
Schodde & Mason (1982) in their "Nocturnal Birds of Australia" provide some
confirmation of my findings.
This work pioneered the sexing of frogmouths, showing that all Papuan and
marbled frogmouth females are "rufous morph". Ian Mason's opinions on
sexing birds are very close to mine and I discussed some problems with him
regarding Chestnut morph Tawny (only females are chestnut but not all
female are; the plumage is rare and restriceted to the humid subtropical
east coast).
On the subject of nesting duties, S&M where uncertain saying things likeWe
suspect that both sexes incubate but confirmation is needed; only males
appear to have been collected off nests by day" (p. 96).
There is not enough space to reproduce the plumages and related matters
texts for frogmouths from HANZAB. Last I heard Vol 4 was to hit the news
stands in Feb. 1999. I can provide some of the relevent snippets from the
Sexing section. Apologies for the (un)readability of technical style. These
sections might be hard to follow when divorced from the detailed
descriptions that identify valid subspecies, describe geographical and
individul variation etc.
Tawny:
SEXING All rufous and chestnut morph birds are female; the one known
exception is a chestnut morph from Woy Woy, NSW, sexed as a male (AM
O.39640); sexing unconfirmed; patterning points to male, but ground colour
otherwise only known in females. Irides said to average paler in males
(Schodde & Mason); this difficult to asses due to geographical variation,
but not supported by Table 2. Nevertheless, irides reported as consistently
yellow in males and more orange in females in s.e. SA. (T. Keens),
suggesting possible localized differences.
grey morph: Differences in plumage between sexes varies geographically,
and sexing straightforward in some areas, difficult in others. In s.e.
mainland females usually easily distinguished by two features: (1)
chestnut-brown, irregular and usually incomplete ring of feathers from chin
to side of neck and across foreneck that encircles plainer throat; (2)
strong chestnut ground-colour to lesser wing-coverts, contrasting with
scapulars ("chestnut shoulders"). Conversely males of s.e. mainland tend to
have: (1) more recognizable, vaguely square blotches on breast in rough
checkered or marbled pattern; (2) more distinct scapular braces; and (3)
more defined broad brown stripe behind eye. These differences not so clear
but possibly still useful in central, arid and tropical Aust; but
unreliable or insufficiently known in s.w. WA., Groote Eylandt and Tas.; in
Tas., males sometimes have "chestnut shoulders". These are average
differences in plumage so using them is likely to lead to some errors in
sexing. More information required on interactions between geographical and
sexual variations.
Papuan:
SEXING Generally, males grey or brown and females rufous. However, much
individual variation and the most grey females are close to the most rufous
males. Other important differences are: (1) males always have marbled
pattern on underparts, formed by roughly square, white blotches outlined
with fine black reticulating lines; females sometimes have a few square
white blotches (especially on belly), but never extensive and never
outlined with fine black reticulating lines to produce sharp marbling
pattern; (2) females consistently have conspicuously plain sandy or
yellow-brown scapular braces with little overlaid pattern; in males,
generally white with pattern of fine reticulating black lines or speckling,
contrasting much less with upperparts; (3) underwing-coverts, distinctly
barred in males, only faintly patterned in females; (4) bill much more
massive in males; almost no overlap between sexes in depth and width of
bill (see Measurements).
Marbled:
SEXING Generally, males grey or brown and marbled underneath, and
females rufous and plainer, but much individual variation. More specific
differences are: (1) Males tend to be grey to brown on the upperparts with
comparatively large black-brown and cream spots at tips of feathers,
whereas females tend to be rufous- or tawny-brown with very fine
black-brown and cream spots at tips of feathers. (2) Males usually have
marbled pattern on underparts, formed by roughly square, cream blotches
outlined with fine black reticulating lines; females either lack marbling
or have faint version, with buff (124) to pale brown (332D) blotches,
mostly on belly and thighs and probably never in centre of breast. (3)
Throat usually marbled on males, uniform on females. (4) Supercilium, broad
and long on males, narrower and shorter on females. (5) Scapular braces
usually conspicuous and cream to white in males, subdued and buff to rufous
in females. For finer differences, see Plumages.
Cheers,
David James
PO BOX 5225
Townsville Mail Centre 4810
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