G’day birders,
I’ve got a question which has been nagging at me for a while. I hope someone will know something.
Brown Falcons keep turning up with yellow ceres and bare facial parts. I have a growing collection of photographs of these birds from Lake Eyre through Central Australia and out to the western extremities of the Tanami Desert.
Where does this colouring come from? Is this a regional variation? Is anyone aware of any research/study that has been done on this subject?
Some photos of my latest encounter with this colour variation are on my blog ;
http://comebirdwatching.blogspot.com/2011/10/brown-falcon-and-thorny-devil-study-of.html
I’m intrigued.
Cheers,
Chris Watson Alice Springs ===============================
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Dear all,
I don’t agree with many of the points raised by David James’ emails, and actually think that they mis-represent and further misunderstand the data and conclusions of my earlier Emu paper (103:21-8) considerably. For these reasons, I feel compelled to respond in some detail here. I’m not convinced that Birding-Aus is necessarily the appropriate venue for this debate, particularly given so long has passed since the publication of the research (’93 and ’03). Given this, I’ll send a more detailed account addressing each of David’s many points to him directly, but will forward that response to anyone interested.
Regardless of what your conclusions are, the point is that we still have much to learn about Brown Falcons. I would encourage all birders to read HANZAB, David’s emails, my responses, the Emu paper in question and have a look at this website (http://tinyurl.com/BrownFpics). More importantly, I implore birders to continue to look at Brown Falcons in detail, wherever you may be. My main points are outlined below:
My argument for age/sex effects is summarised below. Birds that I measured show one of two main patterns:
a. bare parts become increasingly yellow as birds age from blue to blue-grey at fledging. Only in males does this change lead to entire yellow across all bare parts routinely, a point missed in previous emails. In females there was often some yellow in adults, but typically this was less plentiful than a dominant blue-grey colour (http://tinyurl.com/BrownFpics).
b. plumage lightened with increasing age, to a point where females have whitish bellies with a breast band of speckled light brown, whereas the entire ventral surface of males lightens. The breastband seems to be characteristic of adult females, and as such many retained similar looking plumage throughout the project, even when as old as 13 years. In contrast, males that were in their late teens had virtually completely white underparts and rufous dorsal surfaces.
Finally, I want to highlight some important misconceptions of my study as re-stated by James in his previous emails:
– Birds were molecularly sexed after that Emu paper was published (and indeed 40 of the 160 putative sexes were confirmed in the paper, as it states in the Methods). Thus, there is no circularity or doubt over sexing techniques in the Emu paper.
To re-iterate, we need more data and more people watching Brown Falcons. The Emu paper is not meant to throw out HANZAB data or any other study, rather it builds upon that foundation and interprets information at hand given the new lines of evidence available. I argue that my conclusions stand up to the current level of data, and are defended in more detail in another email for those hardy souls interested. I’d be quite happy to be proven wrong, but the point is that we require data to prove this, opinions are not sufficient either for or against.
Cheers,
Paul
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr Paul G. McDonald
paul.mcdonald@une.edu.au
Lecturer Zoology, School of Environmental and Rural Sciences University of New England Armidale NSW 2351 Australia
Ph: +612 6773 3317 Fax: +612 6773 3814
Publication list: http://publicationslist.org/paul.mcdonald Thompson ISI Researcher ID: http://www.researcherid.com/rid/A-5928-2010 Web: http://www.une.edu.au/staff/pmcdon21.php ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Part 2. Addressing some minor matters: The words ‘phase’ and ‘morph’ are not interchangeable, although they sometimes get used as though they are. HANZAB (Vol 1, 1990) defined ‘morph’ as “one of two or more well-defined forms in the same populations of a species. I would go further and say that in birds it refers to one of different colour phenotypes, the outward expression of different forms based on genetic variation within a single gene pool or population. ‘Phase’ implies a temporal component, a temporary position or a transitional state. It has been used for different age classes (transition from juvenile to adult) and also as a substitute for ‘morph’. ‘Morph’ does not imply temporal change and cannot be applied to age-related variation, but it does not exclude individuals from changing over time. ‘Phase’ is no longer widely used in technical literature because of its ambiguity. Simon Mustoe wrote: My response: The plate of the rufous morph in HANZAB shows a yellow cere, but it is a plate of an individual bird, and nowhere is it claimed that all rufous morph birds have yellow ceres. The descriptions of plumages and bare parts in HANZAB are in the plumage and related matters section so this is where you should go to see if HANZAB says that all rufous morph adults have yellow bare parts. The descriptions in the field ID sections are summaries of important features and do not necessarily address all of the details. HANZAB was not misleading on this count, but it does contain errors and mistakes and it can be difficult to interpret. I note a mistake in the HANZAB plate of perched Brown Falcons where image 7 of a juvenile rufous morph bird is labeled as “Adult male rufous morph”. Stephen Debus wrote: My response: McDonald and HANZAB both identify that yellowness increases with age more frequent in males, but neither say it is exclusive to males. HANZAB notes tentatively that it is may be more marked in males while McDonald claims to have proved it is more prevalent in but not exclusive to males. However, McDonald’s arguments are slightly circular. He wrote that all adult males and all adult females had at least some yellow in the cere. But he aged all of these birds on their plumage and bare parts patterns. He noted that birds breed in what he termed “immature” plumage, and presumably these sexually mature (I would call them adult) birds had “immature” greyish ceres. In fact, this line of reasoning merely confirms that McDonald’s ageing methods proved to be consistent with his ageing results. Whether his sexing techniques are similarly circular is difficult to assess from the paper. Stephen Debus wrote: < My remark about longevity was on the assumption that birds in more human-populated areas are more likely to die younger, i.e. get road-killed, shot, trapped, poisoned (from eating carrion baits or poisoned rodents/rabbits), collide with fences/powerlines, get electrocuted on power poles etc.> … and … My comment about longevity (or causes of death) might partly answer David James’ remark about lifespan in the inland. My response: I still don’t buy it. The assumption that mortality rates are higher in human-populated areas may be plausible, but a resulting complete restructure of the population doesn’t fit the evidence. It flies in the face of a few simple principles. first, under this hypothesis there would be more pale birds away from populated areas, and darker birds close to populated areas, along the coast and in the interior. Second, Brown Falcons are common to abundant in populated rural areas; if they were suffering human-induced elevated mortality rates sufficient to change the population structure they would also be facing rates sufficient to change the population size – i.e. they would be rare. Third, if adults were not surviving there would not be increased numbers of immatures because eggs would not be laid. The specimen record dates back a hundred years or so to when the human population was sparser. This could be used to test the hypothesis that there has been a change in population structure of BFs in areas densely populated by humans compared to areas with low human density. I doubt it would survive the test. Jeff Davies wrote: a given population of Brown Falcons say at Werribee or where ever, does not consist of a number of different morphs. The differences in plumage are primarily the result of differences between the sexes overlaid by increasing paleness as the individuals get older. My response: Lets be clear, Paul McDonald makes this claim, but his study does not apply to any given population, only to a single population at Werribee, where he reputedly (but maybe not) found no morphs. Jeff Davies wrote: Yellow cere is apparently only found in the older males especially the pale Central Australian population, Stephen suggested this may possibly be because they are for unknown reason more likely to reach the prerequisite older age.> My response: McDonald did not say that the cere is yellow only in old central males. On the contrary, he wrote that he recorded it in males and females in coastal Vic, though mostly in males. Evidence that Jeff is compiling from photo collections seems to indicate that most, maybe all, rufous morph birds in the interior have yellow bare parts. This presumably includes females. Unless of course the photo sample shows males only, which seems unlikely. Paul McDonald wrote: My response: This is ironic. Paul rejects morphs continent-wide based on a study at a single location across a short 3 years with a fairly small sample size in a habitat that is artificial, though perhaps productive rather than marginal, considering that it is bog farm irrigated through droughts. Surely Werribee bog farm is a more stable environment than the flood and drought cycle of the interior, the over grazed savannah rangelands, or the ever diminishing woodlands. Richard Nowotny wrote: My response: To summarise my argument, of course there really are pale and dark plumaged birds corresponding to morphs, but the pattern is complicated by strong influences of geography, age, sex and individual variation as well. The system is complex. The morphs are not absolute, but there is value in recognising them so that the patterns of variation can be better understood. ===============================
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Part 1. Chris Watson’s original question about the meaning of yellow ceres in Brown Falcons has sparked a lot of responses. Whilst the question has been answered, more or less, there have been some conflicting answers, and a lot of peripheral misinformation about variation in plumages and bare parts. This stems mostly from a study of Brown Falcon by Paul McDonald (2003: Emu 103, 21-28) that, despite being a good study, reaches unsupportable conclusions due to extrapolation of the findings beyond the capacity of the data set, some circular arguments and rejection of prior studies without justification. On this latter point, McDonald (2003) rejected virtually every aspect of the Brown Falcon ‘Field Identification’ and ‘Plumages and Related Matters’ accounts in Marchant & Higgins (1993: HANZAB Vol. 2, pp. 237-8 & 248-51). As the author of that plumages section in HANZAB I wish to correct some matters that have been dismissed or overlooked in this Birding-Aus discussion so far. I agree with Paul McDonald on the relationship between cere colour and age and the lightening of plumage with age (both these processes were identified earlier in Weatherly et al. (1985) and HANZAB (1993)). I recognise that Paul’s study uncovered a significant component of sexual differences in plumages that was not identified in HANZAB or previously. However, I disagree with the assertion there are no plumage morphs or “phases” in Brown Falcon and plumage variation is all due to age and sex. First, let me establish that the Plumages texts in HANZAB were not quick and dirty studies. They involved careful and systematic observations of plumage, bare parts, measurements, structure and moult of museum specimens from throughout the species’ ranges, with large sample sizes when available. Variation was systematically assessed to partition the contributions of age, sex, season, plumage wear, morphs and geography by sorting the specimens by each of these characters to reveal apparent patterns. In the bare parts section of Brown Falcon in HANZAB (V.2, 1993 p. 250) I wrote, for all morphs, that “Cere and orbital ring usually pale grey to pale bluish grey; in a few, yellow, yellowish grey, or greenish yellow; yellowness develops with age, may be more common in males, and is associated with pale iris… [etc]. This largely answers Chris’ question, though Jeff Davies is collecting evidence that it is particularly prevalent in rufous morph birds from arid regions. Condon (1951: Emu 50, 152-74) wrote about yellow ceres too, but I don’t recall whether he made the association between bare part colours and age. Weatherly et al. (1985: Emu 85, 257-60) looked at changes in captive brown morph birds from Tasmania and noted the association between yellower bare part colours and age. McDonald, in his 2003paper and in recent postings to Birding-Aus, has proposed a hypothesis that I will couch as follows. This hypothesis contradicts all previous studies of the subject. However, it is an extrapolation beyond the applicability of McDonald’s data set, because it takes findings from a study at a single small location (Western Treatment Plant in Werribee Vic) over a short 3 years and extrapolates them to the entire continent of Australia. Considerable evidence is published that conflicts with this hypothesis. The descriptions in HANZAB were based on examination of approximately 500 specimens (many more than the 160 (or 14, actually) birds studied by McDonald) from the entire continent, not just a single site, that were accumulated by collectors over more than a century. This evidence has been dismissed by McDonald as under sampling. Some particular problems with McDonald’s hypothesis are: 1) Most juveniles are brown with extensively buff underparts, so if they lighten with age how would dark birds described as the dark morph in HANZAB come to exist? Reliably aged juvenile skins exist that show entirely dark underparts and upperparts consistent with the descriptions of dark morph in HANZAB; at this age there can be no lightening of plumage due to age, and both males and females occur in this plumage. Therefore, juveniles show different morphs. 2) Juveniles from rufous parents (collected together in central Australia) resemble juveniles from brown parents in their underparts, but differ in having consistently broader and more rufous fringes to the brown feathers of the upperparts at the same age. Therefore juveniles show different morphs before any lightening with age occurs (and this holds throughout their lives). 3) There are no rufous birds (rufous morph) or dark birds (dark morph) in Tasmania; this means there is by definition a geographical component to the variation across the country as a whole, not just age and sex components. 4) Brown birds are more common in humid coastal regions, rufous birds more common in arid interior regions, and dark birds only prevalent in tropical northern areas. Once again this is a geographical component to the plumage variation. However, it is not a simple case of all rufous birds inland and all brown birds on the coast, all three forms occur widely, so these are not geographically isolated forms or genetically separated populations (i.e. they are not subspecies). Nor is it a cline of gradual transition from brown to rufous moving inland. That leaves only one parsimonious alternative: varying geographical ratios in the expression of different phenotypes across the continent, presumably as a result of differing evolutionary drivers across a meta-population in a heterogenous environment – or more simply put, different morphs. McDonald studied birds in a single location to generate his hypothesis. He ignored the lack of variation in Tasmania (from where he had no data), implying that it must be present but so far overlooked. Evidence indicates otherwise. Similarly the contradictory evidence for geographical variation (higher ratio of rufous birds in the interior) was dismissed by the contrived suggestion that Brown Falcons live longer in the inland than they do on the coast so more birds live to become pale. Where is the data to support that speculation? Where is a precedent? There are countless precedents for the alternative explanation that there is geographical variation in the expression of colour morphs in Australian birds. It is still the case that the morphs are not distinct but integrade to some extent, and birds do change (mostly get paler) with age. However, the sample sizes in McDonald’s study were rather small. Of 14 individuals recaptured after moulting to a subsequent plumage, 8 got paler but 6 did not. That is not a big sample, not a uniform trend, not statistically significant, and not geographically representative. HANZAB had already noted that birds get paler with age over several moults, without over generalising. HANZAB did not recognise the differences in sexes at the same age (males lighter than females) reported by McDonald. This seems to be an important advancement from McDonald’s study, and an oversight in HANZAB. McDonald’s birds were sexed by methods that have not been totally declared (described merely as “behavioural observations and a variety of morphological characters”) and the HANZAB method of simultaneously comparing a large sample of adult males with a large sample of adult females (sexed by dissection) did not detect this pattern. It is possible that I overlooked it. I suggest that the sexual difference is likely to be true, but technically it needs further evidence before it can accepted as proven. Weatherly et al. (1985) was a longitudinal study of a small number of subjects over a long period of time. HANZAB was a cross-sectional study of many subjects, each preserved at a single point in time (though also incorporating the results of Weatherly et al. and others). McDonald (2003) had a bit of both aspects with mostly one-off captures of many birds and some recaptures of a few banded wild birds, but it lacked the continent-wide coverage and large sample size of HANZAB. An advantage with skins over wild birds is you can compare large numbers simultaneously for extended periods, and even revisit them later. All studies have their advantages and limitations, so combining the insights from multiple lines of evidence is the most effective path. My thoughts are that McDonald does not replace all previous studies, but adds to HANZAB in demonstrating that plumage changes with age and sex are even more marked than previously recognised. (more to come)
David James, Sydney burunglaut07@yahoo.com ==============================
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Dear Richard,
Seems that you now have the paper, but let me know if you need another copy or anything else to do with that project.
As I said in my last B-Aus post, I’m less convinced by the regional colour differences argument, but granted have not spent a huge amount of time in western central Australia or indeed the Kimberley. That said, dark individuals are not uncommon in SE Aust. As sex/age differences were largely overlooked at Werribee, one of the most commonly birded sites in the country, it seems likely that we don’t have a clear idea of what is happening in more rarely visited areas that haven’t been the subject of colour banding studies/longitudinal. I also think that central Australia is likely to be a more harsh environment for young (greater stochasticity in prey availability?), but perhaps better for adults (good conditions with experience/once a territory is established etc). Both factors could lead to skewed age distributions in the population, such that males in these areas are predominately older than elsewhere, and thus lighter and redder. The other factor is that young birds wander f or a year or two after fledging before settling, so if these young birds preferentially stick to one area, say central west of NSW, by default that region becomes ‘darker’ while western areas would become lighter and redder by the age distribution within the population.
Note that I’m not suggesting that this occurs in NSW specifically, but rather that until we have some detailed studies of these apparently aberrant areas I remain unconvinced of the true veracity of these plumage phases/types and so on. It is possible that many young birds leave the central regions to reside in the Kimberley, for example. However, I’d very happily be proved wrong if someone wants to do the work, as they are a very special bird that many ignore due to their common nature.
Hopefully this will let people look at these birds a bit more closely, and also jog the field guides into updating their information.
Cheers, Paul
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr Paul G. McDonald
paul.mcdonald@une.edu.au
Lecturer Zoology, School of Environmental and Rural Sciences University of New England Armidale NSW 2351 Australia
Ph: +612 6773 3317 Fax: +612 6773 3814
Publication list: http://publicationslist.org/paul.mcdonald Thompson ISI Researcher ID: http://www.researcherid.com/rid/A-5928-2010 Web: http://www.une.edu.au/staff/pmcdon21.php ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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THANKS JEFF. FURTHER HELPFUL COMMENTARY FOR ME, AND I HOPE OTHER READERS AS WELL. MY COMMENTS BELOW THUS: ****……..**. REGARDS. RICHARD
I think you have misunderstood what Stephen was saying, three factors to consider.
1- a given population of Brown Falcons say at Werribee or where ever, does not consist of a number of different morphs. The differences in plumage are primarily the result of differences between the sexes overlaid by increasing paleness as the individuals get older. ****THIS WAS INDEED MY UNDERSTANDING FORWARD TO READING HIS ORIGINAL ARTICLE (A COPY OF WHICH I NOW HAVE).**
2- there are regional differences eg. birds in Central Aust are paler more “Kestrel like”, birds from the Kimberley are very dark. There are other features of difference between these regional types beyond pale and dark which I am not going to go into here, but the important thing to understand
is that a pale regional type from Central Aust and a very old pale male from Werribee are not the same thing, they don’t look identical. Same for the dark Kimberley/Top end birds, there is no equivalent found elsewhere. These are regional types. ****THIS IS HELPFUL CLARIFICATION OF REGIONAL DIFFERENCES, OF WHICH I WAS LESS AWARE.**
3- yellow cere is apparently only found in the older males especially the pale Central Australian population, Stephen suggested this may possibly be because they are for unknown reason more likely to reach the prerequisite older age. ****THAT WAS MY UNDERSTANDING OF WHAT HE MEANT.**
Cheers Jeff.
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G’day Richard,
I think you have misunderstood what Stephen was saying, three factors to consider.
1- a given population of Brown Falcons say at Werribee or where ever, does not consist of a number of different morphs. The differences in plumage are primarily the result of differences between the sexes overlaid by increasing paleness as the individuals get older.
2- there are regional differences eg. birds in Central Aust are paler more “Kestrel like”, birds from the Kimberley are very dark. There are other features of difference between these regional types beyond pale and dark which I am not going to go into here, but the important thing to understand is that a pale regional type from Central Aust and a very old pale male from Werribee are not the same thing, they don’t look identical. Same for the dark Kimberley/Top end birds, there is no equivalent found elsewhere. These are regional types.
3- yellow cere is apparently only found in the older males especially the pale Central Australian population, Stephen suggested this may possibly be because they are for unknown reason more likely to reach the prerequisite older age.
Cheers Jeff.
Dear Chris and Simon,
I actually think that this variation is more likely to be associated with age and sex differences than plumage ‘phases’. Male Brown falcons at Werribee tended to be lighter (front) and redder (back, legs) than females. Further, males have more yellow and less blue in their cere and orbital rings than females, and this seems to get brighter as they get older in both sexes. There are some photos in the below article, although they aren’t close enough to see bare parts in detail. For those interested, I can send photos of typical young and adult heads of each sex off-list.
Thus, while it is too early to prove it conclusively, I’m pretty confident that the ‘phases’ of brown falcons aren’t likely to stand up, but rather are more likely to be representative of age and sex differences, with birds becoming lighter and possessing more yellow in their bare parts as they age, particularly males. The lighter part at least is consistent across several raptor species (e.g. think black falcons with white bibs). Differences according to region on the record are most likely due to incomplete sampling, or sampling that is influenced by recent events at given locations, e.g. marginal/ephemeral areas are more likely to have lots of younger and thus darker birds, established areas older, lighter birds that hang onto territories for consecutive years and so on. Nonetheless it would make an interesting study to look at these differences across their range in more detail.
The bird in question looks like it has all the features typical of an adult male that is at least several years old. Their plumage can be variable, granted, but the patterns described below (sadly post-Hanzab) have held up and made sense for the falcons that I have been looking at ever since.
For those interested, the published details of that study can be found here: McDonald P.G. 2003 Variable plumage and bare part colouration in the Brown Falcon Falco berigora: the influence of age and sex. Emu 103(1), 21-28.
Happy birding , Paul
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr Paul G. McDonald
paul.mcdonald@une.edu.au
Lecturer Zoology, School of Environmental and Rural Sciences University of New England Armidale NSW 2351 Australia
Ph: +612 6773 3317 Fax: +612 6773 3814
Publication list: http://publicationslist.org/paul.mcdonald Thompson ISI Researcher ID: http://www.researcherid.com/rid/A-5928-2010 Web: http://www.une.edu.au/staff/pmcdon21.php ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Chris,
Great photos!
HANZAB plates very clearly depict the rufous phase of Brown Falcon as having yellow cere and orbital ring. Though the text misleadingly, only refers to grey or white. So I assume there is a common precedent amongst the rufous forms to have this yellow bare part colouring.
Regards,
Simon.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Simon Mustoe Tel: +61 (0) 405220830 | Skype simonmustoe | Email simonmustoe@ecology-solutions.com.au
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