Latitudinal gradients in avian colourfulness (2 Viewers)

[Peter Kovalik]

Christopher R. Cooney, Yichen He, Zoë K. Varley, Lara O. Nouri, Christopher J. A. Moody, Michael D. Jardine, András Liker, Tamás Székely, and Gavin H. Thomas (2022) Latitudinal gradients in avian colourfulness. Nature Ecology & Evolution 6: 622–629. Published 4 April 2022.
Latitudinal gradients in avian colourfulness - Nature Ecology & Evolution

Abstract
It has long been suggested that tropical species are generally more colourful than temperate species, but whether latitudinal gradients in organismal colourfulness exist remains controversial. Here we quantify global latitudinal trends in colourfulness (within-individual colour diversity) by collating and analysing a photographic dataset of whole-body plumage reflectance information for >4,500 species of passerine birds. We show that male and female birds of tropical passerine species are generally more colourful than their temperate counterparts, both on average and in the extreme. We also show that these geographic gradients can be explained in part by the effects of several latitude-related factors related to classic hypotheses for climatic and ecological determinants of organismal colourfulness. Taken together, our results reveal that species’ colourfulness peaks in the tropics for passerine birds, confirming the existence of a long-suspected yet hitherto elusive trend in the distribution of global biodiversity.

 

[dantheman]

Christopher R. Cooney, Yichen He, Zoë K. Varley, Lara O. Nouri, Christopher J. A. Moody, Michael D. Jardine, András Liker, Tamás Székely, and Gavin H. Thomas (2022) Latitudinal gradients in avian colourfulness. Nature Ecology & Evolution 6: 622–629. Published 4 April 2022.
Latitudinal gradients in avian colourfulness - Nature Ecology & Evolution

Abstract
It has long been suggested that tropical species are generally more colourful than temperate species, but whether latitudinal gradients in organismal colourfulness exist remains controversial. Here we quantify global latitudinal trends in colourfulness (within-individual colour diversity) by collating and analysing a photographic dataset of whole-body plumage reflectance information for >4,500 species of passerine birds. We show that male and female birds of tropical passerine species are generally more colourful than their temperate counterparts, both on average and in the extreme. We also show that these geographic gradients can be explained in part by the effects of several latitude-related factors related to classic hypotheses for climatic and ecological determinants of organismal colourfulness. Taken together, our results reveal that species’ colourfulness peaks in the tropics for passerine birds, confirming the existence of a long-suspected yet hitherto elusive trend in the distribution of global biodiversity.

When they say 'whole-body plumage reflectance' does that mean how we see the birds or how they see themselves? ie are we talking bright reds and blues (as you assume with eg parrots) or the colours more on the UV end (and are the two linked anyway?)

 

[Andy Adcock]

Christopher R. Cooney, Yichen He, Zoë K. Varley, Lara O. Nouri, Christopher J. A. Moody, Michael D. Jardine, András Liker, Tamás Székely, and Gavin H. Thomas (2022) Latitudinal gradients in avian colourfulness. Nature Ecology & Evolution 6: 622–629. Published 4 April 2022.
Latitudinal gradients in avian colourfulness - Nature Ecology & Evolution

Abstract
It has long been suggested that tropical species are generally more colourful than temperate species, but whether latitudinal gradients in organismal colourfulness exist remains controversial. Here we quantify global latitudinal trends in colourfulness (within-individual colour diversity) by collating and analysing a photographic dataset of whole-body plumage reflectance information for >4,500 species of passerine birds. We show that male and female birds of tropical passerine species are generally more colourful than their temperate counterparts, both on average and in the extreme. We also show that these geographic gradients can be explained in part by the effects of several latitude-related factors related to classic hypotheses for climatic and ecological determinants of organismal colourfulness. Taken together, our results reveal that species’ colourfulness peaks in the tropics for passerine birds, confirming the existence of a long-suspected yet hitherto elusive trend in the distribution of global biodiversity.

Isn't this the long established 'Gloger's rule'?

Gloger's rule - Wikipedia

en.wikipedia.org

 

[Mysticete]

Isn't this the long established 'Gloger's rule'?

Gloger's rule - Wikipedia

en.wikipedia.org

Gloger's rule is only about the relative "darkness" of critters. For example, song sparrows tend to be much darker in humid environments like in the Pacific NW, and a lot paler in dryer enviroments, like the desert southwest. It's not about the occurrence of bright patterns in plumage that we would characterize colorful birds by.

 

[Farnboro John]

But what is the "so what" of this?

What are they calling "bright"? Is the green on a turaco, which is actually camouflage against brightly lit leaves and reduces contrast rather than increasing it, considered bright or neutral?

Even if it's the case (and I am always suspicious of such general conclusions when I don't really see anything but "one size does not fit all"), what is (a) the cause (and I mean the evolutionary pressure, not the genes responsible) (b) the effect?

Are there differences between dwellers in forest darkness and open savannah brightness within the latitudinal limits identified as significant? If not why not? If so, what and why?

John

 

[l_raty]

What are they calling "bright"? Is the green on a turaco, which is actually camouflage against brightly lit leaves and reduces contrast rather than increasing it, considered bright or neutral?

Haven't seen the paper, but in the abstract, they're not discussing "brightness", but rather "colourfulness (within-individual colour diversity)".
I assume this means that no single colour, be it emerald green or chrome red, would alone be sufficient to make a plumage "colourful" ?

 

[Mysticete]

I would imagine this is spelled out in the methods and supplementary material, however my institution doesn't have access to this journal.

 

[Björn Bergenholtz]

If of any use/help, see ResearchGate (request + figures)= here.