The evolution of colourful eggs

It is great to see Kiara’s paper now published in Evolution (it can be found here). The paper is focused on the evolution of colour in eggs and uses the Australian passerines to provide insight into the emergence of pigmented eggs in different branches of the family tree. The passerines, are the songbirds, and they make up about half of the world’s species of bird today. This group first evolved in Australia, and the continent is still home to the largest number of passerine families, and can provide insight into what was happening early in the radiation of the group.

In this study we characterised the egg colour variation across different families of Australian songbird, and were able to identify that the ancestral egg colour in the passerine group was most likely to be white, and that pigmented eggs emerged independently in a number of different branches of the family tree over time. Importantly, this seems to have happened after the ancestors of the different families evolved open nests. This makes sense, because the pigment likely evolved to help protect the now exposed eggs from predators and from solar radiation.

This paper builds nicely on the earlier comparative work that was started with Jordan Price, when he visited on sabbatical and Daisy Englert Duursma.

Fig 2. from L’Herpiniere et al 2021, showing how the evolution of colour in the eggs of different species, maps nicely on to the distribution of closed and open nests across the phylogeny of Australian passerines.

Singing it softly

Singing male Zebra Finch. (Photo Hugo Loning)

Zebra finch song is an extremely short-range signal. That is the conclusion from the recent paper by Hugo Loning in Behavioral Ecology. This is the first paper of our project on acoustic communication of the wild zebra finch in collaboration with Marc Naguib from Wageningen University. After quantifying the song amplitude of wild zebra finch recordings, we played them back at natural amplitude and re-recorded them in our field site Fowlers Gap. Afterwards, we analysed these transmitted vocalisations while integrating what is known about the hearing from lab zebra finches. This way, we found out that the detection distance of song is on average about nine meters – an extremely short distance for song. We supported this claim by observations in the field which confirm that group members are often very close, on average within one meter, when a group member is singing. Additionally, we find that even their ‘distance call’ does not reach very far, up to about fourteen meters. Our reported findings are in stark contrast with the classical idea of birdsong as a long-range communication signal. The paper can be freely accessed here.

Cover Page Model

It clearly helps to work on an amazingly beautiful species when it comes to getting a cover page photo for a study, and once again a journal has chosen to use a picture of the Gouldian finch to grace the cover. Here is the August cover of the Journal of Experimental Biology with a great photo supplied by Mark Chappell, one of the co-authors of our new paper. The paper, led by Bill Buttemer demonstrates that although the red and blackheads morphs have some quite different behavioural strategies there is no difference in their basal and maximal metabolic rates.

A male black-headed and male red-headed Gouldian finch.

Mitonuclear incompatibilities in the two subspecies of the Long-tailed finch

It is really great to see our first paper in this exciting space being published with the paper by Kelsie Lopez being published in Evolution. The paper can be found here. In this paper we report the molecular work that Kelsie did with Daniel Hooper at Cornell, finding a divergence in the mitochondrial sequence of two clades that arose around 0.5 million years ago. This is the kind of spilt that recent theoretical work has suggested might help to drive speciation, and the incompatibility of two closely related forms (lots of cool work by Geoff Hill, and Paul Sunnocks in this area). This spilt in mitochondrial haplotypes is coincident with the Z chromosome divergence that we found earlier, and centred around Kununnurra in the Eastern Kimberley. Hybrid zone females are significantly less likely than males to carry an admixed Z chromosome or have mismatched Z-mitochondrial genotypes, which is a strong indication that there is some cool selection happening here. So a female that has a western Z chromosome, will work better if she also has a western mitochondrial haplotype. Females with a mismatch, like a western Z chromosome and an eastern mitochondrial haplotype are probably less fit and tend to perish at an earlier stag of development. We are following this up with more work in the field and laboratory.

Figure 2. From Lopez et al 2021.

Sperm, eggs, and nestlings – 2 days, 3 papers!

The past few days have been particularly productive for the research group with three quite different papers all published online over the past 48 hours. First up was the paper published in Ibis reporting the catastrophic mortality of nearly all embryos, during a heatwave back in 2017. The paper was written by Luke McCowan and myself, and describes this heatwave and the very high level of mortality throughout the population at this time. We will publish more detail on this one very soon.

Second up is the first experimental paper focused on data from the Oroboros Oxygraph machine that we have used to assay mitochondrial function. This paper, published in Frontiers in Physiology, was led by Riccardo Ton, and is focused on the experiment he conducted while first visiting us as an Endeavour Scholar in 2019. The paper is published online and is publicly accessible here.

Finally, less than 12 hours after Riccardo’s paper is the SpermSizer paper written by Callum McDiarmid. This paper, published in Behavioural Ecology and Sociobiology describes a new tool for measuring sperm morphology. The program has been extremely useful in processing the many thousands of sperm that we have now measured in our studies of estrildid finches. The paper can be found here.

Figure of Sperm Sizer in action. From McDiarmid et al 2021.

Why are pair bonds so strong in Australia?

The first fieldwork I ever did in Australia was focused on the silvereye. On my first day in the field, having worked in Europe up to that point, I was so struck by this pair allopreening that I took this photo (on the left). Since that time, one of the questions that I have worked on, has been why pair bonds in Australian birds are so different, and much stronger then those exhibited by similar birds in Europe.

Recently I published a review of empirical work in this area in Frontiers in Ecology and Evolution. The paper is open access, and can be downloaded here. We are continuing to conduct research in this area, with one of our main projects being a collaboration with Marc Naguib from Wageningen, focused on the pair bond and acoustic communication between partners in the zebra finch (pair shown on the right above).

How do Zebra finches cope with heat?

Drinking zebra finches (Picture: Simon Griffith)

In two papers recently published with our collaborator, Dr Christine Cooper from Curtin University, we have looked at the physiological mechanisms through which zebra finches can cope with the extreme conditions that occur regularly at our field site, and specifically air temperatures in excess of 40 degrees Celsius. The papers, published in the Journal of Experimental Biology and Comparative Biochemistry and Physiology, Part A, help us to understand how birds adjust their physiology to cope with such challenging conditions. Zebra finches were better able to cope with heat waves when they were primed by similar conditions, and reduced their metabolic rate, thus lowering the amount of heat being generated internally. Individuals also showed great plasticity in their use of water and their body temperature, enduring short periods with elevated body temperature when required. It is not surprising that these desert adapted birds can cope so well with these hot and arid conditions, but understanding the mechanisms that they can use, and the flexibility that they have helps us to understand likely responses to climate change in desert birds, and the reasons that mortality events have been reported in these and other desert specialists. It is likely that those heat induced deaths have been caused by unpredictable bursts of high temperature, which the birds were not able to prepare for.


For the first time in 15 years the zebra finches at Fowlers Gap, have had a bumper breeding event that has run right through the Austral winter. This followed rains that came in March and April, and brought the drought, that had meant that there was no breeding in the Spring of 2017, 2018 and 2019. The rain filled most of the dams on the station and produced enough winter grass for the crops of nestlings to be filled to bursting. The breeding started in May and has continued right through to the normal start of the breeding season (August).

Extrapair paternity in birds

Our review of extrapair paternity in birds is published today in Molecular Ecology and can be accessed here. The paper, written by Lyanne Brouwer and myself, is an update on the last review that I published on the subject in 2002. There are now over 30 years of molecular data on the incidence of extrapair offspring in socially monogamous species and we present an overview of over 500 studies focused on over 300 species. Overall, in around three quarters of socially monogamous species, some evidence of infidelity has been found. In the species in which it occurs about one fifth of all offspring are fathered by an extrapair sire, and therefore not by the social male who is investing in their care. We also demonstrate that the incidence of extrapair paternity is more likely to occur in some avian families, being particularly prevalent in passerines, and rarer, or completely absent in families that are long-lived, such as owls, or seabirds.

Fig 3 from paper, showing the level of EPP across different species across the avian family tree


Under the weather: the stressful effects of hot and windy days

Hot&windyOur new paper has just come out, from work done at Fowlers Gap a couple of years ago. In the study we looked at how nestlings are affected by both very hot days and very windy days as they are developing in the nest. These conditions are stressful for nestlings, and we found that both types of bad weather affected the level of corticosterone – the stress hormone. These findings are likely to be driven both directly and indirectly. When nestlings are very hot, they find it hard to lose heat and that will be stressful itself. Wind can be stressful because the noise will mask the ability to hear other sounds in the environment, such as communication with parents, and also the noise of approaching predators. In addition, the results may be the indirect effect of hunger, as parents will find it much more difficult themselves to find food to feed to their nestlings when it is hot and windy. The work was led by Ondi Crino, who is an endocrinologist, and expert on stress. The paper can be found here

Choosing to breed in synchrony with neighbours

In the second paper to be published from Hanja’s thesis, we have demonstrated that zebra finches would rather nest next to a pair that are also just starting to breed, than a pair that is further along. Hanja and team demonstrated this by erecting new empty nest boxes near to occupied boxes, at either nest-building, incubating or chick rearing stages. Pairs were far more likely to lay eggs in the experimental boxes that were close to those that had also initially been at the nest building stage. We believe that these results are driven by the social benefits of breeding alongside other pairs at a similar stage of activity. The paper is published in the journal Animal Behaviour, and can be downloaded for free in the next month using this link.  Zebmalebox