Do male Hoopoes judge female quality by inspecting the color of her eggs?

Egg color is determined by the amount of antimicrobial secretion on the eggshell.

Male birds often go to great lengths to attract the attention of female birds. Some bird-of-paradise species exhibit eccentric courtship displays to woo the females. And bowerbirds build elaborate structures with twigs and leaves to convince potential partners. Other species keep it simple and only show off their bright colors. No matter what strategy evolved, in each case the males are advertising their quality. For instance, the tail of a peacock indicates that this male manages to escape predators and stay parasite-free despite dragging such a long and colorful structure behind him. Surely, this bird has very good genes that he can pass on to the next generation. Females choose their partner based on the quality of such traits and thereby influence the evolution of male morphology and behavior. This idea was put forward in 1871 by Charles Darwin and is now generally known as sexual selection.

You might have noticed that the examples above are very male-biased. The male birds dance, strut their feathers and sing, while the female birds silently judge and pick a winner. But how does the male know that he is being picked by a good quality female? In other words, can females also advertise their quality?

The colorful feathers of the Mandarin duck advertise the quality of this male. © Alexandra Sora | Wikimedia Commons

 

Egg Color

This question is particularly relevant in bird species where males provide a lot of parental care. If you are going to invest time and resources in raising young, you need to be sure that your partner is worth it. One way in which males could judge the quality of the female is by inspecting the color of the eggs. For example, the blue-green color of eggs is due to biliverdin, a strong anti-oxidant. Females that lay intense blue-green eggs might thus be advertising their anti-oxidant capacity.

A recent study in the Journal of Avian Biology applied this reasoning to Hoopoes (Upupa epops). Females of this species stain their eggs with a secretion from the uropygial gland (also known as the preen gland, located at the base of the tail). This secretion contains symbiotic bacteria that protect the eggs from pathogens. By applying this antimicrobial substance, the eggs also change color: from bluish to greenish-grey. Hence, the male Hoopoe could judge the quality of the female – in terms of protective bacteria – by looking at the color of the eggshells and adjust his parental care accordingly.

The eggs of a Hoopoe © Didier Descouens | Wikimedia Commons

 

Saturation Levels

This leads to a clear and testable hypothesis: male Hoopoes should bring more food to nests with greenish-grey eggs. Silvia Díaz Lora and her colleagues tested this prediction in Spain by observing 39 Hoopoe nests. First, they established the relationship between egg color and symbiotic bacteria. The color of the eggs was standardized by measuring their saturation (rA). A high saturation points to a brightly colored egg, while a low saturation indicates a grey or white egg. As expected, the saturation of the eggs was negatively related to bacterial density in the uropygial secretion. In other words, the lower the saturation of the eggs (i.e. grey eggs), the more symbiotic bacteria on the eggshell. Next, the researchers correlated the saturation of the eggs with the provisioning effort of the male. And in accordance with their prediction, males brought more food to nests with grey eggs (i.e. low saturation and thus more symbiotic bacteria).

These findings support the idea that females can advertise their quality through the color of the eggs. However, we cannot be completely sure that male Hoopoes are actively inspecting the egg color. Perhaps the relationship is determined by a third factor that is related to female quality. It is possible that males focus on another trait that covaries with number of symbiotic bacteria deposited on the eggshells. Experimental manipulation is needed to check whether the correlation in this study is an actual causation.

The relationship between male provisioning rate and eggshell saturation indicates that males brought more food to nests with lowly saturated eggs (i.e. white or grey eggs). From: Diaz Lora et al. (2020) Journal of Avian Biology.

 

References

Díaz Lora, S., Pérez‐Contreras, T., Azcárate‐García, M., Martínez Bueno, M., Soler, J. J., & Martín‐Vivaldi, M. (2020). Hoopoe Upupa epops male feeding effort is related to female cosmetic egg colouration. Journal of Avian Biology, 51(8).

Featured Image: A Hoopoe in Hungary © Andy Morffew | Wikimedia Commons

Solving the paradox of the great speciator on the Solomon Islands

Rapid loss of dispersal might be key to explain rapid speciation on islands. 

Charles Darwin called the origin of new species “that mystery of mysteries”. And despite decades of intensive evolutionary research, there are still several unsolved questions on speciation. One of my personal favorites is “the paradox of the great speciators”. This conundrum – which would make a great movie title – refers to avian species complexes that occur on islands with different levels of geographic isolation: from narrowly separated to very remote islands. Each island has its own endemic and genetically differentiated population (sometimes considered distinct species or subspecies). This situation raises the question of how some species complexes can disperse over a wide area, often coming into secondary contact and experiencing consequent gene flow, and still rapidly give rise to new species. To solve this paradox, ornithologists have often turned to the White-eyes (family Zosteropidae). This group of birds can be found across the Old World, but also on the archipelagos of the Pacific Ocean where they diversified into numerous (sub)species. A recent study in the journal Evolution focused on White-eyes of the Solomon Islands to find an answer to the paradox of this great speciator.

An overview of the different Zosterops populations on the Solomon Islands. From: Manthey et al. (2020) Evolution.

 

Gene Flow Patterns

To understand how new White-eye species evolve on these islands, we need to know how isolated the different islands populations are from one another. Therefore, Joseph Manthey and his colleagues collected DNA samples across the Solomon Islands to reconstruct patterns of gene flow. Using the software TreeMix, the researchers were able to reconstruct the historical relationships between the island populations and pinpoint gene flow events (indicated with red arrows in the figure below). The findings from TreeMix were supported by other statistical tests, such as D-statistics.

Interestingly, these analyses suggested gene flow between distant populations, but not between nearby islands. For example, there has been gene flow between Grey-throated White-eye (Zosterops ugiensis) and Yellow-throated White-eye (Z. metcalfii) that are separated by at least 50 kilometers of deep waters. In contrast, species in the New Georgia Group, such as Vella Lavella White-eye (Z. vellalavella) and Ranongga White-eye (Z. splendidus), are only a few kilometers apart but do not exchange genetic material. Moreover, the populations on neighboring islands are genetically and morphologically distinct, indicating rapid evolution.

The TreeMix analysis shows the historical relationships between the island populations with several gene flow events (indicated with red arrows). From. Manthey et al. (2020) Evolution.

 

Loss of Dispersal

What can explain these peculiar patterns?  The researchers offer two explanations for the lack of gene flow between neighboring islands: (1) these species do not venture across the narrow straits, or (2) they do visit neighboring islands but they do not mix with the resident species due to differences in plumage or song which evolve rapidly. Because species from distant islands can still interbreed, the researchers argue that the first explanation (a loss in dispersal) is the most likely explanation for the gene flow patterns at nearby islands. After a highly dispersive phase of island colonization, the newly established populations would immediately experience strong selection for reduced dispersal.

I would add another aspect to this scenario. Perhaps the selection for reduced dispersal is related to reproductive isolation between different islands (explanation 2). Early in this process, dispersing individuals end up on neighboring islands and occasionally manage to interbreed with the resident species. However, the resulting hybrids fail to reproduce because their intermediate phenotype prevents them from finding a suitable mate. Over time, this selection against hybrids could strengthen reproductive isolation between the parental species (i.e. a process known as reinforcement). Later on, dispersing birds stop interbreeding with their neighbors, increasing selection against dispersing individuals. Whether this idea makes sense remains to be tested. But slowly we are getting closer to understanding rapid speciation on islands and solving the paradox of the great speciator.

 

References

Manthey, J. D., Oliveros, C. H., Andersen, M. J., Filardi, C. E., & Moyle, R. G. (2020). Gene flow and rapid differentiation characterize a rapid insular radiation in the southwest Pacific (Aves: Zosterops). Evolution, 74(8), 1788-1803.

Featured image: Warbling White-eye (Zosterops japonicus) © Obubu Interns

 

This paper has been added to the Zosteropidae page.

Intermediate color morphs of the Common Buzzard are most successful

Why do intermediate morphs do better than light and dark ones?

When I am driving on the Belgian and Dutch highways, I always keep an eye on the roadside. Occasionally, a Common Buzzard (Buteo buteo) will be sitting on a pole, staring into the distance. The plumage patterns on the chests of these Buzzards vary from almost completely white to dark with a striking crescent of brighter feathers. The occurrence of such color morphs has fascinated birdwatchers and ornithologists for decades.

A 2001 study of the German Buzzard population found that intermediate morphs are more successful – in terms of survival and reproduction – compared to the lighter and darker morphs. To explain this finding, the researchers turned to the putative genetic basis of this trait. Let’s assume that color morph is determined by a single position (i.e. a locus) in the genome with two variants (i.e. alleles): L for light and D for dark. A bird with two L-alleles develops into a white morph, while a bird with two D-alleles will become a dark morph. The combination of L and D, however, results in an intermediate morph. In some traits, a heterozygous combination (LD) has a higher fitness than a homozygous combination (LL or DD). This phenomenon is known as heterozygote advantage and the researchers suggested that this is driving the frequency of intermediate Buzzard morphs in Germany. However, recent studies in the Netherlands question this explanation.

A dark Buzzard morph © Lukasz Lukasik | Wikimedia Commons

 

Intermediate Nestlings

First, the genetic basis of the Buzzard morphs. The German study assumed that this trait is encoded by a single locus with two alleles. This prediction can be tested easily using the Mendelian genetics that you probably learned in high school. If two intermediate morphs pair up, you can predict the likely morphology of their offspring: 25% chance for light (LL), 25% for dark (DD) and 50% for intermediate (LD and DL). To clarify this calculation, I added a Punnett-square below. Elena Frederika Kappers and her colleagues tested this prediction using data from more than 200 Buzzard families. In contrast to the expected 50% intermediate offspring, the researchers found much more intermediate nestlings (74%), indicating that this trait is not encoded by a single gene but probably under the control of multiple genes (i.e. the trait is polygenic). From population genetic theory, we know that heterzygote advantage is not always an effective mechanism to maintain variation in polygenic traits.

A Punnet-square showing the different combinations of L and D alleles. The while boxes indicate the alleles from the parents. The colored boxed show the morphs colors (light, intermediate and dark) depending on the combination of alleles.

 

Parasites?

The genetic underpinnings of Buzzard plumage might make heterozygote advantage less likely, but we cannot discard it completely. In fact, a recent study in the Journal of Evolutionary Biology showed that, similar to the German population, Dutch intermediate morphs performed better than their light and dark cousins. It is still unclear what ecological factor determines the success of intermediate morphs. The researchers speculate that intermediate morphs might breed in the best territories and have a competitive advantage. Or perhaps intermediate morphs are less susceptible for parasite infections (which could actually be due to heterozygote advantage). Indeed, another study showed that Buzzard chicks with darker plumage were more susceptible to infection by carnid flies (Carnus haemapterus) while nestlings with lighter plumage had a higher infection rate with the blood parasite Leucocytozoon toddi.

Light and dark morphs might be more susceptible to parasite infections. Dark morphs have more Carnus-infections (left) and light morphs have more blood parasites. From: Chakarov et al. (2008) Functional Ecology.

 

More Intermediate Morphs

Regardless of the underlying mechanism, it seems that intermediate Buzzard morphs will become more common in the future. Long-term data from the Dutch population showed that the frequency of intermediate morphs increased steadily. This patterns is likely due to the combination of assortative mating (pairing up with a partner that looks like you) and the reproductive success of intermediate morphs. Breeding pairs consisting of intermediate Buzzards produced more offspring and these young birds mostly had intermediate plumage themselves (ca. 75% of the nestlings belonged to the intermediate morph). It does not take a mathematical genuis to see that this positive feedback loop will lead to more intermediate morphs in the coming generations. I will keep an eye on it while I am driving on the highway.

 

References

Chakarov, N., Boerner, M., & Krüger, O. (2008). Fitness in common buzzards at the cross‐point of opposite melanin–parasite interactions. Functional Ecology, 22(6), 1062-1069.

Kappers, E. F., de Vries, C., Alberda, A., Forstmeier, W., Both, C., & Kempenaers, B. (2018). Inheritance patterns of plumage coloration in common buzzards Buteo buteo do not support a one-locus two-allele model. Biology letters, 14(4), 20180007.

Kappers, E. F., de Vries, C., Alberda, A., Kuhn, S., Valcu, M., Kempenaers, B., & Both, C. (2020). Morph‐dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards Buteo buteo. Journal of Evolutionary Biology, 33(9), 1306-1315.

Krüger, O., Lindström, J., & Amos, W. (2001). Maladaptive mate choice maintained by heterozygote advantage. Evolution, 55(6), 1207-1214.

Featured image © Ronald Huijssen | Wikimedia Commons

Misconceptions and regressions: The evolution of bird brains

Recent study traces the evolution of brain size along the avian tree of life.

Despite the growing number of excellent popular science writers, many misconceptions about evolution are still surviving among the general public. One especially tenacious one is “The March of Progress“, mostly depicted a series of walking primates from an ape-like creature over primitive hominids to modern Homo sapiens. This iconic picture misrepresents evolution as a linear process from primitive creatures to complex organisms. This thinking is often extended to the last universal common ancestor and summarized in the phrase “From monad to man.” In each case, modern humans are considered the ultimate goal of the evolutionary process. Or the pinnacle of evolution. Nothing could be further from the truth. Evolution is not a linear sequence, but an ever-branching tree. Humans are just one of the many twigs on this tree of life. We might be more advanced in terms of brain power compared to a bacterium. But some bacteria are clearly superior to us when it comes to processing methane or living in boiling lakes. Which organism can be considered the pinnacle of evolution is thus a non-sensical question.

Given that most evolutionary biologists are aware of these misconceptions, I was surprised to read the following in a recent Current Biology paper: “two groups—parrots and corvids—independently acquired relative brain sizes, neuronal densities, and sophisticated cognitive potential near the pinnacle of the vertebrate world. [my emphasis]” This sentence seems to suggest that there is an avian March of Progress towards larger brains with parrots and corvids at the finish line. This reasoning is obviously incorrect. Brain size is just one of numerous traits under selection in different species. In one environment a large brain and a small body might be beneficial, while in another environment a small brain and large body have the highest chances of survival and reproduction. Hence, the small-brained, large-bodied species could be considered the pinnacle of evolution in its habitat.

The original March of Progress illustration from Early Man (1965).

 

Regressions

Now that I have clarified that misconception and ventilated some frustration, we can finally delve into the Current Biology study on avian brain size evolution. Apart from the hick-up at the end of the paper, this is a beautiful piece of work. The researchers amassed an impressive dataset of brain endocasts of 284 extant bird species, 22 extinct bird species, and 12 non-avian theropod dinosaurs, complemented with data for more than 1,900 extant species from another study.

Next, they investigated the relationship between brain volume and body mass for different bird groups. These relationships can be captured in simple mathematical formula that you probably remember from high school: y = ax + b. The coefficients a and b correspond to the slope of the regression line and the intercept (i.e. the point where the regression line hits the y-axis), respectively. By comparing these coefficient between related bird groups, the researchers were able to reconstruct the evolution of brain size across the avian phylogeny. An increase in the intercept indicates that one bird group increased in brain volume and body mass, but that the relative brain size remained the same. However, a steeper regression line (i.e. an increase in slope) points to an increase in relative brain size in one bird group.

The relationship between body mass (x-axis) and brain volume (y-axis) for different bird groups. Comparing these lines between these bird groups allowed the researchers to study the evolution of relative brain size. From: Ksepka et al. (2020) Current Biology.

 

Mass Extinction

Detailed analyses of these regressions revealed several evolutionary shifts in relative brain size. Interestingly, most significant changes occurred after the mass extinction at the end the Cretaceous when the non-avian dinosaurs disappeared. This catastrophic event might have set the stage for an adaptive radiation in brain size, a scenario that fits the “cognitive buffer hypothesis”. This hypothesis suggests that large brains provide a buffer against frequent or unexpected environmental changes via enhanced capacity for flexible behavioral responses.

After this adaptive radiation, several bird groups showed independent changes in relative brain size. Birds of prey in the orders Accipitriformes, Strigiformes, Falconiformes, and Cariamiformes, for instance, experienced a small increase in relative brain size. A carnivorous lifestyle probably led to the evolution of a larger body, but was not accompanied by a proportional increase in brain size. In the woodpeckers (order Piciformes), we see the opposite pattern where a decrease in body size was not followed by a decrease in brain volume, resulting in a significant increase in relative brain size. This pattern is also apparent in hummingbirds and swifts (order Apodiformes)m and in sandpipers and buttonquails (order Charadriiformes).

Changes in relative brain size across the avian phylogeny. From: Ksepka et al. (2020) Current Biology.

 

Different Evolutionary Paths

And that brings us to the “pinnacle” of avian brain size: the parrots and the corvids. The method outlined above allowed the researchers to pinpoint the exact mechanisms behind the high relative brain sizes of these birds. It turns out that they each took a different path to the top: parrots primarily reduced their body size, whereas corvids increased body and brain size simultaneously. A nice example of convergent evolution.

It is no surprise that parrots and corvids have large relative brain sizes. These species are known for their clever tricks, such as mimicking sounds and using tools. But brain size is just one aspect of intelligent behavior. Other studies have found that the structure of the brain and the connections between the neurons are also important. For example, parrots have an additional vocal learning pathway that is absent in songbirds. And both corvids and parrots have the highest cerebral neuronal densities in birds. There is more to avian life than a large brain.

 

References

Ksepka, D. T. et al. (2020). Tempo and Pattern of Avian Brain Size Evolution. Current Biology.

Featured image: New Caledonian Crow using a tool © National Geographic

From the sky to the island: Flightless rail species converge on the same body plan

Several species independently evolved shorter sterna and stronger hindlegs.

Although birds are known for their aerial lifestyle, several species evolved towards a flightless existence. Common examples include the Ostrich (Struthio camelus) and the Southern Cassowary (Casuarius casuarius). Loss of flight occurred independently in numerous bird families and a recent study in the journal Science Advances showed that we are underestimating the frequency of this evolutionary transition if we only focus on the ca. 10,000 extant birds. Including data from 581 known human-related extinctions quadrupled the number of flightless species, suggesting that loss of flight has occurred independently at least 150 times. The pervasiveness of flightless birds across the avian Tree of Life is a nice example of convergent evolution: the independent evolution of similar features in distantly related species. But how convergent is this evolutionary change? Do birds just lose the ability to fly or do other traits change as well? The rails (Rallidae) provide the ideal bird family to explore these questions.

Taking into account recently extinct species reveals that loss of flight occurred numerous times during the evolution of birds. From: Sayol et al. (2020) Science Advances.

 

Running Rails

The rail family holds about 130 species of which more than 30 have lost the ability to fly. The majority of these flightless species are endemic to remote islands, suggesting that their ancestors could fly to the islands. Once on solid ground, the ancestral populations had little use for flying (perhaps because there were no predators to escape from) and gradually transitioned to a flightless life. Julien Gaspar and his colleagues assembled a dataset with 10 morphological traits for 90 rail species consisting of extant and recently extinct species.

The principal component analysis (PCA) depicted below nicely summarizes the findings of this study, which appeared in the journal Ecology and Evolution. A PCA captures the variation in a dataset – 10 morphological traits in this case – and condenses it into a few principal components. On the graph, you can see that the first component holds 41.8% of the variation while the second component explains 23.4%. These two axes clearly discriminate between flying (in red) and flightless (in black) rail species, although there is some overlap. The blue arrows show how different morphological traits correlate with the principal components. For example, the sternum depth and sternum length point upwards, indicating that species higher in the PCA have deeper and longer sternums. This makes sense because flying birds need a strong sternum to attach their flight muscles. Moreover, the arrows related to the sternum point away from the flightless species in the bottom of the graph. This means that flightless rails have smaller sterna.

A principal component analysis separates flying (red) from flightless (black) rails and shows which morphological traits (blue arrows) are associated with these lifestyles. From: Gaspar et al. (2020) Ecology and Evolution.

 

Genetic Path to a Flightless Life

Take your time to explore the PCA graph and you will see how different traits relate to flying and flightless birds. You should be able to deduce that flightless birds exhibit smaller sterna and wings than flighted taxa along with a wider pelvis and a more robust femur. These findings suggest that flightless rails became heavier and evolved stronger hindlegs to cope with a life on the ground. These traits evolved independently in several species, providing a nice example of convergent evolution on the morphological level.

The next step could be to investigate whether this convergence can be extended to the genetic level. Do mutations in the same genes underlie these morphological changes or are different genetic pathways under selection on different islands? A quick look at the reduction of wing size in other species provides some clues. In the flightless Galapagos Cormorant (Phalacrocorax harrisi), mutations in cilia-related genes contributed to the development of small wings. In the Emu (Dromaius novaehollandiae), however, reduced signaling in the early forelimb progenitor cells led to a delay in wing bud growth, culminating in shorter wings. There are thus several genetic paths to reduced wings. Does this also apply to other morphological traits?

 

References

Gaspar, J., Gibb, G. C., & Trewick, S. A. Convergent morphological responses to loss of flight in rails (Aves: Rallidae). Ecology and Evolution.

Sayol, F., Steinbauer, M., Blackburn, T., Antonelli, A., & Faurby, S. (2020). Anthropogenic extinctions conceal widespread evolution of flightlessness in birds. Science Advances.

Featured image: Guam Rail (Gallirallus owstoni) © Greg Hume | Wikimedia Commons

Three bird species show how to travel between the Andes and the Atlantic Forest

Would they recommend the dry Chaco and the open-vegetation Cerrado?

“A wealth of phylogeographic data is available for many terrestrial and aquatic organisms of the Northern Hemisphere. In fact, a disproportionately 77% of all empirical surveys of the field (or 1874 papers) have focused exclusively on Northern Hemisphere study systems.” This statement comes from a 2008 review by ‪Luciano Beheregaray on the state of phylogeography. His analysis clearly showed a bias towards studies in the Northern Hemisphere, indicating that more studies in the Southern Hemisphere are needed. I do not know whether this bias is still so pronounced, but there seems to be a clear increase in the number of phylogeographic papers on South American birds.

I have covered some of these studies on this blog, telling the evolutionary story of several species, such as the Buff-browed Foliage Gleaner (Syndactyla rufosuperciliata) and the Variable Antshrike (Thamnophilus caerulescens). Both species occur in the Atlantic Forest on the east coast of South America and the Andean region in the west. Interestingly, these regions are separated by the dry Chaco and the open vegetation of the Cerrado. Could it be that bird populations in the Atlantic Forest and the Andean region were connected in the past? And which route did the birds take from one region to the other? These questions provided the starting point for a recent study in the journal Molecular Phylogenetics and Evolution.

An overview of the different regions in South America. The Andes and the Atlantic Forest could have been connected through the Cerrado (path 1) in the north or the Chaco (path 2) in the South. From: Trujillo-Arias et al. (2020) Molecular Phylogenetics and Evolution.

 

Cerrado or Chaco?

Natalia Trujillo-Arias and her colleagues decided to focus on three species that occur in the Atlantic Forest and the Andes: the Ochre-faced Tody-flycatcher (Poecilotriccus plumbeiceps), the  Mottle-cheeked Tyrannulet (Phylloscartes ventralis) and the Golden-winged Cacique (Cacicus chrysopterus). Genetic analyses clearly differentiated between populations in the Atlantic Forest and the Andes, supporting the idea that both regions have been isolated for some time and probably acted as refugia during the Pleistocene.

To test whether these regions have been connected by gene flow, the researchers ran several demographic models (using Approximate Bayesian Computation, for the interested readers). The models with the highest statistical support pointed to a connection through the Cerrado. There was no evidence for gene flow through the Chaco, suggesting that this area forms a formidable barrier for small passerines due to its dry forests, savannahs and wide rivers (e.g., the Paraná-Paraguay river).

The three species in this study can be found in the Andes and in the Atlantic Forest. From: Trujillo-Arias et al. (2020) Molecular Phylogenetics and Evolution.

 

Morphology Lagging Behind

The clear genetic differences between the populations on both sides of the South American continents were not reflected in their morphology. The researchers noted that “A morphologic-genetic disagreement suggests that the phenotype of these species has been impacted by factors other than the demographic history of populations.” What other factors could have prevented the morphological traits from catching up with the genetic differentiation. In other words, why do birds from Andean and Atlantic Forest populations still look alike?

One possibility is neutral evolution: the phenotypes might have been changing by chance, which results in slower evolutionary change compared to strong natural or sexual selection. Alternatively, there might have been balancing selection that maintained certain morphological traits in both environments (also known as phenotypic conservatism). At the moment, the researchers could not discriminate between these possible explanations, opening the door for future research (check out this PNAS paper for more information on phenotypes in phylogeography). This is a common theme in science: answer one question (finding a Cerrado connection) and you are faced with a collection of new challenges (explaining morphological evolution).

A Golden-winged Cacique in Brazil © Dario Sanches | Wikimedia Commons

 

References

Trujillo-Arias, N., Rodríguez-Cajarville, M. J., Sari, E., Miyaki, C. Y., Santos, F. R., Witt, C. C., … & Cabanne, G. S. (2020). Evolution between forest macrorefugia is linked to discordance between genetic and morphological variation in Neotropical passerines. Molecular phylogenetics and evolution, 149, 106849.

Featured image: An Ochre-faced Tody-flycatcher in Brazil. © Dario Sanches | Wikimedia Commons

Mixing Motmots: A hybrid between Rufous and Amazonian Motmot in Brazil

The hybrid resembles a Rufous Motmot but has some peculiar plumage patterns.

How common is hybridization in birds? The answer to this question depends on whether you refer to hybridization on the individual level or the species level. If you consider the individual level, hybridization is mostly rare, only a small proportion of wild bird populations will consist of hybrids. Using the online database eBird, a recent study reported just 0.064 percent avian hybrids in North America (this percentage is probably a lower bound, as explained in this paper). On a species level, hybridization is a relatively common phenomenon among birds. The latest estimate indicated that 16.4 percent of bird species have hybridized in the wild. This percentage is probably an underestimate, given our generally poor knowledge of the breeding biology of several bird groups, such as cryptic tropical species.

Due to the rarity of hybridization on the individual level, it is often challenging to find new hybrid combinations. Occasionally, however, observant ornithologists do manage to identify previously unknown hybrids. A recent paper in the journal Ornithology Research, for example, reported a hybrid between two Motmot species.

A Rufous Motmot in Panama (© Dominic Sherony | Wikimedia Commons) and a captive Amazonian Motmot (© Staycoolandbegood | Wikimedia Commons).

 

Rufous Motmot or not?

During a birding trip in Brazil, a group of birdwatchers noticed a Rufous Motmot (Baryphthengus martii) with some abnormal features. A standard Rufous Motmot can be identified by the black mask that runs along its orange head. This specimen, however, had some conspicuous blue lines above and below the mask. In addition, the birdwatchers noticed a patch of distinct blue feathers on the black spot that adorned its neck. Finally, the tail of this bird sported some terminal racquet-shaped feathers, a feature that is only present in population from the Andes (subspecies semirufus). All these peculiar traits pointed to another Motmot species that occurs in the area: Amazonian Motmot (Momotus momota).

The conclusion that this abnormal specimen might be a hybrid between these two species was supported by an additional observation. When the birdwatchers played the song of the Rufous Motmot to attract the bird for a picture, a mixed group of four motmots (with two Rufous Motmots and two Amazonian Motmots) approached. The intermingling of these species – which also display similarities in courtship – suggests that the occasional hybrid might be produced.

A hybrid between Rufous Motmot and Amazonian Motmot. The abnormal features described in the text are indicated with arrows. From: Cerqueira et al. (2020) Ornithology Research

 

Rare Hybrids

Pablo Vieira Cerqueira and his colleagues searched several online databases for more pictures of this hybrid combination, but only found one possible hybrid in the photographic database Wikiaves. This indicates that hybridization is probably rare on an individual level (as explained above) or that hybrids between these species are difficult to detect.

In general, Motmot hybrids have rarely been documented. Rafael Marcondes and his colleagues described a hybrid between Amazonian Motmot and the Rufous-capped Motmot (Baryphthengus ruficapillus) from central Brazil. And the Handbook of Avian Hybrids of the World by Eugene McCarthy mentions a cross between Amazonian and Andean Motmot (Momotus aequatorialis), but without reliable evidence. Finally, some sources reported a mixed pair of Keel-billed Motmot (Electron carinatum) and Broad-billed Motmot (Electron platyrhynchum), but no hybrid offspring were observed. These cases suggest that hybridization between Motmot species might be more common than we assumed. Who know what curious crosses are hidden in the Brazilian rainforest?

 

References

Cerqueira, P. V., Gonçalves, G. R., & Aleixo, A. (2020). Two intergeneric hybrids between motmots from the Amazon forest: Rufous Motmot (Baryphthengus martii)× Amazonian Motmot (Momotus momota). Ornithology Research, 28(1), 57-60.

 

This paper has been added to the Coraciiformes page.