Category Archives: Ornithology

High temperatures affect the judgement of zebra finches and of humans studying them

by Piter Kehoma Boll

Leia em Português

The zebra finch, Taeniopygia guttata, is an Australian bird that is often used as a model for behavioral studies focused on their vocalization.

Zebra finch (Taeniopygia guttata). Photo by Jim Bendon.*

Recently, a research team from Australia discovered a new call in this species and named it “incubation call”. This particular vocalization was identified as occurring during the last five days of incubation when one of the birds, either the male or the female, was alone with the eggs, and only when temperatures were above 26°C. This raised the hypothesis that this call is used by the parents to communicate to the embryos that the environmental temperature is high and that this information would be used by the nestlings to adapt their behavior and metabolism to higher temperatures.

An experimental study was conducted where eggs were kept in incubators under a constant temperature and exposed (test) or not (control) to recorded incubation calls. The results indicated that nestlings that were exposed to incubation calls grew faster in high temperatures than those that were not exposed to the calls. The mean difference in nestling mass between different temperatures and treatments was of about 2 g only, although the difference in mass between two randomly selected nestlings could be as much as 6 g. Additionally, the R² value of the analyses, which tells how much of the variation is explained by the measured variable, was only 0.1, i.e., temperature explained only 10% of the growth differences between different temperatures in both treatments.

Nestlings in a nest.

One of the most intriguing aspects, however, was the fact that the incubation call was produced at temperatures as low as 26°C, which is not particularly hot in the natural environment of the zebra finch. Thus, another team conducted new studies to understand better how and when the “incubation call” was produced. They decided to rename this call as the “v-call” because their shape is an inverted V in spectrograms. They discovered that the v-call is related to panting, when the birds breathes quickly with its bill open to help reduce body temperature and is likely a side effect of panting and not a deliberate directed call. It is also not produced only during the last 5 days of incubation, but during the whole incubation period and the chick rearing, and some birds are more likely to v-call than others. The results suggest that the v-call is unlikely to have evolved as an incubation call and is more likely a side effect of panting. There is, however, the possibility that embryos can use this information to modulate their growth, although more studies are needed.

Other recent studies with the zebra finch indicate that elevated temperatures can have negative effects on the bird’s reproductive fitness. Temperatures around 40°C reduce sperm quality in male zebra finches and reduce the ability of females to discriminate between songs produced by males of the same species and males of different, distantly related species. A combination of these two effects can lead to a severe decrease in reproductive success by reducing the mating events and reducing sperm ability to fertilize eggs.

A physiological modulation in embryos to deal with the adverse effects of higher temperatures, as suggested by the use of the v-calls, would be certainly benefitial. Maybe this is a behavior still under selection? Let’s see what further studies tell us.

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Coomes CM, Danner RM, Derryberry EP (2019) Elevated temperatures reduce discrimination between conspecific and heterospecific sexual signals. Animal Behavior 147: 9–15.

Hurley LL, McDiarmid CS, Friesen CR, Griffih SC, Rowe M (2018) Experimental heatwaves negatively impact sperm quality in the zebra finch. Proceedings of the Royal Society B: Biological Sciences 285(1871): 20172547.

Mariette MM, Buchanan KL (2016) Prenatal acoustic communication programs offspring for high posthatching temperatures in a songbird. Science 353(6301): 812–814.

McDiarmid CS, Naguib M, Griffith SC (2018) Calling in the heat: the zebra finch “incubation call” depends on heat but not reproductive stage. Behavioral Ecology 29(6): 1245–1254.

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The Dying Melody: Habitat fragmentation is killing the songs of our birds

by Piter Kehoma Boll

Birds, especially passerine birds (those of the order Passeriformes) are known for their ability to produce complex and melodic calls, or songs, used for a variety of purposes. Who doesn’t love to hear the birds singing beautifully in the forest?

Passerine birds include two main groups: the Passeri (songbirds), also called Oscines, and the Tyranni (tyrants), also called Suboscines. Both groups are able to produce complex calls, but those of the Oscines are usually more smooth and melodic and sound less mechanic.

However, there is one more difference between the calls of both groups. The calls of the tyrants are genetically transmitted from the parents to the offspring, i.e., they do not need to learn how to sing with adult birds. Among the songbirds, on the other hand, the complexity of the call is largely culturally inherited, i.e., they learn how to sing with other birds of the same species.


The orange-billed sparrow is a songbird found in the Neotropical region. Photo by Francesco Veronesi.*

A recent study published in the journal Animal Behavior (see reference) analyzed the complexity of the calls of two passerine birds found in the forests of Costa Rica: a songbird, the orange-billed sparrow Arremon aurantiirostris, and a tyrant, the scale-crested pygmy tyrant, Lophotriccus pileatus.


The scale-crested pygmy tyrant is a tyrant found in the Neotropical region. Photo by Chris Jimenez.*

The team compared the complexity of the calls in different populations of each species living in forest fragments of different sizes. The conclusion was that, while fragment size did not affect the complexity of the call in the tyrant bird, it significantly affected the call of the songbird.

Populations of the orange-billed sparrow that live in smaller fragments show a less complex song than those living in larger fragments. As the call in this species is culturally transmitted, this reduction in complexity is most likely a result of cultural erosion. As smaller fragments only support smaller populations, the birds do not interact that much with other individuals of the same species while they are growing up, and as a result their song becomes simpler and simpler.

We, humans, are the ones to blame for that, as you may already know. Our irresponsible practices are not only reducing population size in other species, but are destroying their culture as well.

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Hart, P. J.; Sebastián-González, E.; Tanimoto, A.; Thompson, A.; Speetjens, T.; Hopkins, M.; Atencio-Picado, M. (2018) Birdsong characteristics are related to fragment size in a neotropical forest. Animal Behavior 137: 45–52.

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Friday Fellow: Nothern Screamer

by Rafael Nascimento

A relative of the southern screamer and the horned screamer that is much less known is the northern screamer (Chauna chavaria). These three birds form the family Anhimidae, which, despite superficially not looking like, are relatives of the ducks and geese (previously they were thought to be relatives of the chickens, the Galliformes).

Tachã-de-pescoço-preto. Foto de Brodie Ferguson.*

The northern screamer. Photo by Brodie Ferguson.*

Measuring 76 to 91 cm and being slightly smaller than the southern screamer, with which it shares the genus, the northern screamer is characterized by a darker overall plumage and a larger black mark on the neck. These birds are very vocal and remarkable because of their crests.

While the horned and the southern screamers have a wide distribution, the northern screamer is a rare bird and is considered “near threatened” by the IUCN. It can only be found in north Colombia an northwest Venezuela, inhabiting marshes, lakes and river banks of forest areas. Most of its food is composed by plant material, such as roots, leaves, sprouts and other parts of aquatic plants.

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BirdLife International. 2015. Chauna chavaria. The IUCN Red List of Threatened Species 2015: e.T22679726A83833043. Acessado em 21 de abril de 2016.

Carboneras, C., Boesman, P., Kirwan, G.M. & Sharpe, C.J. (2016). Northern Screamer (Chauna chavaria). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (Retrieved from in April 21, 2016).

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Friday Fellow: Shoebill

by Piter Kehoma Boll

When I first saw a picture of this bird, many years ago, my first thought was that it could not be real. It looked like a character of an old Hanna-Barbera animation and not like a real creature.

A real bird or a cartoon character? Behold the shoebill! Photo by Olaf Oliviero Riemer.

A real bird or a cartoon character? Behold the shoebill! Photo by Olaf Oliviero Riemer.*

The shoebill (Balaeniceps rex), also known as whalehead or shoe-billed stork, is a large African bird originally thought to be closely related to the true storks, as its body somewhat resembles that of a stork. However, molecular studies concluded it to be more closely related to pelicans, as well as to herons and ibises (which previously were also considered to be closer to storks!).

As one can easily notice, the name shoebill comes from the bird’s massive bill. The pointed upper jaw and the sharp edges of the bill help the shoebill to capture prey and tear them to pieces. The most frequent prey are fish, but it may also consume frogs, snakes, small monitors and crocodiles, as well as, more rarely, turtles, rodents and small birds.With a height typically between 110 and 140 cm, but able to reach 150, the shoebill is a tall bird. Its wingspan is also big, reaching up to 260 cm.

Certainly an interesting bird to look at. Photo by wikimedia user Quartl.*

Certainly an interesting bird to look at. Photo by wikimedia user Quartl.*

The shoebills are solitary birds and even in crowded areas they avoid to stay to close to each other.  They apparently love hippos, as the disturbance that these large beasts create in water help them to obtain food by forcing fish to the surface.

The IUCN lists the shoebill as ‘vulnerable’ and its major threats include habitat destruction and hunting. Currently there are about 5,000 to 8,000 individuals with a disconnected distribution along river basins in sub-Saharan Africa.

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John, J. R. M.; Nahonyo, C. L.; Lee, W. S.; Msuya, C. A. 2013. Observations on nesting of shoebill Balaeniceps rex and wattled crane Bugeranus carunculatus in Malagarasi wetlands, western Tanzania. African Journal of Ecology, 51(1): 184-187. DOI: 10.1111/aje.12023

Wikipedia. Shoebill. Available at: <;. Access on January 13, 2016.

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The Story of the Dwarf Rhea

by Rafael Nascimento

The family Rheidae is nowadays represented by two or three (according to different authors) species of rheas, large running flightless birds, similar to the African ostriches, but having three toes on each foot instead of two. The largest one, the common rhea Rhea americana, has five subspecies distributed from northeastern Brazil to eastern Argentina and including Bolivia, Paraguay and Uruguay. The other forms, earlier put in a separate genus, Pterocnemia, are R. pennata and R. tarapacensis (commonly known as Darwin’s rhea and Puna rhea, respectively). Darwin’s rhea, which helped the British naturalist in the elaboration of his theory of natural selection, lives in the Argentinean and Chilean Patagonia. The systematic situation of the Puna rhea (and its possible subspecies), which is found in the area where Peru, Bolivia, Chile and Argentina meet, is not yet clear, and currently it is considered a distinct form based on some physical features, but more clarifying studies are necessary.

Beside these current forms and some fossil species, such as Opisthodactylus horacioperezi and Hinasuri nehensis, respectively from the Argentinian Miocene and Pliocene, another species was described in 1894 by the British Naturalist Richard Lydekker based on a small egg: Rhea nana – therefore representing a possible fourth rhea species living in historical times.

Richard Lydekker, ca 1900.

Richard Lydekker, ca 1900.

Following you can see the original text published in the journal Proceedings of the Zoological Society of London from 1894, with comments regarding this possible new species:

“Mr. R. Lydekker exhibited photographs and a model of a unique egg, the original of which had been obtained many years ago in Southern Patagonia, and now preserved in the Museum at La Plata. If not an abnormal specimen, it could not be assigned to any known species of bird.

When travelling in the district where the specimen was obtained, Dr. P. Moreno, Director of the Museum at La Plata, many years ago saw numbers of small Ratite birds, which he at first took to be small Rheas. By the natives, to whom they were well known, he was, however, assured that they were adult birds, allied to the Rheas. Desirous of confirming this information, Dr. Moreno applied to a friend acquainted with the district; who replied that not only did he well know the birds, but that he possessed an egg, that egg being the original specimen of which a model was now exhibited.

Assuming the egg to be a normal one, Mr. Lydekker was of opinion that, taken in connexion with the evidence of two independent witnesses who had been the birds, it pointed to the existence in Southern Patagonia of a small unknown Ratite bird more or less nearly allied to the Rheas.”

Illustration of Darwin's Rhea by John Gould, 1841.

Illustration of Darwin’s Rhea by John Gould, 1841.

Until today, however, no other similar egg or adult bird of a species different from the three already mentioned has been found. When we deal with potentially extinct species, only know by scarce reports or aberrant specimens, one must watch the data through a skeptical point of view. We need to be certain that those are not variations within the species or a witness confusion. The lack of extensive comparative material due to the date of the descriptions must also be taken into account, as well as the constant advancements in our understanding of science.

Normal egg of R. pennata, at Museum Wiesbaden (Germany). Photo by Klaus Rassinger/Gerhard Cammerer.

Normal egg of R. pennata, at Museum Wiesbaden (Germany). Photo by Klaus Rassinger/Gerhard Cammerer.

This egg is currently treated as an aberrant form of a Rhea pennata egg. The model cited by Lydekker, made of wax, is found in the Tring Natural History Museu, England.

del Hoyo, J., Collar, N. & Garcia, E.F.J. (2015) Puna Rhea (Rhea tarapacensis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from on 24 December 2015).

Folch, A., Jutglar, F., Garcia, E.F.J. & Boesman, P. (2015) Greater Rhea (Rhea americana). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from on 24 December 2015).

Folch, A., Christie, D.A., Jutglar, F. & Garcia, E.F.J. (2015) Lesser Rhea (Rhea pennata). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from on 24 December 2015).

Hume, J. P.; Walters, M. (2012) Extinct Birds. T & AD Poyser. Londres.

Knox, A. G.; Walters M. P. (1994) Extinct and Endangered Birds in the collections of The Natural History Museum. British Ornithologists’ Club Occasional Publications.

Lydekker, R. (1894) Exhibition of, and remarks upon, a photograph and model of an egg from Southern Patagonia in the La Plata Museum. Proceedings of the Zoological Society of London (1894): 654.

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Biological fight: the case of artificial stimuli in behavior research

by Piter Kehoma Boll The study of animal behavior is an important approach to understand several aspects on the ecology and the evolution of living beings, both from the analyzed animals themselves and the species with which they interact. For example, understanding how a bee recognizes a flower as a food source and how it approaches it may explain a lot about the physiology and the evolution of the flower and vice-versa, thus clarifying why such a combination of characters is the one that is found in the current population.

As with virtually any type of study in biology, a research may be done with sampling or experiments. By sampling you obtain non-manipulated information directly from the environment. You collect or observe a small sample of the whole and infer the general situation of the population based on it. On the other hand, in an experiment you manipulate the environment and watches how the organisms will react to the different stimuli presented to them and, from this, you develop your conclusion.

For example, if you want to know what a species of frog eats, you may find out by sampling, observing some frogs in the wild while they feed or capturing some and examining their stomach contents. You may also offer them different kinds of food, either in the environment or in the lab, and observe how the frogs reacts to each one.

Thus, in experiments you control the stimuli the species receives from the environment. This is the point where things start to get nasty. May the stimuli have artificial elements, i.e., elements that cannot be found by the animal in its habitat?

The opinions about it are divergent and recently led to a “formal fight” published in the journal Ethology:

On one side is a group of researchers from several universities around the world (Hauber et al., 2015) that defends the use of artificial stimuli to analyze behavior. They use as a model the studies on the rejection of eggs of parasitic birds by parasitized birds, a well-studied phenomenon.

First, let us contextualize this phenomenon briefly:

Several bird species, mainly cuckoos, do not incubate their own eggs. Instead of doing it, they lay them in the nests of birds of other species and hope that the poor creatures incubate and later feed the chicks as if they were their own. As a result, natural selection favors cuckoos whose eggs are more similar to the ones of the parasitized bird and also favors the parasitized birds that better distinguish their eggs from the ones of the intruders. It is a typical evolutionary race.

Find the intruder. The similarity between the egg of the parasite and the parasitized can vary greatly. Photos by wikipedia user Galawebdesign (left)* and by Grüner Flip (right).

Find the intruder. The similarity between the egg of the parasite and the parasitized can vary greatly. Photos by wikipedia user Galawebdesign (left)* and by Grüner Flip (right).

In experimental studies on egg rejection by parasitized birds, it is common to use artificial eggs that exaggerate features of natural eggs. This includes, for example, changing color and size in order to understand which is the most relevant for the bird to recognize the eggs as being yours or not. However, can we trust the results of such experiments using artificial elements?

Haubert et al. (2015) think that we can. Their arguments in favor of the use of such artificial stimuli are the following:

  1. Real eggs of the studied species are difficult to get in large quantities and could cause significant impacts over the populations if used. So, artificial eggs ensure the integrity of populations.
  2. It is difficult to get a set of natural eggs similar enough to allow the necessary repetitions to validate the test. After all, a result is only considered valid if it is recorded several times in face of the same stimulus. Artificial eggs allow identical copies and, thus, true repetitions.
  3. Natural eggs vary in several aspects at the same time, such as color, size, form, texture… In artificial eggs it is possible to control these aspects and allow only one to show free variation, so isolating the influence of each one during the recognition by the bird.
  4. A variation beyond the ones found in the wild may help to find populations with different degrees of perception of strange eggs and consequently where are the sites of higher selective pressure.

Original eggs of the parasitized species painted to exaggerate color features. Photos by István Zsoldos. Extracted from Moskát et al. 2010.

Original eggs of the parasitized species painted to exaggerate color features. Photos by István Zsoldos. Extracted from Moskát et al. 2010.

Not everyone looks so favorably to such an unrestrained use of artificial stimuli. Soon after the opinion of Hauber et al. we find the reply of David C. Lahti (2015) who faces all by himself the “artificialist” army. Lahti shows some aversion to such exaggerate use of artificial elements that many times are not used in a responsible manner.

Suggesting a more restrict use of artificial elements, he argues the following:

  1. Our perception of the environment is different from the one of the species we are studying. For instance, a bird sees a much wider range of colors than we do. When we paint an artificial egg black and white in order to simulate a natural black and white egg, we don’t know whether the bird really sees both eggs with the same colors. So, while we suppose that the eggs look similar by our perception, the reality from the bird’s point of view can be very different.
  2. When we try to create a set of artificial eggs that vary in only one aspect, such as the size of the spots on the shell, for instance, in order to control the influence of this stimulus only, we always end up including secondary stimuli that are not measured, such as the paint used to make the spots. If the birds shows a different response to eggs with small spots (natural ones) when compared to eggs with large spots (artificial ones), how can we know that the difference was not caused by the perception of the paint, either chemically or visually, by the animal? It would be necessary to perform tests that would discard this possibility, but it does not happen usually.
  3. Exaggerated artificial stimuli may go beyond the species’ range of recognition. An egg with a color too different from any color variation found in the environment could cause the bird not to see it as an egg, which would lead to problems in the interpretation of the results.

Concerning this last argument, Hauber et al. emphasize that is important to take care on a priori interpretations on the species behavior. That is to say, we cannot guess what the bird is thinking. The fact that the bird removes the parasite’s eggs from the nest or not does not mean that it is capable of recognize the egg as an intruder, or even as an egg. The way the bird interprets the stimulus is not as important as its response to it.

Therefore, we can conclude that artificial stimuli can be advantageous and in several circumstances they are the only available alternative. It is important, however, to take care with their use and try to be sure that secondary features, generally neglected, are not considered important by the animal.

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Hauber, M.; Tong, L.; Bán, M.; Croston, R.; Grim, T.; Waterhouse, G.; Shawkey, M.; Barron, A.; & Moskát, C. 2015. The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism Ethology, 121 (6), 521-528 DOI: 10.1111/eth.12359

Lahti, D. 2015. The Limits of Artificial Stimuli in Behavioral Research: The Umwelt Gamble Ethology, 121 (6), 529-537 DOI: 10.1111/eth.12361

Moskat, C.; Ban, M.; Szekely, T.; Komdeur, J.; Lucassen, R.; van Boheemen, L.; & Hauber, M. 2010. Discordancy or template-based recognition? Dissecting the cognitive basis of the rejection of foreign eggs in hosts of avian brood parasites Journal of Experimental Biology, 213 (11), 1976-1983 DOI: 10.1242/​jeb.040394

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Friday Fellow: Tropical Kingbird

by Piter Kehoma Boll

ResearchBlogging.orgThis is the first bird featured in Friday Fellow and I have chosen it for a special reason: it’s binomial name is Tyrannus melancholicus, the melancholic tyrant. Isn’t it almost poetic?

Found from southern United States to the northern half of Argentina, the Tropical Kingbird, known as sirirí or suiriri in Spanish and Portuguese, is very well adapted to human disturbed areas, so it is easily spotted along roads or at gardens and parks. Populations inhabiting areas of great seasonality usually migrate to warmer areas, mainly towards southern United States during the winter in the southern hemisphere.

Tropical kingbird in São Paulo, Brazil. Photo by Dario Sanches. Extracted from

Tropical kingbird in São Paulo, Brazil. Photo by Dario Sanches*. Extracted from

Tropical Kingbirds are mainly predators, capturing insects intercepted in flight. They don’t seem to be very sensitive to chemical defenses of butterflies, eating even some unpalatable ones and species with similar color patterns, though some species highly unpalatable are indeed rejected. Ocasionally they may also eat fruits.

During the breeding season, they form couples and build together a bowl-shaped nest using small branches, straw and nylon and plastic threads. The female usually lays three eggs in the nest and both birds incubate them and take care of the chicks.

As a consequenceof its adaptability to humans, it is not endangered at all, at least until now, and has a status of Least Concern (LC) by IUCN.

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Cintra, R. 1997. Spatial Distribution and Foraging Tactics of Tyrant Flycatchers in Two Habitats in the Brazilian Amazon. Studies on Neotropical Fauna and Environment, 32 (1), 17-27 DOI: 10.1076/snfe.

Legal, E. 2007. Aspectos da nidificação do siriri, Tyrannus melancholicus (Vieillot, 1819), (Aves, Tyrannidae) em Santa Catarina. Atualidades Ornitológicas On-line, 140, 51-52

Pinheiro, C. E. G. 1996. Palatablility and escaping ability in Neotropical butterflies: tests with wild kingbirds (Tyrannus melancholicus, Tyrannidae) Biological Journal of the Linnean Society, 59 (4), 351-365 DOI: 10.1111/j.1095-8312.1996.tb01471.x

Wikipedia. Tropical Kingbird. Available online at < >. Access on March 27, 2014.

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