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Follow your nose: songbirds smell their way back home

Sight, smell or both? How birds find their way back to a feeding site was the subject of a recently published study conducted by a team of researchers at the University of Veterinary Medicine Vienna. The researchers observed great tits and were able to show that olfaction is an essential tool for finding one's way, even in familiar surroundings. These findings highlight that in birds the sense of smell is indeed more important for orientation than previously thought.

The great tit (Parus major) is a common songbird with a wide distribution range. It is a welcome guest at birdfeeders in winter and therefore focus of a  recently published study. A team of scientists tested whether great tits use odours from the environment to find their way back to feeding sites. The researchers captured the birds and in some of the individuals, they briefly dampened their sense of smell by rinsing their noses with zinc sulfate. Afterwards, all birds were released - some in the immediate vicinity and another subset of the animals was let go at a distance of 1.5 km.

Great tits with unaltered olfactory capacity returned more quickly to their home range

Both, the great tits with a reduced sense of smell and those with a normal sense of smell found their way back to the feeding sites. "This result did not surprise us at first, as we deliberately released the birds within their familiar environment," explains study first author Katharina Mahr from the Vetmeduni's Konrad Lorenz Institute of Ethology. "It is interesting, however, that birds with a diminished sense of smell needed significantly more time to return. This effect is pronounced when the birds were released at a greater distance. Our results indicate that odours serve as an important source of information for orientation in a familiar environment, despite the existence of visual cues."

A good sense of smell helps to optimise foraging efficiency

According to the researchers, certain smells and scent cues in the familiar environment could serve as a reliable source of information for finding one's way around. “Similar results have already been obtained for migratory birds. But especially for species such as great tits, which often overwinter in breeding areas, orientation and navigation by means of smell could help to optimize foraging in times with little food supply, for example in the winter,” says last author Herbert Hoi, also from the Vetmeduni’s Konrad Lorenz Institute of Ethology. According to Hoi the results of the study strongly emphasise that olfaction might be of greater importance for the orientation of avian species than previously thought, thereby contributing to the understanding of the functional contexts of smell in avian life.

Chemistry in the air

Airborne chemicals function as sensory cues for many organisms, and their use in navigation may be one of the most important evolutionary mechanisms that explains the development of olfaction in animals. Despite solid evidence for the importance of olfaction in avian life – for example, in foraging or mating – the importance of chemical cues for avian orientation remains largely debated. Olfaction in songbirds is, despite their remarkable orientation skills, surprisingly understudied.

The article "Songbirds use scent cues to relocate to feeding sites after displacement: An experiment in great tits (Parus major)“ by Katharina Mahr, Linda Nowack, Felix Knauer, and Herbert Hoi was published in „Frontiers in Ecology and Evolution“.

 

Scientific article

 

2022-09-09

Together we can – Courtship coalitions in bowerbirds

In many animal species there is strong competition among males to find a willing female partner. For this reason, elaborate courtship rituals have evolved, notably in many bird species who often perform dances that show off their strength and beauty, or, as in the case of bowerbirds, even create a special “stage” to charm females. But despite strong selective pressures inherent in competition for mates, in some species males accept same-sex visitors at display arenas.

Bowerbirds perform courtship dances on elaborate display structures — known as bowers — that are built and defended by one resident male. Several reports have suggested that bower owners tolerate the presence of so-called ‘subordinate’ male visitors at their display arenas, though their role has received little attention. It has been suggested that subordinate males may learn the skills required for successful sexual signalling via prolonged social interactions at adults’ arenas, but it remains unclear whether courtship proficiency changes with experience. It may also be that subordinates actively contribute to enhancing the resident male’s mating success, yet little is known about whether this is the case.

In a study, scientists from the Konrad Lorenz Institute of Ethology and the University of Vienna investigated male-male associations in wild spotted bowerbirds (Ptilonorhynchus maculatus). They first sought to determine whether courtship behaviour differs based on bower ownership status. They then examined whether social interactions between bower owners and subordinate males may qualify as courtship coalitions.

Rudimentary courtship coalitions

Their analysis did not reveal differences between subordinate males and bower owners in specific parameters of courtship related to behavioural flexibility, but they found evidence that male-male associations in spotted bowerbirds may actually be an example of rudimentary courtship coalitions. The subordinate males may in fact be helping the bower owner, even if not by displaying cooperatively or by actively defending the arena from destruction by neighbouring marauders, by sheer strength in numbers that would discourage other males’ attempts to destroy the arenas. The magnitude of subordinate attendance correlated with owner males’ mating success (number of copulations). The researchers also found that male coalitions are stable in subsequent years. The findings point to the possibility that subordinate males in this species may not associate with bower owners as part of a form of apprenticeship, but rather may get other benefits from establishing long-term partnerships. One hypothesis is that saturation of suitable display sites may force sexually mature subordinate males to “queue” in order to gain ownership of established arenas when these become available. Moreover, the male partnerships may allow subordinate males to establish dominance hierarchies with surrounding males and gain social competence.

In the study the researchers also observed a few occurrences of subordinate males copulating or attempting to. Thus subordinate males may also obtain direct fitness benefits from such courtship coalitions — i.e. occasional access to females.

This study provides novel information about social dynamics among male bowerbirds, and further insights into the evolution of coalitionary behaviour in male displays. Further study is needed, for example to find out how these coalitions are formed, and whether subordinate males selectively choose their model, or whether bower owners tolerate some subordinate males and repel others.

The article “Male–male associations in spotted bowerbirds (Ptilonorhynchus maculatus) exhibit attributes of courtship coalitions” by Giovanni Spezie and Leonida Fusani was published in Behavioral Ecology and Sociobiology.

Scientific paper

2022-08-29

Sweet sap, savory ants

Woodpeckers taste sweet, but wrynecks—unusual woodpeckers that specialize on ants—lost the ability to taste sugars

Many mammals have a sweet tooth, but birds lost their sweet receptor during evolution. Although hummingbirds and songbirds independently repurposed their savory receptor to sense sugars, how other birds taste sweet is unclear. Now, an international team of researchers shows that woodpeckers also regained sweet taste. Interestingly, wrynecks, specialized ant-eating woodpeckers, selectively reversed this gain through a simple and unexpected change in the receptor. These results demonstrate a novel mechanism of sensory reversion and highlight how sensory systems adapt to the dietary needs of different species.

Birds, the descendants of carnivorous dinosaurs, lack part of the sweet receptor found in mammals. This should leave them insensitive to sugars. However, recent studies have shown that both hummingbirds and songbirds have regained the ability to sense sugar by repurposing their savory receptor to now detect carbohydrates in fruits and nectar. How other birds sense sugars, and the extent to which taste receptor responses track the immense dietary diversity of birds, is unclear. To investigate this question, Julia Cramer and Maude Baldwin from the Research Group Evolution of Sensory Systems at the Max Planck for Ornithology/Max Planck for Biological Intelligence, together with colleagues from the Cornell Lab of Ornithology, Konrad Lorenz Institute of Ethology of the University of Veterinary Medicine Vienna, University of Vienna, Meiji University, and the Swedish University of Agricultural Science focused on woodpeckers. Although primarily insectivorous, this group of birds also contains multiple species that include sugar-rich sap, nectar, and fruits in their diets.

Using behavioral tests of wild birds, Baldwin’s group showed that woodpeckers clearly prefer sugar and amino-acids over water. Surprisingly, wrynecks – a member of the woodpecker group whose diet is almost exclusively composed of ants – displayed preferences for amino acids but not sugars. “Our next question was whether the observed sugar preference is mirrored by the birds’ receptors,” recaps Baldwin.

Functional analyses of taste receptors confirmed that woodpecker receptors were sensitive to sugars, whereas those of wrynecks were not. Interestingly, ancestral reconstructions indicated that the common ancestor of wrynecks and woodpeckers already possessed a modified savory receptor capable of responding to sugars. “This finding unveiled a third case of independent sugar-sensing evolution via modification of the savory receptor in birds”, says Cramer, the study’s first author. “Yet, what was even more exciting was the implication that wrynecks subsequently lost the receptor’s new function.”

Cramer’s meticulous dissection of differences between wryneck and woodpecker receptors revealed unexpectedly that changes in only a single amino acid in the wryneck receptor selectively turned off sugar-sensing: the birds kept their ability to taste savory, which is likely important for insect-specialist birds that consume a protein-rich diet.

These results trace an evolutionary history in which an early gain of sugar sensing in woodpeckers —possibly arising in an earlier ancestor and therefore older than woodpeckers themselves — was followed by its reversion when the wryneck receptor was later altered. “We were very surprised to find that this reversion is caused by changes in only one single amino acid, acting as a molecular switch to selectively regulate sugar sensitivity in wrynecks,” explains Cramer. “Unexpectedly, the result of this small change is that wrynecks are now again unable to detect sugar in their food but have retained the receptor’s ability to gather information on specific amino acid content. This makes a lot of sense when most of your diet is made up of ants.”

Further investigation will be required to describe how specific changes in taste receptors, and in other physiological and sensory systems, are related to the rich dietary diversity across birds.

The article "A single residue confers selective loss of sugar sensing in wrynecks" von Julia F. Cramer, Eliot T. Miller, Meng-Ching Ko, Qiaoyi Liang, Glenn Cockburn, Tomoya Nakagita, Massimiliano Cardinale, Leonida Fusani, Yasuka Toda, Maude W. Baldwin was published in Current Biology.

Scientific article

2022-08-18

Saker falcon "nursery" on utility poles

For more than ten years, power poles have not only provided saker falcons with a habitat, but also with a place where their young can grow up safely.

The species, which was almost extinct in Austria in the 1970s, has recovered significantly, among other things since the APG cooperation project with BirdLife Austria and the Austrian Ornithological Institute at the University of Veterinary Medicine in Vienna. “The total of 130 nesting boxes that were attached to APG power poles, primarily in northern Burgenland, Lower Austria and Vienna, are becoming increasingly popular with the falcons. This year we observed around 40 breeding pairs in the nest boxes,” says Stefan Walehrach, press spokesman for APG.

Annual ringing of the offspring

Traditionally, standard ringing takes place in the first half of the year, as soon as the young birds have reached their third week of life and fledge shortly thereafter. "This measure helps us not to lose sight of the population and to gain valuable data on the flight routes of the falcons," explains Richard Zink, wildlife ecologist at the Austrian Ornithological Centre at the Vetmeduni.

The saker falcon is a bird species that does not build its own nests and is therefore dependent on high and quiet places. Two requirements that are met by nesting aids on power poles. If there are no tall old trees for nesting in the landscape, power poles offer a good alternative. “The cooperation shows enormous successes that one would never have expected. The project now enjoys a high reputation internationally,” says a delighted Richard Zink. The EVN subsidiary Netz NÖ has also joined the project. "Of course it's particularly nice when our powerline projects go hand in hand with nature and species conservation, as is the case with the saker falcon," says Michael Kovarik, press spokesman for Netz NÖ.

Power grids not only secure the power supply, but also contribute to nature conservation

For more than 25 years, APG, which is responsible for the security of electricity supply in Austria and plays a central role in the secure transformation of the energy system, has been setting an example for biodiversity (nature conservation and species diversity) with targeted habitat management in the area and along the power infrastructure or protection of fauna and flora.

Areas along the APG network infrastructure help to provide a habitat for endangered animal species and support the diversity of flora. Central aspects are:

  •     The design of a nature-friendly energy transition
  •     Compensatory measures, especially for endangered animal and plant species
  •     Ecological route management in regular operation and under specific space-related framework conditions (e.g. floodplain landscapes, nature protection zones)
  •     Promotion of natural nesting aids

APG's electricity infrastructure supplies generations of people in Austria with secure electricity. We also assume this generational responsibility in the area of ​​sustainable nature conservation.

*translated from an APG press release, August 11, 2022

About the Saker falcon project of the AOC

Since 2010, the Austrian Ornithological Centre (AOC), together with BirdLife Austria, has been regularly surveying the population of native saker falcons during the breeding season. While the AOC concentrates on the artificially created nesting sites on the high-voltage pylons, BirdLife takes over the control of those sites that are suitable for natural breeding. In this way, AOC and BirdLife form a strong partnership for the saker falcon in Austria. Together they ensure close monitoring of the populations across the entire Austrian distribution area.


Video: Sakerfalken-"Kinderzimmer" on power poles

The perfect wave - how bald ibises save energy during flight

Many birds use "waves" to move. Phases with rapid wing beats, during which the birds gain height, alternate with gliding phases. A research team led by the Vetmeduni (Research Institute of Wildlife Ecology and the Konrad Lorenz Institute of Ethology) - in cooperation with the Austrian Waldrapp team in Mutters (Tyrol), the ETH Zurich, the University of Vienna and the Vetsuisse in Bern – has now demonstrated for the first time, using data from GPS transmitters, that northern bald ibises significantly reduce their energy requirements with this flight technique.

Birds have an exceptionally high energy requirement during their flight. A visible flight characteristic of some species is the alternation between flapping and gliding, which is said to conserve energy. So far, however, there has been no empirical evidence of an energetic benefit. To change that, the researchers equipped human-reared northern bald ibis (Geronticus eremita) with GPS data loggers for their migration movements. The scientists used it to monitor the position of the birds, the wing beats, the dynamic acceleration of the whole body and the heart rate as a measure of energy consumption.

The northern bald ibis is about the size of a goose and was once a common bird in Europe. Due to intensive hunting, however, it became extinct in Central Europe in the 17th century. As part of the European LIFE+EU project, which is supported by the WWF, among others, the northern bald ibis is to be resettled as a real migratory bird in Central Europe, Spain and Italy.

The article „Empirical Evidence for Energy Efficiency Using Intermittent Gliding Flight in Northern Bald Ibises“ by Ortal Mizrahy-Rewald, Elisa Perinot, Johannes Fritz, Alexei L. Vyssotski, Leonida Fusani, Bernhard Voelkl, and Thomas Ruf was published in „Frontiers in Ecology and Evolution“.

Scientific article

2022-07-07