Archive - Yearbook Articles of the MPI for Ornithology
(full texts in German)

During a good conversation we typically rarely interrupt each other. Although we often already know what we want to say, we suppress our own pronunciation until the other person has finished speaking. How does the brain control this behavior? To better understand the mechanisms involved, we took a closer look at the calling behavior of zebra finches and the neural processes taking place. Like humans, zebra finches coordinate their vocalizations depending on the social situation. This interaction is based on a temporally ordered interplay between inhibiting and excitatory neurons.

Duet singing is a form of social interaction between two individuals which requires the precise interindividual coordination of vocal emissions. How the brain controls this cooperative behavior was so far unknown. Here, the individual vocalizations and the underlying brain activity in free-living pairs of duetting songbirds has been recorded in parallel with novel miniature transmitters. The data revealed that preprogrammed temporal duet patterns in each songbird’s brain were altered by the partner’s vocalizations to enable optimal interindividual coordination during joint singing.

Our sensory systems are our access to the world. In an evolutionary arms race, bats and insects interact as predator and prey based on exclusively acoustic information. Using microphone systems in the lab and field, we investigate which information and sensory strategies bats use for hunting insect prey. To counter the prey’s defence systems, some bats became inaudible for their unsuspecting prey, while other species rely on the prey’s rustling noises or eavesdrop on the foraging calls of other close-by bats.

Birds are among the most important animal groups in biological, medical and pharmaceutical sciences. Over the last few years, new technologies have made genome sequencing accessible to a broad user base. The international B10K project is an initiative to sequence the genomes of all bird species. Comparative studies on trait evolution on the genomic level will lead to a far-reaching understanding of biodiversity and connections towards translational research. The Max Planck scientists in Radolfzell participate in this project with comparative studies on the immune system evolution of birds.

For centuries, people have wondered whether birds sleep on the wing during long, non-stop flights. However, until recently there was no direct evidence for sleep in flight. Measuring the brain activity of frigatebirds in the wild showed that these birds can sleep with either one cerebral hemisphere at a time or both hemispheres simultaneously. Despite being able to engage in all types of sleep in flight, the birds slept less than an hour a day, a mere fraction of the time spent sleeping on land.

Skull and body size usually don't change anymore in fully-grown animals. Red-toothed shrews (Sorex spp.) are a notable exception: they shrink in anticipation of the winter and regrow in preparation for reproduction. This process affects the brain, several other major organs, bones and also the cognitive abilities. The phenomenon is also found in weasels, which share many life history traits, especially an exceedingly high metabolism. The study is important for our understanding of evolution, and has profound implications for medical research.

Species-specific seasonal changes of bird song, that are caused by sex hormones, can be a consequence of distinct gene expression patterns induced in the song control system. In songbirds, different sex hormone activities are based on divergent genomic regulatory mechanisms. However, neuronal wiring of the songbird as well as mammalian brain is modified by sex hormones via to some extent comparable cellular processes.

Anisogamy leads to females being expected to be the choosier sex. However, when females cheat on their social partners, they seek males as mates that are older than their social partner but with whom they produce offspring of lower fitness. This is what a team around researchers of the MPI for Ornithology found in house sparrows. Also, old mothers produced daughters of low fitness compared to young mothers. These findings are important, as this patterns has been found to a limit also in humans. Thus, with increasing age of reproduction we may pass on the costs of this to the next generation.

Environmental factors can have a large impact on behaviour and the underlying physiology. For example, island canaries advance the onset of breeding in response to growing plants. In zebra finches both song and the song control regions in the brain show low heritability but are highly sensitive to changes of the environment. In contrast, brain size largely depends on the interaction between genes and the environment. In this way additive genetic variation is maintained. These results emphasize the major importance of environmental factors for vocal learning and neural development in songbirds.

Hormones, as parts of complex regulatory systems, mediate environmental adjustments of organisms. Can hormonal systems change fast enough to keep up with rapid changes in the environment? In birds, concentrations of the hormone corticosterone are related to evolved differences in reproductive investment. Even within a bird species corticosterone patterns predict the reproductive success of individuals. Future studies will determine selection pressures, heritabilities and rate of evolutionary changes in hormones.

It is well established that urban areas have been successfully colonized by animals. Less is known about the extent to which urbanization causes ecological and micro-evolutionary changes in animals thriving in urban areas. Studies at the MPIO in Radolfzell elucidate that city life causes changes in behavior and underlying physiological mechanisms and that micro-evolutionary effects may play an important role. Current studies using newest radiotelemetry and micrologger technique aim to discover the impact of artificial city light at night on the daily and seasonal organization of urban animals.

A long-term study on the genetic inheritance of sexual behavior in the zebra finch conducted at the MPIO casts new light on the causes of sexual infidelity. Previously, it was always assumed that female infidelity could only evolve if it was beneficial to females. The present study, however, shows that this is not necessarily the case. Since male and female infidelity appear to be controlled by largely the same genes, the existence of female infidelity may simply be explained by the fact that the responsible genetic variants were positively selected in the male ancestors.

The Humboldt Research Group focuses on cognitive complexity underlying gestural signaling in three model groups to uncover the mystery of language evolution: different human cultures; closely related species; and species which live in comparable social systems. In a new study, they showed that ravens use their beaks similarly to hands to show and offer objects to conspecifics. These referential gestures may be used to test the interest of a potential partner or to strengthen an already existing relationship.

Birds and other animals differ in their behaviour like humans differ in personality. Certain individuals are consistently more aggressive, explorative, and bold compared to other animals from the same population, and this variation is in part genetically determined. The department of Behavioural Ecology and Evolutionary Genetics studies individual variation in behaviour with the aim of i) revealing why animal personality has evolved and ii) learning how this variation might be maintained, using wild passerine bird populations (great tits) as an experimental model system.

Scientists at the MPI for Ornithology investigate bird song as a model for sexually selected signals. Female songbirds prefer loud songs, which can be used as a signal of high male body condition. The honesty of the signal is maintained by social aggression of rival males. At the same time, birds need to adjust their songs to the physical properties of their habitats to ensure signal transmission. This results in a complex interplay between natural and sexual selection, during which signal plasticity plays an important role as well as special adaptations of signal structure.

The birds are a specious vertebrate taxon (~9800 species) that show an amazing diversity of life history strategies. A research group from the Max Planck Institute for Ornithology studies this diversity with an aim to understanding the general principles that govern evolutionary and geographical patterns of size dimorphism, clutch sizes and even our knowledge of species themselves.

The Southern Ocean is strongly affected by global change. A long-term study of Thin-billed prions, a small seabird feeding on zooplankton in these vast ocean areas, was designed to further our understanding of the changes that currently take place in this ecosytem. Further, this study will look at adaptations that enable the birds to cope with changing conditions, such as flexible provisioning behaviour and physiological regulation of timing and investments in the breeding cycle.

Scientists at the MPI for Ornithology investigate echolocation and sensory performance in bats. Coexisting bat species often differ in sensory abilities, thus find different prey and reduce interspecific competition for food. It is difficult to detect insects in vegetation by echolocation. Bats rely on the faint rustling sounds of their prey in such a situation and hence run into trouble when exposed to background noise from a wind-moved reed bed or a highway. Bats also eavesdrop to find new tree roosts; conspecifcs’ calls help out.

Individual marking and tracking of birds with inscripted rings at the bird's legs, radio transmitters or other methods is used for the study of the success of individual strategies, demographic benchmarks, the study of bird migration with all it's facetes and the role of birds as vectors for diseases, the long term monitoring of bird populations, the building of survival models, the study of the reaction of birds to climate change and finally the provision of basic data for species conservation.

Sleep during migration in songbirds is the focus of the work of the group of Niels Rattenborg at MPI for Ornithology. With the modern wind-tunnel at Seewiesen and new measuring techniques the scientists want to explore if birds sleep during long distance migratory flights. Ultimately, understanding if and how birds sleep during migration may provide insight into the function of sleep.

Trade-offs with immunity can theoretically enforce honesty on sexual signals through testosterone, that stimulates sexual traits but also suppresses immunity, and/or carotenoids, that can be used in ornaments or support immune functions. Recently, researchers at the Max Planck Institute for Ornithology found evidence for such trade-offs in male mallards.

Studies of cognitive interval timing up to now focused mainly on the range from seconds to some minutes. However, individuals often face situations where they must adjust their behaviour to longer (but not circadian!) intervals. Still lacking for this time range are data and theoretical models, which could explain how animals solve such problems. A marine cleaner wrasse is now the first example, that a not warm-blooded vertebrate is able to time several different intervals simultaneously without external cues.

Zebra finches show remarkable differences in their individual sexual behaviour, and this variation seems to be strongly affected by non-genetic maternal effects. A research group from the Max Planck Institute for Ornithology studies whether mothers strategically program the sexual behaviour of their offspring in response to the current social environment in order to maximise offspring fitness.

In most animals females provide parental care, while males defend resources and try to find additional mates. However, in a small percentage of animals the sex-roles are reversed and the males provide care for the offspring while the females compete amongst each other for resources and additional mates. The African black coucal is the only known bird species that combines an altricial development of young with such a sex-role reversed breeding system, termed ‘classical polyandry’. In the black coucal project we try to combine and integrate mechanistic and evolutionary questions about an unusual mating system. Currently we investigate mainly the following questions: (1) How is territorial, aggressive behaviour regulated in females and what triggers parental behaviour in males? (2) Do male black coucals insure their genetic paternity and how much do they invest in each brood? (3) How did classical polyandry evolve in black coucals?

Human language and bird song are convergently evolved communication systems. A large-scale comparison revealed more developmental and functional parallels than are usually assumed. Song elements copied from foreign species have become a valuable research tool in cognition analysis. Experimentally introduced into the species-specific song such elements can help to elucidate the meaning of single song elements and to test whether birdsong is a recursive system, i.e. that altering the element sequence can change that sequence's general meaning, as is the case in our language. Also, it opens the possibility to pinpoint the evolutionary consequences of traditive (from brain to brain tranferred) behaviour traits. Using canary-raised house sparrows, Lucie H. Salwiczek at the Max Planck Institute for Behavioural Physiology demonstrated the importance of an integrative approach for our understanding of cognitive capabilities in animal behaviour, with a special emphasis on neuro-anatomical correlates of learning and the constraining role of morphological body-structures in reproducing a learnt behaviour.