Genetic monogamy despite frequent extrapair copulations in "strictly monogamous" wild jackdaws.

"Monogamy" refers to different components of pair exclusiveness: the social pair, sexual partners, and the genetic outcome of sexual encounters. Avian monogamy is usually defined socially or genetically, whereas quantifications of sexual behavior remain scarce. Jackdaws (Corvus monedula) are considered a rare example of strict monogamy in songbirds, with lifelong pair bonds and little genetic evidence for extrapair (EP) offspring. Yet jackdaw copulations, although accompanied by loud copulation calls, are rarely observed because they occur visually concealed inside nest cavities. Using full-day nest-box video surveillance and on-bird acoustic bio-logging, we directly observed jackdaw sexual behavior and compared it to the corresponding genetic outcome obtained via molecular parentage analysis. In the video-observed nests, we found genetic monogamy but frequently detected forced EP sexual behavior, accompanied by characteristic male copulation calls. We, thus, challenge the long-held notion of strict jackdaw monogamy at the sexual level. Our data suggest that male mate guarding and frequent intrapair copulations during the female fertile phase, as well as the forced nature of the copulations, could explain the absence of EP offspring. Because EP copulation behavior appeared to be costly for both sexes, we suggest that immediate fitness benefits are an unlikely explanation for its prevalence. Instead, sexual conflict and dominance effects could interact to shape the spatiotemporal pattern of EP sexual behavior in this species. Our results call for larger-scale investigations of jackdaw sexual behavior and parentage and highlight the importance of combining social, sexual, and genetic data sets for a more complete understanding of mating systems.

Individual recognition of opposite sex vocalizations in the zebra finch.

Individual vocal recognition plays an important role in the social lives of many vocally active species. In group-living songbirds the most common vocalizations during communal interactions are low-intensity, soft, unlearned calls. Being able to tell individuals apart solely from a short call would allow a sender to choose a specific group member to address, resulting in the possibility to form complex communication networks. However, little research has yet been carried out to discover whether soft calls contain individual identity. In this study, males and females of zebra finch pairs were tested with six vocalization types - four different soft calls, the distance call and the male song - to investigate whether they are able to distinguish individuals of the opposite sex. For both sexes, we provide the first evidence of individual vocal recognition for a zebra finch soft unlearned call. Moreover, while controlling for habituation and testing for repeatability of the findings, we quantify the effects of hitherto little studied variables such as partners' vocal exchange previous to the experiment, spectral content of playback calls and quality of the answers. We suggest that zebra finches can recognize individuals via soft vocalizations, therefore allowing complex directed communication within vocalizing flocks.

A lightweight telemetry system for recording neuronal activity in freely behaving small animals.

A miniature lightweight radio telemetric device is described which is shown to be suitable for recording neuronal activity in freely behaving animals. Its size (12 x 5 x 8 mm) and weight (1.0-1.1 g with batteries, 0.4-0.5 g without) make the device particularly suitable for recording neuronal units in small animals such as mice or zebra finches. The device combines a high impedance preamplifier, RC-filters and an FM-transmitter. Using the device we recorded action potentials in field L of freely behaving zebra finches (12-17 g) through chronically implanted tungsten electrodes. In freely behaving birds we observed frequency dependent responses of field L units to auditory stimuli for periods of up to 7 days. We investigated the effect of the device on singing and locomotor activity of the zebra finches. Singing and locomotion were significantly affected on the first day after surgery. Both anesthesia and the presence of the transmitter contributed to the observed effect. After 1 day of recovery, singing activity returned to 99.6% and perch-hopping activity to 55.3% of the baseline levels. It is concluded that the device is well suited for recording spike trains from small animals while they behave freely and naturalistically.