Aurelia Strauß

Artificial light at night (ALAN) widely affects wildlife by blurring light-dark differences, including transitions such as sunrise and sunset, thereby affecting regulation of diel rhythms. As a result, activity onsets in many wild diurnal songbirds advance under ALAN. From chronobiological studies, it is known that the direction and strength of the response to light depends on when during the night exposure takes place. However, these experiments are mostly done under continuous light conditions, when animals have free-running rhythms. It remains unclear whether phase-dependence also holds in entrained, wild songbirds; i.e., does the effect of ALAN on activity patterns differ between exposure in the morning compared to the evening? This information is essential to assess the effects of mitigation measures by limiting ALAN to selected times of the night. We exposed incubating great tits (Parus major) inside the nest-box to 4 h of dim light, of which 1 h overlapped with dawn before sunrise or dusk after sunset. We found a small advancing effect of morning-light on activity onset and of evening-light on offset compared to dark controls but not vice versa. Breeding success and chick condition were unaffected by the light treatments. However, light-treated females had lower weights 9–18 days after the end of the treatment compared to the controls, independent of whether ALAN occurred in the morning or the evening, indicating possible costs of ALAN. Despite the weak behavioral response, ALAN might have affected the females' circadian clock or physiology resulting in lower body condition.

Chronotypes describe consistent differences between individuals in biological time-keeping. They have been linked both with underlying variation in the circadian system and fitness. Quantification of chronotypes is usually by time of onset, midpoint, or offset of a rhythmic behaviour or physiological process. However, diel activity patterns respond flexibly to many short-term environmental influences, which can make chronotypes hard to identify. In contrast, rhythmic patterns in physiological processes, such as body temperature, may provide more robust insights into the circadian basis of chronotypes. These can be telemetrically recorded from skin-mounted, temperature-sensitive transmitters, offering minimally invasive opportunities for working on free-ranging animals in the wild. Currently, computational methods for deriving chronotype from skin temperature require further development, as time series are often noisy and incomplete. Here, we investigate such methods using simultaneous radio telemetry recordings of activity and skin temperature in a wild songbird model (Great Tit Parus major) temporarily kept in outdoor aviaries. Our aims were to first develop standardised selection criteria to filter noisy time series of skin temperature and activity, to second assign chronotype based on the filtered recordings, and to third compare chronotype as assigned based on each of the two rhythms. After the selection of rhythmic data using periodicity and autocorrelation parameters, chronotype estimates (onset and offset) were extracted using four different changepoint approaches for skin temperature and one approach for activity records. The estimates based on skin temperature varied between different approaches but were correlated to each other (onset: correlation coefficient r = 0.099–0.841, offset: r = 0.131–0.906). In contrast, chronotype estimates from skin temperature were more weakly correlated to those from activity (onset: r = −0.131–0.612, offset: r = −0.040– −0.681). Overall, chronotype estimates were less variable and timed later in the day for activity than for skin temperature. The distinctions between physiological and behavioural chronotypes in this study might reflect differences in underlying mechanisms and in responsiveness to external and internal cues. Thus, studying each of these rhythms has specific strengths, while parallel studies of both could inform broadly on natural variation in biological time-keeping, and may allow assessment of how biological rhythms relate to changes in the environment.

Bird song transmits information required to defend territories and attract mates. These functions contribute to fitness by affecting survival and reproductive success. Singing is also costly due to physiological costs. We used observational data to evaluate support for the hypothesis that lower temperatures result in decreased singing behaviour in wild great tits due to increased energy consumption during cold conditions required for thermoregulation. More than 6,500 simulated territorial intrusions were performed over an 8-year period in twelve nest box populations of great tits Parus major south of Munich, Germany. We measured song rate as well as the number of alarm calls and the aggressive response of territorial males to a simulated territorial intrusion. We found a decrease in song rate with decreasing current temperature, but also a concurrent increase in the number of alarm calls. Night temperature did not affect these acoustic traits. We conclude that warmer conditions allow birds to choose more energetically expensive (yet functionally superior) activities during territorial intrusions, thereby facilitating avoidance of physical aggressiveness during territorial intrusions.

Seasonal migration of birds between breeding and wintering areas can facilitate the spread of tick species and tick-borne diseases. In this study, 151 birds representing 10 different bird species were captured on Ponza Island, an important migratory stopover off the western coast of Italy and screened for tick infestation. Ticks were collected and identified morphologically. Morphological identification was supported through sequencing a fragment of the 16S mitochondrial gene. In total, 16 captured birds carried ticks from four tick species: Hyalomma rufipes (n = 14), Amblyomma variegatum (n = 1), Amblyomma sp. (n = 1), and Ixodes ventalloi (n = 2). All specimens were either larvae (n = 2) or nymphs (n = 16). All ticks were investigated for tick-borne pathogens using published molecular methods. Rickettsia aeschlimannii was detected in six of the 14 collected H. rufipes ticks. Additionally, the singular A. variegatum nymph tested positive for R. africae. In all 14 H. rufipes specimens (2 larvae and 12 nymphs), Francisella-like endosymbionts were detected. Four H. rufipes ticks tested positive for Borrelia burgdorferi sensu lato in a screening PCR but did not produce sufficient amplicon amounts for species identification. All ticks tested negative for tick-borne encephalitis virus, Crimean-Congo hemorrhagic fever virus, Coxiella burnetii, Coxiella-like organisms, Babesia spp., and Theileria spp. This study confirms the role of migratory birds in the spread and establishment of both exotic tick species and tick-borne pathogens outside their endemic range.