Eberhard Gwinner

STRESS AND THE CITY: URBANIZATION AND ITS EFFECTS ON THE STRESS PHYSIOLOGY IN EUROPEAN BLACKBIRDS

Animals colonizing cities are exposed to many novel and potentially stressful situations. There is evidence that chronic stress can cause deleterious effects. Hence, wild animals would suffer from city life unless they adjusted their stress response to the conditions in a city. Here we show that European Blackbirds born in a city have a lower stress response than their forest conspecifics. We hand-raised urban and forest-living individuals of that species under identical conditions and tested their corticosterone stress response at an age of 5, 8, and 11 months. The results suggest that the difference is genetically determined, although early developmental effects cannot be excluded. Either way, the results support the idea that urbanization creates a shift in coping styles by changing the stress physiology of animals. The reduced stress response could be ubiquitous and, presumably, necessary for all animals that thrive in ecosystems exposed to frequent anthropogenic disturbances, such as those in urban areas.

Predators as stressors? Physiological and reproductive consequences of predation risk in tropical stonechats (Saxicola torquata axillaris)

Tropical birds usually lay smaller clutches and are less likely to initiate a second brood than their temperate–zone relatives. This reduction in annual fecundity is generally explained as an adaptation either to higher rates of nest predation or to a more limited food supply concurrent with higher adult survival in the tropics. However, the physiological parameters associated with lower annual fecundity in tropical birds have not been well investigated. We compared the annual fecundity, behaviour and a number of physiological parameters of stonechat parents feeding fledged juveniles in territories with and without fiscal shrikes, a predator on adult and fledged birds. Stonechat pairs in territories with shrikes were less likely to initiate a second brood and delayed successive broods compared to pairs in territories without shrikes. After fledging of their young, males showed a greater propensity than females to initiate distraction calls after a human intrusion into their territory and, therefore, invested more in the defence of their young. In territories with shrikes stonechat males had higher initial plasma corticosterone levels and lower body conditions than males in territories without shrikes, suggesting that they were chronically stressed. In contrast, the females from both types of territory had low initial plasma corticosterone levels. We conclude that shrike presence might account for the delay in initiation of a second brood and the reduction in the tendency to initiate a second brood. Whether these effects are mediated by the elevated levels of corticosterone remains to be demonstrated.

Slow pace of life in tropical sedentary birds: A common-garden experiment on four stonechat populations from different latitudes

It has been hypothesized that organisms living at different latitudes or in different environments adjust their metabolic activity to the prevailing conditions. However, do differences in energy turnover simply represent a phenotypic adaptation to the local environment, or are they genetically based? To test this, we obtained nestling stonechats (Saxicola torquata) from equatorial Kenya (0° N), Ireland (51.5° N), Austria (47.5° N) and Kazakhstan (51.5° N). Birds were hand-raised and kept in Andechs, Germany. We measured their resting metabolic rates (RMR) and locomotor activity at an age of ca. 14 months (July) and 20 months (January), when birds went through postnuptial moult (July), and neither moulted nor exhibited enlarged gonads or migratory activity (January). RMR was generally higher during moult, but differed among populations: RMR was lowest in the resident Kenyan birds, higher in mostly sedentary Irish birds, and highest in migratory Austrian and Kazakhstan birds. Thus our data demonstrate that even in birds kept from early life under common-garden conditions, the ‘pace of life’, as indicated by metabolic turnover, is lower in sedentary tropical than in north-temperate migratory individuals of the same species. Such intrinsically low energy expenditure in sedentary tropical birds may have important implications for slow development, delayed senescence and high longevity in many tropical organisms.

Synchronization of a circadian rhythm in pinealectomized European starlings by daily injections of melatonin

SummaryWe have tested the hypothesis that the avian pineal hormone, melatonin, which is produced in and secreted from the pineal body in a circadian temporal pattern is a chemical mediator which drives overt circadian functions. Pinealectomized European starlings (Sturnus vulgaris) kept in continuous dim light, received intramuscular injections of melatonin at the same time each day for several weeks. Control birds received only sesame oil injections. In 21 out of 22 birds, melatonin treatment resulted in the synchronization of locomotor activity with the 24 h injection rhythm. In contrast, activity of only one out of 10 control birds became synchronized with the daily control injections. These results are consistent with the hypothesis that the endogenous circadian rhythm of melatonin concentration provides an internal synchronizing agent, acting directly on other circadian oscillators. Alternatively, it seems possible that the exogenous rhythm exerts its effect indirectly by modifying the sleep-wake cycle.

Circannuale Periodik als Grundlage des jahreszeitlichen Funktionswandels bei Zugvögeln. Untersuchungen am Fitis (Phylloscopus trochilus) und am Waldlaubsänger (P. sibilatrix)

1. In der vorliegenden Arbeit wird nachgewiesen, daß zwei in Äquatornähe überwinternde palaearktische Zugvogelarten über einen endogenen und angeborenen Mechanismus verfügen, der ihnen die zeitliche Orientierung im Jahresablauf ermöglicht. Junge Fitis- und Waldlaubsänger (Phylloscopus trochilus undP. sibilatrix), die von Mitte September ihres ersten Lebensjahres an bis mindestens zum Juni des darauffolgenden Jahres in einer temperaturkonstanten Kammer im künstlichen 12 : 12 Stunden-Tag lebten, mauserten ungefähr zur selben Zeit wie die Kontrollen im natürlichen Licht-Dunkel-Wechsel ihres Brut- bzw. Überwinterungsgebietes. Sie entwickelten im Frühjahr ungefähr zur selben Zeit wie diese „Zugunruhe“ und auch ihre Gewichtskurven zeigten einen ähnlichen Verlauf. Bei zwei lange genug in diesen Bedingungen gehaltenen Vögeln konnte auch noch die Sommermauser beobachtet werden (Abb. 3, 4, 6). Ein Versuch mit zwei anderen Fitislaubsängern, die 27 Monate lang im 12 : 12 Stunden-Tag gehalten wurden, brachte den Beweis dafür, daß Mauser und Zugunruhe nicht nur während des Winterhalbjahres ungefähr zeitgerecht spontan auftreten, sondern auch später in der erwarteten Folge periodisch wiederkehren (Abb. 7). Bei einem der Vögel wich die Periodenlänge deutlich von 12 Monaten ab. Damit ist die mögliche Wirkung unkontrollierter Umweltfaktoren als Ursache dieser Periodik ausgeschlossen. — Da keiner der Vögel vor Versuchsbeginn mehr als 8 Monate lang unter natürlichen Lichtbedingungen gelebt hatte, ist zugleich gezeigt, daß diese endogene Periodik angeboren ist. Die Phasenlage der endogenen Jahresperiodik hing bei den jungen Fitislaubsängern des ersten Versuchs vom Geburtstermin ab. Später im Jahr geschlüpfte Vögel beendeten auch später ihre Jugendmauser, wurden später im Herbst zugunruhig, begannen später mit der Wintermauser und wurden später im Frühjahr zugunruhig (Abb. 8). 2. Auf dem Höhepunkt ihrer Zugunruhe im Herbst nach Afrika verfrachtete und dort teilweise unter freiem Himmel gehaltene Vögel blieben genau so lang zugunruhig wie Vögel, die nicht den Umweltreizen ihres Winterquartiers ausgesetzt waren (Abb. 5). Die im Überwinterungsgebiet herrschenden Bedingungen übten demnach keinen hemmenden Einfluß auf die Zugunruhe der Vögel aus. Dieses Ergebnis steht im Widerspruch zu Befunden anderer Autoren. Es wird eine Hypothese diskutiert, nach welcher die Dauer und der zeitliche Ablauf des Herbstzuges junger Fitise vorwiegend von einem endogenen Zeitprogramm bestimmt wird, welches so organisiert ist, daß der ziehende Vogel bei vorgegebenem Wanderweg das Winterquartier erreicht hat, wenn dieses Zeitprogramm abgelaufen ist. In der vorliegenden Arbeit wird nachgewiesen, daß zwei in Äquatornähe überwinternde palaearktische Zugvogelarten über einen endogenen und angeborenen Mechanismus verfügen, der ihnen die zeitliche Orientierung im Jahresablauf ermöglicht. Junge Fitis- und Waldlaubsänger (Phylloscopus trochilus undP. sibilatrix), die von Mitte September ihres ersten Lebensjahres an bis mindestens zum Juni des darauffolgenden Jahres in einer temperaturkonstanten Kammer im künstlichen 12 : 12 Stunden-Tag lebten, mauserten ungefähr zur selben Zeit wie die Kontrollen im natürlichen Licht-Dunkel-Wechsel ihres Brut- bzw. Überwinterungsgebietes. Sie entwickelten im Frühjahr ungefähr zur selben Zeit wie diese „Zugunruhe“ und auch ihre Gewichtskurven zeigten einen ähnlichen Verlauf. Bei zwei lange genug in diesen Bedingungen gehaltenen Vögeln konnte auch noch die Sommermauser beobachtet werden (Abb. 3, 4, 6). Ein Versuch mit zwei anderen Fitislaubsängern, die 27 Monate lang im 12 : 12 Stunden-Tag gehalten wurden, brachte den Beweis dafür, daß Mauser und Zugunruhe nicht nur während des Winterhalbjahres ungefähr zeitgerecht spontan auftreten, sondern auch später in der erwarteten Folge periodisch wiederkehren (Abb. 7). Bei einem der Vögel wich die Periodenlänge deutlich von 12 Monaten ab. Damit ist die mögliche Wirkung unkontrollierter Umweltfaktoren als Ursache dieser Periodik ausgeschlossen. — Da keiner der Vögel vor Versuchsbeginn mehr als 8 Monate lang unter natürlichen Lichtbedingungen gelebt hatte, ist zugleich gezeigt, daß diese endogene Periodik angeboren ist. Die Phasenlage der endogenen Jahresperiodik hing bei den jungen Fitislaubsängern des ersten Versuchs vom Geburtstermin ab. Später im Jahr geschlüpfte Vögel beendeten auch später ihre Jugendmauser, wurden später im Herbst zugunruhig, begannen später mit der Wintermauser und wurden später im Frühjahr zugunruhig (Abb. 8). Auf dem Höhepunkt ihrer Zugunruhe im Herbst nach Afrika verfrachtete und dort teilweise unter freiem Himmel gehaltene Vögel blieben genau so lang zugunruhig wie Vögel, die nicht den Umweltreizen ihres Winterquartiers ausgesetzt waren (Abb. 5). Die im Überwinterungsgebiet herrschenden Bedingungen übten demnach keinen hemmenden Einfluß auf die Zugunruhe der Vögel aus. Dieses Ergebnis steht im Widerspruch zu Befunden anderer Autoren. Es wird eine Hypothese diskutiert, nach welcher die Dauer und der zeitliche Ablauf des Herbstzuges junger Fitise vorwiegend von einem endogenen Zeitprogramm bestimmt wird, welches so organisiert ist, daß der ziehende Vogel bei vorgegebenem Wanderweg das Winterquartier erreicht hat, wenn dieses Zeitprogramm abgelaufen ist. 1. It is demonstrated that two species of migratory birds, that winter close to the Equator have an innate, endogenous mechanism that allows temporal orientation during the year. Young Willow and Wood Warblers (Phylloscopus trochilus andP. sibilatrix) were kept in a 12 : 12 hour light-dark regime with constant temperature from the middle of September when they were about 4 months old till the following June. They moulted at the same time as control birds kept under natural daylight conditions in their wintering as well as in their breeding localities. The experimental birds developed migratory restlessness at the same time as the controls and showed similar weight changes. Two birds which have been kept under experimental conditions up to the end of July also showed the summer moult (Fig. 3, 4, 6). Two other Willow Warblers kept for 27 months under a constant 12 : 12 hour lightdark regime showed that migratory restlessness and moult appeared at the appropriate times not only during the first winter, but also reappeared later at the expected times (Fig. 7). One bird had a circannual period of less than a year showing that no uncontrolled environmental factors were responsible for the observed periodicity. Since none of the birds had lived for more than 8 months under natural light conditions prior to the experiment, the results indicate that the endogenous periodicity is innate. The phase-position of the endogenous annual periodicity of young Willow Warblers depended on the date of birth. Birds hatched late in the year terminated their juvenile moult late, developed autumn and spring migratory restlessness later than birds hatched earlier and started later with the winter moult (Fig. 8). 2. Birds flown to Afrika at the height of their migratory restlessness and kept there, in indoor and in outdoor conditions remained in migratory restlessness just as long as birds which did not experience the environmental stimuli of the wintering areas (Fig. 5). Hence, the environmental stimuli of the wintering area had no inhibitory effect on migratory restlessness. These results contradict those of other authors. It is proposed that the duration and temporal patterning of the fall migration in young birds is determined by an endogenous timing mechanism. According to this hypothesis the migrating bird travelling at a given speed and on a defined migratory route comes to a halt when its “migration programm“ has run out. It then finds itself in its wintering area. It is demonstrated that two species of migratory birds, that winter close to the Equator have an innate, endogenous mechanism that allows temporal orientation during the year. Young Willow and Wood Warblers (Phylloscopus trochilus andP. sibilatrix) were kept in a 12 : 12 hour light-dark regime with constant temperature from the middle of September when they were about 4 months old till the following June. They moulted at the same time as control birds kept under natural daylight conditions in their wintering as well as in their breeding localities. The experimental birds developed migratory restlessness at the same time as the controls and showed similar weight changes. Two birds which have been kept under experimental conditions up to the end of July also showed the summer moult (Fig. 3, 4, 6). Two other Willow Warblers kept for 27 months under a constant 12 : 12 hour lightdark regime showed that migratory restlessness and moult appeared at the appropriate times not only during the first winter, but also reappeared later at the expected times (Fig. 7). One bird had a circannual period of less than a year showing that no uncontrolled environmental factors were responsible for the observed periodicity. Since none of the birds had lived for more than 8 months under natural light conditions prior to the experiment, the results indicate that the endogenous periodicity is innate. The phase-position of the endogenous annual periodicity of young Willow Warblers depended on the date of birth. Birds hatched late in the year terminated their juvenile moult late, developed autumn and spring migratory restlessness later than birds hatched earlier and started later with the winter moult (Fig. 8). Birds flown to Afrika at the height of their migratory restlessness and kept there, in indoor and in outdoor conditions remained in migratory restlessness just as long as birds which did not experience the environmental stimuli of the wintering areas (Fig. 5). Hence, the environmental stimuli of the wintering area had no inhibitory effect on migratory restlessness. These results contradict those of other authors. It is proposed that the duration and temporal patterning of the fall migration in you

INCREASED SEDENTARINESS IN EUROPEAN BLACKBIRDS FOLLOWING URBANIZATION: A CONSEQUENCE OF LOCAL ADAPTATION?

Urbanization changes local environmental conditions and may lead to altered selection regimes for life history traits of organisms thriving in cities. Previous studies have reported changes in breeding phenology and even trends toward increased sedentariness in migratory bird species colonizing urban areas. However, does the change in migratory propensity simply represent a phenotypic adjustment to local urban environment, or is it genetically based and hence the result of local adaptation? To test this, we hand-raised European Blackbirds (Turdus merula) from urban and forest populations, quantified their nocturnal activity and fat deposition covering two complete migratory cycles and examined the consequences of a reduced migratory propensity for the timing of gonadal development (a physiological measure of the seasonal timing of reproduction). Although nocturnal activities differed strikingly between fall and spring seasons, with low activities during the fall and high activities during the spring seasons, our data confirm, even in birds kept from early life under common-garden conditions, a change toward reduced migratoriness in urban blackbirds. The first score of a principal component analysis including amount of nocturnal activity and fat deposition, defined as migratory disposition, was lower in urban than in forest males particularly during their first year, whereas females did not differ. The results suggest that the intrinsic but male-biased difference is genetically determined, although early developmental effects cannot be excluded. Moreover, individuals with low migratory disposition developed their gonads earlier, resulting in longer reproductive seasons. Since urban conditions facilitate earlier breeding, intrinsic shifts to sedentariness thus seem to be adaptive in urban habitats. These results corroborate the idea that urbanization has evolutionary consequences for life history traits such as migratory behavior.

Differences in the timing of reproduction between urban and forest European blackbirds (Turdus merula): result of phenotypic flexibility or genetic differences?

Species which have settled in urban environments are exposed to different conditions from their wild conspecifics. A previous comparative study of an urban and a forest–living European blackbird population had revealed a three weeks earlier onset of gonadal growth in urban individuals. These physiological adjustments are either the result of genetic differences that have evolved during the urbanization process, or of phenotypic flexibility resulting from the birds exposure to the different environmental conditions of town or forest. To identify which of these two mechanisms causes the differences in reproductive timing, hand–reared birds originating from the urban and the forest populations were kept in identical conditions. The substantial differences in the timing of reproduction between urban and forest birds known from the field did not persist under laboratory conditions, indicating that temporal differences in reproductive timing between these two populations are mainly a result of phenotypic flexibility. Nevertheless, urban males initiated plasma luteinizing hormone (LH) secretion and testicular development earlier than forest males in their first reproductive season. Moreover, plasma LH concentration and follicle size declined earlier in urban females than in forest females, suggesting that genetic differences are also involved and might contribute to the variations in the timing of reproduction in the wild.

Effects of pinealectomy on circadian locomotor activity rhythms in european starlings,Sturnus vulgaris

SummaryRemoval of the pineal organ from starlings had drastic effects on their freerunning circadian activity rhythms; in birds kept in continuous darkness the period (τ) shortened and the activity time (α) lengthened. Concomitantly bothτ andα became relatively unstable and the separation between activity and rest time was obscured. In a few birds activity became continuous and apparently arrhythmic. The activity rhythms of the birds were entrainable to a 12∶12 h light-dark cycle.These results differ from those obtained previously by Menaker and his co-workers on the house sparrow, in which pinealectomy always resulted in arrhythmia. Nevertheless, it is suggested that the differences between these two species are only quantitative in nature rather than an expression of a qualitative difference in the organization of the circadian system. The results are consistent with the following modification of the model developed for the house sparrow: The avian pineal is the seat of a self-sustaining circadian pacemaker that acts on a population of secondary self-sustaining oscillators. These secondary oscillators, located outside the pineal, are only weakly coupled to each other but strongly dependent on the pineal driver. Their net circadian period is shorter than that of the pineal driver but, like the pineal driver, they can be synchronized by light. — It is proposed that this model fits both the starling and the sparrow data and clarifies some previously unexplained results.

Hippocampal volume in migratory and non-migratory warblers: effects of age and experience

We tested the hypothesis that experience of migration from Europe to tropical Africa by Garden Warblers is associated with changes in the relative volume of the hippocampus, a brain region thought to be involved in processing spatial information, including that used in navigation. Relative hippocampal volume was larger in birds at least one year old that had migrated to and from Africa, than in naive birds approx. 3 months old. Further comparisons between groups of differing age and experience of migration suggested that both experience and age during the first year have an effect of relative hippocampal volume. The increase in relative hippocampal volume was mainly due to a decrease in the size of the telencephalon; however, the comparison between young, naive birds and older, experienced birds also suggests a possible increase in absolute hippocampal volume. The latter is associated with an increase in number and density of neurons, whilst the former is associated with an increase in density but no change in total number of neurons. In a non-migratory close relative of the garden warbler, the Sardinian warbler, older birds had a smaller telencephalon but there was no change in hippocampal volume, which supports the view that changes in the hippocampus may be associated with migratory experience, whilst changes in the telencephalon are not.

Entrainment of a circadian rhythm in birds by species-specific song cycles (Aves, Fringillidae: Carduelis spinus, Serinus serinus)

Die in konstanten Licht- und Temperaturbedingungen von 24 h abweichende, circadiane Aktivitätsperiodik von 3 Zeisigen und 1 Girlitz, konnte durch Artgesang, der den Tieren täglich 12 h lang in einem 24-stündigen Zyklus über Lautsprecher vorgespielt wurde, synchronisiert werden. Mit diesen Ergebnissen ist nachgewiesen, dass auch akustische (soziale) Reize als Zeitgeber wirken können.