Migratory strategies in the Northern Wheatear (Oenanthe oenanthe)

Kurzfassung der Dissertation an der Carl von Ossietzky-Universität Oldenburg, angefertigt am Institut für Vogelforschung "Vogelwarte Helgoland", Wilhelmshaven, betreut durch Prof. Dr. Franz Bairlein, Institut für Vogelforschung Wilhelmshaven (Erstbetreuer) sowie Prof. Dr. Henrik Mouritsen, Universität Oldenburg (Zweitbetreuer

Heat loss in sleeping Garden Warblers (Sylvia borin) during migration

For small songbirds, energy is often a limiting factor during migration and, for this reason, they are forced to alternate nocturnal flights with stopovers to rest and replenish energy stores. Stopover duration has a key role for a successful migration and may have an important impact on fitness. Thus, migrants need to optimize their energy consumption at this stage to reduce their permanence at the site. A recent study has shown that lean individuals reduce their metabolic rate when tucking the head in the feathers during sleep. The underlying mechanism is very likely a reduction in conductance, but the thermoregulatory benefit of the increased insulation has never been quantified yet. Here, we compared heat loss in individual migratory birds while sleeping in different postures. Using a thermal camera and a within-individual approach, we estimated that Garden Warblers can reduce their rate of heat loss by 54% by sleeping with the head tucked in the feathers. This energy saving has a relevant impact on the individual’s energy balance because it can account for up to 8.69% of daily energy expenditure during stopover. Our study provides novel and important information to understand the fundamental role of thermoregulatory strategies on bird’s energy management

Stopover dynamics of 12 passerine migrant species in a small Mediterranean island during spring migration

Small coastal islands offer landing opportunities for large numbers of migratory birds following long sea crossings. However, they do not always provide sufficient refueling opportunities, thus raising questions about their importance for the success of migratory journeys. Here we analyzed a large dataset collected during 3 years of captures and recaptures of 12 species on the island of Ponza, central Italy, to determine the importance of the island for refueling. Despite the very large amount of birds on the island, only a very small fraction (usually below 2%) stayed on the island for longer than 1 day. These birds had low energy stores and, in most cases, they were not able to successfully refuel on Ponza. Only two species (Subalpine Warbler and Common Chiffchaff) had a positive fuel deposition rate, possibly as a result of the better suitability of the island's habitat to these two species. We underline that the large use of the island despite the relatively low refueling opportunities may be due to other aspects that it may offer to the birds. Possibly, birds just landed after a long sea crossing may require a short rest or sleep and can find opportunities to do that on the islands, reinitiating their onward flight after just a few hours. Understanding the role of these islands for migratory birds will be important for conservation, since setting priorities for protection might be misled if considering only refueling success as an important variable

Energy stores, oxidative balance and sleep in migratory Garden Warblers (Sylvia borin) and Whitethroats (Sylvia communis) at a spring stopover site

Little is known about how songbirds modulate sleep during migratory periods. Due to the alternation of nocturnal endurance flights and diurnal refueling stopovers, sleep is likely to be a major constraint for many migratory passerine species. Sleep may help to increase the endogenous antioxidant capacity that counteracts free radicals produced during endurance flight and reduces energy expenditure. Here, we investigated the relationship between sleep behavior, food intake, and two markers of physiological condition—the amount of energy reserves and oxidative status—in two migratory songbird species, the garden warbler (Sylvia borin) and the whitethroat (Sylvia communis). In garden warblers, birds with high energy stores were more prone to sleep during the day, while this condition-dependent sleep pattern was not present in whitethroats. In both species, birds with low energy stores were more likely to sleep with their head tucked in the feathers during nocturnal sleep. Moreover, we found a positive correlation between food intake and the extent of energy reserves in garden warblers, but not in whitethroats. Finally, we did not find significant correlations between oxidative status and sleep, or oxidative status and energy stores. Despite our study was not comparative, it suggests that different species might use different strategies to manage their energy during stopover and, additionally, it raises the possibility that migrants have evolved physiological adaptations to deal with oxidative damage produced during migration

Leukocyte coping capacity as a complementary stress metric in migrating birds

Corticosterone (Cort) is involved in multiple physiological processes during bird migration, complicating its interpretation in a stress context. We investigated whether the leukocyte coping capacity (LCC) provides useful complementary information on the stress response in migratory Garden Warblers (Sylvia borin) and how it relates to Cort and energetic condition. Contrary to Cort levels, LCC significantly decreased, implying high-stress levels and a diminished capacity to recover after a stressful event. The absence of significant effects of body conditions on the stress parameters shows no simple relationship between these traits and highlights the need for additional stress metrics to measure stress in life-history contexts

Innate Sex Differences in the Timing of Spring Migration in a Songbird

In migrating animals protandry is the phenomenon whereby males of a species arrive at the breeding grounds earlier than females. In the present study we investigated the proximate causes of protandry in a migratory songbird, the northern wheatear Oenanthe oenanthe. Previous experiments with caged birds revealed that males and females show differentiated photoperiod-induced migratory habits. However, it remained open whether protandry would still occur without photoperiodic cues. In this study we kept captive first-year birds under constant photoperiod and environmental conditions in a “common garden” experiment. Male northern wheatears started their spring migratory activity earlier than females, even in the absence of environmental cues. This indicates that protandry in the northern wheatear has an endogenous basis with an innate earlier spring departure of males than females

Co-migration fidelity at a stopover site increases over time in African–European migratory landbirds

Migratory species are changing their timing of departure from wintering areas and arrival to breeding sites (i.e. migration phenology) in response to climate change to exploit maximum food availability at higher latitudes and improve their fitness. Despite the impact of changing migration phenology at population and community level, the extent to which individual and species-specific response affects associations among co-migrating species has been seldom explored. By applying temporal co-occurrence network models on 15 years of standardized bird ringing data at a spring stopover site, we show that African–European migratory landbirds tend to migrate in well-defined groups of species with high temporal overlap. Such ‘co-migration fidelity’ significantly increased over the years and was higher in long-distance (trans-Saharan) than in short-distance (North African) migrants. Our findings suggest non-random patterns of associations in co-migrating species, possibly related to the existence of regulatory mechanisms associated with changing climate conditions and different uses of stopover sites, ultimately influencing the global economy of migration of landbirds in the Palearctic–African migration system

When quills kill. The defence strategy of the crested porcupine Hystrix cristata L., 1758

Quills represent specialized morphological structures evolved by some mammal species to deter predators. Among quilled mammals, crested porcupines Hystrix spp. exhibit the most complex armor. The antipredator behavior of these rodents is poorly known. In this study, we describe in detail the defense strategies of Hystrix cristata when attacked by hunting dogs. We identified four kinds of display exhibited by porcupines. Tail rattling seems to be sufficient to repel solitary predators, while backyard/sideways attacks are exhibited only in extreme situations, or when numerical disparity among potential prey and predators occurs. We also report four cases of wild species killing by porcupines

Reaction times

Data to reaction times for manuscript ICB-2024-003