Ivan Maggini

Endogenous Rhythms of Seasonal Migratory Body Mass Changes and Nocturnal Restlessness in Different Populations of Northern Wheatear Oenanthe oenanthe

The Northern Wheatear (Oenanthe oenanthe) is a migratory bird species that shows different strategies of migration between populations, adapted to cope with different ecological barriers. This raises the question whether and to which extent these adaptations are endogenously determined. We studied seasonal patterns of body mass change and nocturnal restlessness in wheatears from Iceland, which face an initial sea crossing of at least 800 km; from Norway, which fly a similar distance as Icelandic birds but without a long sea crossing; and from Morocco, which fly a shorter distance to reach their wintering grounds. To isolate the endogenous component of the regulation of these migratory traits, we kept the wheatears in a “common garden,” all 3 populations experiencing the same environmental conditions and a constant photoperiod during their first year of life. Icelandic birds showed a greater increase of their body mass in autumn than the other 2 populations, indicating preparation for the initial barrier crossing. The autumnal timing of nocturnal restlessness and the total activity during autumn were related to the distance to be covered, although the differences between populations were smaller than expected. In all 3 populations, body mass increased to a greater extent in autumn than in spring, whereas nocturnal activity was higher in spring than in autumn. This suggests that the endogenous program responds to specific seasonal needs, with more time invested in storing fuel for a safe journey in autumn and more time invested in flying to reach the breeding grounds early in spring. Contrary to expectations, the timing of onset of body mass increase and nocturnal restlessness in spring did not differ between populations. This might be explained by the lack of external cues, most likely photoperiod, which are responsible for the fine tuning of the expression of migratory behavior.

Stopover optimization in a long-distance migrant: the role of fuel load and nocturnal take-off time in Alaskan northern wheatears (Oenanthe oenanthe).

IntroductionIn long-distance migrants, a considerably higher proportion of time and energy is allocated to stopovers rather than to flights. Stopover duration and departure decisions affect consequently subsequent flight stages and overall speed of migration. In Arctic nocturnal songbird migrants the trade-off between a relatively long migration distance and short nights available for travelling may impose a significant time pressure on migrants. Therefore, we hypothesize that Alaskan northern wheatears (Oenanthe oenanthe) use a time-minimizing migration strategy to reach their African wintering area 15,000 km away.ResultsWe estimated the factors influencing the birds’ daily departure probability from an Arctic stopover before crossing the Bering Strait by using a Cormack-Jolly-Seber model. To identify in which direction and when migration was resumed departing birds were radio-tracked. Here we show that Alaskan northern wheatears did not behave as strict time minimizers, because their departure fuel load was unrelated to fuel deposition rate. All birds departed with more fuel load than necessary for the sea crossing. Departure probability increased with stopover duration, evening fuel load and decreasing temperature. Birds took-off towards southwest and hence, followed in general the constant magnetic and geographic course but not the alternative great circle route. Nocturnal departure times were concentrated immediately after sunset.ConclusionAlthough birds did not behave like time-minimizers in respect of the optimal migration strategies their surplus of fuel load clearly contradicted an energy saving strategy in terms of the minimization of overall energy cost of transport. The observed low variation in nocturnal take-off time in relation to local night length compared to similar studies in the temperate zone revealed that migrants have an innate ability to respond to changes in the external cue of night length. Likely, birds maximized their potential nightly flight range by taking off early in the night which in turn maximizes their overall migration speed. Hence, nocturnal departure time may be a crucial parameter shaping the speed of migration indicating the significance of its integration in future migration models.

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.

Numbers, foraging and refuelling of passerine migrants at a stopover site in the western Sahara: diverse strategies to cross a desert

Twice a year, songbirds breeding in the Western Palaearctic cross the largest desert of the world, the Sahara, to reach their African winter quarters. Recently, a radar study quantified this migration and demonstrated that almost all passerines cross the western Sahara with an intermittent strategy, i.e. they fly during the night and rest during the day. Before crossing the desert, most passerines accumulate fat stores because they will not find appropriate resting sites for feeding in the Sahara. However, it has also been reported that birds use the vegetation around oases for refuelling. Since birds resting at oases had smaller fat deposits than birds resting in the open desert, it was hypothesised that mainly lean birds or fall-outs use the oases for feeding. In this study, we investigated which species or individuals use oases in the western Sahara during spring migration and how they use them. We demonstrate that a minority of species adapted to dry vegetation may cross the Sahara with low energy stores and intermittent refuelling in vegetation patches. These birds avoid the costs of transporting large energy stores, in contrast to most other passerine migrants which fuel up before crossing the Sahara and adopt an intermittent strategy without refuelling. The birds which rely on refuelling at oases probably often have a slow refuelling rate and may even run the risk of not finding appropriate habitats. The available studies reveal that birds use a wide variety of strategies to cross the Sahara. The particular strategy adopted depends on the species, and is modulated according to weather conditions aloft at the time, existing energy stores, the availability of stopover sites, and the suitability (food availability, competitors) of stopover sites.

When quills kill: the defense strategy of the crested porcupine Hystrix cristata L., 1758

Abstract 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.

Body condition and stopover of trans-Saharan spring migrant passerines caught at a site in southern Morocco

To answer the question whether and how migrating songbirds use the first vegetated areas in southern Morocco after crossing the Sahara Desert in spring, before continuing their northward migration successfully, we investigated the body condition and phenology of birds captured at a stopover site in Tafilalt from 2 April to 3 May 2005. The median date of passage of all Palaearctic species combined was 13 April. Only Pied Flycatchers Ficedula hypoleuca clearly peaked later, on 22 April. Of the seven species caught most often, only Pied Flycatchers were mostly in good-enough condition to reach Europe without refuelling, whereas in the other species most of the birds would have needed to refuel before crossing the Mediterranean. The majority of Northern Wheatears Oenanthe oenanthe and Woodchat Shrikes Lanius senator were in poor body condition and would have needed to refuel to continue their flight further north, but the low recapture rates suggest that these species stored only enough fat to reach the next available stopover sites rather than to fuel a longer flight north. Within all species, the recapture rate of birds staying longer than one day was low (2.9%) and most of the recaptured birds were in relatively good condition when first caught, indicating that their longer stopover time was not enforced by poor body condition. In general, our study showed that these stopover sites immediately north of the desert may not offer optimal refuelling opportunities for reaching northern destinations and that for many birds they are used simply as a temporary refuge to recover from fatigue or, in some species, as a necessary refuelling site, albeit suboptimal, in order to reach better refuelling sites further north.

Movement patterns and habitat use during incubation and chick-rearing of Cory's shearwaters (Calonectris diomedea diomedea) (Aves: Vertebrata) from Central Mediterranean: influence of seascape and breeding stage

Abstract We analysed the patterns of movement and habitat use of Corys shearwaters (Calonectris diomedea diomedea) from two colonies in the central Mediterranean Sea: the island of Linosa and the Tremiti Archipelago. The colony of Linosa is placed in a rather pelagic environment, being about 160 km distant from the coasts of both Sicily and Tunisia, while the colony of Tremiti is rather near to the coast of the Adriatic Sea, being only 25 km from the Italian coast. Field work during incubation was carried out at both colonies and throughout chick-rearing only at Linosa. We aimed to test first whether birds from the two colonies differ significantly in habitat use, and secondly whether constraints during incubation and chick-rearing lead birds to explore different habitats. Trip duration was correlated with the farthest distance covered in both colonies and, for Linosa birds, it decreased at the start of chick-rearing but increased later. During incubation the expanse of explored areas did not differ between the colonies, but for Tremiti these were generally characterized by higher average primary production and shallower waters than those for Linosa. Furthermore, during the incubation period Linosa birds explored areas with higher values of primary production and shallower waters than during chick-rearing. Chick-rearing is therefore likely to constrain birds to use sub-optimal areas closer to their colony due to the intense pressures of chick provisioning. Our data indicate that conservation efforts should therefore aim not only to protect the best foraging areas but also to conserve areas closer to the colonies, which will be profitable enough to provide adult birds with sufficient food for chick-rearing.

Light oiling of feathers increases flight energy expenditure in a migratory shorebird

ABSTRACT Flying birds depend on their feathers to undertake most activities, and maintain them in peak condition through periodic molt and frequent preening. Even small exposures to crude oil reduce the integrity of feathers, and could impair flight performance. We trained wild western sandpipers (Calidris mauri) to perform endurance flights in a wind tunnel, and used magnetic resonance body composition analysis to measure energy expenditure after birds were exposed to weathered MC252 crude oil from the Deepwater Horizon oil spill. The cost of transport was 0.26±0.04 kJ km−1 in controls, and increased by 22% when the trailing edges of the wing and tail were oiled (<20% of body surface; considered light oiling). Additional crude oil on breast and back feathers (∼30% total surface; moderate oiling) increased the cost of transport by 45% above controls. Oiling tended to decrease flight control, and only half of moderately oiled birds completed the flight test. We then flew birds at a range of speeds to estimate basic kinematic parameters. At low speeds, light and moderately oiled birds had larger wingbeat amplitudes than controls, while moderately oiled birds showed greater wingbeat frequencies across all speeds, and a shift in optimal flight speed towards higher wind speeds. We suggest these changes reflect poorer lift production and increased drag on the wings and body. Oiling will increase the difficulty and energy costs of locomotion for daily and seasonal activities such as foraging, predator evasion, territory defense, courtship, chick provisioning, commuting and long-distance migration. These sub-lethal effects must be considered in oil spill impact assessments. Highlighted Article: Light to moderate contamination of feathers with crude oil increases the energy cost of flight by 22–45% and has important implications for all activities requiring flight, including long-distance migration.

Trouble on takeoff: Crude oil on feathers reduces escape performance of shorebirds

The ability to takeoff quickly and accelerate away from predators is crucial to bird survival. Crude oil can disrupt the fine structure and function of feathers, and here we tested for the first time how small amounts of oil on the trailing edges of the wings and tail of Western sandpipers (Calidris mauri) affected takeoff flight performance. In oiled birds, the distance travelled during the first 0.4s after takeoff was reduced by 29%, and takeoff angle was decreased by 10° compared to unoiled birds. Three-axis accelerometry indicated that oiled sandpipers produced less mechanical power output per wingbeat during the initial phase of flight. Slower and lower takeoff would make oiled birds more likely to be targeted and captured by predators, reducing survival and facilitating the exposure of predators to oil. Whereas the direct mortality of heavily-oiled birds is often obvious and can be quantified, our results show that there are significant sub-lethal effects of small amounts crude oil on feathers, which must be considered in natural resource injury assessments for birds.

Differential migration and body condition in Northern Wheatears (Oenanthe oenanthe) at a Mediterranean spring stopover site

AbstractIn many species of migratory birds, individuals of different populations, sexes and age classes migrate at different times and manage their energy reserves according to their specific migratory strategies. In this study, we analyzed the migratory patterns related to geographic provenance, sex and age in the Northern Wheatear Oenanthe oenanthe, a long-distance migratory passerine, during one spring season on the island of Ventotene (Italy), a Mediterranean stopover site. Individuals of different sex and age did not differ significantly in their average date of passage, but birds with longer and more pointed wings passed through later in the season than birds with shorter wings. Morphometric measurements combined with isotopic analysis revealed that late-arriving birds probably belonged to more distant breeding populations and this later date of passage probably mirrors the delayed arrival observed at their northern breeding grounds. Adult birds arrived in better condition than second-year birds, possibly as a result of better energy management. Birds passing through later in the season were also in better condition, which might be explained by their wing morphology favoring endurance flights and thus improving energetic efficiency when crossing the Mediterranean. Birds which migrate longer distances might also carry larger fuel loads to safely complete their journey. This intra-specific study shows that the birds’ organization of their migration schedule is population-specific in correspondence to the temporal requirements which depend on the different environmental conditions on the breeding grounds.ZusammenfassungDifferentielles Zugverhalten und Körperkondition beim Steinschmätzer (Oenanthe oenanthe) an einen Rastplatz im Mittelmeer im Frühjahr Bei vielen Zugvögeln ziehen verschiedene Populationen, Männchen und Weibchen und/oder verschiedene Altersgruppen zu verschiedenen Zeiten und gestalten ihre Energiereserven entsprechend ihrer spezifischen Zugstrategie. Wir betrachteten die Zugmuster des Steinschmätzer Oenanthe oenanthe, eines Langstreckenziehers, in Beziehung zur Lage des Brutgebietes, zu Geschlecht und Alter während einer Frühjahrssaison auf der italienischen Mittelmeerinsel Ventotene. Die Geschlechter und Altersgruppen unterschieden sich nicht in ihren mittleren Durchzugszeiten, doch zogen Vögel mit längeren und spitzeren Flügeln signifikant später durch als Vögel mit kürzeren Flügeln. Morphometrische Messungen in Kombination mit Isotopenanalysen zeigen, dass die spät durchziehenden Vögel wahrscheinlich zu weiter entfernten Brutpopulationen gehörten, korrespondierend zu deren späterer Ankunft in den nördlichen Brutgebieten. Altvögel kamen auf Ventotene in besserer Kondition an als Vögel in ihrem zweiten Kalenderjahr, möglicherweise eine Folge davon, dass Altvögel mit ihrer Energie besser haushalten. Auch waren später in der Saison durchziehende Vögel in besserer Kondition. Dies könnte eine Folge ihrer Flügelmorphologie sein, die lange Flüge begünstigt und so die Energiebilanz beim Flug über das Mittelmeer verbessert. Auch könnten die weiter ziehenden Vögel mehr Energiereserven für erfolgreichen Zug an sich benötigen. Diese intra-spezifische Studie zeigt, dass der Zugablauf populationsspezifisch ist, korrespondierend mit den zeitlichen Anforderungen, die von den unterschiedlichen Umweltbedingungen im Brutgebiet bestimmt sind.