Confronting the winds: orientation and flight behaviour of roosting swifts, Apus apus

Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and airspeed to show only a marginal increase in strong winds. The swifts were often moving "backwards", heading straight into the wind but being overpowered by wind speeds exceeding their airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing.     

Breeding success and survival in the common swift Apus apus: a long-term study on the effects of weather

In an analysis of data collected between 1954 and 1993, the breeding success of swifts Apus apus was found to have been positively related to temperatures in June, especially in recent years. Adult survival until the next breeding season, by contrast, was found to have been more vulnerable to low temperatures in July, at the end of the breeding season. In addition to the effects of changes in June and July temperatures, both breeding success and survival have shown further long-term trends, increasing and then decreasing through the study period. A simulation integrating all these effects suggests that lifetime reproductive success (LRS) in influenced more by changes in lifespan than annual breeding success, and so fluctutations in July temperatures, but not June temperatures, would have important effects.     

Cost of reproduction and allocation of food between parent and young in the swift (Apus apus)

We manipulated brood sizes to promote different levels of parentaleffort in the common swift (Apus apus). This provided a powerfulmethod for testing hypotheses regarding parental investmentdecisions concerning optimal allocation strategies between parentsand young. Data were analyzed on a visit-by-visit basis regardingchanges in parental and chick body mass, the mass of prey delivered,and the estimated mass of parental self-feeding. Our resultswere consistent with current theory in that food delivery increasedwith brood size, whereas the food received per chick, and hencemean chick body mass, decreased with brood size. Parental bodymass decreased with brood size and increasing parental effortbut recovered quickly during lower levels of chick feeding immediatelybefore fledging, suggesting some short-term cost of reproduction.Parents feeding at the highest level experienced criticallylow body mass and responded by a temporary cessation of chickfeeding. On any one foraging trip, total mass of prey captureddid not differ between brood sizes, but load mass deliveredto the young was negatively related to the amount of estimatedparental self-feeding. Allocation decisions of parents feedingthemselves and their young matched differential allocation theories,but estimated provisioning efficiency of parents at differentbody masses did not suggest any adaptive advantage from parentalmass loss.     

Migration routes and strategies in a highly aerial migrant, the common swift Apus apus, revealed by light-level geolocators

The tracking of small avian migrants has only recently become possible by the use of small light-level geolocators, allowing the reconstruction of whole migration routes, as well as timing and speed of migration and identification of wintering areas. Such information is crucial for evaluating theories about migration strategies and pinpointing critical areas for migrants of potential conservation value. Here we report data about migration in the common swift, a highly aerial and long-distance migrating species for which only limited information based on ringing recoveries about migration routes and wintering areas is available. Six individuals were successfully tracked throughout a complete migration cycle from Sweden to Africa and back. The autumn migration followed a similar route in all individuals, with an initial southward movement through Europe followed by a more southwest-bound course through Western Sahara to Sub-Saharan stopovers, before a south-eastward approach to the final wintering areas in the Congo basin. After approximately six months at wintering sites, which shifted in three of the individuals, spring migration commenced in late April towards a restricted stopover area in West Africa in all but one individual that migrated directly towards north from the wintering area. The first part of spring migration involved a crossing of the Gulf of Guinea in those individuals that visited West Africa. Spring migration was generally wind assisted within Africa, while through Europe variable or head winds were encountered. The average detour at about 50% could be explained by the existence of key feeding sites and wind patterns. The common swift adopts a mixed fly-and-forage strategy, facilitated by its favourable aerodynamic design allowing for efficient use of fuel. This strategy allowed swifts to reach average migration speeds well above 300 km/day in spring, which is higher than possible for similar sized passerines. This study demonstrates that new technology may drastically change our views about migration routes and strategies in small birds, as well as showing the unexpected use of very limited geographical areas during migration that may have important consequences for conservation strategies for migrants.     

Brood size, sibling competition, and the cost of begging in great tits (Parus major)

Evolutionary theory of parent-offspring conflict explains beggingdisplays of nestling birds as selfish attempts to influenceparental food allocation. Models predict that this conflictmay be resolved by honest signaling of offspring need to parents,or by competition among nestmates, leading to escalated beggingscrambles. Although the former type of models has been qualitativelysupported by experimental studies, the potential for a beggingcomponent driven by scramble competition cannot be excludedby the evidence. In a brood-size manipulation experiment withgreat tits, Parus major, we explored the scramble componentin the begging activity of great tit nestlings by investigatingthe mechanisms of sibling competition in relation to brood size.While under full parental compensation, the feeding rate pernestling will remain constant over all brood sizes for bothtypes of models; the scramble begging models alone predict anincrease in begging intensity with brood size, if begging costsdo not arise exclusively through predation. Great tit parentsadjusted feeding rates to brood size and fed nestlings at similarrates and with similar prey sizes in all three brood-size categories.Despite full parental compensation, the begging and food solicitationactivities increased with experimental brood size, whereas nestlingbody condition deteriorated. These findings support a scramblecomponent in begging and suggest that the competition-inducedcosts of food solicitation behavior play an important role inthe evolution of parent-offspring communication.     

Brood parasitism,female condition and clutch reduction in the common eider Somateria mollisima

Conspecific brood parasitism (CBP) is an alternative reproductive tactic found in many animals with parental care. Parasitizing females lay eggs in the nests of other females (hosts) of the same species, which incubate and raise both their own and the foreign offspring. The causes and consequences of CBP are debated. Using albumen fingerprinting of eggs for accurately detecting parasitism, we here analyse its relation to female condition and clutch size in High Arctic common eiders Somateria mollissima borealis. Among 166 clutches in a Svalbard colony, 31 (19%) contained eggs from more than one female, and 40 of 670 eggs (6%) were parasitic. In 6 cases an active nest with egg(s) was taken over by another female. Many suitable nest sites were unoccupied, indicating that CBP and nest takeover are reproductive tactics, not only consequences of nest site shortage. Similarity in body mass between female categories suggests that condition does not determine whether a nesting female becomes parasitised. There was no evidence of low condition in parasites: egg size was similar in hosts and parasites, and parasitism was equally frequent early and late in the laying season. Meta‐analysis of this and 3 other eider studies shows that there is a cost of being parasitised in this precocial species: host females laid on average 7% fewer eggs than other females.     

Prey choice and cannibalistic behaviour in the theropod Coelophysis

Direct evidence of prey choice in carnivorous dinosaurs is rare in the fossil record. The most celebrated example pertains to purported stomach contents in the carnivorous dinosaur Coelophysis bauri, which besides revealing prey choice, also points to cannibalistic behaviour as being commonplace (Colbert 1989, 1995). Here, we test this hypothesis by conducting the first comprehensive anatomical and histological examination of the famed Coelophysis 'cannibals'. The results unequivocally show that the gut contents derive from early crocodylomorphs rather than juveniles of Coelophysis. These findings suggest that this taxon is not cannibalistic and bring into question the commonality of this behaviour among non-avian dinosaurs.     

Nestling testosterone is associated with begging behaviour and fledging success in the pied flycatcher, Ficedula hypoleuca

Animal signals are hypothesized to be costly in order to honestly reflect individual quality. Offspring solicitation signals given by nestling birds are thought to have evolved to advertise either need or individual quality. We tested the potential role of testosterone (T) in controlling the intensity of these signals by measuring begging behaviour as: (i) duration of the begging display and (ii) maximum height of the begging stretch, and by sampling endogenous T levels in nestling blood. We tested nestling pied flycatchers (Ficedula hypoleuca) using well-established experimental paradigm involving transient food deprivation to encourage begging behaviour and then blood-sampled nestlings at the end of these tests for T levels. Our results show that individual nestlings with the most intense begging displays had the highest circulating levels of T immediately after testing. In addition, we found substantial differences between broods in terms of circulating T. Finally, we found evidence that broods with higher levels of T showed increased fledging success, indicating a benefit for increased T production in nestlings. The potential trade-offs involved in T-mediated begging behaviour are discussed.     

Parent-absent begging: evidence for sibling honesty and cooperation in the spotless starling (Sturnus unicolor)

Begging in avian nestlings is a highly conspicuous behaviorwith important implications for the study of parent–offspringconflict. In some species, nestlings also call for long boutsin the absence of parents, and it has been proposed that thisbehavior is used by nestlings as a means of negotiating accessto food. We studied this phenomenon in the spotless starling(Sturnus unicolor). We found that parent-absent calls were acousticallydistinct from parent-present calls. Observations showed thatthe probability of parent-absent begging increased with nestlingage and brood size, whereas it decreased with increasing bodycondition. This result was confirmed by an experiment that showedthat nestlings produced higher parent-absent begging rates whenfood deprived than when satiated. Finally, we carried out aplayback experiment to test the reaction of nestlings to parent-absentbegging by fellow nestlings. Principle components analyses yielded2 independent components of begging: 1) a general begging componentand 2) a second factor that measures the relative contributionof communicative begging over competitive begging. Nestlingsexposed to playback decreased their general begging levels andsimultaneously increased the relative contribution of communicativeover competitive begging. This behavior may favor needy nestlingsto obtain impending feedings while keeping high levels of foodsolicitation from parents and is consistent with a cooperativestrategy among nestlings. Future research should consider theactual response of parents to these signals.     

There is no evidence that mitochondria are the main source of reactive oxygen species in mammalian cells

It is often assumed that mitochondria are the main source of reactive oxygen species (ROS) in mammalian cells, but there is no convincing experimental evidence for this in the literature. What evidence there is suggests mitochondria are a significant source for ROS, which may have physiological and pathological effects. But quantitatively, endoplasmic reticulum and peroxisomes have a greater capacity to produce ROS than mitochondria, at least in liver. In most cells and physiological or pathological conditions there is a lack of evidence for or against mitochondria being the main source of cellular ROS. Mitochondria can rapidly degrade ROS and thus are potential sinks for ROS, but whether mitochondria act as net sources or sinks within cells in particular conditions is unknown.     

Odour and colour information in the foraging choice behaviour of the honeybee

1. Honeybees Apis mellifera ligustica were trained to work on a patch with artificial rewarding and non-rewarding flowers, coupled to an air extractor. The perceptual colour distance between the rewarding and the non-rewarding flowers was varied and the flower choice and the repellent scent-marking behaviour of the bees were recorded. 2. The discrimination between rewarding and non-rewarding flowers depended on their colour distance, improving with a greater colour difference. This task was guided thus visually and was not affected by activating the air extractor. 3. The scent-marking activity was only observable when the colour information of both groups of flowers was the same or very similar. This thus represents the first reported case of a modulation of an olfactory activity through the visual input provided by colour distances. When the air extractor was activated, rejections associated with the scent-marking behaviour disappeared, thus confirming the olfactory nature of this behaviour. 4. Honeybees are thus capable of using one or more sensory cues to enhance their foraging efficiency, according to the environmental situation. This great plasticity allows them to attain an enhanced efficiency while foraging. 5. We successfully applied the model of colour choice behaviour of the honeybee. Since the original theory was developed for Apis mellifera carnica, this work also constitutes the first attempt to describe the behaviour of the honeybee race, Apis mellifera ligustica, using the postulated model, and reaffirms thus its generality.     

Experimental evidence that adult antipredator behaviour is heritable and not influenced by behavioural copying in a wild bird

Knowledge of the relative importance of genetics and behavioural copying is crucial to appraise the evolvability of behavioural consistencies. Yet, genetic and non-genetic factors are often deeply intertwined, and experiments are required to address this issue. We investigated the sources of variation of adult antipredator behaviour in the Alpine swift (Apus melba) by making use of long-term behavioural observations on parents and cross-fostered offspring. By applying an 'animal model' approach to observational data, we show that antipredator behaviour of adult Alpine swifts was significantly repeatable over lifetime (r = 0.273) and heritable (h(2) = 0.146). Regression models also show that antipredator behaviours differed between colonies and sexes (females were more tame), and varied with the hour and year of capture. By applying a parent-offspring regression approach to 59 offspring that were exchanged as eggs or hatchlings between pairs of nests, we demonstrate that offspring behaved like their biological parents rather than like their foster parents when they were adults themselves. Those findings provide strong evidence that antipredator behaviour of adult Alpine swifts is shaped by genetics and/or pre-hatching maternal effects taking place at conception but not by behavioural copying.     

Brood defense and brood size in the great tit (Parus major): a test of a model of unshared parental investment

To understand the interaction of the many contextual variablesthat affect parental behavior a number of static optimalitymodels have been developed. Among these the one by Lazarus andInglis (1986) is the only one to specifically predict the magnitudeof unshared parental investment (PI), i.e., of parental carethat carries a cost to the parent and that benefits all currentoffspring equally because it cannot be divided among them. Weinvestigated specifically how parent great tits (Parus major)gear their brood defense, a form of unshared PI, to the sizeof the brood at stake and to the risk incurred as a functionof the type of predator. The predators used were dummies ofthe great spotted woodpecker (Picoides major) and of the tawnyowl (Strix aluco). Normally, adults can approach the woodpeckerwith impunity; it had inflicted heavy losses to nestlings ofthe study populations of great tits near Wolfsburg, Lower Saxony.Parent great tits whose brood had been artificially reducedto two young responded to the dummy with less defense than dida control group with their pre-test brood size left intact.The nature of defense was qualitatively the same as that elicitedby a live woodpecker. Parents confronting the owl near theirbrood decreased their response with an artificial reductionin brood size much less. Because the owl used poses a seriousrisk to the defenders, as compared to the woodpecker, the resultlends powerful support to the "total loss" version of the modelof unshared PI; it predicts brood size to affect unshared PImore strongly when there is less risk to the parent. This interpretationis correct to the extent that one premise of the model, namelythat of uncompromised parentage, can be relaxed; great tit broodscontain a sizeable number of extrapair young. Males defendedtheir brood more strongly than did females. Sex and brood manipulationadded up linearly when affecting defense level, i.e., therewas no interaction.     

Experimental evidence that partner choice is a driving force in the payoff distribution among cooperators or mutualists: the cleaner fish case

Supply and demand largely determine the price of goods on human markets. It has been proposed that in animals, similar forces influence the payoff distribution between trading partners in sexual selection, intraspecific cooperation and interspecific mutualism. Here we present the first experimental evidence supporting biological market theory in a study on cleaner fish, Labroides dimidiatus . Cleaners interact with two classes of clients: choosy client species with access to several cleaners usually do not queue for service and do not return if ignored, while resident client species with access to only one cleaning station do queue or return. We used plexiglas plates with equal amounts of food to simulate these behaviours of the two client classes. Cleaners soon inspected 'choosy' plates before 'resident' plates. This supports previous field observations that suggest that client species with access to several cleaners exert choice to receive better (immediate) service.