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Do fledgling and pre‐breeding Common Swifts Apus apus take part in aerial roosting? An answer from a radiotracking experiment
Abstract
This study has shown that fledgling Common Swifts Apus apus spend the first post-fledging night of their life on the wing and that pre-breeders also spend the full night on the wing. Even though this work was conducted during an unusually cold, wet period, the results show that fledglings do not return to their natal colony in the week after fledging. It also demonstrates that yearlings are only slightly more likely than fledglings to spend any time at a particular colony, but are more likely to move from colony to colony. Older pre-breeders are more likely to spend more time at and revisit a particular colony more often than yearlings. It is our observation that only right at the end of the breeding duties will the parents participate in an evening ascent, and even then many of them return to their nest for the evening. Breeding adults displayed the greatest devotion to a particular colony. But even among such adults we detected some that ceased caring for their young a few days prior to their fledging. Adults roost in their nestbox if they meet with bad weather.
... Furthermore, up to 11 birds have been observed to show banging behaviour one after another: Thus it is rather unlikely that all of them were raised in the particular nest site the previous year, even in case of secondary brood (Lack & Lack 1952, Thomson et al. 1996, Kaiser 2004. Also, the breeders were found to spend their nights in the nests, whilst the nonbreeders (including yearlings) mostly spent the night on a wing (Tarburton & Kaiser 2001), suggesting that banging behaviour at dusk (when banging behaviour was observed most frequently) was more likely to be shown by the breeding individuals. Finally, banging behaviour was often directed towards conspecifics, rather than the nest sites, and towards locations which surely were not nesting sites. ...
... If banging was presented by the breeders and nonbreeders alike, then the relationship inside a typical colony between these two groups should be studied further, because the data currently available is contradictory concerning at what age the swifts start to breed (Lack 1956, Perrins 1971, Kaiser 1992) and how many of the one or two-year old nonbreeders return to their natal colony the following year (Lack 1956, Tarburton & Kaiser 2001. None of the birds were seen to break away from the screaming party flights to perform banging behavior, yet some banging behavior was displayed during the same time as the screaming parties activity (some birds participating in screaming parties did perform banging behaviour just after). ...
... Furthermore, banging behaviour was observed in the beginning of May, when breeding birds are the only birds so far in the colony. Finally, banging behavior was observed during dusk, when nonbreeders would have gone for aerial roosting, thus banging behaviour during this period can only be expressed by breeding birds (Bruderer & Weitnauer 1972, Tarburton & Kaiser 2001. Therefore, immature birds imitating the breeders also cannot be considered as a complete explanation. ...
Prey species show various types of antipredator behaviors to avoid predator attacks. Common Swifts (Apus apus) show specific behaviour where birdsmake almost a full stop during flight - this is referred to as "banging" behavior. This behaviour may be directed towards a conspecificswhich, for example, enters a nesting or a roosting site, or clings to a wall of a building. The bird showing this behavior is usually accompanied by conspecifics, which also copy its flight pattern. Actual explanations for this behavior are often inconsistent and unclear. This study has reconsidered such explanations and focused on the novel role of this behaviour as a potential antipredatory adaptation against the Common Kestrel (Falco tinnunculus). Observations of Common Swift behaviour were carried out inMay-September 2014 and May-August 2015 in Opole, SW Poland, giving 1,367 observations of nesting/roosting activities, 868 observations of "banging" behavior and 37 attacks of kestrels on swifts. Therewas a negative correlation between the number of successful hunting attempts and the number of Common Swifts showing banging behaviour. The study covers different aspects of banging behavior andmajor factors correlatingwith its occurrence.
... Artificial lighting had a dramatic effect on the swifts' daily activity patterns in "Wall" colony. This is a diurnal species, and while outside of the breeding season they may fly continuously and sleep on the wing 16,17 , during the breeding season the parents spend the night in the nest and activity in the colony ceases around sunset 18,20,21 . This was indeed the case in the other three colonies we studied that were exposed to low-to-medium ALAN intensity; however, in the fourth -"Wall" colony, which is exposed to extremely high-intensity ALAN, swifts' activity at the colony continued throughout the night (Fig. 1). ...
Abstract The use of artificial light at night (ALAN) is a rapidly expanding anthropogenic effect that transforms nightscapes throughout the world, causing light pollution that affects ecosystems in a myriad of ways. One of these is changing or shifting activity rhythms, largely synchronized by light cues. We used acoustic loggers to record and quantify activity patterns during the night of a diurnal bird – the common swift – in a nesting colony exposed to extremely intensive artificial illumination throughout the night at Jerusalem’s Western Wall. We compared that to activity patterns at three other colonies exposed to none, medium, or medium-high ALAN. We found that in the lower-intensity ALAN colonies swifts ceased activity around sunset, later the more intense the lighting. At the Western Wall, however, swifts remained active throughout the night. This may have important implications for the birds’ physiology, breeding cycle, and fitness, and may have cascading effects on their ecosystems.
... Several actigraphy methods have been used to measure movement in free-living animals. Radio tags used to determine an animal's location also provide information about their movements [100,101], even on a fine scale. Depending on an animal's orientation, the strength of the radio signal emanating from the tag varies relative to a fixed receiving location, thereby providing an estimate of movement [102]. ...
Despite being a prominent aspect of animal life, sleep and its functions remain poorly understood. As with any biological process, the functions of sleep can only be fully understood when examined in the ecological context in which they evolved. Owing to technological constraints, until recently, sleep has primarily been examined in the artificial laboratory environment. However, new tools are enabling researchers to study sleep behaviour and neurophysiology in the wild. Here, we summarize the various methods that have enabled sleep researchers to go wild, their strengths and weaknesses, and the discoveries resulting from these first steps outside the laboratory. The initial studies to ‘go wild’ have revealed a wealth of interindividual variation in sleep, and shown that sleep duration is not even fixed within an individual, but instead varies in response to an assortment of ecological demands. Determining the costs and benefits of this inter- and intraindividual variation in sleep may reveal clues to the functions of sleep. Perhaps the greatest surprise from these initial studies is that the reduction in neurobehavioural performance resulting from sleep loss demonstrated in the laboratory is not an obligatory outcome of reduced sleep in the wild.
This article is part of the themed issue ‘Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals’.
... Although these radar studies clearly demonstrate that swifts are flying at all hours of the night, individual swifts have not been tracked throughout the night using this method. By contrast, using radio tags, Tarburton & Kaiser [26] were able to follow individual swifts and confirmed that they do fly throughout the night. Remarkably, even juveniles spend their first night outside the nest-box on the wing. ...
Wakefulness enables animals to interface adaptively with the environment. Paradoxically, in insects to humans, the efficacy of wakefulness depends on daily sleep, a mysterious, usually quiescent state of reduced environmental awareness. However, several birds fly non-stop for days, weeks or months without landing, questioning whether and how they sleep. It is commonly assumed that such birds sleep with one cerebral hemisphere at a time (i.e. unihemispherically) and with only the corresponding eye closed, as observed in swimming dolphins. However, the discovery that birds on land can perform adaptively despite sleeping very little raised the possibility that birds forgo sleep during long flights. In the first study to measure the brain state of birds during long flights, great frigatebirds (Fregata minor) slept, but only during soaring and gliding flight. Although sleep was more unihemispheric in flight than on land, sleep also occurred with both brain hemispheres, indicating that having at least one hemisphere awake is not required to maintain the aerodynamic control of flight. Nonetheless, soaring frigatebirds appeared to use unihemispheric sleep to watch where they were going while circling in rising air currents. Despite being able to engage in all types of sleep in flight, the birds only slept for 0.7 h d⁻¹ during flights lasting up to 10 days. By contrast, once back on land they slept 12.8 h d⁻¹. This suggests that the ecological demands for attention usually exceeded that afforded by sleeping unihemispherically. The ability to interface adaptively with the environment despite sleeping very little challenges commonly held views regarding sleep, and therefore serves as a powerful system for examining the functions of sleep and the consequences of its loss. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
... These facts fit my own observations when radio-tracking fledgling and nonbreeding Common Swifts in Germany (Tarburton & Kaiser 2001). The pre-breeders and some of the fledglings left the colony in the daytime, but some of the fledglings departed from the nest about an hour after sunset when most normally make their maiden (and only) nest departure (Kaiser 1984). ...
It is now known that swifts (Apodidae) are morphologically and physiologically designed to fly at high altitudes, and that they do so when flying towards their nests. Consequently, it is here proposed that both White-throated Needletails Hirundapus caudacutus and Fork-tailed Swifts Apus pacificus leave Australia at high altitudes and so are not sighted very often in northern Australia when departing. This contrasts with their arrival in Australia, where they are most often first seen flying at low altitude into Australian waters.
Many avian species co-roost with other avian species, but roost sharing has not previously been reported for species that roost in enclosed spaces. We report co-roosting of chimney swifts (Chaetura pelagica (Linnaeus 1758)) and rock pigeons (Columba livia (Linnaeus 1758)) in a Sault Ste Marie, ON chimney. We predicted that life history and behavioural differences between the two species would lead to disturbance in chimney swifts, but not pigeons. Of two chimneys examined, swifts exited earlier in the morning in the chimney with co-roosting than in the chimney where they roosted alone. While pigeons appeared undisturbed by moving swifts unless swifts landed on them, swifts were sensitive to pigeon activity. In the evening, pigeon movements caused swifts to relocate within the chimney or to exit the chimney. Not all departed swifts re-entered the roost following the disturbance. In the morning swifts appeared more tolerant of pigeon movement, but were often disturbed by pigeon exit or entry. Permanently exiting the roost in the evening or departing too early in the morning may increase energy expenditure costs for migrating swifts. Installing pigeon deterrent devices at the chimney may reduce disturbance to chimney swifts within the roost and potentially prevent early exit in the morning.
A carcass of a House Swift (Apus nipalensis) found in Ladner, British Columbia on 18 May 2012 appears to be the first documented record of this species in the Americas. Identification is based on DNA sequencing and morphometric characters. University of British Columbia Beaty Biodiversity Museum Cowan Tetrapod Collection catalogue number B017056 has been assigned to this specimen (round study skin, spread wing, partial skeleton, and tissue samples).
A modelling approach is presented for describing the unique flight mode of aerial roosting Swifts. With reference to measurement results, a mathematical model of this flight mode is developed that describes the energy state of the bird and, in an expanded version, allows for unsteady motion characteristics caused by brief force impulses associated with short flapping and gliding phases. Because of these unsteady effects, the flight mode is here termed ‘dynamic flap-gliding flight’. Results are presented on the mechanical power output, which is the relevant performance quantity for the energy cost of aerial roosting Swifts. It is shown that dynamic flap-gliding flight yields a significant energy saving when compared with the best continuous flapping flight. The flapping ratio has a considerable effect, with the result that the energy saving is the higher the smaller the flapping ratio. Furthermore, the duration of the flap-gliding cycle, which is varied by aerial roosting Swifts in a wide range, has only a minor effect. Introducing an appropriate non-dimensionalization of the governing relations, results which are less sensitive to uncertainties in model parameters are obtained.
Birds have evolved a mobile lifestyle in which vision is of major importance when controlling movements, avoiding predators, finding food and selecting mates. Birds have extraordinary colour vision and have been suggested to perceive the linear polarisation of light. Behavioural experiments support this idea, but still the exact physiological mechanism involved is not known. The twilight period, when the sun is near the horizon at sunrise and sunset, is of crucial importance for migrating birds. At this time millions of songbirds initiate migration when the degree of skylight polarisation is the highest and all compass cues are visible in a short range of time. The biological compasses are based on information from the stars, the sun and the related pattern of skylight polarisation, as well as the geomagnetic field, and may be recalibrated relative to each other. The celestial polarisation pattern near the horizon has been shown to be used in the recalibration of the magnetic compass, but conflicting results have been obtained in experiments with different bird species. For the future we should understand the physiological mechanisms of avian polarisation vision and investigate the interrelationship and calibrations between the different compasses, including the one based on the pattern of skylight polarisation. A conditioning paradigm may be fruitful, but the risk of introducing optical artefacts needs to be minimised in behavioural experiments, as well as in cage experiments with migratory birds.
Seven cases of presumed epimeletic behaviour of adult Common Swifts toward flying young were recorded. The behaviour varied from adults escorting the young, over episodes when part of the colony swirled around the newcomer, to instances when an adult touched the young from below. A flying dummy was also encircled when exposed to adults. An eighth case was a non-aggressive behaviour of a migrating Swift toward a fledged soliciting House Martin. The behaviour seems to be a parallel to the care-giving (epimeletic) behaviour in cetaceans, e.g. dolphins, and is therefore seen as an airborne epimeletic behaviour. The Common Swift and dolphins have adapted to elements which are extreme to birds and mammals. If a Swift fledgling falls to the ground or a new-born dolphin (or an injured adult) sinks in the water, each will succumb. Over evolutionary time, therefore, epimeletic behaviour should have been favoured. The identical behaviour of adults of different animal taxa in different environments is here seen as behavioural convergence.
Eight homing pigeons (Columba livia) were flown distances of 90 and 320 km with and without transmitters (weighing either 2.5% or 5.0% of the pigeon's body mass, MB) mounted on a back harness. Flight times in April through June for the 90-km distance were 60 min without a transmitter or harness, 69 min with a harness alone and about 76 min with a harness and transmitter (weighing either 2.5% or 5.0% of MB). Flight times for the 320-km distance were 4 hr 16 min for the controls and 5 hr 35 min for the two fastest pigeons wearing a harness and transmitter weighing 2.5% of MB. The results show that on 90-km flights harnesses alone slow birds by 15% and harnesses and transmitters (≤ 5%MB) slow birds 25 to 28%; on 320-km flights harnesses and transmitters slow birds >31%. Moreover, on the 320-km flights, CO2 production of the pigeons (measured with the doubly-labeled water method) was 41 to 52% higher per hour when encumbered with a transmitter and harness. Thus, encumbered pigeons produced 85 to 100% more total CO2 covering the 320-km distance. Therefore, high performance homing pigeons work substantially harder and longer during a long distance flight when wearing harnesses and transmitters.
The paper presents data on survival rates of adult Swifts and the age at which they first breed. Survival rates were measured on a study population nesting in boxes and also from the recoveries of birds ringed under the national ringing scheme. The former method produces a higher survival rate; this is true also where survival rates of other species have been examined by both methods. Possible reasons for this are discussed.