Biological Earth observation with animal sensors

Space-based tracking technology using low-cost miniature tags is now delivering data on fine-scale animal movement at near-global scale. Linked with remotely sensed environmental data, this offers a biological lens on habitat integrity and connectivity for conservation and human health; a global network of animal sentinels of environmen-tal change

Autumn departure of adult nocturnally migrating passerines from their breeding sites. Avian Ecol Behav

Due to methodical problems it is very difficult to obtain information on where, when and in which condition individual passerines take off for their first nocturnal migratory flight towards winter quarters in autumn or towards breeding grounds in spring. This paper reports the data on eight adult individual passerine nocturnal migrants (six Reed Warblers Acrocephalus scirpaceus, one Blackcap Sylvia atricapilla, and one Whitethroat S. communis) recaptured on the Courish Spit on the Baltic Sea in 1997-2002 in high mist nets at night during autumn migration. Capture histories of these birds suggest that they had been breeding at the capture site, therefore their recapture at nocturnal take-off could be related to their nocturnal migratory departure towards winter quarters. Five of eight adult migrants departed in the second or third hours into the night after sunset. The remaining three individuals took off in the second half of the night. Fuel stores of these birds varied between 8.3% and 24.3% of their lean body mass. Nocturnal flights of all migrants were started under winds favourable for migration

Commencement of nocturnal restlessness in the European Robin Erithacus rubecula during migration

Abstract: Bulyuk, V.N. & Mukhin, A. (1999): Commencement of nocturnal restlessness in the European Robin Erithacus rubecula during migration. Avian Ecol. Behav. 3: 79-90. We studied the time of onset of nocturnal migratory restlessness in the European Robin during spring and autumn migration. In 1996-1998 birds were specially trapped an hour or two before sunset in spring (10 April -20 May; n = 219) and in autumn (7 September-4 November; n = 287) and put in separate cages under the open sky with a view of sunset and the stars. Their behaviour was watched through infrared vision binoculars or recorded in automatic registration cages. Birds were released before sunset. In autumn, nocturnal restlessness was recorded in 18.1% of freshly captured Robins (15.7% and 22.6% in September and October, respectively). The proportion of Robins that displayed nocturnal activity was significantly positively related to their fat stores. Time of onset of nocturnal activity varied in different individuals between the second and the ninth hour after sunset (median 180 min). In September the median time was 155 min, in October 195 min. In November in four Robins out of seven nocturnal activity started five hours after sunset. In birds with large fat stores there was an observable trend to start nocturnal activity earlier in respect to sunset, than in leaner birds. In spring, nocturnal activity was recorded in 17.3% of freshly trapped Robins (16.7% and 18.4% in April and May, respectively). The time of onset of nocturnal restlessness varied between the second and the sixth hour after sunset (median 150 min). In late April the median was 147 min, in early May 153 min. Birds trapped during waves of passage (mass transit migration) tended to start nocturnal restlessness earlier in respect to sunset than conspecifics captured during migratory pauses. In birds held in captivity for some time, the proportion of active birds was much higher than in freshly trapped ones (65.8% in autumn, 60% in spring), the median being shifted towards the sunset: for 28 min in autumn and for 47 min in spring. The difference between freshly trapped and caged individuals are explained by higher fat scores of the latter, and by their delay on the migratory route. Variation in the timing of the onset of nocturnal activity in caged Robins is discussed, together with the relationship between behaviour in cages and migratory take-off activity in the wild

To what extent do environmental factors affect the long-distance nocturnal post-fledging movements of the Reed Warbler?

We studied the effects of weather and the lunar cycle on long-distance nocturnal pre-migratory flights of Reed Warblers (Acrocephalus scirpaceus). Noturnal tape luring was used to capture the birds, and the study was carried out in a habitat atypical of this species on the Courish Spit (southeastern Baltic) between1999 and 2002. A total of 443 juvenile Reed Warblers were captured during 120 nights of trapping. Based on data on the moult and body condition of the birds, it was possible to identify 163 individuals as being on post-fledging movements. More than half of the birds (54.0%) were captured at the end of night during the nautical and civil twilight period; the remaining individuals were caught during the astronomical twilight period and darkest periods of night. Many birds performed pre-migratory flights in the middle of the night, the period during which a large part of the moon was visible. We suggest that the increased visibility under the full moon may provide conditions in which Reed Warblers increase the distance or intensity of nocturnal post-fledging movements. During the entire course of the night, the birds generally preferred to fly under rainless conditions, limited cloud cover and/or in still air. The birds performed flights under winds stronger than 2 m s−1 when the wind was blowing along the axis of the spit. We also suggest that the birds generally fly along the spit. We found a weak but significant relationship between the numbers of Reed Warblers captured during post-fledging movements and the individual weather parameters and their interaction. Our data suggest that endogenous stimuli rather than weather parameters or lunar cycle phase determine the decision of Reed Warblers to undertake pre-migratory long-distance flights at night

Do flight-calls of Redwings differ during nocturnal and diurnal migration and daytime stopovers?

In the present study, we analyzed 173 spectrograms of acoustic signals of Redwings (Turdus iliacus). These were issued during diurnal and nocturnalmigratory flight and also during feeding, when resting and before take-off at daytime stopovers.During nocturnal and diurnal migration flights and daytime stopovers, Redwings use a single type of signal, a long tsii. It is classified as a species-specific attraction call. In flight Redwings emit shorter calls than during daytime stopovers.We did not find confirmation of the hypothesis that during nocturnalmigration in the absence of visual contact with each other, due to lowlight levels andmuch looser flocks in the course of daytime migration, Redwings emit longer signals with wider frequency spectrum than in the daytime

Juvenile dispersal in Reed Warblers Acrocephalus scirpaceus at night

The aim of this study was to test whether juvenile dispersal in Reed Warblers Acrocephalus scirpaceus takes place at night. If this does occur then the questions arise: “in which part of the night, at what age and physiological condition do they disperse?” In 1999 on the Courish Spit on the Baltic we ringed large numbers of Reed Warbler pulli at three isolated reedbed sites. Each night from late July until mid September we tape-lured Reed Warblers in a habitat atypical of this species. The trapping site was nearly equidistant from the two main plots where pulli were ringed. Additionally, in 1997-1999 at one of the reedbed study sites Reed Warblers starting and ending nocturnal flights were captured in high nets while at the same site, during the daytime, birds were trapped in standard mist nets. Our results suggest that juvenile dispersal of Reed Warblers takes place at night. The analysis of capture histories of ten birds ringed as pulli or just after fledging shows that: (1) age of birds during nocturnal movements was 33-49 days; (2) birds moved towards the NE and SW mainly during the last two hours before sunrise; (3) flight duration did not exceed 75 min; (4) all birds had low fuel stores and were in active moult; (5) nocturnal juvenile dispersal occurs by movements from one isolated reedbed area to another

Airspeed of the Song Thrush in relation to the wind during autumnal nocturnal migration

Birds possess behavioural and physiological adaptations which permit them to minimize time and energy expenditure during migration in a broad spectrum of winds, for instance, by varying their airspeed. Nocturnally migrating birds were recorded by an optical-electronic matrix system, which permitted recording their images and flight parameters in the dark. Among medium size birds, Song Thrushes (Turdus philomelos) were identified by their silhouette, linear size, wing-beat pattern, and phenology. The equivalent airspeed at sea level (VEq) of the observed thrushes without wind assistance (mean value 14.4 m/s) was close to the maximum range speed (Vmr) predicted from flight mechanical theory. This indicated an energy-selected migration strategy of the thrushes in autumn. The characteristic speed Vmr is wind-dependent: it increases with increasing velocity of head- and sidewinds. The airspeeds of the Song Thrushes showed a similar pattern of wind-dependence