102 research outputs found
Flight directions of passerine migrants in daylight and darkness: A radar and direct visual study
The application of radar and visual techniques to determine the migratory habits of passerine birds during daylight and darkness is discussed. The effects of wind on the direction of migration are examined. Scatter diagrams of daytime and nocturnal migration track directions correlated with wind direction are presented. It is concluded that migratory birds will fly at altitudes where wind direction and migratory direction are nearly the same. The effects of cloud cover and solar obscuration are considered negligible
A long winter for the Red Queen: rethinking the evolution of seasonal migration
This paper advances an hypothesis that the primary adaptive driver of seasonal migration is maintenance of site fidelity to familiar breeding locations. We argue that seasonal migration is therefore principally an adaptation for geographic persistence when confronted with seasonality â analogous to hibernation, freeze tolerance, or other organismal adaptations to cyclically fluctuating environments. These ideas stand in contrast to traditional views that bird migration evolved as an adaptive dispersal strategy for exploiting new breeding areas and avoiding competitors. Our synthesis is supported by a large body of research on avian breeding biology that demonstrates the reproductive benefits of breedingâsite fidelity. Conceptualizing migration as an adaptation for persistence places new emphasis on understanding the evolutionary tradeâoffs between migratory behaviour and other adaptations to fluctuating environments both within and across species. Seasonalityâinduced departures from breeding areas, coupled with the reproductive benefits of maintaining breedingâsite fidelity, also provide a mechanism for explaining the evolution of migration that is agnostic to the geographic origin of migratory lineages (i.e. temperate or tropical). Thus, our framework reconciles much of the conflict in previous research on the historical biogeography of migratory species. Although migratory behaviour and geographic range change fluidly and rapidly in many populations, we argue that the loss of plasticity for migration via canalization is an overlooked aspect of the evolutionary dynamics of migration and helps explain the idiosyncratic distributions and migratory routes of longâdistance migrants. Our synthesis, which revolves around the insight that migratory organisms travel long distances simply to stay in the same place, provides a necessary evolutionary context for understanding historical biogeographic patterns in migratory lineages as well as the ecological dynamics of migratory connectivity between breeding and nonâbreeding locations.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149253/1/brv12476.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149253/2/brv12476_am.pd
Inherent limits of light-level geolocation may lead to over-interpretation
In their 2015 Current Biology paper, Streby et al. [1] reported that Golden-winged Warblers (Vermivora chrysoptera), which had just migrated to their breeding location in eastern Tennessee, performed a facultative and up to â>1,500 km roundtripâ to the Gulf of Mexico to avoid a severe tornadic storm. From light-level geolocator data, wherein geographical locations are estimated via the timing of sunrise and sunset, Streby et al. [1] concluded that the warblers had evacuated their breeding area approximately 24 hours before the storm and returned about five days later. The authors presented this finding as evidence that migratory birds avoid severe storms by temporarily moving long-distances. However, the tracking method employed by Streby et al. [1] is prone to considerable error and uncertainty. Here, we argue that this interpretation of the data oversteps the limits of the used tracking technique. By calculating the expected geographical error range for the tracked birds, we demonstrate that the hypothesized movements fell well within the geolocatorsâ inherent error range for this species and that such deviations in latitude occur frequently even if individuals remain stationary
Juvenile Songbirds Compensate for Displacement to Oceanic Islands during Autumn Migration
To what degree juvenile migrant birds are able to correct for orientation errors
or wind drift is still largely unknown. We studied the orientation of passerines
on the Faroe Islands far off the normal migration routes of European migrants.
The ability to compensate for displacement was tested in naturally occurring
vagrants presumably displaced by wind and in birds experimentally displaced 1100
km from Denmark to the Faroes. The orientation was studied in orientation cages
as well as in the free-flying birds after release by tracking departures using
small radio transmitters. Both the naturally displaced and the experimentally
displaced birds oriented in more easterly directions on the Faroes than was
observed in Denmark prior to displacement. This pattern was even more pronounced
in departure directions, perhaps because of wind influence. The clear
directional compensation found even in experimentally displaced birds indicates
that first-year birds can also possess the ability to correct for displacement
in some circumstances, possibly involving either some primitive form of true
navigation, or âsign postsâ, but the cues used for this are highly
speculative. We also found some indications of differences between species in
the reaction to displacement. Such differences might be involved in the
diversity of results reported in displacement studies so far
Perspectives and challenges for the use of radar in biological conservation
Radar is at the forefront for the study of broad-scale aerial movements of birds, bats and insects and related issues in biological conservation. Radar techniques are especially useful for investigating species which fly at high altitudes, in darkness, or which are too small for applying electronic tags. Here, we present an overview of radar applications in biological conservation and highlight its future possibilities. Depending on the type of radar, information can be gathered on local- to continental-scale movements of airborne organisms and their behaviour. Such data can quantify flyway usage, biomass and nutrient transport (bioflow), population sizes, dynamics and distributions, times and dimensions of movements, areas and times of mass emergence and swarming, habitat use and activity ranges. Radar also captures behavioural responses to anthropogenic disturbances, artificial light and man-made structures. Weather surveillance and other long-range radar networks allow spatially broad overviews of important stopover areas, songbird mass roosts and emergences from bat caves. Mobile radars, including repurposed marine radars and commercially dedicated âbird radarsâ, offer the ability to track and monitor the local movements of individuals or groups of flying animals. Harmonic radar techniques have been used for tracking short-range movements of insects and other small animals of conservation interest. However, a major challenge in aeroecology is determining the taxonomic identity of the targets, which often requires ancillary data obtained from other methods. Radar data have become a global source of information on ecosystem structure, composition, services and function and will play an increasing role in the monitoring and conservation of flying animals and threatened habitats worldwide
Innovative Visualizations Shed Light on Avian Nocturnal Migration
We acknowledge the support provided by COSTâEuropean Cooperation in Science and Technology through the Action ES1305 âEuropean Network for the Radar Surveillance of Animal Movementâ (ENRAM) in facilitating this collaboration. We thank ENRAM members and researchers attending the EOU round table discussion âRadar aeroecology: unravelling population scale patterns of avian movementâ for feedback on the visualizations. We thank Arie Dekker for his feedback as jury member of the bird migration visualization challenge & hackathon hosted at the University of Amsterdam, 25â27 March 2015. We thank Willem Bouten and Kevin Winner for discussion of methodological design. We thank Kevin Webb and Jed Irvine for assistance with downloading, managing, and reviewing US radar data. We thank the Royal Meteorological Institute of Belgium for providing weather radar data.Globally, billions of flying animals undergo seasonal migrations, many of which occur at night. The temporal and spatial scales at which migrations occur and our inability to directly observe these nocturnal movements makes monitoring and characterizing this critical period in migratory animalsâ life cycles difficult. Remote sensing, therefore, has played an important role in our understanding of large-scale nocturnal bird migrations. Weather surveillance radar networks in Europe and North America have great potential for long-term low-cost monitoring of bird migration at scales that have previously been impossible to achieve. Such long-term monitoring, however, poses a number of challenges for the ornithological and ecological communities: how does one take advantage of this vast data resource, integrate information across multiple sensors and large spatial and temporal scales, and visually represent the data for interpretation and dissemination, considering the dynamic nature of migration? We assembled an interdisciplinary team of ecologists, meteorologists, computer scientists, and graphic designers to develop two different flow visualizations, which are interactive and open source, in order to create novel representations of broad-front nocturnal bird migration to address a primary impediment to long-term, large-scale nocturnal migration monitoring. We have applied these visualization techniques to mass bird migration events recorded by two different weather surveillance radar networks covering regions in Europe and North America. These applications show the flexibility and portability of such an approach. The visualizations provide an intuitive representation of the scale and dynamics of these complex systems, are easily accessible for a broad interest group, and are biologically insightful. Additionally, they facilitate fundamental ecological research, conservation, mitigation of humanâwildlife conflicts, improvement of meteorological products, and public outreach, education, and engagement.Yeshttp://www.plosone.org/static/editorial#pee
Metabolic characteristics and body composition in house finches: effects of seasonal acclimatization
House finches ( Carpodacus mexicanus ) from the introduced population in the eastern United States were examined to assess metabolic characteristics and aspects of body composition associated with seasonal acclimatization. Wild birds were captured during winter (January and February) and late spring (May and June) in southeastern Michigan. Standard metabolic rates did not differ seasonally, but cold-induced âpeakâ metabolic rate was 28% greater in winter than late spring. The capacity to maintain elevated metabolic rates during cold exposure (âthermogenic enduranceâ) increased significantly from an average of 26.1 to 101.3 min in late spring and winter, respectively. House finches captured in the late afternoon during winter had twice as much stored fat as those during late spring. Both the wet mass and lean dry mass of the pectoralis muscle, a primary shivering effector, were significantly greater during winter. The seasonal changes in peak metabolism and thermogenic endurance demonstrate the existence and magnitude of metabolic seasonal acclimatization in eastern house finches. Increased quantities of stored fat during winter appear to play a role in acclimatization, yet other physiological adjustments such as lipid mobilization and catabolism are also likely to be involved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47132/1/360_2004_Article_BF00367313.pd
- âŚ