62 research outputs found
Avian Communities of the Northern Mackenzie Mountains, Northwest Territories, Canada
Basic knowledge of the abundance and distribution of birds and their habitats and the relationships between them is limited for many parts of Arctic Canada, including montane regions. This information is important for conservation purposes as bird populations and habitats shift and as interest in development of northern areas increases. We characterized bird communities in the Mackenzie Mountains of the Northwest Territories by conducting point counts (n = 376) in June 2009 and 2010 and using community analysis metrics (multiple response permutation procedures, indicator species analysis, non-metric multidimensional scaling) to statistically and graphically describe bird data in six habitat types: coniferous forest, deciduous forest, shrub (short and tall), alpine tundra, and open water wetlands. Distinct habitats had significantly different bird communities, as shown by using multiple response permutation procedures (p < 0.005). Of 51 species, 32 had significant (p < 0.05) indicator values for one habitat type (n = 15) or groups of habitats (n = 17) in an indicator species analysis. The tall shrub habitat type had the most indicator species (six species) followed by alpine tundra (five species), then the combined conifer, deciduous, and wetland habitat group (four species) and the deciduous forest habitat types (three species). Species richness was highest in the tall shrub (n = 37), alpine (n = 30), and conifer and short shrub (n = 29) habitats. We also observed eight bird species not previously known to occur in the area, or which were outside published ranges. Our results highlight the variability in bird community composition between the major habitat types in the Mackenzie Mountains, serve as a baseline for future bird studies in the region, and underscore the need for more research in the area with impending anthropogenic changes.Pour de nombreuses parties de l’Arctique canadien, y compris les régions montagnardes, les connaissances de base portant sur l’abondance et la répartition des oiseaux et de leurs habitats, de même que sur leurs relations entre eux, sont restreintes. Ces renseignements revêtent de l’importance en matière de conservation, au moment où les habitats et les populations d’oiseaux changent et où l’on s’intéresse de plus en plus au développement des régions du nord. Nous avons caractérisé les communautés d’oiseaux des monts Mackenzie, dans les Territoires du Nord-Ouest, en effectuant des dénombrements ponctuels (n = 376) en juin 2009 et 2010 et en recourant à diverses mesures d’analyse des communautés (test de permutations multiples, analyse des espèces indicatrices, analyse multidimensionnelle non métrique) afin de décrire à l’aide de statistiques et de graphiques les données relatives aux oiseaux de six types d’habitats : forêts de conifères, forêts de feuillus, arbustaies (petits arbustes et grands arbustes), toundra alpine et terres humides avec étendues d’eaux libres. D’après les tests de permutations multiples (p < 0,005), les communautés d’oiseaux diffèrent considérablement en présence d’habitats distincts. L’analyse des espèces indicatrices a également permis de démontrer que parmi les 51 espèces, 32 avaient des valeurs indicatrices importantes (< 0,05) pour un type d’habitat (n = 15) ou des groupes d’habitats (n = 17). L’habitat des grands arbustes comptait le plus grand nombre d’espèces indicatrices (six espèces), suivi de la toundra alpine (cinq espèces), puis du groupe composé de la forêt de conifères, de la forêt de feuillus et des terres humides (quatre espèces), et de la forêt de feuillus (trois espèces). La richesse des espèces était plus grande dans les habitats des grands arbustes (n = 37), de la toundra alpine (n = 30) et des conifères et petits arbustes (n = 29). Nous avons également observé huit espèces d’oiseaux qui n’avaient jamais été répertoriées dans la région ou qui se trouvaient en dehors de leur parcours naturel. Nos résultats mettent en évidence la variabilité de la composition des communautés d’oiseaux dans les principaux types d’habitats des monts Mackenzie. Ils serviront également de référence aux autres études d’oiseaux qui seront effectuées dans la région, et font ressortir la nécessité de faire d’autres recherches dans la région à la lumière des changements anthropiques imminents
High speed single photon detection in the near-infrared
InGaAs avalanche photodiodes (APDs) are convenient for single photon
detection in the near-infrared (NIR) including the fibre communication bands
(1.31/1.55 m). However, to suppress afterpulse noise due to trapped
avalanche charge, they must be gated with MHz repetition frequencies, thereby
severely limiting the count rate in NIR applications. Here we show gating
frequencies for InGaAs-APDs well beyond 1 GHz. Using a self-differencing
technique to sense much weaker avalanches, we reduce drastically afterpulse
noise. At 1.25 GHz, we obtain a detection efficiency of 10.8% with an
afterpulse probability of 6.16%. In addition, the detector features low jitter
(55 ps) and a count rate of 100 MHz
Spin-orbit coupling in interacting quasi-one-dimensional electron systems
We present a new model for the study of spin-orbit coupling in interacting
quasi-one-dimensional systems and solve it exactly to find the spectral
properties of such systems. We show that the combination of spin-orbit coupling
and electron-electron interactions results in: the replacement of separate spin
and charge excitations with two new kinds of bosonic mixed-spin-charge
excitation, and a characteristic modification of the spectral function and
single-particle density of states. Our results show how manipulation of the
spin-orbit coupling, with external electric fields, can be used for the
experimental determination of microscopic interaction parameters in quantum
wires.Comment: 5 pages including 4 figures; RevTeX; to appear in Phys.Rev.Let
Identifying the winter grounds of the recently described Barbary Reed Warbler (Acrocephalus baeticatus ambiguus)
The Iberian and North African populations of reed warblers have been described recently as a separate taxon, ambiguus, forming a sister clade to the Sahelian subspecies minor of African Reed Warbler Acrocephalus baeticatus. Although the breeding range of ambiguus has been identified, the migration strategy of its populations remained unknown. We deployed geolocators and sampled the innermost primary from breeding adults in Spain for stable hydrogen (d2H) analyses and also analysed stable carbon (d13C) and nitrogen (d15N) isotopes in feathers collected in two reed warbler taxa (Acrocephalus scirpaceus and Acrocephalus baeticatus ambiguus) in Morocco, to identify the moulting and wintering sites of these populations. Ring recoveries, geolocator tracks and probabilistic assignments to origin from d2H values indicate that Spanish ambiguus are likely to moult south of the Sahara and winter in West Africa, probably from Mauretania to southern Mali and Ivory Coast. Moroccan ambiguus, however, undergo post-breeding moult north of the Sahara, and possibly then migrate to West Africa. With other populations of ambiguus breeding from Algeria to Libya and probably wintering further east in the Sahelian belt, the Barbary Reed Warbler can therefore be considered a trans-Saharan migrant, with a post-breeding moult strategy that varies between populations, and probably structured according to breeding latitude
Measuring measurement
Measurement connects the world of quantum phenomena to the world of classical
events. It plays both a passive role, observing quantum systems, and an active
one, preparing quantum states and controlling them. Surprisingly - in the light
of the central status of measurement in quantum mechanics - there is no general
recipe for designing a detector that measures a given observable. Compounding
this, the characterization of existing detectors is typically based on partial
calibrations or elaborate models. Thus, experimental specification (i.e.
tomography) of a detector is of fundamental and practical importance. Here, we
present the realization of quantum detector tomography: we identify the optimal
positive-operator-valued measure describing the detector, with no ancillary
assumptions. This result completes the triad, state, process, and detector
tomography, required to fully specify an experiment. We characterize an
avalanche photodiode and a photon number resolving detector capable of
detecting up to eight photons. This creates a new set of tools for accurately
detecting and preparing non-classical light.Comment: 6 pages, 4 figures,see video abstract at
http://www.quantiki.org/video_abstracts/0807244
Avalanche amplification of a single exciton in a semiconductor nanowire
Interfacing single photons and electrons is a crucial ingredient for sharing
quantum information between remote solid-state qubits. Semiconductor nanowires
offer the unique possibility to combine optical quantum dots with avalanche
photodiodes, thus enabling the conversion of an incoming single photon into a
macroscopic current for efficient electrical detection. Currently, millions of
excitation events are required to perform electrical read-out of an exciton
qubit state. Here we demonstrate multiplication of carriers from only a single
exciton generated in a quantum dot after tunneling into a nanowire avalanche
photodiode. Due to the large amplification of both electrons and holes (>
10^4), we reduce by four orders of magnitude the number of excitation events
required to electrically detect a single exciton generated in a quantum dot.
This work represents a significant step towards single-shot electrical read-out
and offers a new functionality for on-chip quantum information circuits
Superconducting nanowire photon number resolving detector at telecom wavelength
The optical-to-electrical conversion, which is the basis of optical
detectors, can be linear or nonlinear. When high sensitivities are needed
single-photon detectors (SPDs) are used, which operate in a strongly nonlinear
mode, their response being independent of the photon number. Nevertheless,
photon-number resolving (PNR) detectors are needed, particularly in quantum
optics, where n-photon states are routinely produced. In quantum communication,
the PNR functionality is key to many protocols for establishing, swapping and
measuring entanglement, and can be used to detect photon-number-splitting
attacks. A linear detector with single-photon sensitivity can also be used for
measuring a temporal waveform at extremely low light levels, e.g. in
long-distance optical communications, fluorescence spectroscopy, optical
time-domain reflectometry. We demonstrate here a PNR detector based on parallel
superconducting nanowires and capable of counting up to 4 photons at
telecommunication wavelengths, with ultralow dark count rate and high counting
frequency
Unravelling migration connectivity reveals unsustainable hunting of the declining ortolan bunting
In France, illegal hunting of the endangered ortolan bunting Emberiza hortulana has been defended for the sake of tradition and gastronomy. Hunters argued that ortolan buntings trapped in southwest France originate from large and stable populations across the whole of Europe. Yet, the European Commission referred France to the Court of Justice of the European Union (EU) in December 2016 for infringements to legislation (IP/16/4213). To better assess the impact of hunting in France, we combined Pan-European data from archival light loggers, stable isotopes, and genetics to determine the migration strategy of the species across continents. Ortolan buntings migrating through France come from northern and western populations, which are small, fragmented and declining. Population viability modeling further revealed that harvesting in southwest France is far from sustainable and increases extinction risk. These results provide the sufficient scientific evidence for justifying the ban on ortolan harvesting in France.Peer reviewe
Multi-isotope (δ 2H, δ 13C, δ 15N) feather profiles and morphometrics inform patterns of migratory connectivity in three species of North American swallows
Abstract Aerial insectivorous birds have suffered steep population declines in North America over the last 60 years. A lack of information on migratory connectivity between breeding and non-breeding grounds for these species limits our ability to interpret factors affecting their population-specific trends. We determined likely Latin American non-breeding regions of Bank (Riparia riparia), Barn (Hirundo rustica) and Cliff (Petrochelidon pyrrhonota) swallow from populations across their breeding ranges. We used predicted feather hydrogen (δ 2Hf) and carbon (δ 13Cf) isoscapes for winter-grown feathers to indicate areas of highest probability of moult origin and incorporated these results into a cluster analysis to determine likely broad non-breeding regions. We also assessed variation in wing length among populations to determine the potential for this metric to differentiate population moult origins. We then investigated patterns of multi-isotopic (δ 2Hf, δ 13Cf, δ 15Nf) and wing-length niche occupancy by quantifying niche size and overlap among populations under the assumption that broad niches were consistent with low within-species migratory connectivity and narrow and non-overlapping niches with higher connectivity. Multivariate assignment identified different non-breeding regions and potential clusters of moult origin generally corresponding to Central America and northern South America, eastern and south-central South America, and the western and southern part of that continent, with variation within and among populations and species. Separate niche space indicated different wintering habitat or areas used by species or populations whereas niche overlap indicated only potential spatial similarity. Wing length varied significantly among populations by species, being longer in the west and north for Bank and Cliff Swallow and longer in eastern Canadian Barn Swallow populations. Barn Swallow occupied consistently larger isotopic and wing length niche space than the other species. Comparisons among populations across species showed variable isotopic and wing-length niche overlap generally being greater within breeding regions and lower between western and eastern breeding populations supporting a general North American continental divide for all species with generally low migratory connectivity for all species. We present a novel approach to assessing connectivity using inexpensive and broad isotopic approaches that provides the basis for hypothesis testing using more spatially explicit expensive techniques
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