Biology subjects

Nussbaumer, R.

Publications and source records attributed to Nussbaumer, R..

4 recordsLinked to original sources

bioRxiv2024

Variations in flight strategy of small migratory birds crossing major ecological barriers

The recent development of tracking technologies has revealed remarkable diel flight altitude changes over the Sahara Desert in small migratory bird species. However, the drivers and the traits that explain these crossing strategies remain poorly understood in part because so few species and barriers have been studied. Using a unique dataset from 67 recovered multi-sensor loggers, deployed across 17 species, we investigated when, where, and how birds cross two major marine barriers (Bay of Biscay, Mediterranean Sea) and a desert barrier (Sahara). Then, we relied on a comparative approach to examine the influence of wing morphology and plumage colour on these strategies. Our findings reveal important differences across barrier types. On average, birds fly at 1,600 m over the desert during nighttime, ascending to 2,800 m for prolonged daytime flights, while species crossing marine barriers fly significantly lower (750 m on average), in some cases flying just above the water surface during prolonged daytime flights. Wing morphology and plumage colour influence barrier-crossing strategies: flight altitude increases with wing area during both sea and desert crossings, and darker birds ascend to higher elevations during daytime Sahara crossings, likely to access cooler air and reduce solar heating. These findings refine hypotheses on barrier-crossing strategies and suggest broader ecological and evolutionary implications for migratory birds facing extreme environments.

ecology↗

bioRxiv2021

A simple method to separate birds and insects in single-pol weather radar data

Recent and archived data from weather radar networks are extensively used for quantification of continent-wide bird migration pattern. While discriminating birds from weather signals is well established, insect contamination is still a problem. We present a simple method combining two doppler radar products within a single Gaussian-mixture model to estimate the proportions of birds and insects within a single measurement, as well as the density and speed of birds and insects. The method can be applied to any existing archives of vertical bird profiles, such as the ENRAM repository (enram.eu) with no need to recalculate the huge amount of original polar volume data, which often are not available.

ecology↗

bioRxiv2020

Modelling the flow of nocturnal bird migration with year-round European weather radar network

The movements of migratory birds constitute huge biomass flows that influence ecosystems and human economy, agriculture and health through the transport of energy, nutrients, seeds, and parasites. To better understand the influence on ecosystems and the corresponding services and disservices, we need to characterize and quantify the migratory movements at various spatial and temporal scales. Representing the flow of birds in the air as a fluid, we applied a flow model to interpolated maps of bird density and velocity retrieved from the European weather radar network, covering almost a full year. Using this model, we quantified how many birds take-off, fly, and land across Western Europe, (1) to track waves of bird migration between nights, (2) cumulate the number of bird on the ground and (3) quantify the seasonal flow into and out of the study area through several regional transects. Our results show that up to 188 million (M) birds take-off over a single night. Exemplarily, we tracked a migration wave in spring, in which birds crossed the study area in 4 days with nocturnal flights of approximately 300 km. Over the course of a season, we estimated that 494 million (M) birds entered through the southern transects and, at the same time, 251 M left in the northern transects, creating a surplus of 243 M birds within the study area. Similarly, in autumn, 544 M more birds departed than arrived: 314 M birds entered through the northern transects while 858 M left through the southern transects. Our study show-cases the potential of combining interdisciplinary data and methods to elucidate the dynamics of avian migration from nightly to seasonal and yearly time-scales and from regional to continental spatial scales.

ecology↗

bioRxiv2019

A geostatistical approach to estimate high resolution nocturnal bird migration densities from a weather radar network.

O_LIQuantifying nocturnal bird migration at high resolution is essential for (1) understanding the phenology of migration and its drivers, (2) identifying critical spatio-temporal protection zones for migratory birds, and (3) assessing the risk of collision with man-made structures.\nC_LIO_LIWe propose a tailored geostatistical model to interpolate migration intensity monitored by a network of weather radars. The model is applied to data collected in autumn 2016 from 69 European weather radars. To cross-validate the model, we compared our results with independent measurements of two bird radars.\nC_LIO_LIOur model estimated bird densities at high resolution (0.2{degrees}latitude-longitude, 15min) and assessed the associated uncertainty. Within the area covered by the radar network, we estimated that around 120 million birds were simultaneously in flight [10-90 quantiles: 107-134]. Local estimations can be easily visualized and retrieved from a dedicated interactive website: birdmigrationmap.vogelwarte.ch.\nC_LIO_LIThis proof-of-concept study demonstrates that a network of weather radar is able to quantify bird migration at high resolution and accuracy. The model presented has the ability to monitor population of migratory birds at scales ranging from regional to continental in space and daily to yearly in time. Near-real-time estimation should soon be possible with an update of the infrastructure and processing software.\nC_LI

ecology↗