Biology subjects

Anthes, N.

Publications and source records attributed to Anthes, N..

5 recordsLinked to original sources

bioRxiv2024

Spatial and temporal variation in farmland bird nesting ecology: Implications for effective Corn Bunting Emberiza calandra conservation

1Farmland bird populations continue to decline despite intense conservation efforts, possibly also because of incomplete knowledge on the drivers of local productivity. We therefore investigated spatial and temporal variation in nest site selection, breeding phenology, and nest survival for 225 nests of the Corn Bunting, a species of conservation concern in Central and Western Europe, in cropland-dominated, mixed, and grassland-dominated landscapes in SW Central Europe. Nesting phenology spread from April to August, started earlier at lower altitudes and progressed from grassland habitats to arable crops and eco-scheme flower fields. Most nests were placed in cultivated land, with substantial variation between landscape types but also between years within sites, so that large fractions of breeding attempts are prone to fail through land use operations in particular years. When nests were individually protected from land use, apparent and Mayfield survival rates differed substantially between nest habitats, with lowest survival in 2nd year flower fields and highest survival in fallow grassland. Accounting for land use survival from patch-specific mowing, harvesting, and grazing dates, total Mayfield nest survival estimates dropped by about half to 21 %, 13 %, and 20 % for (hay) meadows, alfalfa / clover-grass leys, and pastures, respectively, which held about 2/3 of nests in mixed landscapes. To enhance productivity beyond the thresholds required for local population persistence, we propose refined conservation schemes that improve survival within production farmland, best coupled with the development of prolific "Corn Bunting Landscapes".

ecology↗

bioRxiv2024

Analysing bird population trends from monitoring data with highly structured sampling designs

Population trends derived from systematic monitoring programmes are essential to identify species of conservation concern and to evaluate conservation measures. However, monitoring data pose several challenges for statistical analysis, including spatial bias due to an unbalanced sampling of natural regions or habitats, variation in observer expertise, frequent observer changes, and overdispersion or zero-inflation in the raw data. An additional challenge arises from so-called rolling survey designs, where each site is only visited once within each multi-year rotation cycle. We developed a GAMM-based workflow that addresses these challenges and exemplify its application with the highly structured data from the Ecological Area Sampling (EAS) in the German federal state North Rhine-Westphalia (NRW). First, we derive a routine that allows informed decisions about the most appropriate combination of distribution family (Poisson or negative binomial), model covariates (e.g., habitat characteristics), and zero-inflation formulations to reflect species-specific data distributions. Second, we develop a correction factor that buffers population trend estimates for variation in observer expertise as reflected in variation in total bird abundance. Third, we integrate region-specific trends that adjust for between-year variation in the representation of habitat or natural regions within the yearly subset of sampled sites. In a consistency check, we found good match between our GAMM-based EAS trends and TRIM-based trends from the German Common Bird Monitoring scheme. The study provides a template script for R statistical software so the workflow can be adapted to other monitoring programmes with comparable survey designs and data structures.

ecology↗

bioRxiv2020

Criteria for effective fallow field eco schemes for farmland birds during non-breeding

O_LIFarmland eco schemes implemented under the current Common Agricultural Policy (CAP) of the European Union are often considered ineffective in halting farmland bird declines. Fallow fields, often seeded with dedicated seed mixtures, rate among the more beneficial eco scheme types. Yet, the CAP currently defines no minimum criteria for fallow fields to qualify as eco scheme, likely jeopardizing their potential biodiversity benefits. C_LIO_LIWe investigated the attractiveness of four fallow field types established under CAP eco schemes and dedicated bird conservation programs in Southern Germany. Our 2-year surveys on > 100 fields focused on the non-breeding season, where food limitation can become particularly problematic. We modelled bird incidences also in response to vegetation structure and adjacent landscape features to derive minimum criteria for effective fallow field eco schemes. C_LIO_LIFallow field types varied only mildly in overall species richness but showed striking differences in the attracted species. Finches in particular tended to preferentially visit 1-year fallow fields, while buntings tended towards 2-year and older field types. 1-year CAP fallows, however, are typically removed before mid-winter, and thus potentially act as a trap to farmland birds and other wildlife. C_LIO_LIThe investigated species consistently preferred larger fallow fields with a more differentiated vegetation structure. Placement close to woods and hedgerows positively affected birds inhabiting woodland ecotones, while classic farmland species showed higher incidences on fallow fields embedded in open landscapes. C_LIO_LI Policy implications Our findings call for the ongoing CAP revisions to specify minimum requirements that qualify fallow fields as eco schemes. These should include an at least biennial cycle, a diversification of seed mixtures, standards for fallow field size, and criteria for their placement in the landscape matrix. C_LI

ecology↗

bioRxiv2018

Diurnal active photolocation enhances predator detection in a marine fish

Active sensing by means of light is rare. In vertebrates, it is known only from chemiluminescent fish with light organs below their pupils, an anatomical arrangement that is ideal to generate eyeshine in the pupils of nearby organisms. Here, we test whether diurnal fish can achieve the same by redirecting sunlight through reflection instead. We recently showed that small (< 5 cm), benthic, marine triplefin fish actively redirect downwelling light using their iris. We hypothesized that this mechanism allows triplefins to improve detection of a cryptic organism by generating eyeshine in its pupil. Here, we tested this by attaching small dark hats to triplefins to shade their iris from downwelling light. Two controls consisted of triplefins with a clear or no hat. These treatments test the prediction that light redirection increases the visual detection ability of triplefins. To this end, we placed treated fish in a tank with a display compartment containing either a stone as the control stimulus, or a scorpionfish, i.e. a cryptic, motionless triplefin predator with retroreflective eyes. After overnight acclimatization, we determined the average distance triplefins kept from the display compartment over two days. Both in the laboratory (n = 15 replicates per treatment) and in a similar field experiment at 15 m depth (n = 43 replicates per treatment) fish kept longer distances from the scorpionfish than from the stone. This response varied between hat treatments: shaded triplefins stayed significantly closer to the scorpionfish in the laboratory and in one of two orientations tested in the field. A follow-up field experiment at 10 m depth revealed the immediate response of triplefins to a scorpionfish. At first, many individuals (n = 80) moved towards it, with shaded triplefins getting significantly closer. All individuals then gradually moved to a safer distance at the opposite half of the tank. Visual modelling supported the experimental results by showing that triplefins can redirect enough light with their iris to increase a scorpionfishs pupil brightness above detection threshold at a distance of 7 cm under average field conditions and at more than 12 cm under favorable conditions. We conclude that triplefins are generally good in the visual detection of a cryptic predator, but can significantly improve this ability when able to redirect downwelling light with their iris and induce eyeshine in the predators pupil. We discuss the consequences of \"diurnal active photolocation\" for visual detection and camouflage among fish species.

zoology↗

bioRxiv2017

Controlled ocular radiance in a diurnal fish looking at prey

1.Active sensing using light, or active photolocation, is only known from deep sea and nocturnal fish with chemiluminescent \"search\" lights. Bright irides in diurnal fish species have recently been proposed as a potential analogue. Here, we contribute to this discussion by testing whether iris radiance is actively modulated. The focus is on behaviourally controlled iris reflections, called \"ocular sparks\". The triplefin Tripterygion delaisi can alternate between red and blue ocular sparks, allowing us to test the prediction that spark frequency and hue depend on background hue and prey presence. In a first experiment, we found that blue ocular sparks were significantly more often \"on\" against red backgrounds, and red ocular sparks against blue backgrounds, particularly when copepods were present. A second experiment tested whether hungry fish showed more ocular sparks, which was not the case. Again, background hue resulted in differential use of ocular spark types. We conclude that iris radiance through ocular sparks in T. delaisi is not a side effect of eye movement, but adaptively modulated in response to the context under which prey are detected. We discuss the possible alternative functions of ocular sparks, including an as yet speculative role in active photolocation.

animal behavior and cognition↗