Assessing plastic pollution in farmland: Impact of agricultural practices on bird nesting materials.

Farmland, a vital terrestrial environment, has seen significant changes due to intensified agricultural practices and plastic pollution. Assessing plastic pollution in farmed areas remains challenging, and understanding its impacts on agricultural ecosystems is limited. The aim of the was to determine whether plastic pollution in agricultural landscapes depends on the type of crops. We used the Red-backed Shrike (Lanius collurio), an indicator bird species and investigated plastic contamination of 122 of its nests. We found plastic waste in 82.1 % of nests, totalling 6234 items weighing 197.2 g. On average, each nest contained 55.7 waste items, constituting approximately 4.3 % of the nest's mass. Plastic string fibres were predominant, making up 95.6 % of the items and 90.7 % of the mass. This variation may be due to different straw and hay management practices and varying levels of vigilance in removing plastic remnants. Contamination levels varied significantly among farmland types, with cultivated fields showing the highest contamination and meadows the lowest.

Presence of the cloud cover and elevation angle of the sun affect measurements of eggshell coloration and patterning obtained from calibrated digital images.

Calibrated digital photography is frequently used in studies focusing on avian eggshell appearance to measure colour and pattern features. Photographs are often taken in natural light conditions, yet little is known to what extent the normalisation process is able to control for varied light. Here, we photographed 36 blown eggs of the Japanese quail Coturnix japonica at five different elevation angles of the sun on both sunny and uniformly overcast days alongside grey standards. We normalised and processed the photographs in the MICA Toolbox software and checked how much noise was introduced by different natural light conditions to the colour and pattern measurements of the same set of eggs. Our results indicate that natural variation of light conditions affects eggshell colour and pattern measurements obtained by means of calibrated digital photography. Depending on a trait, the elevation angle of the sun had similar or even greater effect on the measurement than the presence of the cloud cover. Furthermore, measurements taken in cloudy conditions were more repeatable than those taken in sunny conditions. Based on the results, we propose practical guidelines regarding measuring colour and pattern of eggshells using calibrated digital photography in outdoor conditions.

Effect of light intensity in the nest site on eggshell pigmentation in a hole-nesting passerine.

Daylight is an important factor necessary for the proper embryonic development of birds, which raises the question, what happens when birds nest in relatively dim sites? The study experimentally tested whether there is a relationship between light conditions at the nesting site and the protoporphyrin-based pigmentation in the eggshell of the Great Tit (Parus major). We hypothesised that at lower light levels, eggs are less pigmented to increase the amount of light reaching the embryo. Our study system consisted of two types of nest boxes: "dark", in which the only source of light was the entrance hole, and "bright", which had two additional side windows. Photographs of clutches taken during the incubation period were used to quantify eggshell pigmentation. Multispectral image analyses were performed to measure variables correlating with protoporphyrin content, such as spot brightness, average spot size, spotting coverage, and spot red chroma. Repeatability analysis indicated that eggshell colouration characteristics were significantly and moderately repeatable between eggs from a single clutch, which suggests that they are under genetic and environmental control. However, none of the pigmentation traits differed significantly between the two types of nest boxes. We speculate about other ecological aspects that might have influenced the observed variability in eggshell pigmentation.