The use of trail cameras to monitor species inhabiting artificial nest boxes

Using live videography observation and Bayesian isotope mixing model to identify food composition and dietary contribution to inorganic mercury and methylmercury intake by songbird nestlings

Mercury (Hg) exposure is increasing in terrestrial birds; however, studies on its sources are scarce. In the present study, we elucidated the food composition of green-backed tit nestlings from three urban forest parks (CPL, AHL, and LCG) using live videography observation (LVO). Furthermore, the daily dietary intakes of inorganic Hg (IHg) (MDIIHg) and methylmercury (MeHg) (MDIMeHg) were determined using the Bayesian isotope mixing model (BIMM) to uncover the nestlings' specific dietary Hg contribution. Both LVO and BIMM indicated that Lepidoptera (primarily caterpillar) constituted the primary food source for the nestlings in the three forests, accounting for approximately 60% of their diet in all three forest parks. The estimated MDI of Hg revealed that lepidopterans and spiders primarily contributed to IHg exposure, with a co-contribution ratio of 71.8%-97.7%. Unexpectedly, dietary MeHg was mostly derived from spiders; the highest contribution ratio of 93.6% was recorded at CPL, followed by another peak ratio of 92.9% at LCG. However, the dietary exposure was primarily IHg, accounting for 69.8% (AHL), 62.0% (LCG), and 61.3% (CPL) of the nestlings. Our study findings highlight the importance of dietary IHg transfer in evaluating the effects of Hg in nestlings. LVO, coupled with BIMM, is an effective tool for determining the food compositions of songbird nestlings and estimating the contribution of specific diets.

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.

The importance of population contextual data for large-scale biomonitoring using an apex predator: The Tawny Owl (Strix aluco)

Top predators are often used as sentinel species in contaminant monitoring due to their exposure and vulnerability to persistent, bioaccumulative and, in some cases, biomagnificable contaminants. Some of their ecological traits can vary in space and time, and are known to influence the contamination levels and therefore information on ecological traits should be used as contextual data for correct interpretation of large-scale contaminant spatial patterns. These traits can explain spatiotemporal variation in contaminant exposure (traits such as diet and dispersal distances) or contaminant impacts (traits such as population trend and clutch size). The aim of our research was to review the spatial variation in selected contextual parameters in the Tawny Owl (Strix aluco), a species identified by the COST Action European Raptor Biomonitoring Facility as one of the most suitable candidates for pan-European biomonitoring. A considerable variation in availability of published and unpublished contextual data across Europe was found, with diet being the most extensively studied trait. We demonstrate that the Tawny Owl is a suitable biomonitor at local scale but also that taking spatial variation of other contextual data (e.g. diet) into account is necessary. We found spatial gaps in knowledge about the species ecology and biology in Southern Europe, along with gaps in certain population parameters (e.g. population trends) in several countries. Based on our findings, we proposed a minimal recommended scheme for monitoring of population contextual data as one of the first steps towards a pan-European monitoring scheme using the Tawny Owl.