Study area.
The study was conducted in southern Poland within the Krakow metropolitan area, and comprises three communes of Krakow, Wieliczka, and Niepolomice, representing various levels of urbanisation (Fig. 6, Table 2). The urban commune of Krakow encompasses an area of 327 km2 and has a human population of 779,115 (DSIPM 2020). It is an important transportation hub for major national and international roads, and is bisected by the Vistula River, a natural migration corridor for many wildlife species (Baścik and Degórska 2015). In terms of Krakow’s landcover, built-up and urbanised areas constitute over 45% of the city, with 44% of the city used for agricultural purposes including crops, orchards, meadows and pastures.
Table 2
Main descriptors of the study areas
Commune
|
Level of
urbanisation
|
Total area (km2)
|
Total population
|
Population density (person/km2)
|
Agricultural land (%)
|
Forested land (%)
|
Built-up area (%)
|
Krakow
|
Urban
|
326.9
|
779115
|
2383
|
43.8
|
1.7
|
46.9
|
Wieliczka
|
Suburban
|
99.7
|
60781
|
610
|
73
|
7.8
|
19
|
Niepolomice
|
Suburban
|
96.3
|
29141
|
303
|
67
|
15
|
17
|
Wieliczka and Niepolomice are mainly agricultural and forested suburban communes neighbouring Krakow (Fig. 6), each covering an area of approximately 100 km2, with a population of 60,781 and 29,141 citizens, respectively. In terms of land cover, built-up and urbanised areas constitute approximately 20% and agricultural land constitutes almost 70% in both suburban communes (Table 2).
Wild animals are common in the study area. In urban parks and in forest patches at the outskirts of the Krakow city, red fox, roe deer and wild boar can be found. The common wild animals found in Wieliczka are red deer (Cervus elaphus), roe deer, red fox and Eurasian badger. Niepolomice commune, on the other hand, encompasses the large Niepolomice forest, a special protection area and Natura 2000 site, inhabited by large wild ungulates including moose (Alces alces), red deer, roe deer and wild boar. For this reason, we primarily focused on effect of lockdown on AVC of mammals and have grouped all birds together.
Data collection and processing.
AVC data were collected daily in 2019 and 2020 by KABAN Company under contract from a range of local authorities. KABAN Co., working for Krakow Municipality and the Regional Directorate of Nature Protection in Krakow, was obliged to manage each AVC incident (from birds to large mammals) reported by municipal institutions, such as Police, City Guard Service, District Centre of Crisis Management and Krakow Animal Shelter. All of these institutions have emergency phone numbers that operates 24 hours, 7 days a week, and any AVC incident must legally be reported immediately, especially in the densely inhabited areas. KABAN Co. officers received phone calls from these institutions about AVC and verified each reported incident by visiting the locations followed by undertaking appropriate procedure e.g., translocating the wounded animal to animal shelter. The reporting time between an AVC incident and the phone calls to KABAN Co is approximately 30 minutes (Maciej Lesiak personal information). The details of each AVC including date and location of incident, animal species, incident characteristics and time of reporting were recorded in a database (Table S1).
The exact point addresses were available only for 48% of the AVC, thus, we analysed the locations of AVC in relation to street names, which were provided in all reports. Street network data were obtained from OpenStreetMap (accessed on 29.11.2020), with main streets defined as those of primary, secondary and tertiary road type. We have further divided the study area into smaller regions (n=533), where each region contains a main street with smaller streets connected to it and their neighbouring areas (defined using closest Euclidean proximity rule), which allowed to investigate the change in spatial pattern of AVC. AVC were summarised within these regions with regard to year (2019 and 2020) and month (January-February, March-May, and June).
Traffic volume data (i.e., number of vehicles per hour) were available only from Krakow and were obtained from the Department of City Traffic through the light detection system installed at major roads for the city of Krakow. The detection system counts the number of vehicles crossing the road at 19 major roads in the city and collected data for the entire period on an hourly basis (Table S2). The traffic volume data for Krakow can be, however, use as a proxy to reflect the traffic situation not only within the city itself, but also in the whole agglomeration, as large part of the within-city traffic on major roads is connected with commuters traveling from suburban areas to the city.
Statistical Analysis.
AVC data were analysed using unconstrained (Multidimensional Scaling or, MDS) and constrained (Canonical Correlation Analysis or, CCA) ordination methods. Ordination methods are used in multivariate data for determining differences between samples in a graphical manner. Unconstrained ordination is useful for viewing overall variation in the data (i.e., to represent, the pairwise dissimilarity between objects), whereas constrained ordinations reveal variation of a fixed factor(s) by minimising the effect size of the random factors 18. All data analyses were performed in the R environment 19, using tidyverse 20, Vegan 21 and RVAideMemoire 22 packages. All packages and dependencies were encapsulated in anaconda environment at https://github.com/SAYANTANI26/ProjectAVC/. The detailed data stratification and workflow has been shown in Fig. 7.
Analysis for influence of AVC in urban and suburban areas.
To assess the impact of lockdown associated with COVID-19 on AVC, the AVC data were stratified by location (understood as commune, i.e., Krakow, Wieliczka and Niepolomice), month (January, February, March, April, May, and June), and year (2019 and 2020) (see for data stratification Fig. 7). The stratified data was normalised and scaled to 1 for all further analysis. The MDS analysis was performed by computing pairwise Jaccard index (Hancock 2014) as a distance measure. The dataset was further estimated by CCA using location as constrained variable and conditioned by year. Statistical significance (p≤0.05) of locations was determined by performing PERMANOVA and the variation within location by pairwise PERMANOVA (over 1,000 permutations). The p-value for pairwise analysis was adjusted using the Benjamini–Hochberg (BH) procedure. Next, we represented AVC patterns for each species (mammals and birds) using heat maps for visual inspection. Heat maps generally help to visualise the intensity (high or low) of AVC for each species in three locations. Finally, by generalised linear model (GLM) we analysed the mean difference of AVC between locations and lockdown (fixed factors). The statistical significance was computed by conducting Tukey’s Honest Significance Difference (HSD) test and the p-value was adjusted using the BH procedure. Animal species that showed a mean difference with false discovery rate (FDR) ≤ 0.05 were considered to be significant and the percentage of AVC for those animals were represented in the boxplots.
Analysis for AVC during working hours.
To assess the impact of AVC during working hours, the AVC data was grouped by summing the AVC reports for each day and each month within the 24-hour (h) time period of the corresponding location (commune). The time period was split into six intervals of 4h time periods (00:00 - 04:00h, 04:00 - 08:00h, 08:00 - 12:00h, 12:00 - 16:00h, 16:00 - 20:00h and 20:00 - 00:00h). Additionally, we estimated the total AVC across time by stratifying month, year and location (see for data stratification Fig. 7). The dataset was then treated similarly as in 2.3.1, i.e., normalised to 1, and presented using heat maps for visual inspection. The normalised data was subjected to MDS (with Jaccard index) and CCA analysis with the lockdown and location as constrained factors and day, month and year as random factors. The statistical significance was reported by conducting PERMANOVA on CCA over 1000 iterations. By GLM we analysed the mean difference in AVC reported for specific animals between locations during the lockdown period. The trend of variation in total AVC along the time range was represented by fitting the total AVC by locally estimated scatterplot smoothing (LOESS) method and MDS analysis for respective time period.
Analysis for AVC and traffic volume in the urban area.
Finally, to assess the influence of traffic volume (i.e., number of vehicles per hour) on AVC during the lockdown, the traffic and the AVC dataset (stratified by month and 24h time period) for Krakow was integrated to analyse the association of vehicle movement and its impact on AVC. The traffic volume data was normalised by dividing the number of vehicles (per hour) by 1 000 000 (in million) to ease calculation. We independently compared the datasets for each parameter (animal species, total AVC and traffic volume) within Krakow between the exact months of 2019 and 2020 (fixed factor) and lockdown. By GLM, we analysed the effect of lockdown and year for each parameter and the statistical significance was reported (same as in 3.2.1). The relationship between the traffic volume (converted to per million within 24h time period) and AVC was determined by conducting Spearman's rank correlation (rho) on the respective mean difference and also by combining component 1 and 2 of their MDS analysis.