Anthropogenic materials in the nests of Passerine birds: does the environment matter?

Background. For several past decades, a notable pollution of the environment by different kinds of solid waste has been noted. The number of studies addressing the issue of utilising debris for nest construction by various species of birds has increased over the past century. It is important to understand the extent to which anthropogenic transformation of the environment in the form of debris affects the nest-building beha­viour of birds and the architecture of the nest itself. In our research we analyse how the pollution of the environment with solid household waste affects the appearance of the debris in bird nests. Materials and Methods. Materials for this article included 520 nests of 44 passe­rines species. Nests were collected unevenly during the last two decades (2002–2024) in different types of habitats mainly across the western part of Ukraine and in Poland. Collected after the breeding season, nests were decomposed in a laboratory and nest components were identified as natural (grass, plant stems, tree leaves, grass roots, moss, mammals’ hair, bird feather and others) and anthropogenic (threads, synthetic fibres, plastic ropes, fishing line, cigarette filters, paper, tissue, wires and others), and their percentage by volume was defined. Results and Discussion. Birds in the human settlements used debris for nest construction more often. The number of nests with debris in natural environment was the lowest and debris were found there in very small amounts. Even a sufficient amount of natural nest materials in the environment does not prevent birds from using debris. Part of nests collected in the natural environment included debris indicating environmental pollution in the surrounding area. There was a significant difference in the presence, amount and number of kinds of debris in the nests collected in different environments. In the natural environment far from human settlements, the proportion of nests with debris (6.6 %), the number of kinds (mean ± standard error 0.08±0.02; median value 0.00, Q1-Q3 values 0.00–0.00, n = 293) (further the numbers are presented as mean ± standard error; median value, Q1–Q3 values, n) and amount (0.07±0.04 % by volume; 0.00 %, 0.00–0.00 %, n = 293) were the lowest. In the natural environment far from human settlements, debris still was present in nests, indicating the presence of pollution in such territories and demonstrating birds’ ability to use debris, intentionally or unintentionally, even if natural nest materials are readily available. Nests with debris collected on the outskirts are relatively high (63.2 % of nests), the number of kinds (1.12±0.10; 1.00, 0.00–2.00, n = 163) and amount (4.90±0.85 % by volume; 0.10 %, 0.00–4.00 %, n = 163) in debris, which may indicate randomly polluted environment as well as a presence of garbage dumps outside human settlements. Debris in bird nests usually appeared in populated areas, where it is available and accessible in significant quantities. Most frequently, debris was found in passerine bird nests within human settlements (87.5 % of nests), however some nests did not include debris. The number of kinds of anthropogenic materials (ANMs) incorporated in the nests was the highest in populated areas (2.22±0.19; 2.00, 1.00-3.00, n = 64); it was more numerous in cities and towns (3.04±0.30; 3.00, 2.00–4.00, n = 25) than in villages (1.69±0.21; 1.00, 1.00–2.00, n = 39). The amount of debris in the nests was also the highest in human settlements (5.52±0.89 %; 2.00 %, 0.10–8.50 %, n = 64), being higher in cities and towns (6.93±1.22 %; 6.00 %, 2.00–10.00 %, n = 25) than in villages (4.62±1.23 %; 1.00 %, 0.10–5.00 %, n = 39). Turdus merula from human settlements used debris a lot (92.9 % of nests). On the outskirts, 40.0 % of nests still contained debris (we assume that the number of nests in every environment is 100%), whereas in natural environment its nests consisted only of natural materials. On the outskirts, blackbird nests contained fewer kinds (0.50±0.22; 0.00, 0.00–1.00, n = 10) and a smaller amount (0.08±0.05 %; 0.00 %, 0.00–0.10 %, n = 14) of debris than in human settlements (3.00±0.50; 3.50, 1.00–4.00, n = 14; 7.30±1.55 %; 7.50 %, 3.00-10.00 %, n = 14). Conclusion. The environment affects the presence of debris in bird nests. In the anthropogenic environment (human settlements) the share of nests with debris, the amount and number of kinds of debris were the highest. Birds do not always use ANMs in the polluted environment. On the other hand, even when the amount of natural materials was sufficient, birds could include debris into their nests.