Abstract
Simple SummaryThe population of goshawks crashed in the middle of the 20th century due to persecution, forest management practices, and the usage of toxic pesticides (DDT) in agriculture. Now, it has rebuilt, yet the population trend is not equal across countries. Here, we focused on a goshawk population in central Poland for which monitoring started in the 1980s (high densities were recorded at that time of 16.3 pairs/100 km2) to see how changing environmental factors influenced the current population trend. In the field and forest mosaic, these birds build their nests in small forest complexes, but important prey tend to be caught near farmsteads. This has previously resulted in the persecution of the birds by farmers. Anthropogenic food (poultry and domestic pigeons) played a key role in their population density. Consequently, when the anthropogenic food base was limited (due to changes in the Polish farmland), population abundance dropped by half. As supplementary prey (including small-game and most corvid species) were not abundant, goshawks could not replace their staple food of anthropogenic origin. This demonstrates the complex way in which socioeconomic changes in agriculture can influence a raptor population: both positively (fewer cases of persecution are being recorded now) and negatively (small-scale breeding of pigeons and poultry became unimportant and unprofitable, and small game abundance decreased due to changes in farming practices and farmland structure). In this study, we focused on a goshawk population in central Poland (study area 105 km2, forests 24 km2, seven small forest complexes) which was monitored long-term (with high densities recorded in the 1980s of 16.3 pairs/100 km2 despite persecution by farmers) to analyse how environmental factors (prey availability and changes in the forest structure) influenced population abundance, breeding parameters, and diet composition. The study was undertaken from 2011–2018, and the results were compared with published data from two previous study periods (1982–1992 and 2001–2003). The number of breeding pairs dropped from 17.1 to 8.0; the breeding success was around 75% in all study periods. The selection of nesting trees followed the changes in stand species and age structure. More nesting attempts per one nest were recorded in the current time period (1.7 vs. 1.1), which probably reflected lower anthropopressure (i.e., no cases of persecution were recorded in this study). Diet composition seemed to follow changes in the prey availability: The share of domestic pigeons and poultry (the main prey in the 1980s) as well as small game dropped, while the share of Eurasian jay and wood pigeon increased. Our studies suggested that anthropogenic food (poultry and domestic pigeons) played a key role for the goshawk population in the transformed habitats of the field and forest mosaic.
Highlights
The goshawk, Accipiter gentilis, is a widespread species inhabiting North America and Eurasia [1,2].Its abundance in Europe fluctuated throughout the first half of the 20th century due to the persecution of raptors by hunters and forest management practices crashing in the 1950s and 1960s due to the usage of highly toxic pesticides (DDT) in agriculture [3,4,5,6,7]
Our studies suggested that anthropogenic food played a key role for the goshawk population in the transformed habitats of the field and forest mosaic
Our study showed that the goshawk population decrease observed in central Poland in the last few years (2011–2018) was combined with a forced diet shift, as a response to changes in anthropogenic prey availability
Summary
The goshawk, Accipiter gentilis, is a widespread species inhabiting North America and Eurasia [1,2].Its abundance in Europe fluctuated throughout the first half of the 20th century due to the persecution of raptors by hunters and forest management practices crashing in the 1950s and 1960s due to the usage of highly toxic pesticides (DDT) in agriculture [3,4,5,6,7]. Since the 1970s, the European population of goshawks started to rise moderately [3,8], yet this trend was not consistent for all countries. In the UK, the goshawk went extinct in the 1980s. It was reintroduced, and its population grew in number; a systematic growth in the forest cover was conducive to this process of population restoration [5,9]. In the USA, the population trend was equivocal [13,14], and many authors pointed to the potentially negative influence of forest management practices on goshawk populations, both in Europe and in North America [6,14,15,16]
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