DOI: 10.5061/dryad.kkwh70s42
title: Changes in the Montagu’s Harrier Circus pygargus diet in Eastern Poland across decades promote insects and reptilians, but not birds and rodents

description: We investigated temporal changes in diet composition of the Montagu’s
 Harrier Circus pygargus breeding in natural habitat (calcareous peat bog)
 in SE Poland. We characterized diet composition in a three-year period
 (2007-2009), based on pellet analyses. We investigated whether diet
 composition was affected by years or stage of breeding. We compared diet
 of the studied population between 2000s and 1990s and with other
 populations. We found that the food of the studied population was
 dominated by insects and mammals (by number) and mammals and birds (by
 biomass). Biomass and abundance of main prey items differed between
 studied years because of different air temperatures. We found some
 interannual differences in contribution of some prey items including
 higher number of thermophilic prey (insects and amphibians) in warmer
 years. Comparison of pellet composition in the 1990s and 2000s revealed
 significant increase in the abundance of thermophilic prey (insects,
 reptiles) and decrease of mammals including Microtus voles and birds.
 Those changes may be linked to habitat changes in areas neighboring peat
 bogs and climate change induced changes in prey communities. The studied
 population was able to respond to changes in foraging habitats and prey
 composition by opportunistic foraging on easily available prey. The diet
 of the studied population is the most similar to the geographically
 closest populations foraging in similar habitats and characterized by high
 contribution of insects.
description: We reconstructed diet composition of the Montagu’s Harrier
 breeding in calcareous peat bogs near Chełm in SE Poland based on prey
 remains in pellets. We collected them from spring to summer in 2007, 2008
 and 2009. Pellets were collected from the railway embankment crossing the
 “Bagno Sereberyjskie” reserve. We
 disintegrated collected pellets in order to extract all the solid
 material, for example, bones, beaks, scales and insect remains. We
 determined prey items using keys for the identification of mammals and
 birds. We identified mammals by bones and teeth, birds by bones, beaks and
 feathers, and lizards by skulls, jaws, skin and scales. We grouped Insects
 not identified to the species level into the three most frequent taxa
 (Coleoptera, Hemiptera, Tettigonideae). To avoid possible biases
 associated with a secondary predation, we excluded remains of small
 beetles from the analysis when they were found together with lizard scales
 or bird remains in the same pellets. As many collected pellets in the
 field were broken, to avoid multiplication of prey number from fragmented
 pellets we pooled all pellet fragments collected during one visit to form
 one sample. We estimated abundance of particular prey items in all pellets
 collected during one sampling. We estimated biomass of particular prey
 item categories based on literature data. We collected
 pellets in the consecutive stages of the Monatgu's Harier breeding
 season. We considered the period 15 April - 15 May as a pre-laying period,
 16 May – 15 June as incubation, 16 June – 15 July as chick rearing period,
 16 July – 15 August as post-fledging period. To
 characterize climatic/meteorological conditions in particular stages of
 the Montagu’s Harrier breeding period we collected data from the closest
 meteorological station in Włodawa (40 km north of the studied area) from
 https://www.tutiempo.net/. We considered the following daily parameters:
 average temperature [<sup>o</sup>C], maximal temperature
 [<sup>o</sup>C], minimal temperature
 [<sup>o</sup>C], average relative humidity [%], and total
 precipitation [mm].
description: See more details in the file Read_me.txt