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Combining data from multiple sources to design a raptor census - the first national survey of the Montagu’s Harrier Circus pygargus in Poland


The effective conservation management of vulnerable taxa requires up-to-date evaluation of population size. Montagu’s Harrier Circus pygargus is a farmland raptor of high conservation concern and threatened by agricultural intensification. However, within many European countries, including Poland, the status of this species remains unknown or questionable and information on its breeding is incomplete or imprecise. Here, we estimate the size of the national population of the Montagu’s Harrier and argue that using data from multiple sources may help to design national bird surveys and better contribute to identifying population trends. We built a predictive model based on a presence-absence data obtained by volunteer-based citizen-science projects conducted in Poland during 2000–2012. Afterwards, from the set of 10 km x 10 km squares of high predicted habitat suitability, 100 sampling plots were randomly chosen and regularly surveyed by experienced ornithologists in 2013 and 2014. The evaluation of fieldwork efficiency by the double-observer approach allowed detectability to be estimated and accounted for while estimating population size. We estimated the Polish Montagu’s Harrier population at almost 3,400 breeding pairs (95% CI: 2,700–4,300), thus constituting 20% of the European Union (EU) population. Furthermore, we showed that public-gathered data originating from multiple sources offered great potential for regular surveys to obtain large-scale estimates of population size.

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Arroyo, B. and García, J. (2007) El aguilucho cenizo y el aguilucho pálido en España. Población en 2006 y método de censo. Madrid, Spain: SEO BirdLife.
Arroyo, B., García, J. T. and Bretagnolle, V. (2002) Conservation of the Montagu’s Harrier (Circus pygargus) in agricultural areas. Anim. Conserv. 5: 283290.
Avilés, J. M. and Parejo, D. (2004) Farming practices and Roller Coracias garrulus conservation in south-west Spain. Bird Conserv. Internatn. 14: 173181.
Bashta, A-T. and Domashevsky, S. (2009) Distribution and protection of Montagu’s Harrier Circus pygargus in Ukraine. Pp. 335342 in Wiącek, J., Polak, M., Kucharczyk, M., Grzywaczewski, G. and Jerzak, L., eds. Ptaki - Środowisko - Zagrożenia - Ochrona. Wybrane aspekty ekologii ptaków. Lublin, Poland: LTO.
BirdLife International (2004) Birds in Europe: population estimates, trends and conservation status. Cambridge, UK: BirdLife International. (Conservation Series No. 12).
BirdLife International (2015) European Red List of birds. Luxembourg: Office for Official Publications of the European Communities.
BirdLife International (2016) Species factsheet: Circus pygargus. Downloaded from on 09/11/2016
Braunisch, V. and Suchant, R. (2010) Predicting species distributions based on incomplete survey data: the trade-off between precision and scale. Ecography 33: 826840.
Breiman, L. (2001) Random forests. Machine learning 45: 532.
Butet, A. and Leroux, A. B. A. (2001) Effects of agriculture development on vole dynamics and conservation of Montagu’s harrier in western French wetlands. Biol. Conserv. 100: 289295.
Chodkiewicz, T., Kuczyński, L., Sikora, A., Chylarecki, P., Neubauer, G., Ławicki, Ł. and Stawarczyk, T. (2015) Ocena liczebności populacji ptaków lęgowych w Polsce w latach 2008–2012. Ornis Polonica 56: 149189.
Cormier, J.-P., Fustec, J., Pithon, J. and Choicy, P. (2008) Selection of nesting habitat by Montagu’s Harriers Circus pygargus and Hen Harriers Circus cyaneus in managed heaths. Bird Study 55: 8693.
Estrada, A. and Arroyo, B. (2012) Occurrence vs abundance models: Differences between species with varying aggregation patterns. Biol. Conserv. 152: 3745.
García, J. T. and Arroyo, B. E. (2002) Population trends and conservation of Montagu’s Harrier in Spain. Ornithologisher Anzeiger 41: 183190.
Głowaciński, Z., ed. (2001) Polska Czerwona Księga Zwierząt. Warszawa, Poland: Państwowe Wydawnictwo Rolnicze i Leśne.
He, H. and Garcia, E. A. (2009) Learning from imbalanced data. IEEE Transactions on Knowledge and Data Engineering 21: 12631284.
Kitowski, I. (2002) Present status and conservation problems of Montagu’s Harrier in southeast Poland. Ornithologisher Anzeiger 41: 167174.
Kragten, S., Tamis, W. L. M., Gertenaar, E., Midcap Ramiro, S. M., van der Poll, R. J., Wang, J. and de Snoo, G. R. (2011) Abundance of invertebrate prey for birds on organic and conventional arable farms in the Netherlands. Bird Conserv. Internatn. 21: 111.
Krupiński, D. (2013) Błotniak łąkowy Circus pygargus. Pp. 3540. in Zawadzka, D., Ciach, M., Figarski, T., Kajtoch, Ł. and Rejt, Ł., eds. Materiały do wyznaczania i określania stanu zachowania siedlisk ptasich w obszarach specjalnej ochrony ptaków Natura 2000. Warszawa, Poland: GDOŚ.
Krupiński, D., Lewtak, J. and Kuczyński, L. (2015) Krajowy Plan Ochrony Błotniaka Łąkowego. Warszawa, Poland: The Society of Nature Protection “Stork”.
Kuczyński, L. and Chylarecki, P. (2012) Atlas pospolitych ptaków lęgowych Polski. Rozmieszczenie, wybiórczość siedliskowa, trendy. Warszawa, Poland: GIOŚ.
Le Rest, K., Pinaud, D. and Bretagnolle, V. (2015) Volunteer-based surveys offer enhanced opportunities for biodiversity monitoring across broad spatial extent. Ecol. Informatics 30: 313317.
MacKenzie, D. I., Nichols, J. D., Royle, J. A., Pollock, K. H., Bailey, L. L. and Hines, J. E. (2006) Occupancy estimation and modeling: Inferring patterns and dynamics of species occurrence. San Diego, USA: Academic Press.
McGarigal, K. and Marks, M. (1995) Spatial pattern analysis program for quantifying landscape structure. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station.
Millon, A., Bretagnolle, V. and Leroux, A. (2004) Busard Cendré. Circus pygargus. Pp. 7074 in Thiollay, J. M. and Bretagnolle, V., eds. Rapaces nicheurs de France. Distribution, effectifs et conservation. Paris, France Delachaux et Niestlé.
Nichols, J. D., Hines, J. E., Sauer, J. R., Fallon, F. W., Fallon, J. E. and Heglund, P. J. (2000) A double-observer approach for estimating detection probability and abundance from point counts. The Auk 117: 393408.
Plummer, M. (2003) JAGS: A program for analysis of Bayesian graphical models using Gibbs sampling. Pp. 20–22 in Proceedings of the 3rd International Workshop on Distributed Statistical Computing (DSC 2003).
Poprach, K., Machar, I. and Vrbková, J. (2013) Population trend, distribution and habitat requirements of the Montagu’s Harrier (Circus pygargus) in central Moravia (Czech Republic). Sylvia 49: 111134.
R Development Core Team (2015) R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing.
Robinson, R. A., Morrison, C. A. and Baillie, S. R. (2014) Integrating demographic data: towards a framework for monitoring wildlife populations at large spatial scales. Methods Ecol. Evol. 5: 13611372.
Royle, J. A. and Dorazio, R. M. (2012) Parameter-expanded data augmentation for Bayesian analysis of capture–recapture models. J. Ornithol. 152: 521537.
Royle, J., Kéry, M., Gautier, R. and Schmid, H. (2007) Hierarchical spatial models of abundance and occurrence from imperfect survey data. Ecol. Monogr. 77: 465481.
Santangeli, A., Arroyo, B., Millon, A. and Bretagnolle, V. (2015) Identifying effective actions to guide volunteer-based and nationwide conservation efforts for a ground-nesting farmland bird. J. Appl. Ecol. 52: 10821091.
Santangeli, A., Di Minin, E. and Arroyo, B. (2014) Bridging the research implementation gap – Identifying cost-effective protection measures for Montagu’s harrier nests in Spanish farmlands. Biol. Conserv. 177: 126133.
Sikora, A., Rohde, Z., Gromadzki, M., Neubauer, G. and Chylarecki, P., eds. (2007) Atlas rozmieszczenia ptaków lęgowych Polski 1985-2004. Poznań, Poland: Bogucki Wydawnictwo Naukowe.
Sim, I. M. W., Gibbons, D. W., Bainbridge, I. P. and Mattingley, W. A. (2001) Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 1998. Bird Study, 48: 341353.
Su, Y-S and Yajima, M. (2015) R2jags: Using R to Run “JAGS.” Available from (accessed November 22, 2016).
Sullivan, B. L., Wood, C. L., Iliff, M. J., Bonney, R. E., Fink, D. and Kelling, S. (2009) eBird: a citizen-based bird observation network in the biological sciences. Biol. Conserv. 142: 22822292.
Terraube, J., Arroyo, B. E., Mougeot, F., Katzner, T. E. and Bragin, E. A. (2010) Breeding biology of Montagu’s Harrier Circus pygargus in north-central Kazakhstan. J. Ornithol. 151: 713722.
Tomiałojć, L. (1990) Ptaki Polski. Rozmieszczenie i liczebność. Warszawa, Poland: PWN.
Tomiałojć, L. and Stawarczyk, T. (2003) Awifauna Polski. Rozmieszczenie, liczebność i zmiany. Wrocław, Polskie Towarzystwo Przyjaciół Przyrody ‘pro Natura’.
Tóth, L. (2002) Historical and recent distribution, population trends and protection strategies of Montagu’s Harrier Circus pygargus in Hungary. Ornithologisher Anzeiger 41: 109117.
Trierweiler, C. (2010) Travels to feed and food to breed: The annual cycle of a migratory raptor, Montagu’s Harrier, in a modern world. PhD Thesis, Rijksuniversiteit Groningen.
Trierweiler, C., Drent, R. H., Komdeur, J. and Koks, B. J. (2010) Home range size and habitat selection of the endangered Montagu’s harrier Circus pygargus in NW-Europe: implications for conservation. In Trierweiler C. (2010) Travels to feed and food to breed. PhD Thesis, Rijksuniversiteit Groningen.
Tulloch, A. I. T., Possingham, H. P., Joseph, L. N., Szabo, J. and Martin, T. G. (2013) Realising the full potential of citizen science monitoring programs. Biol. Conserv. 165: 128138.
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