We focus on the Black Harrier Circus maurus, one of the world's rarest harriers (Simmons and Simmons 2000), that exhibits very low genetic diversity \citep{Fuchs2014}. This species is endemic to Southern Africa, with c. 99% of its population in South Africa  \citep{Simmons2005}. The Black Harrier population has undergone a long-term reduction in numbers due to habitat loss over the last century \citep{Curtis2004,Taylor2015}.
Elsewhere in the world, the effect of wind energy facilities on other harriers (Circus spp.) appears to have been relatively minor. Few fatalities are recorded for North American Northern Harriers Circus hudsonius (7 deaths in 17 years at Altamont:  \citep{b2008} and from the three Circus species found in Europe \citep{frank2011,Wilson_2016}. However, in the secondary literature there are over a hundred mortality records of European harriers \citep{2006,a2014,brandeburg2020}, putting them in the top 25% of raptors experiencing wind farm deaths \cite{brandeburg2020}. The reason why relatively few harrier could be that they "show particular caution around turbines" (\citealt*{Smallwood_2009}) or breeding birds tend to move away from operational wind farms \citep{Dohm_2019}. Hen Harriers breeding in Ireland tended to move away from operational turbines and few fatalities were recorded over a decade long study \citep{Wilson_2016}. The same was found with Montagu's Harriers  Circus pygargus  followed with GPS trackers breeding near wind farms which showed significant macro-avoidance behaviours around turbines \citep{Schaub_2020}. With its small, range-restricted population, the Black Harrier could be critically impacted by both mortality and displacement. It is therefore important to predict the consequences of impacts associated with wind energy production, as well as identify knowledge gaps that hinder our understanding of the population dynamics of this species, and consequently, our conservation efforts.
We conduct a population viability assessment for the Black Harrier adopting an integrated population modelling approach. Population viability analysis, based on population matrices is a widely adopted approach to predict the evolution of populations under different scenarios \citep{Boyce_1992,May_2019}. Integrated population modelling allows estimation of life history parameters and population numbers from different data sets simultaneously in the same model. This provides important benefits in terms of the number of parameters that can be estimated, as well as in the precision of the estimates \citep{Schaub_2010}. However,  one of the main obstacles when conducting a population viability assessment is the availability of detailed demographic data for the species of interest, which could compromise the quality of the assessment \citep{Brook_2000,Coulson_2001}.  We overcame the need to have detailed count data to estimate different life history parameters by using presence/absence data collected during the South African Bird Atlas Project (SABAP2, \citealt{Brooks2020}) to fit a Bayesian dynamic occupancy model.  However, our main objective is not to estimate occupancy probabilities \citep[see][]{Royle_2007}, but to investigate changes in the population underlying occupancy, and how these changes relate to specific life history parameters \citep{Royle2003,Rossman_2016}. We allow the model to simultaneously estimate population size and life history parameters, but we use information published on the breeding ecology and satellite-tracked movements of the Black Harrier \citep{Curtis2004,Simmons2005,Garcia_Heras_2016,Garcia_Heras_2017,Garcia_Heras_2019} to define sensible priors for the model parameters. With a model for the population dynamics, undertake a population viability assessment for the species using Monte Carlo simulations to forecast scenarios under different levels of added mortality produced by wind farms.