We considered that mean survival rates are constant across years, because we have not found information to guide other hypothesis. To inform our estimates on adult survival rates we fitted an exponential survival curve to observations from \citet{Garcia_Heras_2019}, who confirmed 3 fatalities out of 13 tracked breeding birds (followed for an average of 365 days). There is no information with regards to juvenile survival of Black Harriers, because of the poor return rate (six birds) from 465 ringed harriers in the national ringing scheme \citep{SAFRING2020}. Thus, we simply assumed lower survival rates for birds in their first year than older birds, as found for other species of harriers from Europe \citep{Arroyo_2002,Etheridge_1997,Newton_2016}.