Another factor to consider is that as Black Harrier population decreases, density dependent regulatory mechanisms might come into play. There is no evidence of this type of mechanism acting on Black Harrier populations at present, but it does play a role among other raptor species \citep{SIMMONS_1993,2002,Elliott_2011}, influencing both productivity and age at first breeding, which may have a significant impact on rare or recovering populations \citep{Morandini_2019}.