We used the following conventions: i) population censuses are conducted post-breeding,  ii) years span the period from one breeding event to the next, iii) birds breed on their birthday once they reach sexual maturity, iv) there is an even sex ratio of males and females, and v) we assume a spatially homogeneous population. Each year harriers go through three phases: survive, age and reproduce, in that order. This means that a fledgling that survives the first year, becomes a sub-adult, and a surviving sub-adult, an adult. It also means that a sub-adult individual that survives the year, becomes and adult and is immediately capable of breeding. This is important to ensure that sub-adult individuals in a given year will be able to reproduce in the following year as adults (see figure \ref{316349} and  \citealt{Kendall_2019}).