KIN LANDOWNERSHIP, DIFFERENTIAL AGGRESSION BETWEEN KIN AND NONKIN, AND POPULATION FLUCTUATIONS IN RED GROUSE

1. Previous work on red grouse (Lagopus lagopus scoticus) on a north-e ast Scottish moor showed that recruitment of young to the territorial population in autumn largely determined changes in numbers between spr ings. 2. This paper analyses territory locations of individually marke d fathers and sons during a big cyclic-type population fluctuation in 1969-77. 3. In years of increasing numbers, sons took territories clos e to their fathers. When fathers did not keep their territories for an other year, sons took territories on or close to their natal territori es. In years of declining numbers, kin moved further from their natal areas to establish territories. 4. This fits ideas that some animal po pulations comprise distinct sub-populations or demes. It is consistent with a model whereby changes in recruitment depend partly on the size of such demes, and cyclic declines in numbers are due to greater stri fe because demes are smaller and neighbouring cocks less closely relat ed than during the increase phase. 5. Over the winter, territorial coc ks had a lower rate of aggressive boundary disputes with territorial n eighbours which were close kin than with those which were not closely related. 6. During two population fluctuations, the rates of territori al cocks' song flights and boundary disputes in winter were related to the young cocks' relative recruitment rate to the territorial populat ion. Thus, winter interaction rates were low in winters when enough yo ung cocks had been reared in the population to supply the observed rec ruitment, and high when the observed recruitment must have included im migrants. 7. The dispute rate also tended to reach its maximum one yea r after peak densities, and then to decrease.