Seasonal variation in lek attendance and lekking behaviour by male Black Grouse Tetrao tetrix.
Eleven Black Grouse Tetrao tetrix leks in the Scottish Highlands were visited at dawn once every week for a year. Apart from July and three leks which were unoccupied in winter, males visited leks throughout the year. Total numbers of males attending leks peaked in March in one study area (six leks) and in April in the second (five leks). The number of males present and the proportion of leks occupied varied seasonally. The proportion of males at leks was at a maximum in April (80% of males) when all leks were attended, with a secondary peak in September when 60% of leks had males present. Males spent the most time displaying in April. The optimal conditions for attendance were calm, dry mornings just after dawn. Most reliable counts of numbers of males were those made between the last week of March and the end of the first week of May.
Black Grouse Tetrao tetrix typically exhibit the arena type of displaying behaviour described by de Vos (1978). Where each male defends a small territory situated within a tight cluster of territories called a lek. From within these territories, males attempt to attract females for copulation. Females tend to visit leks only in spring. Despite this, males attend leks and can be seen displaying towards rival males at most times of the year (Kruijt & Hogan 1967).
Few studies have attempted to examine in detail the degree of variation in lek attendance throughout the year. Repeated counts of males at four leks in North Wales in one spring showed that maximum numbers of males were present in April and early May (Cayford & Walker 1991). However, these observations were restricted to the period March to June.
This study describes the annual pattern of lek attendance at dawn, variations in the intensity of displaying and how this may vary both between leks and in relation to weather. I suggest when surveys of displaying males should be conducted for census work.