Having written about young birds avoiding the leks earlier in the week (see below), the situation became a little bit clearer while I was up doing a quick tour of leks in Angus and Kincardineshire. It is important to say from the outset that birds in prosperous areas behave very differently to the birds that I am used to seeing in Dumfries and Galloway, but the principle remains the same: that black grouse had a very productive year in 2013, but the number of displaying cocks (which, for better or worse, we use to determine population size) this spring does not reflect this. This is borne out by my personal observations of 20 leks this spring, as well as notes from friends and fellow enthusiasts. Perhaps it is not true everywhere in the country, but with so many young birds on the go, it is susprising how few of them have been seen at the leks.
By comparison to the “weird” south west (of which more to come), I had a chance to see where the young cocks go in April when there are lots of them. The answer in some cases seems to be that they start their own leks. In north east Scotland, the fruit of several large broods might add up to a dozen cocks in April, and the cohesion between these youngsters allows them in some cases to make a mini-community, particularly if the established local lek is made up of crotchety oldsters who don’t take kindly to first year cocks. This seems to lead to an age-based division in cock packs so that some are “old bird leks” and others are “young bird leks”.
One moor near Banchory had some very clear cut divisions between leks made up of old birds and leks made up of youngsters. One lek was made up of ten old birds and one youngster. Another lek was made up of six birds, five of which were in their first year and the remaining one was a 2012 bird.
Leks are almost always made up of directly related cocks; fathers, sons, brothers, uncles and grandfathers. This is because cocks are normally recruited to the “local” lek, and this is usually the lek that they were conceived upon. Greyhens usually nest within a short distance of the lek site (less than 1Km), so depending upon a reasonably small range while rearing the young poults, the chances are in a healthy population that the cocks will go straight into the local cock pack when they colour up. One or two might be absorbed by the neighbouring group, but this exchange will probably end up with a net balance.
In this way, these “young bird leks” have a simple explanation in terms of their formation; one or two young cocks fail to join the main lek (for a range of possible reasons) and begin to display with each other on a site of their own choosing, away from the main body of birds. They serve a couple of greyhens during the course of the season, and their sons are directly recruited straight back into this new group come autumn. Say, for example, that two cocks call in two greyhens and serve them both in the first year of the new lek. With a good rearing season there is no reason why their male offspring from both broods should not number six or seven in October, and four or five in April. In a short period from the inception of the new lek to its second year of existence, it can grow very dramatically, and this is without young cocks wandering in from the neighbours in the autumn.
Perhaps it is unlikely that a whole new lek could spring up without any human being noticing it, but in a situation where the focus is always on counting established leks, it is certainly possible. Assuming that (in the main) they are counted, it could mean that figures for black grouse lek counts in areas like Angus and Aberdeenshire will shoot up for 2014, whereas they might wallow in the doldrums in less well populated areas. As above, this would not be a truly accurate picture of the real situation, since behavioural mechanisms at work behind the scenes make it easier to register a sudden boost in a prosperous population than in a sparse one.
There are many problems facing single birds in Dumfries and Galloway, and while they are no doubt alive after this past winter, their ability to procreate and contribute to the gene pool is limited by their isolation and solitude. Circumstances have dictated that the birds which were produced during the long, hot summer of 2013 are not showing up on the established leks, but if “normal”, productive, communal behaviour doesn’t kick in in later life (and it seldom does), then perhaps they are not worth counting anyway. Much will rest on this summer’s weather, and whether or not we can produce a new wave of poults to bolster these lonely pioneers.