Timing of breeding in Black Grouse Tetrao tetrix and Capercaillie Tetrao urogallus and distribution of insect food for the chicks.
In Perthshire (Scotland), Black Grouse Tetrao tetrix broods less than 3 weeks old preferred herb-rich grassy flushes with Bog Myrtle Myrica gale, whereas in the northern Pennines (England), all broods were found on grass-dominated moorland or enclosed rough grazing habitats chiefly of grass and rushes. In both areas, broods used habitats with taller vegetation that had more invertebrates, particularly moth caterpillars and sawfly larvae (Symphyta, Hymenoptera). Within preferred habitats, broods were found in vegetation containing more flies (Diptera), plant bugs (Hemiptera) and ichneumon flies (Hymenoptera) than at randomly chosen sites, The main hatch of Black Grouse chicks in Perthshire coincided with the peak availability of moth caterpillars preferred by chicks, Broods in the Pennines hatched 1 week later than those in Scotland, and this later breeding in the south may be an adaptation to utilize the later peak biomass of sawfly larvae, the chief insect prey there . Data collected for Capercaillie Tetrao urogallus suggest a similar degree of synchronization between their peak hatch and the availability of moth caterpillars on Bilberry Vaccinium myrtillus.