Summary 1.The capercaillie Tetrao urogallus and black grouse Tetrao tetrix are declining in the UK, and low breeding success has been identified as the key factor in the decline of the former. To investigate possible causes, breeding productivity was studied in relation to predation, weather, vegetation changes and deer numbers over an 11-year period (1989-99) within native pinewood at Abernethy Forest, Scotland. The abundance of predators (crows Corvus corone and red foxes Vulpes vulpes ) was experimentally manipulated in 1992-96 by culling. Productivity (chicks reared per female) was compared between forests with and without experimental predator management. 2. During predator control, the number of breeding crows was reduced from 10 pairs to one. The attempted reduction in red fox abundance was unsuccessful; only small numbers of adults were killed, and neither scat nor den counts declined significantly. 3. Predation on artificial nests containing six hen eggs and a hen egg filled with wax was measured as an index of predator activity from 1991 to 1999. Predation was lowest during the last three years of predator control, 1994-96. Predators could sometimes be distinguished by signs on depredated eggs. Predation on artificial nests by crows was highest during 1991-93. However, after predator removal stopped in 1997 few crows returned, and increased predation on artificial nests did not involve increased signs of crow predation. Pine marten Martes martes numbers increased during the study period and became significant predators of artificial nests. 4. The total number of capercaillie eggs and nests depredated by crows was estimated from the number of depredated capercaillie eggs found and the proportion of crowpredated hen eggs in artificial nests. The values ranged from 18 to 158 eggs over 3 years, equivalent to 3-23 capercaillie nests year − 1 . 5. Capercaillie productivity was low (< 1 chick per female) during 1989-93 and 1997-99 but higher during 1994 -96. Compared with nine other forests in Scotland, changes in capercaillie productivity at Abernethy were different. Productivity at Abernethy was negatively related to June rainfall, and to the minimum daily predation rate on artificial nests by crows. There was also a significant interaction in that capercaillie were most productive when low rainfall coincided with low predation by crows on artificial nests. 6. The productivities of black grouse and capercaillie were positively correlated, but greater in the former. As in capercaillie, black grouse productivity was negatively related both to June rainfall and the minimum daily predation rate on artificial nests by crows, and there was an interaction. 7. Synthesis and applications . The long-term increase in crows and red foxes and the predicted increase in rainfall in Scotland may have negative effects on capercaillie and black grouse. In the short term, control of crows is likely to improve productivity. In the long term, increased woodland size and some reversal of fragmentation might decrease the access...

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The breeding biology and cone size selection of crossbills was studied mainly during 1995 to 2002 at Abernethy Forest, Scotland, an ancient native Scots pine Pinus sylvestris wood, where only a single crossbill species, the Scottish crossbill Loxia scotica, was assumed to occur and to be adapted to feed on seeds in Scots pine cones. However, three crossbill species (common Loxia curvirostra, Scottish and parrot crossbills Loxia pytyopsittacus) nested in some years, with the parrot crossbill being the most abundant. Most nests were in old large pines, with the three crossbill species not differing in their use of tree size or stand density for nesting. The mean clutch and brood sizes were 3.8 and 2.9, and their mean survivals were 86 and 74%, respectively, with no significant differences among species. The timing of breeding differed between species, with parrot crossbills breeding earliest (median date 21 March, including second attempts) and common crossbills breeding last (median date 21 April), probably in response to the differing accessibility of Scots pine seeds to these species. The difference in the time of breeding may reduce mixed mating. Crossbills foraged preferentially on trees with small cones when the cones were closed. Small cones had thinner scales than large cones, suggesting that the preference for small cones was related to higher feeding rates on these cones when cones are closed. Such a preference was also found for captive crossbills with the Scottish crossbill showing a more pronounced preference for smaller cones than the larger‐billed parrot crossbill. However, crossbills selected larger cones within trees and trees with larger cones once the cones opened in April. Such a shift occurred presumably because variation in scale thickness has little impact on seed accessibility once cones open, and larger cones have larger and more seeds. The greater ability of parrot crossbills to exploit seeds in closed Scots pine cones allowed parrot crossbills to start breeding earlier and to have young when seeds were most accessible. Only after the cones opened were the smaller‐billed common crossbills able to easily access seeds and to start breeding. The time of breeding of Scottish crossbills was intermediate between common and parrot crossbills, and they probably had an intermediate ability to exploit Scots pine cones. The reason why there were few Scottish crossbills nesting in Abernethy Forest remains a puzzle, considering that native pine wood is assumed to be the ancestral habitat to which the Scottish crossbill is adapted. The breeding season for all crossbills ended in June, when most of the seed from a given cone cohort was shed. This is when starved broods were found, not associated with bad weather.

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