Factors influencing nest-site choice\ud and reproductive success in Cyanistes\ud caeruleus (blue tit), Parus major (great tit)\ud and Ficedula hypoleuca (pied flycatcher):\ud A study based at Nagshead RSPB Nature Reserve,\ud Gloucestershire, U. K

This research examines factors influencing avian reproductive biology in three co-occurring\ud woodland passerines, Cyanistes caeruleus (blue tit), Parus major (great tit), and Ficedula hypoleuca\ud (pied flycatcher), breeding in nestboxes at Nagshead Nature Reserve (Gloucestershire, U. K. ). The\ud study uses breeding data on the study species collected by the Royal Society for the Protection of\ud Birds (RSPB) between 1990 and 2004, together with site-based ringing records for F. hypoleuca and\ud primary data from field and laboratory work undertaken during 2005 and 2006.\ud Breeding productivity of C. caeruleus and P. major declined over the study period, despite breeding\ud populations that were increasing (C. caeruleus) and stable (P. major). The breeding population of\ud F. hypoleuca declined by 73% (much more severely than nationally). Decline was apparently driven\ud by decreasing productivity and changes in the North Atlantic Oscillation cycle. Phenological changes\ud in lay date were apparent for C. caeruleus (mean lay date advanced by five days in 15 years) and\ud P. major (increased within-season variability in clutch initiation). No change was apparent for\ud F. hypoleuca, possibly due to migration constraining phenological adjustment. The relationship\ud between lay date and clutch size was found to be annually variable, rather than a constant as\ud hitherto assumed. The strength of this relationship correlated with breeding density (C. caeruleus and\ud P. major), the "earliness" of the breeding season (P. major), and mean May temperature (F. hypoleuca).\ud The potential influence of nestbox orientation on nest-site selection and reproductive success was\ud investigated. Orientation correlated with nestling survival for F. hypoleuca and offspring quality for\ud P. major (both lowest in boxes oriented south-southwest). In the case of P. major, boxes facing\ud south-southwest were avoided by adult birds, suggesting adaptive nest-site selection. Microbial load\ud (specifically the abundance of the fungus Epicoccump urpurascens)was related to both orientation and\ud P. major offspring quality, providing a possible explanation for observed patterns of nest-site selection\ud behaviour. Ectoparasite load was not linked to nestbox orientation or P. major offspring quality.\ud These findings provide insights into aspects of population biology (relationship between phenology\ud and productivity), evolutionary ecology (adaptive nest-site choice to maximise offspring fitness) and\ud the interactions between species and their abiotic and biotic environments (influence of orientation\ud and microbial load on breeding success). Relevance of these results to conservation and in situ\ud species management is discussed. Recommendations for optimal siting of nestboxes are given