Breeding biology of the Blue Tit (Parus caeruleus) in an oak forest in central Spain.
Published: Volume 35(1), June 1988. Pages 31-43.
Original Title: La reproducción del Herrerillo Común (Parus caeruleus) en un robledal del centro de España
Laying dates, clutch size,hatching asynchrony and breeding success across two breeding seasons are reported for a population of Blue Tits,a montane (1.300-1.400 m.a.s.l.) deciduous oak (Quercus pyrenaica) forest in central Spain. Blue Tits raised a single brood in each breeding season. The breeding season of the first study year (1984) was much delayed when compared to that in 1985 (Table 1), this being due to inusual hard snowstorm conditions in May 1984. Clutch size ranged between 2 and 11, 7,7 being the average figure for the two years combined. There was seasonal decline in clutch size (Fig. 1). Nestling mortality due to starvation was significantly higher in 1984 than 1985 (Table II). In the former year the commonest clutch size was 8, and the most productive clutch size was 7, while in 1985 the commonest clutch size (9) was conservative with regard to the most productive (10) (Table III). Hatching asynchrony was quantified by means of two different criteria for the 1985 breeding season. We found that hatching asynchrony increased as the season progressed (Fig. 2). Data on the clutch size of the Blue Tit in other Spanish areas are extracted both from the literature and from nest-record cards in the Sociedad Española de Ornitología (S. E. O.) (Table IV). Though the data are few, there seems to exist much variation in clutch size linked to the position of the areas in the bioclimatic gradient of the Iberian Peninsula, no consistent trends emerging when examining this variation under Ashmole's hypothesis. We suggest that latitudinal and elevational gradients in clutch size may be confounded by a non monotonous geographical variation of environmental and ecological parameters along these gradients. Hence, clutch size may be higher in middle elevations and/or latitudes, at least in the diversified Mediterranean landscapes.