Laying date and clutch size of Great Tits (Parus major) in the Mediterranean region: a comparison of four habitat types

Laying date and clutch size of Great Tits were studied in four different habitats in eastern Spain: two holm oak (Quercus ilex) forests, at 500 and 900-950 m a.s.1., a zeen oak (Quercusfaginea) forest, at 900-1100 m a.s.l., a pine (Pinus sylvestris) forest, at 1000.1050 m a.s.1., and orange (Citrus aurantium) plantations, at 30 m a.s.1. All sites were placed at about the same latitude (39-41°N), and all were studied during the same years (1992-95). Our results show that (1) laying date did not differ between the natural habitats at the same altitude (range of the means of yearly means 4-8 May); (2) within the same habitat type (holm oak forest) laying date was earlier at low altitude (30 April vs. 8 May); (3) laying date was earlier in the orange plantations (21 April) than in natural habitats; (4) among natural habitats at the same altitude, clutch size decreased from zeen oak (mean of yearly means 7.3 eggs) to holm oak (7.0 eggs) to pine forests (6.4 eggs), though only the difference between zeen oak and pine forests was significant; (5) within the same habitat type (holm oak forest), the clutch size tended to be larger at high altitude (7.0 vs. 5.9 eggs); and (6) clutch size in orange plantations (7.7 eggs) did not differ significantly from that of the zeen oak forest, but was larger than in the holm oak and pine forests. We discuss the effect of the habitat type on laying date and clutch size of Great Tits.