Breeding patterns of great tits (Parus major) in pine forests along the Portuguese west coast

The breeding biology of great tits (Parus major) was studied in two forests of maritime pine (Pinus pinaster) on the west coast of Portugal, 200 km apart: Leiria (north) and Apostica (south). These two forests are located in a transition zone between Atlantic climate in the north, and Mediterranean climate in the south. Breeding onset was, on average, in the second and third week of March, which are the earliest records of breeding for this species. The southern population started to breed earlier than the northern one and produced a larger first clutch, 8.3 and 7.4 eggs, respectively. Corresponding to larger clutch sizes, we also found a higher first brood fledgling production in Apostica compared to Leiria, 6.1 and 5.4 fledglings, respectively. However, the total number of fledglings produced per pair was higher in Leiria (8.3) than in Apostica (7.7), due to higher productivity of second clutches (4.7 and 2.7 fledglings, respectively). Accordingly, the allocation of eggs between successive breeding attempts was more equal in Leiria. Results are discussed in accordance to the different climatic patterns in the two areas. It is suggested that the timing of breeding and different allocation of reproductive investment between successive breeding attempts play an important role in optimizing breeding tactics in this facultative, multiple-brooded passerine in different climatic areas