Breeding ecology of woodchat shrikes Lanius senator was investigated in the EL-Kala National Park in North-East Algeria (36°53’N; 8°30’E) in 1998–1999. Quercus suber was the tree species most frequently used as support for nests, which were constructed at a mean height of 5 m. First eggs in clutches were laid 7 May, and clutch size was 4.9. Approximately 42% eggs gave fledglings. Clutch size declined during the course of the breeding season but fledgling success did not. Fledging success was positively correlated with per clutch mean egg length and the height of the nest location above ground. We suggest that the major selective pressures that shape the life history of Algerian woodchat shrikes are relatively heavy predation and poor food availability.
Nest boxes for breeding tawny owls Strix aluco were sited in a mixed oak/hornbeam/beech forest located in the Pilis Biosphere Reserve, 30 km northwest of Budapest, Hungary, during the period 1992–2000. We hypothesized that both within-pair differences in age composition and weather conditions affect the breeding success of the parents. To test our hypothesis, we marked the owl parents in their first known breeding year and related their reproductive performance was to within-pair age composition through three subsequent breeding seasons. Sex-related age differences affected the breeding performance of the parents in their first and second known breeding year: number of eggs and hatching success were influenced by the age of females, while fledging success was influenced by the age of males. Within-pair age differences did not affect the breeding performance at their third known breeding year. Reproductive performance was lower in snowy years than in years without snow cover in all of their three subsequent breeding seasons. On basis of the lower mean body mass and shorter mean tarsi of the nestlings before fledging recorded in adverse weather conditions, we suggest that parents favour the sex that demands less investment in care. As a consequence, the sex-ratio becomes skewed towards the male in a poor food environment.