Misschien interessant voor degenen die er iets van begrijpen (voor mij komen er nogal wat moeilijke woorden in voor:
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In birds living in mid and high latitudes the annual change in day length controls the timing of breeding; photoperiod is thus the predominant proximate factor for birds living in such regions (Follett, 1984). Other environmental factors can accelerate or retard photoperiodically-induced gonadal growth (Farner and Follett, 1979). These include rainfall (Leopold et al., 1976), ambient temperature (Perrins, 1973), and the presence of males for stimulating ovarian development (Marshall, 1936; Hinde, 1965; Cheng, 1979; Bentley and Ball, 2000). On the other hand, it is thought that photoperiod is not the proximate factor for many tropical and desert species (Marshall, 1970). The proximate factors used to time breeding in tropical birds remain largely unknown although correlative analyses suggest rainfall, territory, nest site availability, nest materials, and food supply are involved (Immelmann, 1971; Zann et al., 1995). The reproductive axis of tropical birds may remain in a state of “readiness to breed,” and full functionality may be triggered by the relevant proximate cues (Perfito et al., 2006).
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