Circannual basis of geographically distinct bird schedules

Abstract

Most environments are to some extent seasonal. Their inhabitants time annual activities like reproduction, germination, pupation, moult, hibernation or migration to match the changing seasons and often anticipate conducive conditions well in advance. Seasonal activities must be accurately timed because mismatches with the environment can have severe fitness consequences; however, the particular timing differs considerably with species ecology, environmental seasonality and year-to-year conditions (Lack, 1950;Bradshaw and Holzapfel, 2007;Newton, 2008;Foster and Kreitzman, 2009). Understanding the intricacies of timing has become of urgent interest in view of the disconcerting rate of global change and its implications for seasonality (Bradshaw and Holzapfel, 2006;Bradshaw and Holzapfel, 2007;Visser, 2008). Birds, as a highly visible group, are regarded as sentinels of change and their scheduling is particularly well documented (e.g. Jonzén et al., 2007;McNamara and Houston, 2008;Wingfield et al., 2008).Avian itineraries differ between species in a given habitat and often also within species, depending on geographical location. With increasing latitude, birds generally have shorter reproductive periods, breed later and moult faster than at lower latitudes. Schedules also differ between habitats at given latitudes, e.g. associated with altitude, urbanisation and climatic gradients (Baker, 1938;Lack, 1950;Curry-Lindhal, 1963;Klein, 1974;Murton and Westwood, 1977;Widmer, 1998;Partecke et al., 2004;Perfito et al., 2004;Moore et al., 2005;Partecke et al., 2005;Newton, 2008). Hence, closely related taxa and populations may show distinct timing.The basis of these distinct schedules is still largely unclear. In general, timing involves an inherited background mechanism that provides a temporal framework. It buffers organisms from misleading information, e.g. warm spells in winter, while integrating reliable, predictive, temporal cues -predominantly photoperiod (i.e. the light fraction of the day) (Murton and Westwood, 1977;Gwinner, 1986;Prendergast et al., 2002;Bradshaw and Holzapfel, 2007). Within this framework, schedules may be further modified by environmental conditions, for instance, temperature or food availability (Wingfield, 1980;Hahn et al., 1992;Hahn et al., 1997;Dawson, 2008). The resulting compromise between rigid preprogrammed timing and environmental flexibility should accommodate the requirements of a given species in its given habitat.Geographical differences could therefore arise from phenotypic plasticity in response to local conditions (Perfito et al., 2004;Dawson, 2008;Hahn and MacDougall-Shackleton, 2008). Yet direct environmental control is an insufficient explanation for the scheduling of most seasonal species studied so far. Timing in captivity approximated timing in the wild (Davies et al., 1969;König and Gwinner, 1995;Lambrechts et al., 1997;Lambrechts et al., 1999;Partecke et al., 2004) [but see Perfito et al. (Perfito et al., 2004;Perfito et al., 2008)], indicating the presence of internal tim...

Rainfall-induced changes in food availability modify the spring departure programme of a migratory bird

“…Regardless of sex, redstarts in both xeric, second-growth scrub and mesic, mangrove forest delayed spring migration by 3-5 days when drought conditions prevailed. Photoperiod change has been shown experimentally to provide the ultimate cue for migratory activity, and its influence undoubtedly underlies much of the geographical variation spring departure phenology, especially across latitude [16,24]. However, because we detected similar longitudinal change in the onset of spring migration in males and females and for birds in habitats that differ widely in quality, it is possible that environmental modification of spring departure is common across the non-breeding range of this species.…”

Annual rhythms that underlie phenology: biological time-keeping meets environmental change

“…By contrast, in other species, the response to calendar information depends on the phase of the underlying circannual rhythm [16,47,48]. In birds, reproductive activation is usually stimulated by increasing photoperiod, but most species do not retain breeding condition indefinitely under long day length [47]. The phenomenon, whereby reproductive condition is terminated on long photoperiods and often initially not even re-stimulated by constant light, has been termed 'photo-refractoriness' [49], although birds certainly remain responsive to photoperiod, and shortening days accelerate post-breeding processes like moult.…”

Circadian rhythms are not involved in the regulation of circannual reproductive cycles in a sub-tropical bird, the spotted munia

“…In birds, as in several other vertebrates, circannual (circa=about, annum=year) rhythms are involved in the regulation of the timing and duration of yearly gonadal phases and associated phenotypic traits like body mass (Gwinner, 1986). Several bird species show repeated circannual cycles in food intake, body mass and reproductive phenotype (gonadal maturation, post-nuptial molt and feather regeneration) under constant 12 h photoperiods (Gwinner, 1981;Gwinner, 1986;Gwinner and Dittami, 1990;Cadee et al, 1996;Piersma et al, 2008;Wikelski et al, 2008;Helm et al, 2009) and constant bright [90 lx (Bhatt and Chandola, 1985)] or dim [1-3 lx (Holberton and Able, 1992), ~22 lx ] light. In the wild, circannual reproductive rhythms are synchronized with annual photoperiodic (zeitgeber: from the German zeit=time, geber=giver) cycle and exhibited as an annual reproductive cycle (Gwinner, 1981;Gwinner, 1986).…”