Seasonal Time Keeping in a Long-Distance Migrating Shorebird

Abstract

Because of the complications in achieving the necessary long-term observations and experiments, the nature and adaptive value of seasonal time-keeping mechanisms in long-lived organisms remain understudied. Here we present the results of a 20-year-long study of the repeated seasonal changes in body mass, plumage state, and primary molt of 45 captive red knots Calidris canutus islandica, a High Arctic breeding shorebird that spends the nonbreeding season in temperate coastal areas. Birds kept outdoors and experiencing the natural photoperiod of the nonbreeding area maintained sequences of life-cycle stages, roughly following the timing in nature. For 6 to 8 years, 14 of these birds were exposed to unvarying ambient temperature (12 °C) and photoperiodic conditions (12:12 LD). Under these conditions, for at least 5 years they expressed free-running circannual cycles of body mass, plumage state, and wing molt. The circannual cycles of the free-running traits gradually became longer than 12 months, but at different rates. The prebreeding events (onset and offset of prealternate molt and the onset of spring body mass increase) occurred at the same time of the year as in the wild population for 1 or several cycles. As a result, after 4 years in 12:12 LD, the circannual cycles of prealternate plumage state had drifted less than the cycles of prebasic plumage state and wing molt. As the onset of body mass gain drifted less than the offset, the period of high body mass became longer under unvarying conditions. We see these differences between the prebreeding and postbreeding life-cycle stages as evidence for adaptive seasonal time keeping in red knots: the life-cycle stages linked to the initiation of reproduction rely mostly on endogenous oscillators, whereas the later stages rather respond to environmental conditions. Postbreeding stages are also prone to carryover effects from the earlier stages.

Two sides of a coin: ecological and chronobiological perspectives of timing in the wild

“…return to roost) [55,152], and the timing of one activity may be more important than that of others. A recent study of waders found that different aspects of their annual cycle were varying in ways suggestive of process-specific chronotypes, making it difficult to define the most appropriate descriptor [16,153]. Furthermore, plasticity of chronotype to environmental factors, as described above, can complicate analyses, especially if repeated measurements are not feasible (e.g.…”

“…As an example of species-specific effects, migratory species that utilize seasonal resources at sequential sites over the course of the year now have to cope with strongly diverging changes in phenology at the various sites. They will have to adjust multiple components of their annual cycles, putting multiple selection pressures on the integrated chronotypes [153]. On the level of species interactions, a potential powder barrel are changes in host-parasite relationships, if for example parasites and vectors can extend their annual temporal niches and expand into regions that no longer show prohibitive seasonal changes [23,103].…”

Timing avian long-distance migration: from internal clock mechanisms to global flights

“…As the birds approach the breeding grounds, environmental cues will become progressively more 14 . In contrast, the post-breeding life-cycle stages of red knots drifted more swiftly toward later dates (i.e.…”

“…These observations prompted Kramer 8 to propose that the integration of an inherited sense of time with an inherited sense of direction could function as a "clock and compass" mechanism, which could guide inexperienced birds on their first journey before learning about the environment en route. Since then, captive studies of a wide range of migratory species, and systematic experimentation of the captive environment have identified detailed time programs and their interactions with selected environmental factors 4,10,13,14,16 . Many of the sophisticated adaptations of migratory programs can best be studied in individually migrating songbird species, especially in hand-raised individuals during their first journey when young birds are still naïve.…”

Annual chronotypes functionally link life histories and life cycles in birds

“…The data included circannual periods for all available life cycle stages. However, circannual‐period lengths often change in the course of cue‐deprived treatments (Gwinner, ; Karagicheva, Rakhimberdiev, et al., ), and most of the circannual‐period lengths were available for the first one or two years spent under experimental conditions. We therefore limited our sample to transitory cycles during which the animals were transferred from natural to constant photoperiods (cycle 0), and the first cycle (cycle 1) when animals were exposed to a constant photoregime the whole year (Table ).…”