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Abrupt switch to migratory night flight in a wild migratory songbird

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ABSTRACT

Every year, billions of wild diurnal songbirds migrate at night. To do so, they shift their daily rhythm from diurnality to nocturnality. In captivity this is observed as a gradual transition of daytime activity developing into nocturnal activity, but how wild birds prepare their daily rhythms for migration remains largely unknown. Using an automated radio-telemetry system, we compared activity patterns of free-living migrant and resident European blackbirds (Turdus merula) in a partially migratory population during the pre-migratory season. We found that activity patterns between migrant and resident birds did not differ during day and night. Migrants did not change their daily rhythm in a progressive manner as has been observed in captivity, but instead abruptly became active during the night of departure. The rapid shift in rhythmicity might be more common across migratory songbird species, but may not have been observed before in wild animals due to a lack of technology.

No MeSH data available.


Double-plotted actograms (48 hours) showing activity of a ‘‘resident’’ captive, “migrant” captive, free-living resident and free-living migrant European blackbirds (Turdus merula) during autumn.Captive “resident” (a) and captive “migrant” (b) were exposed to natural photoperiod during the autumn (Sep. 1–Oct. 31). These two actograms were plotted using raw data from Partecke & Gwinner (2007). In the case of the captive “migrant” (b), around mid-September a morning component of activity moves gradually into the night-time, developing nocturnal activity (Zugunruhe). Zugunruhe peaks the night of October 2. Activity of a free-living resident bird (c) was recorded using the automated telemetry system (ARU) continuously from the autumn until the consecutive spring. (d) Activity of a free-living migrant bird was recorded also using the ARU, during the autumn until its departure. The departure time of the free-living migrant is indicated by *. After departure, the ARU showed some false positive inactivity due to noise in the recording. Day and night time activity coloured red and blue, respectively.
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f1: Double-plotted actograms (48 hours) showing activity of a ‘‘resident’’ captive, “migrant” captive, free-living resident and free-living migrant European blackbirds (Turdus merula) during autumn.Captive “resident” (a) and captive “migrant” (b) were exposed to natural photoperiod during the autumn (Sep. 1–Oct. 31). These two actograms were plotted using raw data from Partecke & Gwinner (2007). In the case of the captive “migrant” (b), around mid-September a morning component of activity moves gradually into the night-time, developing nocturnal activity (Zugunruhe). Zugunruhe peaks the night of October 2. Activity of a free-living resident bird (c) was recorded using the automated telemetry system (ARU) continuously from the autumn until the consecutive spring. (d) Activity of a free-living migrant bird was recorded also using the ARU, during the autumn until its departure. The departure time of the free-living migrant is indicated by *. After departure, the ARU showed some false positive inactivity due to noise in the recording. Day and night time activity coloured red and blue, respectively.

Mentions: Under laboratory conditions, migratory behaviour of nocturnal migrant bird species is expressed by nocturnal locomotor activity (Zugunruhe) during the autumn and spring when migration occurs in the wild8910. Zugunruhe is composed of a set of stereotyped behaviours mostly characterized by wing whirring but also includes hopping and fluttering11. The amount of Zugunruhe has been used as a proxy for the propensity of individuals to migrate12 and has been related to genetic, physiological and behavioural aspects of bird migration8910131415. The seasonal change in rhythmicity from diurnality to nocturnality that leads to the full expression of Zugunruhe is assumed to be controlled by endogenous circadian rhythms externally entrained by changes in photoperiod (reviewed in refs 16 and 17). It has been assumed that two circadian oscillators–one controlling the daytime activity and the other controlling the night-time activity–are the main components of the avian circadian clock that triggers migratory nocturnality1819. During migration seasons, the oscillators seem to slowly uncouple and stabilize in antiphase1819 (reviewed in ref. 16). This process can be observed as an evening or early morning component of activity which separates from the daytime activity and slowly moves into the night18. This shift in activity can be visualized as a gradual increase of night activity over time18 and has been observed in several bird species e.g. European starlings (Sturnus vulgaris)20, bramblings (Fringilla montifringilla)21, garden warblers (Sylvia borin)9, common quail (Coturnix coturnix)22 and European blackbirds. In captive European blackbirds, a gradual onset of nocturnality occurs when an early morning component of activity slowly moves into the night (Fig. 1b). Individuals have previously been classified as migrants or residents based on the amount of nocturnal restlessness displayed2324 (Fig. 1a,b).


Abrupt switch to migratory night flight in a wild migratory songbird
Double-plotted actograms (48 hours) showing activity of a ‘‘resident’’ captive, “migrant” captive, free-living resident and free-living migrant European blackbirds (Turdus merula) during autumn.Captive “resident” (a) and captive “migrant” (b) were exposed to natural photoperiod during the autumn (Sep. 1–Oct. 31). These two actograms were plotted using raw data from Partecke & Gwinner (2007). In the case of the captive “migrant” (b), around mid-September a morning component of activity moves gradually into the night-time, developing nocturnal activity (Zugunruhe). Zugunruhe peaks the night of October 2. Activity of a free-living resident bird (c) was recorded using the automated telemetry system (ARU) continuously from the autumn until the consecutive spring. (d) Activity of a free-living migrant bird was recorded also using the ARU, during the autumn until its departure. The departure time of the free-living migrant is indicated by *. After departure, the ARU showed some false positive inactivity due to noise in the recording. Day and night time activity coloured red and blue, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035921&req=5

f1: Double-plotted actograms (48 hours) showing activity of a ‘‘resident’’ captive, “migrant” captive, free-living resident and free-living migrant European blackbirds (Turdus merula) during autumn.Captive “resident” (a) and captive “migrant” (b) were exposed to natural photoperiod during the autumn (Sep. 1–Oct. 31). These two actograms were plotted using raw data from Partecke & Gwinner (2007). In the case of the captive “migrant” (b), around mid-September a morning component of activity moves gradually into the night-time, developing nocturnal activity (Zugunruhe). Zugunruhe peaks the night of October 2. Activity of a free-living resident bird (c) was recorded using the automated telemetry system (ARU) continuously from the autumn until the consecutive spring. (d) Activity of a free-living migrant bird was recorded also using the ARU, during the autumn until its departure. The departure time of the free-living migrant is indicated by *. After departure, the ARU showed some false positive inactivity due to noise in the recording. Day and night time activity coloured red and blue, respectively.
Mentions: Under laboratory conditions, migratory behaviour of nocturnal migrant bird species is expressed by nocturnal locomotor activity (Zugunruhe) during the autumn and spring when migration occurs in the wild8910. Zugunruhe is composed of a set of stereotyped behaviours mostly characterized by wing whirring but also includes hopping and fluttering11. The amount of Zugunruhe has been used as a proxy for the propensity of individuals to migrate12 and has been related to genetic, physiological and behavioural aspects of bird migration8910131415. The seasonal change in rhythmicity from diurnality to nocturnality that leads to the full expression of Zugunruhe is assumed to be controlled by endogenous circadian rhythms externally entrained by changes in photoperiod (reviewed in refs 16 and 17). It has been assumed that two circadian oscillators–one controlling the daytime activity and the other controlling the night-time activity–are the main components of the avian circadian clock that triggers migratory nocturnality1819. During migration seasons, the oscillators seem to slowly uncouple and stabilize in antiphase1819 (reviewed in ref. 16). This process can be observed as an evening or early morning component of activity which separates from the daytime activity and slowly moves into the night18. This shift in activity can be visualized as a gradual increase of night activity over time18 and has been observed in several bird species e.g. European starlings (Sturnus vulgaris)20, bramblings (Fringilla montifringilla)21, garden warblers (Sylvia borin)9, common quail (Coturnix coturnix)22 and European blackbirds. In captive European blackbirds, a gradual onset of nocturnality occurs when an early morning component of activity slowly moves into the night (Fig. 1b). Individuals have previously been classified as migrants or residents based on the amount of nocturnal restlessness displayed2324 (Fig. 1a,b).

View Article: PubMed Central - PubMed

ABSTRACT

Every year, billions of wild diurnal songbirds migrate at night. To do so, they shift their daily rhythm from diurnality to nocturnality. In captivity this is observed as a gradual transition of daytime activity developing into nocturnal activity, but how wild birds prepare their daily rhythms for migration remains largely unknown. Using an automated radio-telemetry system, we compared activity patterns of free-living migrant and resident European blackbirds (Turdus merula) in a partially migratory population during the pre-migratory season. We found that activity patterns between migrant and resident birds did not differ during day and night. Migrants did not change their daily rhythm in a progressive manner as has been observed in captivity, but instead abruptly became active during the night of departure. The rapid shift in rhythmicity might be more common across migratory songbird species, but may not have been observed before in wild animals due to a lack of technology.

No MeSH data available.