Position at the migratory route as a factor controlling the duration of the directed movements in migratory birds

Position at the migratory route as a factor controlling the duration of the directed movements in migratory birds

M.E.Shumakov, N.V.Vinogradova, A.V.Sukhov

Zoological Institute, Russian Academy of Sciences, St.-Petersburg, 199034, Russia

Received 10 July 2002

The birds migratory state is characterised by the three main features which are easily registered in the wild and in the experimental conditions: fat deposition, specific rhythm and high level of activity and orientation (Дольник 1975). The birds in cages and aviaries, like free-living conspecifics, accumulate fuel, show activity peaks during the flight hours and try to move at the seasonally appropriate migratory direction (Дольник 1961, 1962, 1974; Шумаков 1967). The metabolic and behavioural components are controlled independently during onset and the termination of the migratory state (Kendeigh, West, Cox 1960; Kling, Farner 1963; Дольник 1963; Merkel 1966). The activity and the orientation are usually correlated, but may start and disappear before or after migratory fattening onset or termination.

The analysis of the own and the literature data allows to conclude that the main factor controlling the timing of the migratory behaviour in relation to the metabolic basis of the migratory state is the ability of birds to determine their position in relation to migratory goal (Шумаков, Виноградова 1969). When the adult birds are kept far away from the nesting places in spring or far from the wintering areas in autumn they prolonged the migratory behavior (activity rhythm and orientation) more longer time than it occurs in natural situation. When the birds are tested in the breeding or wintering areas, migratory activity and directed tendency are quickly terminated (Виноградова, Шумаков 1974; Шумаков 1976; Шумаков и др. 1975).

In most studies, the migratory behavior is recorded on the basis of its level and rhythm, without reference of its directivity as a main characteristic (Schwabl et al. 1991). Here we present the results of testing the orientation of local and transient populations of different species obtained at the field station “Fringilla” (Biological Station Rybachy) at the Courish spit.

Chaffinches Fringilla coelebs from the transient populations, captured by big traps before 10 April and kept here in open aviaries, showed the migratory rhythm activity and significant spring orientation in Kramer’s cages until late July (Table 1). The orientation was displayed late in the season, in spite of the low level of fat stores and active moult.

In parallel tests, the most of local Chaffinches quickly terminated their migratory behavior and did not show any directional preferences even though their fat stores were retained for some time (Table 1).

The activity of Bramblings Fringilla montifringilla, which are transient diurnal migrants, that do not usually breed further south then 60° N, was recorded after keeping the birds on the Courish Spit in spring. They showed a significant pref- erence of the north-easterly directions until late August, i.e. long after their normal migration was completed (Table 2).

Mass releases of delayed Bramblings at habitats similar with their breeding habitats showed that all birds released before mid June, have left the study area. As few as three yearling pears, released at the second half of June, remained at the study site and started breeding (Шумаков и др. 1975).

Similar differences in the duration of the migratory orientation and the period of nocturnal activity were recorded in some species of nocturnal migrants, whose origin can not be established exactly.

Two groups of Garden Warblers Sylvia borin captured in the begining and in the end of the spring migratory period, defined in their behaviour. The birds from the “early” group displayed the nocturnal activity and significant migratory orientation during the daytime and at night during July and August (Table 3). The Garden Warblers captured late did not show a nocturnal activity and significant directional preference until late September (Table 3, right column). It is

Table 1. Orientation of local and transient Chaffinches delayed at Courish spit

Test period	Transient birds			Local birds
	n	A	r	n	A	r
March	6	31°	0.85 **
April	20	289°	0.47*	10	278°	0.41 ns
May	30	17°	0.49 ***	15	35°	0.33 ns
June	21	9°	0.70 ***	60	43°	0.25*
July	21	345°	0.48 **	56	243°	0.15 ns

P (Rayleigh test): ns - nonsignificant; * - P < 0.05;

** - P < 0.01; *** - P < 0.001; **** - P < 0.0001.

Table 2. Orientation of Bramblings delayed at Courish spit during spring migration (Rayleigh test)

Test period	n	A	r	P
16.5-26.5	102	358°	0.58	< 0.0001
27.5-10.6	119	341°	0.53	< 0.0001
11.6-20.6	113	28°	0.44	< 0.0001
21.6-30.6	153	16°	0.50	< 0.0001
01.7-10.7	93	34°	0.58	< 0.0001
11.7-20.7	68	26°	0.60	< 0.0001
21.7-31.7	59	47°	0.37	<0.01
01.8-10.8	115	38°	0.46	< 0.0001
11.8-20.8	65	26°	0.36	<0.01
21.8-31.8	91	54°	0.46	< 0.0001
01.9-10.9	65	57°	0.18	ns
11.9-20.9	52	64°	0.22	ns

Table 3. Orientation of Garden Warblers trapped at the beginning and at the end of spring migration (Rayleigh test)

Ten days periods Early group Late group n Mean asimuth r P n Mean asimuth r P 3 June 6 336° 0.57 ns 6 58° 0.30 ns 1 July 11 329° 0.96 6 12° 0.28 ns 2 July 10 333° 0.95 < 0.0001 14 355° 0.54 <0.05 3 July 14 346° 0.57 11 251° 0.17 ns 1 August 9 341° 0.70 <0.01 9 255° 0.27 ns 2 August 11 352° 0.30 ns 9 329° 0.46 ns 3 August 8 354° 0.63 <0.05 4 277° 0.62 ns possible to distinguish between the local and the passage birds on the basis of constant individual reaction of birds captured in different periods (Виноградова 1976).

Scarlet Rosefinches Carpodacus erythrinus captured in spring also showed clear individual variations in the duration of their migratory behaviour. These birds have a mixed rhythm of migratory activity. When kept in cages and aviaries, most birds showed the high level of activity and significant orientation towards the north-west until the summer solstice (21-25 June). After this time birds abruptly changed for the orientation towards the south-east. However, some birds terminate their migratory behavior soon after capture and do not show a significant orientation until July. In Scarlet Rosefinches, the duration of the migratory behaviour can be regulated in cages also without an access to the astronomical orientation cues. The birds kept in closed aviary under the natural geomagnetic field and local photoperiod, behaved identically with the birds in the open cages.

The orientation abilities of the birds should be regarded as an important mechanism which controls the duration of their migratory behaviour during different violations of their normal schedule of moving along the migratory route.