Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

Baggerman B., Baerends G.P., Heikens H.S. & Mook J.H. (1956) Observations on the behaviour of the Black Tern, Chlidonias n. niger (L.), in the breeding area. ARDEA 44 (1-3): 1-71
PrFont34Bin0BinSub0Frac0Def1Margin0Margin0Jc1Indent1440Lim0Lim1After a short introduction in chapter I a description is given in chapter II of the three colonies where the Black Tern was studied and of the method of observation. In chapter III a brief survey of the most important events in the life-history of the Black Tern is given, together with records on the dates of arrival in the breeding area, nest-occupation and laying of the first egg in seven subsequent years. In chapter IV different types of behaviour of the Black Tern in the breeding area are described. First a short description of non-reproductive activities like migration, hunting and reaction to birds of prey (whirl-flight) is given. Then follows a detailed description of the various reproductive activities. The Black Tern shows two conspicuous courting activities away from the nest-sites. The first is the high-flight which starts with a joint 'kreerk-call' and in which two or usually more birds take part. While circling the birds ascend high into the air (the ascent) and divide into small groups. Then these small groups, consisting of 2-5 (usually 2 or 3) birds perform a downward glide with wings kept still (the glide). The second activity is the fish-flight. When performing this, a male flies around in a typical way (rowing-flight) and carries a prey while uttering the fish-call continuously. Usually he is followed by one female which flies in a normal way (sometimes, however, two birds may follow). At the end of the fish-flight, the female alights somewhere outside the colony and is fed by the male. There is no+ regularity in the sequence of high-flight and fish-flight nor in the timing of their onset. On the nest-site the Black Tern performs a number of other activities. A description is given of the simultaneous occupation of all nest-sites within one day. During nest-occupation agonistic activities like chasing, fighting, threatening and hovering are seen. The nest-sites of the terns are described and also the way of establishing and building the nests. Further a detailed description of a number of courting activities is given. One of them is the feeding-ceremony in which a sitting female on the nest is fed by her mate. Stooping is performed by the male standing on the nest while the female approaches. The male holds its head close to the ground while the rest of the body points obliquely into the air and in this position he turns around with the circling female. A female standing on the nest may stoop when the male arrives without food, but she usually begs when he arrives with food. After alighting both birds assume the erect posture in which the neck is stretched and the bill points obliquely into the air, while the rest of the body slopes downward. Mutual stooping occurs when two birds are present on the nest. The body postures of both birds resemble stooping while pecking at material occurs. Copulation may be preceded and is also very often followed by a repeated feeding of the female by the male. During the first week after nest-occupation the birds often perform a joint silent flight low over the water and away from the colony, which has been called the swerve-flight. Incubation is shared by both sexes and records are given of the duration of the brooding-bouts in male and female and also of the total duration of incubation. During incubation the birds often perform nest building movements, particularly during nest relief. A description is given of the raising of the young. In chapter V an attempt is made to analyse the derivation of the reproductive activities in the Black Tern and to compare them, where possible, with similar activities in other species of Lari. In the introduction a short survey is given of the methods for the study of the phylogenetical origin of behaviour elements. The high flight seems to be a ritualised aerial display in which tendencies to attack and escape may be present. With regard to the feeding ceremonies there are no indications that they must have originated through displacement. It is more likely that they are derived from autochthonous parental feeding behaviour and after ritualisation have become part of the courting performances. Begging in the female is considered to be a displacement activity derived from infantile behaviour. In the whirl-flight and swerve-flight, it seems that tendencies to attack and to escape exist. In the whirl-flight the tendency to attack seems to be stronger than the tendency to escape, while the reverse may be true in the swerve-flight. The synchronization of nest-occupation is most probably caused by the joint action of an internal process of ripening and external factors. In different types of agonistic behaviour elements of attack and escape seem to exist. Nest building movements are described in a number of cases. In part of these cases the nest building seems to be autochthonous, while in other situations it seems to be a displacement activity caused by a conflict between incompatible motivations. In the case of nest building during nest-relief, data were collected which show that the duration of nest building is proportional to the degree to which the brooding instinct is still activated. Mutual stooping resembles the first intention movements of the scrape in other terns, while nest building is at least one of the components. Stooping resembles the intention movements of scraping and may be caused as a result of a conflict. The constancy of the incomplete form and the orienting component suggest a strong degree of ritualisation. In the erect posture many elements indicate a tendency to fly up. It seems that there is a rather strong tendency to escape. The various calls uttered in different situations each seem to express a definite level of reproductive motivation. In chapter VI an attempt is made to analyse the biological significance of activities with a signal function. For this purpose the frequencies in which the different activities are carried out in the course of time were studied. The data showed that in the beginning of the season relatively more high-flights than fish-flights are carried out, while later the frequencies change in favour of the fish-flights. Further the number of glides of two birds in the course of time increases at the cost of the glides carried out by more than two birds. Finally it was observed that the majority of glides of two birds consisted of one male and one female. This lead to the conclusion that the high-flight primarily serves the formation of pairs. The fish-flight is supposed to strengthen the bond between the partners and to synchronise their behaviour. The feeding ceremonies may have the function of increasing the number of encounters and thus of giving the birds an opportunity to get used to each other. The postures assumed during these encounters like stooping, begging erect and mutual stooping seem to have the function of discharging fleeing and aggressive motivation without disturbing the approach 0 the partners. Stooping also seems to have a function in luring the partner or the young to the nest.


[close window] [previous abstract] [next abstract]