A comparative behaviour study of the Paridae

I. Introduction
The family Paridae contains five important genera – Parus, Aegithalos, Psaltiparus, Auriparus and Remiz. Each of these genera includes a group of vary similar species, but the different genera appear to be widely separated from each other.
The objects of the present study were:-
To ascertain the annual cycle of behaviour of the Great Tit (Parus major), and to attempt an analysis of some aspects of it.
To compare the behaviour of the Great Tit with that of other tits, particularly with other species of Parus. To this end parallel observations were made on the other members of the family present in the study area, and the relevant literature was reviewed. Comparative study is of value in facilitating the interpretation of behaviour patterns, and in indicating relationships between species and genera.
The study was carried out in Wytham Wood, Berkshire.
II. Methods
A field study was made on a wild population of tits. Birds were trapped and ringed so that individuals were recognisable in the field.
III. Flocking
Outside the breeding season Great Tits live in flocks which show a moderate decree of integration and which move irregularly over a limited area at rates of up to 200 yds. per hour. The flocks show two types of movement:- (i) Drifting movements occurring during feeding. (ii) Integrated movements, during which the birds stop feeding and move for some distance. In the latter the flocks are integrated by: (a) The 'Twink' call, which brings other individuals into a ready-to-fly mood. (b) The situation "other-bird-flying-away" which releases flying. The tendency to integration of the flock is balanced by certain disruptive tendencies, the most important of which are due to aggressive behaviour.
IV. Winter Fighting
Fighting over food is common in winter flocks. The most important behaviour patterns are:- (i) The supplanting attack, in which one bird flies at another and dispossesses it of its food. (ii) The wings-raised, and (iii) the head-forward postures, used to threaten nearby individuals, (iv) Avoiding behaviour: tits with food avoid others which approach too closely. (v) Flying away with food particles too large to be eaten immediately. The study of such behaviour can be amplified by allowing, the tits to feed in front of a mirror: they then behave towards their image as they would towards a rival. The image may provoke attack, or flight, or intermediate responses. Supplanting attacks are most common in mid-winter, and occur sufficiently often for such behaviour to be of definite ecological importance.
V. Movements
Adult Great Tits are completely sedentary, and remain on or near their previous year's territory the whole year round. Juvenile Great Tits disperse soon after becoming independent of their parents: they may wander up to several miles from their birth-place. Many juveniles hare settled in a restricted range by the Autumn, though some continue to wander until the nesting; season. The winter range is approximately 10–20 acres.
VI. Pair Formation
The Great Tit flocks begin to break up in January, but the process is gradual, and in cold weather some flocks say be seen as late as April. Some birds are paired during the winter, but most pair formation takes place when the flocks break up. The mechanism is not yet fully understood, but it appears that the male makes supplanting attacks on other members of the flock, and that his further behaviour depends on that of the attacked individual. Once pair formation has occurred, there is a marked difference in the behaviour of the sexes, the males being much more 'alert' and lass retiring than the females. Certain courtship displays appear at this time of year.
VII. Territory
Soon after the pairs separate out from the flock, the male Great Tits start to use certain sites in preference to others for singing. Fighting against other males is more intense in the neighbourhood of these sites (preferred stations) than elsewhere. In this way an area round the preferred stations (the preferred area) comes to be defended from other Great Tits. The boundaries of this area become defined through skirmishes with other pairs. The preferred area is at first unstable and its boundaries vague: it changes only gradually into a territory in the classical sense. Territorial behaviour is thus much less rigid in the titmice than in most species which have previously been studied. The average size of Great Tit territories in the study area was 2.0 acres. Territories seem to differ considerably in size for the same species in different areas, and also for different Parus species in the same area. The biological value of territorial behaviour is difficult to assess.
VIII. Song
Each Parus species has a characteristic song, though in each species there is considerable variation. The song period is roughly similar in all the Parus species studied: song starts in December, becomes common and well marked in early spring, and dies away at about the time when the young leave the nest. Song nay also be heard from juvenile birds in late summer, and during the autumn period of sexual behaviour. The singing of a male attracts females and warns off other males. The stimulus situations in which it occurs are similar to those in other Passerine species.
IX. Reproductive Fighting
Reproductive fighting occurs in relation to the defence of a female, a territory and a rest-site. The most important behaviour patterns are: (i) The supplanting attack, (ii) The head-up posture, (iii) Upright flight, and (iv) Displacement pecking. Although the behaviour is complex, it can be understood on the assumption that each of the combatants is activated by two drives – a fighting drive and an escape drive. The fighting drive is expressed primarily in the supplanting attack:, and the escape drive in flying away. In a skirmish the two drives are in approximate equilibrium. The strengths, and relative strengths, of these two drives determine which of the several possible responses will be given to each stimulus situation. In the Great Tit the head-up posture is very elaborate, and is accentuated by a black ventral stripe. In the Blue Tit the posture is less elaborate, and there is no corresponding structure. Although the displays used in intraspecific reproductive fighting are very similar in the different Parus species, they do not appear in the interspecific disputes over nest-sites.
X. Copulation and Courtship Feeding
In all Parus species it is usually the male who initiates copulation, though the female sometimes does so. The precopulatory display consists of a rapid shivering of the wings, a crouching posture, and a high pitched 'zeedling' note. This is given by both sexes.
Courtship feeding often follows copulation. It becomes very common during the egg-laying period, the female begging almost continuously all day. The male continues tc feed the female during incubation. The begging display of the female is similar to the precopulatory display, and to the begging of the young. Wing shivering seems to be a ritualized intention movement of flight.
XI. Nest Site
All Parus species build in holes. The different species have slightly different requirements for nest-sites, though there is a very large overlap. During the pre-nesting season the male inspects suitable sites, and his display causes the female to shiver her wings and inspect the hole.
XII. Nest Building
Building is usually carried out by the female alone. The males possess the necessary nervous structure, but the motivational factors are usually too low for them to exhibit complete building behaviour. The female at first builds in several different sites, but soon becomes conditioned to one of them.
XIII. Incubation
In all Parus species incubation is carried out by the female alone. Periods on the nest of about 30 minutes alternate with periods off of about 8 minutes. There is a slight tendency for the periods off to be longer in the afternoon than in the morning.
XIV. Care of the Young
The young are brooded by the female for the first few days after hatching. During this time they are fed principally by the male. Later both sexes share in bringing food, and also in nest sanitation, though the male normally does more than the female. The young leave the nest in rapid succession, and are fed by the adults for another 2–4 weeks. The begging display of the young is similar to that of the female in courtship feeding. In some years a few pairs lay a second clutch at about the time when the first brood leaves the next. All birds show some recrudescence of sexual behaviour at this time.
XV. Aggressive and Sexual Behaviour in Late Summer and Autumn
Juveniles of all Parus species show indications of sexual behaviour soon after they become independent. This appears principally in song and reproductive fighting. The latter is often associated with food fighting. In P. palustris this sexual behaviour is more marked than in the other species.
There is also a recrudescence of sexual behaviour in early autumn, manifested by paired behaviour, song and reproductive fighting.
XVI. The Relations between the Forms of Aggressive Behaviour
Food fighting and reproductive fighting are released by different stimulus situations, depend on different internal states (drives) and utilize different motor patterns. They are thus distinct. Nevertheless there are indications of certain relations between them. These are: (i) The activation of one type of fighting behaviour seems to lower the threshold for the appearance of other types; (ii) An animal with a high reproductive fighting drive appears also to have a high food fighting drive, and vice versa.
XVII. Behaviour towards Predators
The response towards a predator depends on the activation of three drives: (i) The drive which had been previously governing the activities of the animal. (ii) Escape. (iii) Attack. Grey Squirrels are normally ignored, or a weak escape response is given: once, however, a Great Tit was seen to give an elaborate display to a Grey Squirrel. In winter, man causes a simple escape response, which is subject to slight variation according to the strength of the drive. The full response occurs in two stages: in the first the bird flies up into a branch, giving the alarm call, and then its further behaviour is determined by the stimulus situation. In spring an attack component is also activated, and complex behaviour (scolding) results: the exact nature of this depends on the strengths of the three drives. When disturbed on the nest, a display is used which gives a human observer the impression that a snake is in the hole. Tits also have a complicated distraction display which is released by the cry of the young.
Tits show two responses to avian predators, if the predator is in flight, they take cover in thick bushes and utter a special alarm note. If the predator is perched, they come towards it and scold it in a manner similar to that used against human intruders in spring.
XVIII. Roosting
Tits of the genus Parus, with certain exceptions, roost in holes in winter and in foliage in summer, when the birds are in pairs, Great and Blue Tits have a "Good-night" ceremony which is performed at roosting time: the male also waits outside the female's roosting site after she has gone to roost and before she emerges at dawn.
Data on the winter roosting and awakening times were obtained for P. major and P. caeruleus, and also for Dryobates major and Sitta europoea, all of which roost in holes. The average length of the day's activity for each of these species increased with decreasing body size: all had shorter days than at least the majority of the species living in the same area which did not roost in holes. In all cases the roosting times were later (relative to sunset) in mid-winter than in Autumn or spring; in Dryobates major and P. major this is even more marked in high latitudes than in England. The dawn emergency times (relative to sunrise) of P. major and P. caeruleus remained constant from late November to March in the area of the present study: P. major in the sub-arctic, and Dryobates major in both sub-arctic and mid-temperate latitudes, emerge earlier relative to sunrise in mid-winter than in spring. All species emerged at dawn at a lower light intensity than that at which they went to roost.
During egg-laying and incubation, males emerge earlier and females later than during winter.
In general, there is an optimum length of the active day which varies with the latitude and season, Each bird has an internal diurnal rhythm of activity which causes it to be active for a period near to the optimum. This internal rhythm is also modified by certain environmental stimuli which are not considered here.
XIX. Periodic Variations in the Frequency of Instinctive Activities
As well as the obvious rhythm of roosting and awakening, many other activities show a marked diurnal periodicity. Those associated with flocking behaviour, and many of those associated with the reproductive drive, show a peak of activity early in the clay, a minimum in the afternoon, and sometimes a second peak in the evening. Other activities show different types of diurnal fluctuation.
Within the main diurnal rhythm, shorter fluctuations in activity can be distinguished. Each activity appears at irregular intervals, which are determined by the fluctuations of the internal drive, by interactions between drives, and by the changing stimulus situation.
XX. The Genus Parus
In the preceding sections comparisons have been made between various aspects of the behaviour of the different Parus species. This comparison has shown that there are few essential differences between the behaviour of the different species: most of the differences which do exist are of degree only.