Long-range call use in dominance-structured Crested Tit Parus cristatus winter groups

In this study on free-ranging Crested Tits Parus cristatus , I examine the relationship between social dominance and the frequency of use of long-range communication calls. Calling rates of trills were highest among socially dominant individuals and they gave more calls when close to the boundary of their territories. Dominant females uttered fewer calls than their mates. However, they gave significantly more calls than subordinate males and subordinate females, the latter calling least. A removal and playback experiment revealed a relationship between the utterance of trilled calls and the defence of the winter territory in the Crested Tit. Although territorial vocalizations could incur costs, territorial individuals may gain from improved winter survival by decreasing the risk of food stealing by Crested Tits from adjacent territories.     

Effects of population growth on Crested Tit Parus cristatus post-fledging settlement

From 1987 to 1993, the winter density of Crested Tits Parus cristatus in north Belgium increased 2.76 times. The increase was the result of high annual survival rates of both adult and first-year birds despite a low reproductive success (number of fledglings per female) due to high predation of nestlings. A fc-factor analysis assuming intermediate costs of post-fledging dispersal and settlement gave the best fit. First-year birds had two options when trying to settle in a prospective breeding territory: (1) establish a new territory during August or early September and defend it against neighbouring flocks during winter or immigrants in early spring or both, or (2) overwinter as a subordinate in a mixed-age flock and pair with a widowed adult or replace a territory owner in early spring (hopeful dominant stategy). Settlement strategies varied with density; at low density, only the hopeful dominant strategy was observed, whereas at higher density, both strategies occurred.     

Effects of habitat fragmentation on the timing of Crested Tit Parus cristatus natal dispersal

Crested Tit Parus cristatus young from first broods dispersed 1 week later if they were born in small isolated pine plots ('habitat fragments') compared with individuals in a large pine forest ('continuous habitat'). This delay in dispersal was caused by an extended period between fledging and dispersal. In second broods, the delay was even longer due to the interbrood interval being 9 days longer in habitat fragments. As nestlings in habitat fragments had a lower body-mass, and age at dispersal was negatively correlated with nestling body-mass within each nest, the postponed dispersal from fragments might be explained partly by a lower body-mass. Alternatively, postponed dispersal from fragments could result from a barrier effect caused by reluctance to cross inhospitable habitat.
Immigration by young from first broods into habitat fragments was delayed by approximately 3 weeks, and proportionally more second brood emigrants were recovered in this type of habitat. These results are in agreement with the hypothesis that fragments are second-choice habitat. Early immigrants into continuous habitat had a higher probability of settlement in winter flocks compared with late ones, independent of condition or age. Therefore, Crested Tits born in habitat fragments probably have a lower chance of settling in first-choice habitat.     

Habitat and laying date of Great and Blue Tit Parus major and P. caeruleus

Using 19 year's data from nine study areas at Ghent we investigated the effect of habitat on laying date, and found it to be quite different for Great and Blue Tits. In Great Tits we found a clear gradient in laying dates from urban over suburban to rural habitats. Blue Tits laid earliest in a suburban habitat and latest in a rural habitat. All other areas, including urban, suburban and rural ones, formed one intermediate group. The overall average laying date for the Great Tit, 18.9 April, was slightly earlier than that of the Blue Tit, 19.4 April. In urban areas Great Tits laid significantly earlier than Blue Tits, in optimal oak habitat and in one suburban area Blue Tits laid earlier, whereas in the five remaining areas no significant differences between the two species were found.
We argue that the differences in laying dates, although correlated to temperature, are probably caused by differences in the timing of food availability. We suggest that differences in laying dates of Great and Blue Tits are caused by a different response to environmental variations through differences in feeding ecology.     

Competition and egg-weight in the Great Tit Parus major

The mean weight of eggs in clutches of the Great Tit Parus major varies markedly between clutches. Eggs are lighter in years of high density of breeding pairs than in years of low density, but egg weight is also inversely correlated with the density of breeding Blue Tits Parus caeruleus .     

Effect of increased food abundance near forest edges on flocking patterns of Coal Tit Parus ater winter groups in mountain coniferous forests

CapsuleIndividuals concentrated near forest edges in bigger social groups than in forest interiors and foraged more on pine cones which were more abundant there.

Aims To evaluate differences in food distribution between forest edges and forest interiors and their effects on the non-breeding flocking patterns of Coal Tit populations inhabiting mountain coniferous forests.

Methods We collected cone production data at forests edges and interiors in mountain pine forests located in the Pyrenees (northeast Iberian peninsula). At the same sites, we also quantified Coal Tit abundance, flocking patterns and foraging behaviour by means of paired bird surveys during autumn and early winter.

Results We recorded a larger abundance of pine cones available on trees along forest edges compared with forest interiors. Coal Tit groups were of bigger size along forest edges, although the number of social groups detected did not differ from forest interiors. Our observations on foraging behaviour supported the hypothesis that differences in flock sizes and overall abundances associated with distance to the edge are due to differences in the availability of pine cones and to the heavier use of these foraging substrates by birds along forest edges.

Conclusions Our results suggest that by changing food distribution, edge effects on pine cone production may be significantly involved in local changes in the social structure of the Coal Tit. An increase in resource heterogeneity and local population density may have important implications at a population level, such as favouring mobility of individuals searching for food resources and thus a transient life, and increasing the costs of territory defence to resident individuals.     

Song evolution in the coal tit Parus ater

Since in oscine birds song divergence often leads to premating reproductive isolation, we asked which factors drive the evolution of song in a widespread species, the coal tit Parus ater. Based on an almost taxon‐complete phylogeny we correlated song divergence with morphometric (ecology), genetic (time), and geographic distances (separation). We found eight well‐supported mitochondrial lineages, one of which consists of melanolophus (usually treated as a separate species) and whose relationships remain generally unresolved. Due to intense song variability even sophisticated sonametric analyses failed to separate sub‐specific units. We tested for the role of song in reproductive isolation by playing songs from China and the Himalayas to Central European males. They recognize them as conspecific, but react to their playbacks less aggressively than to local songs. While morphological divergence is correlated with neither time nor separation, song divergence coincides more with geographic than genetic distance. This is mainly driven by differences along longitude and is especially prominent in the southern part of the species’ range, where six lineages persisted during the last glaciation while the north was subsequently re‐occupied by two lineages.     

Detection distance influences escape behaviour in two parids, Parus major and P. caeruleus

When birds are attacked by aerial predators they should benefit by adjusting their escape to the prevailing attack situation. One important factor likely to affect escape decisions of prey, to our knowledge not previously studied, is the distance at which the attacking predator is detected. We investigated if great tits Parus major and blue tits P. caeruleus alter their escape behaviour to two different detection distances (2.3 m and 1m) by simulating surprise attacks using a predator model. Both species used the information about detection distance when escaping by increasing the escape angle at the shorter detection distance. In addition, blue tits adjusted to the shorter detection distance by dodging sideways more frequently. Great tits escaped initially steeper and faster than blue tits, whereas blue tits increased escape angle and speed more than great tits along the measured distance after taking wing.     

Dawn chorus and female behaviour in the Willow Tit Parus montanus

We studied the effect of female behaviour on the dawn chorus of Willow Tits Parus montanus. Ten females were temporarily kept in their nest holes in order to delay their dawn emergence. Simultaneously, their mates' singing behaviour was measured. We compared the control dawn behaviour (during which the females emerged when they wanted) with that during the experimental delay. The dawn song by the males lasted longer when the females' emergences were delayed. Our results show that the duration of the dawn chorus is directly related to the female's behaviour. We suggest that at least one function of the dawn song is intrapair signalling, which is often linked to sperm competition.     

Differential Responsiveness of Great Tit Nestlings,Parus major,to Natural Auditory Stimuli

In one field and two laboratory experiments, wild, wild-captured and partly laboratory-raised 16 to 18-day old great tit nestlings were subjected to repeated presentations of auditory stimuli of varying biological significance. The frequency of occurrence of the stimuli in the study area was censused. — All nestlings showed strong aversive reactions to the ‘seeet’ alarm-call of the species. It is concluded that a selective responsiveness to this call develops independently of previous exposure to it. A functional interpretation of this reaction is derived from its presumed adaptive value. Three hypothetical interpretations are suggested to explain its emergence in the individual nestling; The ‘seeet’-call elicits aversive reactions because of, 1) its novelty, 2) its intensity in terms of relative concentration of energy over its frequency range and 3) its contrasting acoustic structure compared to the nestlings' begging-call which has become strongly associated with approach behavior.     

Reproduction and survival of polygynous and monogamous Blue Tit Parus caeruleus

In a seven-year study of Blue Tits in optimal habitat near Antwerp, Belgium, 45 polygynous broods involving 22 males out of 667 successful first broods were found. In another 43 nests no male was found, although a major effort was made to trap all adults. The estimated proportion of polygynous males is 3.4%, if only confirmed cases are considered, but 10.8% if all possible cases are included. One male was paired simultaneously to three females.
Primary females (laying earliest in a triangle) were as successful as monogamous ones. Secondary (laying later in a triangle) and deserted females (nests in which no male was trapped), although still quite successful, raised fewer young and in one plot had a lower probability of recruiting offspring.
Both in males and females, the frequency of polygyny was independent of age. Adult survival did not differ between monogamous and polygynous males. Among females no effect of pairing status on survival was found in one plot, but in a second plot monogamous females survived better than others. It is concluded that in any study of Blue Tits in optimal habitat one could expect to find polygyny.     

Personality and Nest Defence in the Great Tit (Parus major)

A growing number of studies have shown that individuals differ consistently in a suite of correlated behavioural traits across various contexts and situations. Yet, most work on animal personalities has been performed under laboratory conditions and still little is known about the ecological significance of differences in personality in the wild, and the behavioural mechanisms underlying possible fitness consequences. In this study, we investigated individual differences in personality in relation to nest defence behaviour in wild great tits. Nest defence is an important aspect of parental care and involves a trade‐off between two fitness components (i.e. survival and reproduction). As a measure of personality we used exploratory behaviour in a novel environment as this has been shown to be correlated with several other behavioural traits including risk‐taking and aggression, two important behavioural components of nest defence. We found that the intensity of alarm calling towards a human intruder was positively associated with exploratory behaviour, while there was a negative association between exploration score and number of movements during nest defence. Thus, fast explorers are shown to respond more boldly towards predators in the field. More generally we show that individuals with different personalities vary in their anti‐predator and reproductive investment strategies.     

Effect of Daily Body Mass Variation on the Foraging Behaviour of Tit Species (Parus spp.)

We studied the effect of daily body mass increase on the foraging preferences of two tit species, crested tit, Parus cristatus and blue tit, P. caeruleus, contrasting in morphology and behaviour. We found that both species show a diurnal increase in body mass during winter. Using an experiment with feeders we show that in the crested tit, the proportion of time spent foraging while hanging decreased as body mass increased. In contrast, in the blue tit, foraging behaviour did not change with mass gain. We propose that the species with a morphological design providing a high ecological plasticity in terms of foraging postures can counteract the negative effect of body mass on the ecological options (foraging niche) more than species with a morphological design providing a low ecological plasticity in terms of foraging postures. Our results suggest that blue tits had the advantage of being able to choose to feed on different patches in the habitat throughout the day, which makes resources more predictable for them. In contrast, crested tits might be more restricted in their foraging options as their body mass increases, and this might explain why they hoard food.     

Genetic evidence for extra-pair fertilizations in a monogamous passerine, the Great Tit Parus major

The incidence of extra-pair paternity in a Great Tit Parus major population at Wytham Wood, Oxford, in 1985–1987 was determined using two polymorphic allozymes. In 831 nestlings from 94 broods, 27 genetic exclusions were detected in 25 (3%) nestlings from 16 broods. Seven (44%) of these broods contained offspring that excluded the putative male parent from being the genetic parent. The distribution of exclusion types indicated that excluded offspring were the result of fertilizations by extra-pair males and not of egg-dumping. The true frequency of extra-pair paternity was estimated as 14% of offspring. These results suggest a mixed reproductive strategy for males in which they breed mo-nogamously whilst simultaneously seeking extra-pair matings with females of other pairs.     

Clutch Defence in Great Tit (Parus major) Pairs and the Concorde Fallacy

We conducted an experiment to test whether great tits (Parus major) base their decisions of clutch defence on past investment or future benefits. Results were obtained by manipulation of future benefits. Great tit pairs of an experimental group with reduced clutch-size and thus diminished benefits defended their offspring against a live raptor significantly less than a comparable, non-manipulated control group with the same amount of past investment (clutch-size, incubation stage, time of year). While in the females the difference between the two groups was obvious from the beginning of a trial, the difference in the males developed only during the course of a trial, suggesting that the male bases its response on the female's response deficit. A more onerous explanation of the female signaling the male the egg loss by using a language-like symbol is not supported by the data. The experiment thereby permits the conclusion that at least the great tit female avoids committing the Concorde fallacy in the strict sense.     

Sparrowhawk Accipiter nisus predation and Blue Tit Parus caeruleus adult annual survival rate

The adult annual survival rate of breeding Blue Tits Parus caeruleus decreased from 0.485 to 0.376 after a pair of Sparrowhawks Accipiter nisus started to breed in the study plot in 1990, whereas in two neighbouring plots, survival rates did not change. This decrease was likely caused by the Sparrowhawk predation mainly in spring. Although the size of the Blue Tit breeding population did not decrease, there remained fewer nonbreeding floaters, and as a result, replacement polygyny became more common.