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.     

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.     

Prey Detection in Two Tit Species,Parus ater and P. cristatus

We studied the prey-detection response of two related tit species (Parus ater, coal tit, and P. cristatus, crested tit) which occur in similar habitats and which are separated by microhabitat use and mode of locomotion. Specifically, we tested whether the two species differ in their ability to detect cryptic prey, with the hypothesis that coal tits perform better because of their longer stays in microhabitat patches. We expected that interspecific differences and the flexible responses within species to different levels of prey crypticity both depend on search intensity. In the experiments, tits had to forage in four different prey conditions: conspicuous + small, conspicuous + large, cryptic + small, and cryptic + large. Capture success, the time needed to detect prey, and stare duration were measured. Both species were less successful with cryptic than with conspicuous prey and did worst with small and cryptic prey. They also needed more time for detection and stared longer when prey was cryptic. When prey had been overlooked, preceding stare durations were shorter than those ending in successful searches. There were clear differences between the species in performance, with the crested tit doing worse. Coal tits, on average, were more successful in detecting prey, returned less frequently to already emptied patches, detected prey faster and yet they stared more briefly. The within-species results support current notions on predator search, but the differences between species cannot be explained with the same mechanisms. We discuss these findings in the context of the foraging ecology of these species and conclude that crested tits use different cues to detect prey and/or search a larger area per unit time.     

Effects of Cover on Loud Trill-Call and Soft Seet-Call Use in the Crested tit Parus Cristatus

Predation is one of the main factors responsible for winter mortality in small birds. Contact vocalizations of crested tits ( Parus cristatus ) can be divided into two categories: long- and short-range communication calls. The long-range calls are loud, frequency-modulated trills, which are well suited for acoustic communication over long distances. The short-range calls, in contrast, are soft, high-pitched tones, which are strongly attenuated as they radiate through the environment. As the predation cost in this species is mostly associated with the use of loud calls, we investigated whether crested tits adjust the use of loud trill-calls and of soft seet-calls to changes in habitat safety. We arranged two feeding sites that differed with respect to predicted safety, and observed the utterance of loud trill-calls and soft seet-calls. Calling rates of the loud trill-calls were highest when male crested tits foraged at the safe site. The loud trill-calls were given significantly less often while visiting risky feeders placed just a few metres away from the safe sites. The soft seet-calls were uttered both at risky and safe feeders at similar rates. This study suggests that the long-range part of contact communication in crested tits is strongly affected by the level of perceived predation risk. In accordance with the data on hearing ability of predators, dominant male crested tits decrease their exposure to predation in risky habitats by choosing a less risky type of communication with high-pitched sounds.     

Impact of Great Crested Grebes (Podiceps cristatus L.) on fish ponds

Because Great Crested Grebes (Podiceps cristatus L.) mainly feed on fish, fish-farmers sometimes claim that economic losses are caused by grebes (EIFAC, 1988). Such claims were not based on scientific research.Therefore, a study was carried out to measure the impact of Great Crested Grebes on a fish-farm, managed by the Organization for the Improvement of Inland Fisheries (O.V.B.) in Valkenswaard (The Netherlands) during the period 1986–1988. The O.V.B. provided fish data for each pond including fish density and fresh fish weight for each fish species. The number of grebes was counted at least once a week. Activity patterns, including nocturnal activity, were determined both for the period with and without young. No nocturnal foraging activity was observed. Furthermore, fish biomass consumed per 1000 s foraging time by adult birds and chicks was calculated.In some fish-ponds grebes ate coarse fish, and chicks especially were fed these fish. The average daily fish consumption was 222 g for adults and 108 g for juveniles.Based on available fish data, it can be concluded that grebes consumed fewer fish than the number expected to die, and only marginally influenced the fish populations in the aquaculture ponds studied.     

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.     

One Norwegian territory of the Marsh Tit Parus palustris during 35 years

One Norwegian territory was occupied by successive pairs of Marsh Tits Parus palustris during 35 breeding seasons. Only ten males and seven females were involved. Each pair showed strict site fidelity and kept to the territory all year round. The pair bond lasted throughout life, and the duration varied from one to eight successive years. The number of successive mates varied for the males from one to two females and for the females from one to four males. Assuming that the birds were juveniles or 1 year old when ringed, they survived, on the average, 4.4 years. The oldest male survived for at least 10 years 4 months and the oldest female for 8 years 4 months. The mean survival rate of adults from one breeding season to the next was 75.8%, which is remarkably high when compared with the genera! findings in tits.     

Seasonal variation of circulating plasma carotenoids in Mediterranean Great Tit males Parus major

Capsule Mediterranean Great Tits showed a marked increase in levels of circulating carotenoids during moult and autumn.

Aims To study seasonal variation in plasma carotenoid content during a whole annual cycle for Great Tits Parus major inhabiting a Mediterranean woodland.

Methods We used a sample of 71 adult male Great Tits captured in NE Spain during a whole year. Data were organized into four seasons (winter, breeding, moult and autumn). We sampled blood to extract plasma. Carotenoid plasma concentrations were analysed by High-performance liquid chromatography (HPLC).

Results Lutein and zeaxanthin content varied seasonally, with a marked increase in levels during moult and autumn. Within the moulting period, levels increased gradually as the season progressed. This pattern differed significantly from that previously described in northern European populations, where high values appear mainly in the breeding season. Carotenoid concentrations (lutein: 1.2?±?0.25, zeaxanthin: 0.07?±?0.03?µg mL^?1) were also lower than in northern Europe.

Conclusion Mediterranean Great Tits show a very different pattern of circulating carotenoids and lower levels than northern European populations. The increasing pattern of carotenoid availability found within the moulting period raises the need to control for the effect of sampling date when analysing data on carotenoid concentrations at different times of year.     

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.     

Paraphyly of the Blue Tit (Parus caeruleus) suggested from cytochrome b sequences

The phylogenetic relationships of the Blue Tit-Azure Tit assemblage (genus Parus; Aves: Passeriformes) were studied using mitochondrial DNA sequences of 24 specimens representing seven subspecies from Eurasia and North Africa. Previous work based on comparative morphological and acoustic data suggested a division of the Blue Tit (Parus caeruleus) into two species. Our analyses clearly indicate that the Blue Tit represents a paraphyletic assemblage, including a European/Middle Asian clade that is the sister group to the Azure Tit (Parus cyanus) and a North African clade. The North African clade (teneriffae subspecies group) is a sister group to the European Blue Tit/Azure Tit clade. We suggest a division of the Blue Tit into two separate species, Eurasian Blue Tit (Parus caeruleus s. str.) and African Blue Tit (Parus teneriffae). However, our data give no support for assigning species rank to Parus cyanus flavipectus, a subspecies of the Azure Tit, as suggested by several authors on morphological grounds.     

Parasites as mediators of heterozygosity-fitness correlations in the Great Tit (Parus major)

Positive correlations between heterozygosity and fitness traits are frequently observed, and it has been hypothesized, but rarely tested experimentally, that parasites play a key role in mediating the heterozygosity-fitness association. We evaluated this hypothesis in a wild great tit (Parus major) population by testing the prediction that the heterozygosity-fitness association would appear in broods experimentally infested with a common ectoparasite, but not in parasite-free broods. We simultaneously assessed the effects of parental and offspring heterozygosity on nestling growth and found that body mass of nestlings close to independence, which is a strong predictor of post-fledging survival, increased significantly with nestling levels of heterozygosity in experimentally infested nests, but not in parasite-free nests. Heterozygosity level of the fathers also showed a significant positive correlation with offspring body mass under an experimental parasite load, whereas there was no correlation with the mothers' level of heterozygosity. Thus, our results indicate a key role for parasites as mediators of the heterozygosity-fitness correlations.     

False Alarm Calls as a Means of Resource Usurpation in the Great Tit Parus major

Great tits Parus major regularly gave alarm calls in winter without the presence of actual or potential predators. Such false alarm calls were given to deceive both conspecifics and heterospecifics. False calls were given when flock-feeding sparrows Passer spp. monopolized a concentrated food source; if the food resource was dispersed false alarm calls were not used, independently of the presence of sparrows. Dominant great tits used alarm calls deceptively if a dominant conspecific was present on a concentrated food source but not if a subdominant individual was present; subdominant great tits were displaced by means of threat displays. Subdominant individuals gave false alarm calls both if dominant or subdominant conspecifics were present. False alarm calls were especially used when food was scarce or when great tits were feeding at a high rate, i.e. during snow storms and in the morning and the afternoon.     

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.     

Role of extrinsic factors in the control of clutch-size in the Blue Tit Parus caeruleus

Extrinsic factors that play a role in the control of clutch-size in Blue Tits Parus caeruleus were investigated. The disruption of ovarian follicular growth, and hence the cessation of egg-laying, is caused by a stimulus generated by eggs present in the nest. The timing of this disruption varies among females during the laying period and may happen as late as after the laying of the eighth egg of the clutch; the larger the clutch, the later the disruption of follicular growth. The timing of follicular disruption is also related to ambient temperature because the proportion of female Blue Tits that cease to lay increases when higher temperatures occur toward the end of laying. It is suggested that the use of temperature to control clutch-size may be adaptive because the food peak on which parents rely to feed their chicks is likewise affected by temperature.