Priit Kilgas

Hematological Health State Indices Predict Local Survival in a Small Passerine Bird, the Great Tit (Parus major)

In birds, it has been shown that reproductive effort may impair parental condition, while the relation of different condition indices to subsequent survival is still poorly understood. In this study, we measured body mass and various hematological condition indices in breeding great tits in relation to local survival. Number and quality of nestlings and the occurrence of second broods, potentially reflecting parents’ breeding effort, were also considered in analyses. The great tits, both male and female, that returned the following year had had a higher albumin/globulin ratio, lower plasma globulin concentration, and a lower heterophile/lymphocyte ratio during breeding in the preceding year, compared to those who did not return. Surviving males (but not females) also had had a higher level of circulating lymphocytes, compared to nonsurvivors. There was no correlation between breeding effort and survival. We conclude that better immunological state and lower stress in great tits during breeding were positively related to their survival probability.

Low Reproductive Success of Great Tits in the Preferred Habitat: A Role of Food Availability

Abstract: Habitat-related variation has been revealed in the seasonal reproductive patterns of great tits inhabiting mosaics of deciduous woodland fragments and managed coniferous forests. The number and quality of offspring tend to be higher in the non-preferred coniferous habitat compared with the preferred deciduous habitat. We explored whether these patterns can be explained by variation in food abundance and/or parental provisioning ability. Frass fall seemed not to be a reliable measure of the seasonal dynamics of nestling feeding conditions, although it is widely used for this purpose. No habitat-related differences were found in the tendency of parents to increase provisioning frequency in response to increased hunger levels of nestlings, suggesting that provisioning frequency as such is not a limiting factor for nestling growth. Higher feeding rates in deciduous habitat were associated with lower proportions of high-quality food items among prey delivered to offspring. These findings confirm that relatively high nestling feeding rates in birds may reflect the low quality of available food rather than the quality of parental care or an abundance of food in the environment. The results also indicate that deciduous forest habitat, though preferred by tits, may sometimes provide poorer brood-rearing conditions than the non-preferred, coniferous habitat. We suggest that the great tits preference for deciduous habitat, which presumably evolved in more southern regions, may be maladaptive in northern regions where deciduous woods are mainly young, secondary stands of alder and birch. Nomenclature: Tutin et al., 1993; Dickinson, 2003.

Long-term consequences of early ontogeny in free-living Great Tits Parus major

Environmental factors during early development may have profound effects on subsequent life-history traits in many bird species. In wild birds, sex-specific effects of early ontogeny on natal dispersal and future reproduction are not well understood. The objective of this work was to determine whether hatching date and pre-fledging mass and condition of free-living Great Tits Parus major have any subsequent effect on individuals’ natal dispersal and reproductive performance at first breeding. Both males and females dispersed longer distances in coniferous than in deciduous forests, while dispersal was condition-dependent only in males (heavier as nestlings dispersed farther). In females, mass and condition at pre-fledging stage correlated significantly with clutch size, but not with subsequent reproductive performance as measured by fledging success or offspring quality. In contrast, heavier males as nestlings had higher future fledging success and heavier offspring in their broods compared with those in worse condition as nestlings. The hatching date of female as well as male parents was the only parental parameter related to the number of eggs hatched at first breeding. These results indicate that pre-fledging mass and condition predict subsequent fitness components in this bird species. We suggest that sex-specific relationships between a disperser’s condition and its selectivity with respect to breeding habitat and subsequent performance need to be considered in future models of life-history evolution.

Calcium availability affects bone growth in nestlings of free‐living great tits (Parus major), as detected by plasma alkaline phosphatase

Recent studies have revealed that calcium limitation of avian reproduction may be a widespread phenomenon, affecting both egg properties and chick development. The effect of calcium shortage on the final body size of fledglings is usually rather weak, possibly owing to compensatory growth. Achieving full skeletal size is not, however, a reliable indication of complete ossification and it is possible that chicks with similar tarsus lengths are in different stages of skeletal development. We hypothesized that measuring plasma activity of the bone alkaline phosphatase (ALP), a highly specific marker for bone calcification, may reveal subtle developmental differences in full-grown fledglings, having experienced different levels of calcium availability during growth. In two seasons, a number of pairs of great tit Parus major were provided with calcium-rich material during the nestling period, while others were not supplemented (controls). While no significant differences in size of fledglings were detected between groups, bone-ALP activity at the pre-fledging stage was lower in the calcium-provided nestlings than in the control nestlings. This may indicate that supplemented chicks had completed the rapid phase of bone formation, but this process was delayed in controls. Measuring ALP as a marker of skeletal development expands our knowledge of how delayed skeletal development of chicks can result in protraction of the nestling period, thereby reducing the breeding success of adult birds.

Plumage Bacterial Assemblages in a Breeding Wild Passerine: Relationships with Ecological Factors and Body Condition

Microorganisms have been shown to play an important role in shaping the life histories of animals, and it has recently been suggested that feather-degrading bacteria influence the trade-off between parental effort and self-preening behavior in birds. We studied a wild breeding population of great tits (Parus major) to explore habitat-, seasonal-, and sex-related variation in feather-degrading and free-living bacteria inhabiting the birds yellow ventral feathers and to investigate associations with body condition. The density and species richness of bacterial assemblages was studied using flow cytometry and ribosomal intergenic spacer analysis. The density of studied bacteria declined between the nest-building period and the first brood. The number of bacterial phylotypes per bird was higher in coniferous habitat, while bacterial densities were higher in deciduous habitat. Free-living bacterial density was positively correlated with female mass; conversely, there was a negative correlation between attached bacterial density and female mass during the period of peak reproductive effort. Bacterial species richness was sex dependent, with more diverse bacterial assemblages present on males than females. Thus, this study revealed that bacterial assemblages on the feathers of breeding birds are affected both by life history and ecological factors and are related to body condition.

Chick Development in Free‐Living Great Tits Parus major in Relation to Calcium Availability and Egg Composition

Evidence from a number of avian studies suggests that limitation of exogenous calcium (Ca) may reduce egg quality and retard nestling growth. However, it is poorly understood whether reduction in chick growth in Ca‐poor areas is due to insufficient intake of dietary Ca or caused by maternal Ca limitation mediated through subtle changes in composition of eggs. In this study, we provide new evidence that Ca availability during egg formation may indeed affect egg composition and influence chick development of the great tit Parus major at early developmental stages. Ca‐supplemented birds breeding in base‐poor pine forests produced eggs with elevated yolk Ca concentration compared with controls, while no such effect of supplementation was detected in case of eggshell thickness. Nestling tarsus length in the first half of the nestling period was positively influenced by both yolk dry mass and yolk Ca concentration. The effect of supplementary Ca did not persist throughout the nestling period; initial effects of egg components disappeared as nestlings aged. We conclude that apparently normal eggs may harbor poor nutrient and mineral conditions for chick growth. Such subtle changes in composition of eggs can depress chick growth, especially in harsh years.

The Rate of Bone Mineralization in Birds Is Directly Related to Alkaline Phosphatase Activity

Recent studies have suggested that a biochemical marker, plasma alkaline phosphatase (ALP), can be used as a general indicator of skeletal development in vertebrate animals. In birds, age‐related variation in ALP activity, presumably due to bone formation processes, has been demonstrated, but to date, a direct connection between bone mineralization and enzyme activity has been elusive. In this study, we show that the activity of a bone isoform of ALP (bone ALP) is closely related to the overall rate of skeletal mineralization in nestlings of a small passerine bird, the great tit (Parus major L). Moreover, bone ALP activity predicted the rate of mineralization of leg and wing bones but not that of the skull. Liver isoform of ALP was only marginally related to the overall rate of skeletal mineralization, while no association with the mineralization of long bones was found. We conclude that bone ALP activity in the blood plasma is a reliable biomarker for skeletal mineralization in birds. This marker enables detection of subtle developmental differences between chicks of similar structural size, potentially facilitating the prediction of offspring mid‐ and long‐term survival.

Physiological Condition of Incubating and Brood Rearing Female Great Tits Parus major in Two Contrasting Habitats

Abstract. n Little is known about the physiological causes and consequences of habitat choice decisions in birds. We compared size-corrected body mass, hematocrit, plasma albumin, beta- and gamma-globulin and triglyceride concentrations, as well as the albumin/globulin ratio of female Great Tits breeding in deciduous and coniferous forests in Estonia. Females were sampled during incubation and during the chick-rearing period. Whereas the nest box occupation rate and clutch size were higher in the deciduous habitat, the female nutritional condition during incubation was better in the coniferous habitat. This habitat difference in condition was not explained by the differences in the start of egg-laying or clutch size. Females lost more mass from incubation to the chick-rearing stage in the coniferous than in the deciduous forests. Although the values of most blood parameters changed from incubation to the chick-rearing stage, no habitat-related change was observed. There were no habitat differences in the number and quality of fledglings or in female condition during the chick-rearing period. Our results indicate that incubating female Great Tits are in a worse nutritional state in the preferred deciduous habitat fragments than those in the non-preferred coniferous habitat. However, habitat-related differences in condition during incubation seem to be unrelated to habitat-specific reproductive decisions.

Antioxidant protection, immune function and growth of nestling great tits Parus major in relation to within-brood hierarchy

Differences in competitive abilities of siblings in birds can be caused by a combination of hatching asynchrony and intra-clutch variation in egg quality. However, very little is known how within-brood hierarchies affect the allocation of resources between different functions of the body. We examined the effects of within-brood hierarchy on growth of morphological parameters, blood plasma antioxidant protection and immune function of free-living great tit Parus major nestlings. To assure that competitive hierarchies occur, we experimentally delayed the start of incubation of the last two eggs in the clutch. At pre-fledging stage (day 13 post-hatch), late-hatched nestlings were smaller in body mass and wing length when compared to early-hatched nestlings, but no differences between siblings were found in tarsus length, plasma antioxidant potential, uric acid concentration, residual antioxidant potential (from regression with uric acid), hematocrit and response to phytohaemagglutinin injection. In early-hatched nestlings, the antioxidant potential and residual antioxidant potential measured in the middle of nestling period (day 6 post-hatch) were negatively related to body mass growth at early nestling stage, indicating that fast initial growth could reduce antioxidant properties of blood plasma.

Age-Related Changes in the Activity of Bone Alkaline Phosphatase and its Application as a Marker of Prefledging Maturity of Nestlings in Wild Passerines

Abstract Recent studies have suggested that bone alkaline phosphatase (ALP) may be a valuable indicator of skeletal development in wild birds. However, the information about age-related dynamics of ALP isoforms in passerines is very scanty. We examined age-related changes in the activity of bone ALP and liver ALP and tested the applicability of these isoenzymes as indicators of chick maturity in randomly selected nestlings of a small passerine bird, the Great Tit (Parus major). Bone ALP activity was elevated in the middle of the nestling period (day 8), when skeletal growth is assumed to be most rapid, and declined significantly during the prefledging stage (day 15 posthatch). Bone ALP activity at this age was positively and highly significantly related to the overall duration of nestling period and negatively and less significantly related to wing length and body mass. All three morphological traits of the 15-day-old nestlings were nearly significantly negatively correlated with the duration of the nestling period. Liver ALP activity neither changed with nestling age nor was related to nestling morphology. We suggest that prefledging activity of bone ALP is a more reliable indicator of nestling maturity than traditionally used morphological measurements.