Parental differences in brood provisioning by Hen Harriers Circus cyaneus

Capsule Females varied their provisioning patterns according to brood age and brood size, whereas males did not.

Aims To quantify how parents balance the needs of their offspring for food and protection.

Methods We studied 13 nests from hides and spent on average 101 hours per nest monitoring prey types, provisioning rate and the time spent at the nest by both sexes in relation to brood size and brood age.

Results Males always provided more food than females. Males brought similar amounts of prey items irrespective of brood size and nestling age, whereas females brought more prey and bigger items to larger and older broods. Females spent less time brooding larger broods, particularly early on.

Conclusions Hen Harrier parents share the provisioning burden, with each parent delivering prey as a function of brood care requirements, hunting capability and the behaviour of the other parent.     

Selection of foraging habitat and nestling diet by Meadow Pipits Anthus pratensis breeding on intensively grazed moorland

Capsule Foraging sites with low vegetation height and density, but with high arthropod biomass, are selected.

Aims To test the hypothesis that on intensively grazed moorland, breeding Meadow Pipits forage for nestling food where arthropod prey are most readily available, and therefore that foraging site choice is a function of prey abundance and vegetation structure.

Methods Observations of adults provisioning nestlings were made from hides positioned close to 19 nests within grazed, 3.3-hectare experimental plots at Glen Finglas, Scotland. Vegetation height and density and arthropod abundance from mapped foraging sites were compared with control sites. Prey items fed to nestlings were quantified and compared with their relative abundance.

Results Meadow Pipits selected foraging sites with significantly lower vegetation height and density, but with significantly higher arthropod biomass. Our data suggest that within foraging sites, Meadow Pipits select particular prey types to provision nestlings, in particular, Lepidoptera larvae, adult Tipulidae and Arachnida.

Conclusions In intensively grazed upland systems, it appears that Meadow Pipits select foraging sites that optimize total food abundance and accessibility. In order to understand how anticipated changes to livestock farming in Europe will affect grassland birds, we recommend that future studies should investigate the foraging and vigilance behaviour, diet composition and breeding success of a variety of bird species provisioning nestlings under a range of livestock management scenarios.     

Nest and foraging‐site selection in Yellowhammers Emberiza citrinella: implications for chick provisioning

Capsule Vegetation structure and invertebrate abundance interact to influence both foraging sites and nestling provisioning rate; when invertebrate availability is low, adults may take greater risks to provide food for their young.

Aims To investigate nesting and foraging ecology in a declining farmland bird whose fledging success is influenced by the availability of invertebrate prey suitable for feeding to offspring, and where perceived predation risk during foraging can be mediated by vegetation structure.

Methods Provisioning rates of adult Yellowhammers feeding nestlings were measured at nests on arable farmland. Foraging sites were compared with control sites of both the same and different microhabitats; provisioning rate was related to habitat features of foraging‐sites.

Results Foraging sites had low vegetation density, probably enhancing detection of predators, or high invertebrate abundance at high vegetation density. Parental provisioning rate decreased with increasing vegetation cover at foraging sites with high invertebrate abundance; conversely, where invertebrate abundance was low, provisioning rate increased with increasing vegetation cover.

Conclusions Vegetation structure at foraging sites suggests that a trade‐off between predator detection and prey availability influences foraging site selection in Yellowhammers. Associations between parental provisioning rate and vegetation variables suggest that where invertebrate abundance is high birds increase time spent scanning for predators at higher vegetation densities; however, when prey are scarce, adults may take more risks to provide food for their young.     

Diversionary feeding and nestling diet of Hen Harriers Circus cyaneus

Capsule: Diversionary feeding reduced Hen Harrier Circus cyaneus nestlings’ natural food intake by half. Red Grouse Lagopus lagopus scotica chicks constituted 0–4% of all nestling food items. Annually, this reduced annual grouse chick production by 0–6%.

Aim: To quantify proportions of diversionary and natural food (including grouse) delivered to Hen Harrier nestlings in relation to brood size, male status and natural prey abundance.

Methods: We recorded diversionary food provisioned to 25 Hen Harrier broods (2008–15) and studied the diet of 15 broods using observations from hides, nest cameras and regurgitated pellet analysis. Variation in nestling diet was analysed using compositional analysis.

Results: Hen Harriers took 76% of diversionary food provided. Depending on assessment method, average nestling diet was 44–53% diversionary food, 39–55% natural prey (including 24–45% passerines, 4–15% small mammals, 0–4% grouse chicks) and 0–9% unknown items. The amount of diversionary food consumed was not influenced by male status, brood size or natural prey abundance. The number of Red Grouse chicks delivered annually was 34–100% lower than expected under unfed conditions, however, the confidence intervals associated with these estimates were large.

Conclusion: Diversionary food influenced Hen Harrier nestling diet and reduced the number of Red Grouse chicks taken relative to modelled predictions. It may help reduce conflict between Hen Harrier conservation and Red Grouse shooting, but only if overall grouse productivity is thereby maintained or increased.     

Breeding behaviour and time-activity budgets of Bonelli’s Eagles Aquila fasciata: marked sexual differences in parental activities

ABSTRACT

Capsule: Differences in parental investment between sexes and stage of the breeding period were found in Bonelli’s Eagles Aquila fasciata.

Aims: To describe the sexual differences in parental behaviour of Bonelli’s Eagles and to assess the sex-specific pattern of variation in parental investment in relation to the breeding period.

Methods: Between 2006 and 2016, we monitored the parental behaviour of 11 pairs of Bonelli’s Eagles during the incubation and chick-rearing periods in southeastern Spain. Observations were made using 20–60× telescopes from points overlooking the territory at a distance of about 500–800?m from the nest.

Results: Our results reveal a marked division in parental duties in Bonelli’s Eagles. Females invested more effort in incubation, nest attendance, chick feeding and nest-building, while males contributed more to food provisioning. Nest attendance and feeding by females decreased with time, and both parents adjusted their provisioning effort in relation to nestling age. Most changeovers took place during the middle of the day, when male provisioning rates and temperatures reach their maximum.

Conclusion: Intersexual differences are discussed in the context of the prey capture difficulty hypothesis, which proposes that intra-pair prey differences, due to large sexual size dimorphism, should be particularly advantageous among raptors that pursue agile prey.     

6. ANOTHER NOTE ON SAROTHRURA ELEGANS

Summary

Dowsett-Lemaire, F. 1983. Studies of a breeding population of Waller's Redwinged Starlings in montane forests of south-central Africa. Ostrich. 54:105-112.

The breeding biology and behaviour of Waller's Redwinged Starling Onychognuthus walleri was studied for two seasons in forest patches on the Nyika Plateau, 2 200 m ad. (Mala?i-Zambia). In general behaviour (e.g. strong pair bond, fidelity to the nest site), O. walleri resembles other species of the genus. Twenty-six egg-laying records are from late August to mid-November (i.e. end of dry season to early rains). Suitable nest sites (natural holes in trees) seem to be in short supply, and the non-breeding population is far in excess of the breeding one. Incubation periods lasted 13 days (2) to 16 days (1). One nestling period was 29 days. Insects are more important than fruits in the diet of nestlings. Annual breeding productivity is low (0,5-0,6 young/breeding pair) because of heavy nest predation, and at tunes insect-food shortages leading to starvation of young. There were few re-laying attempts, and only one abnormal attempt at a second brood.

Two other congeneric species, the Slenderbilled Redwinged Starling O. tenuirostris and the African Redwinged Starling O. morio also breed on the Nyika. Notes on their feeding habits, numbers and nest sites are given. One nest site of O. tenuirostris on a wet rock face by waterfalls was taken over by O. morio in the following season.     

Diets of adult and nestling starlings (Sturnus vulgaris) in Hawke’s Bay,New Zealand

Abstract

Gizzards were examined from 334 adult and 62 nestling starlings collected in mixed farmland during 1971–72. The birds ate insects, spiders, earthworms, snails, millipedes, centipedes, seeds, and fruits. Starlings ate fewer subterranean animals (7%) than those usually living partially hidden (45%), on the ground (31%), or on vegetation (18%). About half the invertebrates eaten were 2–5 mm long and about a quarter 6–10 mm long. Nestlings tend to be fed significantly larger items than were eaten by adults. The commonest items in adult starlings were Coleoptera adults, Lepidoptera larvae, Hemiptera, and fruits; in nestlings, Coleoptera adults and Diptera adults and larvae were important. Earthworms were found in all the nestlings. More than 50% of adult gizzards contained earthworm chaetae in wetter months, but fewer in drier months. The diet of starlings, despite considerable overlap with the foods eaten by mynas, rooks, and magpies, included somewhat different components and proportions of the food supply. Fruits were found in adults only; most were probably eaten after harvest. Although predation on two major pasture pests—Costelytra zealandica and Wiseana cervinata larvae—was insubstantial, nearly 40% of the total invertebrates eaten by adult starlings were insect pest species.     

Importance of feeding ecology to the reproductive success of Blackbirds Turdus merula nesting in rural habitats

The feeding ecology of Blackbirds Turdus merula breeding in contiguous woodland and farmland habitats was studied over three years. The aim of the study was to investigate how reproductive success was influenced by nestling diet and the provisioning rates of parents feeding nestlings. Parental provisioning rates increased with brood size, and consequently individual nestlings were no lighter in larger broods. None of the environmental factors measured had strong effects on parental provisioning rate. The nestling diet was dominated by caterpillars and earthworms, the former occurring in a short period in the middle of the breeding season. The availability of earthworms was higher in woodland and was dependent on rainfall in farmland. Nestling mass and provisioning rates were marginally higher under predominantly earthworm diets. Nestling mass increased with rainfall in farmland only, and was higher in farmland than in woodland or woodland-edge, although it is doubtful whether this result is of any significance for fledgling survival. Overall, Blackbirds were able to provision their nestlings adequately throughout the breeding season across a range of conditions. There was no evidence to suggest that reproductive success was constrained by aspects of feeding ecology within the natural range of brood size.     

Parental behaviour of Spanish Imperial Eagles Aquila adalberti: sexual differences in a moderately dimorphic raptor

Capsule The sexes make significantly different contributions in the tasks of nest-building, incubation and food provisioning to chicks.

Aims To determine the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding).

Methods Between 1991 and 1998 focal observations were made at nests using 20–60× telescopes. During the incubation period, 11 pairs were studied involving a total of 2812 observation hours over 269 days. During the chick-rearing period, seven pairs were studied involving a total of 5499 observation hours spread over 503 days. The birds were sexed and identified individually on the basis of size, position during copulation, vocalization and plumage differences.

Results Significant differences were found between the sexes in parental behaviour. Males scarcely participated in incubation and contributed significantly more than the females only in food provisioning, both during incubation (food transfers to feed the female) and during chick-rearing (to feed the chicks). Females were responsible for most of the incubation, nest-building (during incubation and chick-rearing), brooding, shading and feeding of chicks. Nest attendance by females decreased over time. In both sexes, food provisioning increased with brood size.

Conclusion Intersexual differences are discussed in the context of the reversed sexual size dimorphism and parental investment strategies. We suggest that in Spanish Imperial Eagles reversed sexual size dimorphism is best explained by the prey capture difficulty hypothesis, than by parental role division during reproduction.     

The importance of a main dish: nestling diet and foraging behaviour in Mediterranean blue tits in relation to prey phenology

Insectivorous birds rely on a short period of food abundance to feed their young; they must time their reproduction to match the timing of Lepidoptera larvae, their main prey. Apart from the net result (i.e. birds are timed or mistimed with respect to the food's peak), an important aspect is the possible influence of other factors, such as the seasonality of the environment or the abundance and diversity of species contributing to the caterpillar peak, on birds' phenology and their ability to cope well with unpredictable food supplies. In a 2-year study, we explored the seasonal variation of nestling diet in Mediterranean blue tits Cyanistes caeruleus and how reproductive parameters (nestling condition, provisioning rates) are affected by the phenology and composition of food. We also examined the influence of the synchrony between offspring needs and caterpillar peak in shaping the composition of the nestlings' diet. We found that the effect of synchrony on nestling condition varied between years which may be partially due to differences in food peak attributes. The adequacy of birds' timing in relation to prey phenology affected foraging decisions; those birds that were not able to correctly adjust their timing were forced to rely on less preferred prey (tortricids). In this sense, we found that relative contribution of tortricids (smaller caterpillars but easier to get) and noctuids (preferred prey but more difficult to find) to the diet influenced nestling condition and parental provisioning effort; parents performed fewer feeding events and reared heavier nestlings as the contribution of noctuids to the diet increased. The relationship between the proportion of caterpillars and nestling mass was curvilinear, whereas that parameter was negatively affected by the percentage of pupae. Our results show how changes in diet composition may contribute to explain the effect of mismatching on birds' breeding performance.     

Relative influence of male and female care in determining nestling mass in a migratory songbird

Biparental care is common in birds, with the allocation of effort being highly variable between the sexes. In most songbird species, the female typically provides the most care early in the breeding cycle with both parents providing care when provisioning young. Food provisioning should be directly related to offspring quality; however, the relative influence each parent has on offspring quality has rarely been assessed at the nest level. Consequently, we were interested in assessing the relative influence male and female provisioning has on one measurement of offspring quality, nestling mass, in the black‐throated blue warbler Dendroica caerulescens. Over a six year period, 2003–2008, we collected information on average nestling mass per brood on day 6 of the nestling cycle and parental provisioning rates on day 7 of the nestling cycle from 182 first brood nests on three different study plots. We found that average nestling mass was directly related to male provisioning rate, while it was not related to female provisioning rate. On the other hand, estimated biomass provisioned had little influence on average nestling mass, calling into question its utility in assessing parental quality. Finally, there was some indication that parental influence on average nestling mass was dependent on the other parent's provisioning rate, suggesting that parents work in concert to influence nestling quality.     

Flexibility in the Foraging Behavior of Blue Tits in Response to Short‐Term Manipulations of Brood Size

Previous work suggests that short‐term changes in feeding rate are usually produced by the parent‐offspring interaction. However, few studies have properly tested this assumption. In this study, we attempt to explore the short‐term consequences of daily (within‐pair) brood size manipulations (reduced, original, and enlarged) on feeding behavior (provisioning rates, prey size, and prey type) of Mediterranean blue tits Cyanistes caeruleus. Total provisioning rates were lowest when broods were reduced in size and greatest when broods were enlarged. Mean prey size was also affected by the brood size changes: parents tended to bring larger prey when confronted with low brood demand reinforcing the view that a trade‐off exists between minimizing foraging time and maximizing food quantity. Such differences in feeding frequencies and the load sizes delivered may be explained by changes in the parents’ foraging tactic. Increase of brood size compelled parents to work harder and be less selective in prey choice; we found that stressed birds with a high level of feeding responsibility (hungry nestlings) opted to concentrate on more readily available food items (Tortricids). On the other hand, their immediate reaction when faced with a low level of feeding responsibility was to decrease this prey type in the diet, so that the percentage of other preys (Noctuids) in the diet increased. There was no intersexual difference in the way in which parents responded to the manipulation. In sum, our results revealed a flexibility in foraging strategies of blue tits to cope with changing scenarios, which supports the idea that provisioning behavior is largely governed by nestling demand.     

Demographic consequences of prey availability and diet of Red-billed Choughs Pyrrhocorax pyrrhocorax

Capsule Variation in prey availability appears to influence Chough fledging success and juvenile survival.

Aims To determine seasonal and annual variations in Chough prey and how these influence fledging success and juvenile survival.

Methods Chough faeces (n = 437, 3905 invertebrates) were collected year-round and analysed to determine diet composition. Seasonal and annual variation in prey abundance in Chough foraging habitat was assessed using pitfall trapping (n = 747, 27 124 invertebrates) between 1996 and 2003. Fledging success was estimated for a population of 12 breeding pairs; juvenile survival was estimated by year-round resighting (n < 2500) of individual birds that were colour-ringed as nestlings.

Results From April to June a high biomass of prey and a great variety of species were observed. Between July and October, both biomass and species diversity were reduced; prey consisted mainly of ants and a few beetle species. From November to March, biomass availability was intermediate, with the diet consisting mostly of Tipulidae larvae, plants and dung beetles. Chough juvenile monthly survival was low in August, November and December. Annual variation in fledging success was correlated with prey biomass availability in May.

Conclusion Seasonal variation in the availability of prey species and their biomass influences Chough demography.     

Habitat quality, nestling diet, and provisioning behaviour in great tits Parus major

Variation in early nutrition is often a strong predictor of offspring condition and fitness. In the case of woodland passerine birds, nestling diet is determined by the spatiotemporal distribution of prey items such as caterpillars during the nestling period, and is usually quantified as differences in provisioning behaviour between habitats. However, the habitat level does not account for variation between individual territories, the level at which competition and selection are assumed to operate. Here we use nestbox cameras and Radio Frequency Identification technology (RFID) to simultaneously assess variation in both nestling diet (components) and provisioning rates (quantity) among a sample (n=22) of different quality great tit Parus major territories selected from a larger breeding population (n=310 fledged broods) in a single year. Caterpillars were by far the most numerous item provisioned to nestlings (mean=75% of prey items), as expected given the known importance of this food source for this species. Broods raised close to an oak tree, or far from the woodland edge, were provisioned the highest proportion of caterpillars. Provisioning rates declined seasonally and there was a weak association between low provisioning rates and caterpillar rich diets. During the first week of the nestling stage, nestling condition was unrelated to the proportion of caterpillars in the diet, provisioning rates and oak proximity. Condition at fledging was slightly improved in broods fed a higher proportion of caterpillars in the diet and in broods raised close to an oak tree. However, in our data early breeding was the only predictor of recruitment success, although power was low for this test. Analyses of long‐term data (41 years) from the same population confirmed a relationship between oak proximity and fledgling mass, but not recruitment success. Our results suggest that territory level environmental variation can affect offspring condition, probably through observed changes in nestling diet, but that such variation does not necessarily produce discernable effects on offspring fitness.     

Feeding behaviour and diet composition of Marsh Harriers Circus aeruginosus in agricultural landscapes

Capsule Diet composition and feeding behaviour of breeding birds differed between areas of high and low agricultural intensification.

Aims To analyze diet composition and feeding behaviour of Marsh Harriers Circus aeruginosus in agricultural landscapes with different degrees of agricultural intensification.

Methods Diet composition and feeding behaviour was assessed by focal observations at nests during breeding seasons in 2001–03 in two agricultural areas within the eastern Ebro Basin (on the northern Iberian Peninsula) which differed in their degree of agricultural intensification: a traditional non-irrigated and non-intensively managed farmland area; and an irrigated and intensively managed farmland area.

Results Marsh Harriers in the intensively managed area took higher percentages of small mammals than harriers in the traditional area managed at low-intensity, where they also had a more diverse diet. Male delivery rates increased throughout the breeding season in the intensively managed area. On the contrary, no significant trend in delivery rates was observed in the traditional area, where harriers turned to larger prey late in the season.

Conclusion Marsh Harriers probably took advantage of different prey types in intensively managed and traditional farmland according to prey availability. Differences in diet composition seem to be related to different foraging strategies adopted by harriers in traditional and intensively managed farmlands. In the traditionally managed farmlands, harriers responded to increases in the energy requirements of the brood over the course of the breeding season by taking larger prey, whereas in the intensively managed farmlands harriers increased feeding rates.     

Habitat structure modulates nestling diet composition and fitness of Blue Tits Cyanistes caeruleus in the Mediterranean region

Capsule: The nestling diet of Blue Tits Cyanistes caeruleus is influenced by parental effort and habitat type, and consequently has an impact on breeding success.

Aims: In a three-year study, we compared the nestling diet of Blue Tits in two Mediterranean forests (pinewood and oakwood) and tested its implications for breeding success.

Methods: Adults were captured at the nest to obtain morphological measurements, and provisioning behaviour was recorded when chicks were 11 days old. Nestling tarsus length and body mass were measured on day 13 after hatching.

Results: Caterpillars constituted the largest proportion of nestling diet in both habitats, however, higher numbers and biomass of noctuid, as well as higher numbers of tortricid larvae, were provided to nestlings in the pinewood. Furthermore, females provided tortricids more often than males, whereas males supplied more geometrid larvae and spiders. We found a more generalist diet for nestlings raised in the pinewood. Also, a greater number of young fledged when their diet included more tortricids and was more generalist, and Blue Tit nestlings raised on a diet with a higher number of spiders were in better body condition.

Conclusion: Differences in nestling diet between habitat types contribute to explain variance in breeding performance and therefore demonstrate diverse foraging behaviour strategies among populations.     

Offspring growth and mobility in response to variation in parental care: a comparison between populations

Life history theory emphasizes the importance of trade‐offs in how time and energy are allocated to the competing demands of growth, fecundity, and survival. However, avian studies have historically emphasized the importance of resource acquisition over resource allocation to explain geographic variation in fecundity, parental care, and offspring development. We compared the brood sizes and nestling mass and feather growth trajectories between orange‐crowned warblers Oreothlypis celata breeding in Alaska versus California, and used 24‐h video recordings to study the relationship between parental care and growth rates. Per‐offspring provisioning rates were highest in the smallest broods, and food delivery was positively correlated with nestling growth over the 24‐h period only in Alaska. Females in Alaska spent more time brooding, and juveniles there showed faster feather growth and earlier mobility compared with those in California. We also found differences in the energetic and nutritional content of insect larvae that could facilitate the observed differences in nestling growth relative to food provisioning. Our results point to the potential importance of food quality and parental provisioning of warmth, in addition to food, for explaining avian growth patterns. We highlight the need to quantify multiple dimensions of parental care and of offspring growth and development, and to better understand the relationships between feather growth, nestling period length, and fledgling mobility.     

Brood provisioning rates and fledgling behavior of Cordilleran Flycatchers in southwestern Colorado

The behavior of young songbirds after fledging is one of the least understood phases of the breeding cycle, although parental provisioning rates and movement of fledglings are key to understanding life history evolution. We studied Cordilleran Flycatchers (Empidonax occidentalis) at two sites in southwestern Colorado, USA, from 2012 to 2017. We banded and sexed breeding adults to determine the relative contributions of males and females to nestling and fledgling care, and attached radio‐transmitters to nestlings to facilitate observations of brood behavior after fledging. Females made 60% and 78% of total observed feedings of nestlings and fledglings, respectively. Parental provisioning rates increased with nestling age, and per‐nestling provisioning rates increased with brood size. Parental provisioning rates declined just before fledging, then increased just after fledging. Fledging times of individuals in broods were asynchronous and concentrated during the late afternoon and early evening. Males stopped caring for fledglings before females even though this species is single‐brooded, with some late‐season broods being abandoned by males. Broods spent the first three weeks after fledging within 400 m of nests, after which they began to disperse. Most aspects of the breeding biology of Cordilleran Flycatchers in our study, including the duration of nestling and fledging periods, female‐dominated provisioning, and movement patterns of fledglings, were similar to those of other Empidonax species. However, the times when young fledged were not concentrated in the morning as reported in most other songbirds, and this result warrants additional study of the timing of fledging in ecologically and taxonomically similar species. The increased per‐nestling provisioning rate with increasing brood size was unexpected, and additional study is needed to determine if this increase results from a trade‐off between adult annual survival and productivity favoring increased provisioning of young in larger broods, or from the existence of high‐quality individuals where larger clutches and higher provisioning rates are linked.     

Parental investment asymmetries of a globally endangered scavenger: unravelling the role of gender,weather conditions and stage of the nesting cycle

ABSTRACT

Capsule: In Egyptian Vultures Neophron percnopterus, both sexes invested similar parental effort throughout the breeding period. However, there was variation in the degree of intensity of parental care during some stages of the breeding period, suggesting that sex-role specialization exists for some activities.

Aims: To quantify parental care behaviour of Egyptian Vultures for the first time and to examine the role of sex, weather conditions, and stage of nesting cycle on breeding ecology.

Methods: We monitored 15 nests of Egyptian Vultures to analyse parental care investment. We collected data on nine different behavioural parameters/activities per sex, which were recorded throughout the entire breeding period. Variation in parental investment was analysed using generalized linear mixed models.

Results: Females invested more effort in incubation/brooding (61.45% for females and 31.54% for males) and egg turning (0.45?events/h for females and 0.37?events/h for males) while males contributed more to nest material delivery to the nest (0.67?deliveries/h for males and 0.14?deliveries/h for females). Conversely, both sexes invested the same effort in nestling attendance (21.89% for females and 21.21% for males) and food provisioning (0.28?items/h for females and 0.25?items/h for males). Furthermore, parental investment was not affected by weather, especially during critical moments such as incubation/brooding, however, changeover rate was positively related to temperature.

Conclusion: Our results suggest that, in the Egyptian Vulture, one sex is not entirely responsible for a particular task and the compensatory effort of the other mate is required. Finally, our findings indicate that major events such as incubation onset and hatching caused important shifts in the patterns of parental investment.     

The pattern of Dunlin Calidris alpina distribution and abundance in relation to habitat variation in the Flow Country of northern Scotland

Capsule Folivorous caterpillars constituted the majority of nestlings’ food in a primeval forest. Blue Tit broods only partially matched the caterpillar peak, and the mismatch did not affect food composition or nesting success.

Aims To describe factors influencing the timing of reproduction in Blue Tits under primeval conditions (Bia?owie?a National Park, Poland) and to check whether they schedule breeding so as to synchronize broods with a seasonal caterpillar peak.

Methods We gathered information on phenology of leaf development, seasonal availability of folivorous caterpillars (frass collection), timing of Blue Tit breeding, composition of its nestling food, and nest fate over a three-year period.

Results Caterpillars constituted c. 74% of nestling diet, but only 17–65% of broods matched the caterpillar peak in any season. Neither total nest loss, nor frequency of brood reduction depended on the level of mismatch. Caterpillar availability was probably adequate every year, regardless of the amount of mismatch, and no selective advantage of precise matching was detectable. Phenological events at all trophic levels occurred earlier in warmer springs. Egg-laying coincided with tree bud burst and appearance of caterpillars, but was not critically dependent on their timing.

Conclusion The observations are consistent with the view that Blue Tits under primeval conditions in Bia?owie?a National Park, Poland, breed as early as possible, rather than synchronizing their breeding with the caterpillar peak later in the season.