Diet Of Nestlings Research Articles

Food resource exploitation strategies of two reedbed specialist passerines: Reed Parrotbill and Oriental Reed Warbler

We studied the nestling diet of two reedbed specialist passerines, Reed Parrotbill (Paradoxornis heudei) and Oriental Reed Warbler (Acrocephalus orientalis) in a tidal reedbed in the Changjiang River Estuary, China. Reed Parrotbills delivered mainly Homoptera, Diptera, and Leptidoptera to their nestlings, and Oriental Reed Warblers delivered mainly Diptera, Hymenoptera, Araneida, and Lepidoptera to their nestlings. More than 98% of the diet of nestling Reed Parrotbills consisted of wingless items and .97% consisted of concealed items, indicating that Reed Parrotbills are limited in their ability to catch winged prey capable of strong flight and rather they retrieve prey from within reed shoots using their large and strong beaks. About 85% of the diet of nestling Oriental Reed Warblers consisted of winged items and .99% consisted of exposed items, indicating that Oriental Reed Warblers are limited in their ability to retrieve prey from within reed shoots and depend on their flight ability to catch prey capable of flight. Oriental Reed Warblers had significantly more taxonomic categories of prey in their diet, significantly wider diet niche, and significantly higher diversity in nestling diet than Reed Parrotbills. Our study demonstrates that although these two species breed sympatrically in reedbeds as reedbed specialist, Reed Parrotbills and Oriental Reed Warblers use different strategies in their exploitation of food resources. Received 14 May 2013. Accepted 26 October 2013.

Breeding ecology of the Chestnut-backed Sparrowlark Eremopterix leucotis in an agroecosystem in the Limpopo province, South Africa

We studied the breeding ecology of the Chestnut-backed Sparrowlark Eremopterix leucotis over three years between 2008 and 2010. The breeding season was bimodal with a main peak in laying in autumn (March–April) and another smaller peak in spring (September–October). Nest microhabitat analyses showed they prefer nesting in open areas with lots of bare ground (median 67.5%). Nest entrance directions were biased towards the south (mean vector (µ) = 186.44°). The majority of nests (78.2%) had an apron at the nest entrance. The mean clutch size was 1.88 but there was geographic variation in clutch size between northern and southern races of the species. The mean incubation and nestling periods were 10.33 d (range 10–11 d) and 9.20 d (range 8–10 d), respectively. The results suggest that parental contributions during incubation are almost equal, but females made significantly more food deliveries during the nestling period compared to males. The diet of nestlings comprised mainly of invertebrates (50.2%), seeds (34.4%) and unidentified food items (15.4%). Breeding success was low, averaging 16.1% (range 8.1–20.6%), and the average number of fledged young per pair was 0.36 ± 0.71. Replacement broods were common and we also recorded repeat brooding attempts.

Seasonal dynamics of leaf-eating insects biomass and its influence on carotenoid content in feathers of Great Tit nestlings

Studies performed at the Zvenigorod Biological Station of the Moscow State University in 2010 showed that the biomass of leaf-eating insects during the first nesting cycle of the Great Tit was three times higher than that during the second cycle. As estimated from video recordings made at the nests, the proportions of leaf-eating larvae in the diet of first-and second-brood nestlings were 84.3 and 46.0%, respectively. In both cases, most of them were caterpillars of butterflies and moths (Lepidoptera), and their total proportion in the diet was higher in the first-than in second-brood nestlings. Lepidopteran larvae are the main source of carotenoids for the birds, and Raman spectroscopic analysis for carotenoids in ventral feathers confirmed that their content was also higher in the first-brood nestlings.

Nestling Diets and Provisioning Rates of Sympatric Golden-fronted and Ladder-backed Woodpeckers

We examined comparative food use and provisioning of Golden-fronted (Melanerpes auri- frons) and Ladder-backed (Picoides scalaris) wood- peckers at the Rob and Bessie Welder Wildlife Foundation Refuge, in San Patricio County, Texas. We combined video surveillance and direct observa- tions to monitor provisioning rates and identify items delivered by adult woodpeckers to nestlings. We collected 328 hours of data at Ladder-backed Wood- pecker nest cavities and 230 hours of data at Golden- fronted Woodpecker nest cavities. Ladder-backed Woodpecker nestling diets consisted of 100% animal matter, comprised of invertebrate larvae (99%) and invertebrate adults (,1%). Diets of Golden-fronted Woodpecker nestlings were also high in animal matter (77%) with more invertebrate adults (55%) and fewer invertebrate larvae (27%), but also included vegetable matter (16%). Morisita's measure of overlap suggested a relatively low dietary overlap of 31% between ne- stlings of these two sympatric woodpecker species. Foraging methods used by these species may explain their low dietary overlap and facilitate their coexistence. Received 8 March 2012. Accepted 2 August 2012.

Diet of Starling Sturnus vulgaris nestlings on farmland: the importance of Tipulidae larvae

Capsule Tipulidae larvae are a key resource for adult Starlings provisioning their young on lowland farmland. Aims (i) To describe Starling nestling diet on lowland farmland. (ii) To examine the effects of brood size variation and nestling age on Starling parental food provisioning. Methods Over 4 years, we observed parental food provisioning at 42 nests across 4 sites on lowland farmland in Oxfordshire, UK using nestbox video recorders. Results Tipulidae larvae were the most frequent prey item recorded in provisioning loads (52%), the next most frequent were winged insects (11%), then Coleoptera larvae (6%), Lepidoptera larvae (5%) and Lumbricidae (5%), with 21% of prey unidentified. Estimates of prey lengths, dry mass and total energy content also confirmed that Tipulidae larvae were the key prey source. Generalized linear mixed-effects models showed that larger broods received fewer Tipulidae larvae per nestling per day and that the proportion of Tipulidae larvae in the diet did not vary with brood size or nestling age. Conclusion Our results support the idea that Tipulidae larvae are the primary dietary item for nestling Starlings on lowland farmland.

Breeding Ecology of the Pink-Billed Lark,Spizocorys conirostris, in an Agricultural Landscape in South Africa

We studied the breeding ecology, parental care and nesting success of the pink-billed lark, Spizocorys conirostris, in an agricultural landscape in the Limpopo Province of South Africa, from October 2008 to October 2010. The results are compared with data in Birdlife South Africa's Nest Record Card Scheme. Nesting was observed between February and May, with peak activity in April and May. Fifty-three nests were found and the nest structure, dimensions and microhabitat characteristics are described. Egg mass and dimensions showed no regional variation but there was evidence of geographical variation in clutch size. There was no significant difference (P ≥ 0.05) in the rate of food delivery by males and females, but the results suggest there may be inter-sexual differences in the type of food delivered to nestlings. Invertebrates comprised two-thirds of the diet of nestlings while seed made up the remainder. The growth and development of nestlings are described for the first time. The incubation period was 12 days and the nestlings fledged after 10–13 days. Breeding success was very low, averaging 12.8% over the two years of this study.

Breeding ecology of the pink-billed lark, Spizocorys conirostris, in an agricultural landscape in South Africa

We studied the breeding ecology, parental care and nesting success of the pink-billed lark, Spizocorys conirostris, in an agricultural landscape in the Limpopo Province of South Africa, from October 2008 to October 2010. The results are compared with data in Birdlife South Africa’s Nest Record Card Scheme. Nesting was observed between February and May, with peak activity in April and May. Fifty-three nests were found and the nest structure, dimensions and microhabitat characteristics are described. Egg mass and dimensions showed no regional variation but there was evidence of geographical variation in clutch size. There was no significant difference (P ⩾ 0.05) in the rate of food delivery by males and females, but the results suggest there may be inter-sexual differences in the type of food delivered to nestlings. Invertebrates comprised two-thirds of the diet of nestlings while seed made up the remainder. The growth and development of nestlings are described for the first time. The incubation period was 12 days and the nestlings fledged after 10–13 days. Breeding success was very low, averaging 12.8% over the two years of this study.

Prey selectivity and parental feeding rates of Blue Tits Cyanistes caeruleus in relation to nestling age

Capsule The effect of nestling age (7, 10 and 13 days old) on prey choice by Blue Tits Cyanistes caeruleus seems to be related to time constraints on food selectivity rather than chick gape-size limitations.Aims To study age differences in the nestling diet of Blue Tits and how the relative contribution of each parent varies as the nestlings grow older.Methods The provisioning activity of Blue Tit parents was recorded using infrared video cameras when chicks were 7, 10 and 13 days old.Results Nestling age had no influence on the percentage of folivorous caterpillars in the diet of nestlings. Male and female parents changed their provisioning strategy with nestling age; this change was similar in adults of both sexes. Blue Tit nestlings received a smaller proportion of spiders and a greater proportion of Tortricid larvae (small, low-mobility caterpillars) as they grew older. At the age of seven days, females brought a lower proportion of Noctuids (large caterpillars) to the nest than their mates. The role of each parent in provisioning young varied with nestling age. Males fed their young at a lower rate when they were seven days old compared with later in the nestling period, whereas females tended to invest more in provisioning effort early in the nestling period in comparison with subsequent age-classes.Conclusion Contrary to what would be expected based on the gape-size constraint hypothesis, the youngest nestlings (seven days old) were fed with a higher proportion of large caterpillars (Tortricidae). Our results suggest that at these ages nestling gape-size does not restrict parents' prey-choice strategies.

The condition of nestling House Sparrows Passer domesticus in relation to diet composition and the total amount of food consumed

Capsule A higher animal component in the diet and a greater amount of food result in better condition. Aims To investigate the relative importance of different food types to nestling House Sparrows. Methods Faecal sac samples (n = 206) from 106 nestlings of 31 broods were analyzed in 2 breeding seasons (2008, 2009). The nests were in a nestbox colony on a farm in south Bohemia, Czech Republic. Results Faecal sacs contained 362 identifiable animal food objects belonging to 5 arthropod orders. The nestlings were fed primarily on beetles (mainly Scarabeidae) and Diptera (mainly muscids and tipulids). The total amount of food found in the faecal samples increased with nestling age. This increase was because of an increase in the total mass of plant material; the total mass of animal component did not change with nestling age. The total amount of food, and the mass of animal component in the diet of older nestlings were all positively related to nestling body condition. Conclusions To compensate for the increasing demands of older nestlings, the parents increased the mass of plant material in the nestlings' diet. This might have been caused by an upper limit to their ability to catch invertebrate prey, or by the growing nestlings' preference for plant material. The effect of food amount and animal component in nestling diet on their condition stressed the importance of arthropods for the breeding success of House Sparrows.

¿Cómo reproducirse exitosamente en un ambiente cambiante? biología reproductiva del Loro Barranquero (Cyanoliseus patagonus) en el Noreste de la Patagonia

HOW TO REPRODUCE SUCCESSFULLY IN A CHANGING ENVIRONMENT? BREEDING BIOLOGY OF THE BURROWING PARROT CYANOLISEUS PATAGONUS IN NORTHEASTERN PATAGONIA.— During more than 14 years, detailed studies have been carried out on the breeding biology of a population of Burrowing Parrot (Cyanoliseus patagonus) in north-eastern Patagonia, Argentina. Here, we review results of these studies on colonial nesting, predation, breeding habitat selection, and the diet of adults and nestlings during the breeding season. We also review information about movements during the breeding season and along the year, abundance estimates and the genetic structure of different populations of this species. The ecological role of the Burrowing Parrot in the Monte region is here discussed in detail. We emphasise those studies on the relationships of breeding success, individual body condition, physiological stress, and environmental conditions during the breeding season, particularly those related to El Nino and La Nina phases of the El Nino Southern Oscillation. Finally, we discuss research lines under development in Argentina, including the study of feather pigments (psittacofulvins), the apparent absence of hemoparasites, the high numbers of ectoparasites, the apparent strong innate immunity in this species, and the species' dispersion patterns.

Faecal Analysis as a Method of Nestling Diet Determination in Insectivorous Birds: A Case Study in Blue TitsCyanistes caeruleusand Great TitsParus major

Abstract. Insectivorous birds have very diversified diet, but particular species usually show some specialisation, which leads to a varying level of dependence on special prey. Their reproductive cycles are dependent on the availability of appropriate arthropods; in the case of Blue Tits Cyanistes caeruleus and Great Tits Parus major reproduction is usually coordinated with the availability of caterpillars as the key food for nestlings. Therefore a picture of nestling diet, with some estimates of the actual frequency of caterpillars and alternative prey, is an important component of explanations of aspects of Tit life-histories. As in most cases a rough assessment of diet composition and relative proportions of prey items is satisfactory, we suggest that faecal analysis is a feasible method to get such a picture. Droppings may be collected to examine the diet of individual nestlings grouped in broods, at a particular age stage or at many stages reflecting development. The most time-consuming part of this ...

Using Stable Isotopes To Determine Dietary Patterns In Bonelli's Eagle (Aquila fasciata) Nestlings

Bonelli's Eagle (Aquila fasciata) is one of the most endangered raptor species in Europe due to high adult and subadult mortality rates, habitat loss, and a decrease in populations of its most important prey, European rabbits (Oryctolagus cuniculus) and Red-legged Partridges (Alectoris rufa). During the breeding season of 2008, we studied the diet of Bonelli's Eagles at 15 breeding territories in Catalonia, northeastern Iberian Peninsula, through a conventional pellet analysis and stable isotope analyses (SIA) of nestlings' feathers. Our objectives were to investigate the diet of Bonelli's Eagle nestlings and to determine whether SIA allowed accurate representation of their dietary patterns. The pellet analysis revealed a broad diet including pigeons (Columba spp.; 31.1%), European rabbits (27.9%), “other birds” (16.2%), Red-legged Partridges (13.1%), Eurasian red squirrels (Sciurus vulgaris; 5.2%), ocellated lizards (Timon lepidus; 2.6%), Yellow-legged Gulls (Larus michahellis; 2.2%) and “other mammals” (1.7%). Diet composition was heterogeneous and varied markedly among nestlings from different breeding territories. We found a significant positive correlation between δ13C and the frequency of Eurasian red squirrels in the diet, and a significant negative correlation between δ13C and the frequency of Red-legged Partridges, which are species that occur in forested and open habitats, respectively. The values of δ15N were not correlated with the consumption of any prey category. However, its wide range of values suggested a global diet with a broad diversity of prey species from at least two different trophic levels. Finally, δ34S were higher for those nestlings that fed on Yellow-legged Gulls. Our study provided the first isotopic approach to the trophic ecology of Bonelli's Eagle nestlings, and we concluded that δ13C, δ15N, and δ34S may be useful for assessing nestlings' dietary patterns in terms of main prey consumption and prey trophic level.El águila Aquila fasciata es una de las rapaces más amenazadas de Europa debido a la elevada tasa de mortalidad adulta y preadulta, la degradación y pérdida del hábitat, así como una disminución de sus principales presas como el conejo europeo (Oryctolagus cuniculus) o la perdiz roja (Alectoris rufa). Durante la temporada de cría de 2008 se estudió la dieta de 15 parejas reproductoras de A. fasciata en Catalunya, noreste de la Península Ibérica, a través del análisis convencional de egagrópilas y el análisis de isótopos estables (AIE) en las plumas de los pollos. Nuestros objetivos fueron investigar la dieta de los pollos de A. fasciata, así como determinar si el AIE permite representar con exactitud sus patrones tróficos. El análisis de egagrópilas reveló una dieta variada que incluyó palomas (Columba spp.; 31.1%), conejo europeo (27.9%), “otras aves” (16.2%), perdiz roja (13.1%), la ardilla Sciurus vulgaris (5.2%), el lagarto Timon lepidus (2.6%), la gaviota Larus michahellis (2.2%) y “otros mamíferos” (1.7%) como principales categorías de presas. Sin embargo, la composición de la dieta fue heterogénea y se hallaron diversos patrones tróficos entre pollos pertenecientes a diferentes territorios de cría. Asimismo, se halló correlación positiva entre δ13C y la frecuencia de ardilla roja en la dieta, y negativa entre δ13C y la frecuencia de perdiz roja, especies presentes en hábitats boscosos y abiertos, respectivamente. No hubo correlación entre δ15N y el consumo de presas. Sin embargo, su amplio rango de valores sugirió una dieta con diversidad de presas pertenecientes, al menos, a dos niveles tróficos diferentes. Finalmente, δ34S fue mayor en aquellos pollos que consumieron la gaviota L. michahellis. Este estudio aborda por vez primera la ecología trófica en pollos de A. fascista a partir del AIE, concluyendo que δ13C, δ15N y δ34S son útiles para la evaluación de sus patrones tróficos en términos de consumo de las principales presas y niveles tróficos de las mismas.

No Effect of Carotenoid Supplementation on Phytohemagglutinin Response or Body Condition of Nestling House Wrens

Carotenoids are an essential and often limiting resource in animals and play important roles in immune system function. In birds, the period shortly after hatching is an energetically demanding stage characterized by rapid growth in body size and organ systems, including the immune system. Availability of carotenoids for the growing nestlings may be of particular importance and potentially limiting at this stage of development. We tested the hypothesis that the availability of carotenoids for the embryo in the egg and in the diet of nestlings limits the condition and immune responses of nestling house wrens (Troglodytes aedon Vieillot 1809), a species with melanin-based plumage pigments. In one experiment, nestlings within females' second broods were randomly assigned to receive either a control or a lutein supplement (2008); in a second experiment, females, before their first broods, were either induced to lay additional eggs or not induced, and nestlings within both kinds of broods were supplemented as in the first experiment (2009). There were no significant effects of lutein supplementation on nestling condition or phytohemagglutinin response. There was a significant effect of lutein supplementation on nestling mass in 2008, but the difference was opposite to that predicted. Moreover, even when breeding females were stressed by inducing them to lay supernumerary eggs, lutein supplementation of nestlings had no effect on the size or condition of nestlings hatching from these eggs. These results suggest that maternally derived lutein in the egg and that provided in the diet of nestlings are not limiting to normal development and to the components of the immune system involved in the phytohemagglutinin response of nestling house wrens.

Nestling diet of the Common Magpie (Pica pica) in urban and agricultural habitats

Several processes may be responsible for the urbanization of the Common Magpie (Pica pica), a species spreading widely in European towns during the last 50 years. Greater supply or better availability of food could play a role in the successful colonization of urban habitats by this species. We compared the nestling diet of Magpies within (urban) and adjacent to the city (rural) of Prague, Czech Republic, using the neck-collar method, and studied parental foraging behavior and micro-habitat associations in the city of Prague. Although the nestling diet was different between urban and rural areas, invertebrates (mainly Coleoptera) were the most frequent prey in both areas. Anthropogenic food was more abundant in urban than in rural areas. The nestling diet differed from the potentially available food supply in both urban and rural areas: Annelida and Lepidoptera were preferred, while Isopoda, Diplopoda, Orthoptera and Hymenoptera were neglected. In urban areas, Magpies foraged actively (i.e., by walking) and by perching. Prey was collected mostly from the ground. Magpies foraged mainly at sites covered with short vegetation. Utilization of short vegetation was proportional to its availability, whereas tall vegetation was used less than could be expected by availability. Short vegetation dominated the home ranges of Magpies in urban areas, while tall vegetation was more common in the Magpie home ranges in rural areas.

Diet of red-breasted flycatcher and Siberian tit nestlings in Central Yakutia

Results of comparative analysis of food selectivity patterns for two ecologically close hollow-nesting birds—red-breasted flycatcher Ficedula parva (Muscicapidae) and Siberian tit Parus cinctus (Paridae)—according to the way of catching, the place of foraging and the daily activity in nestling feeding are considered.

The diet of Great Tit Parus major nestlings in a Mediterranean Iberian forest: the important role of spiders

The diet of the Great Tit Parus major when rearing chicks has been described in many studies. However, data from the Mediterranean area is scarce. Here we describe the diet of nestlings in a population of Great Tits in a Mediterranean forest in Barcelona (north–east Spain) during two breeding seasons using two methods: neck–collars and video recording. The main prey were caterpillars (44% from neck–collar data and 62% from video–recorded data), but in our latitudes spiders also seemed to be an important food resource (24% from neck–collar data and 42% from video–recorded data). We did not find any significant differences in the quantity of spiders collected by parents in relation to stage of chick development, main vegetation surrounding nest boxes, size of the brood, or year. Our results stress the importance of spiders as a food source in Mediterranean habitats.

The feeding constraint hypothesis: prey preparation as a function of nestling age and prey mass in the Eurasian kestrel

The feeding constraint hypothesis states that an inability of young nestlings to ingest prey included in the diet of older nestlings and adult birds affects the evolution of parental behaviour, and predicts that the extent of prey preparation would increase with prey size and decrease with nestling age. In the Eurasian kestrel, Falco tinnunculus, a small raptor with a wide diet, parents often prepare prey prior to delivery at the nest, most notably by decapitation. We studied this behaviour by video monitoring prey deliveries at 29 nests for a total of about 200 days over 3 years. The probability of a prey item being decapitated prior to delivery differed between prey types and prey sizes; none of the insects or common lizards, Zootoca vivipara, and almost none of the shrews (Soricidae) were decapitated, whereas voles (Microtinae) and birds were commonly decapitated. For voles the probability of being decapitated decreased with nestling age, which supports the feeding constraint hypothesis because the nestlings’ gape size limit and swallowing capacity would increase with age. For both voles and birds the probability of being decapitated increased with prey body mass, suggesting that kestrel nestlings may be unable to swallow, digest or egest skulls from larger prey. We suggest that the extent to which kestrel parents decapitate prey prior to delivery is an effect of their nestlings’ age-dependent swallowing capacity and that the age of the nestlings therefore imposes constraints on the kestrel parents’ foraging behaviour.

Effect of Age and Diet on Total and Paracellular Glucose Absorption in Nestling House Sparrows

Size and hydrolytic activity of the gastrointestinal tracts of altricial birds undergo large and rapid changes during ontogeny. However, nothing is known about the development of the capacity of absorption of products of digestion, a factor that can limit total digestive performance. Using pharmacokinetic methods applied to wild-collected and laboratory-raised altricial nestlings of house sparrows (Passer domesticus), we addressed several questions of general significance about absorption in young birds. We found that both rate and efficiency of absorption of radiolabeled 3-O-methyl-D-glucose (3-OMD-glucose; absorbed by both transporter-mediated and nonmediated mechanisms) increased significantly between days 3 and 12 posthatch. We hypothesize that these changes can explain improvements in whole-diet digestion rate and efficiency observed in the young of house sparrows and of many other avian species, even after intestinal growth has ceased. We also tested the hypothesis that a high level of nonmediated, paracellular glucose absorption, as is typical in adult house sparrows, would already be observed in nestlings, and that their glucose absorption efficiency would not depend on glucose load because absorption rate is nonsaturable and is matched to substrate concentration. Using l-glucose (which is absorbed by nonmediated mechanism[s]), we found that, as predicted, paracellular absorption accounted for the majority of total absorption in nestlings of all ages, and starch content (0% vs. 25%) in the diet of laboratory-raised nestlings had no effect on efficiency of absorption of 3-OMD-glucose. Presumably, reliance on nonmediated absorption in young sparrows can save energy for growth. Also, during the transition from an almost starch-free, insect-based diet during the first days posthatch to the starch-rich, seed-based diet that is typical of adults, reliance on passive absorption is advantageous because the rate of absorption can easily match the current carbohydrate level in the intestines and the activity of hydrolytic enzymes.

Habitat and Temporal Variation in Diet of Great Cormorant Nestlings in Greek Colonies

Abstract Diet of Great Cormorant (Phalacrocorax carbo sinensis) nestlings was studied during four consecutive breeding seasons (1999-2002) at three Greek colonies (Axios Delta, and Lakes Kerkini and Mikri Prespa) in order to assess variation and commercial value of prey. A variety of fish taxa were found in nestlings’ regurgitates in each area and season, but only one or two dominated by numbers or biomass. Black Goby (Gobius jozo), Round Sardinella (Sardinella aurita) and Twaite Shad (Alosa fallax) were the most important prey in the Axios Delta; Bleak (Alburnus alburnus), Giebel (Carassius auratus gibelio) and Roach (Rutilus rutilus) at Lake Kerkini; Chalcalburnus belvica and Giebel at Lake Mikri Prespa. Nestling diet varied both seasonally (but only at Lake Kerkini significantly so) and annually (significantly in the Axios Delta and at Lake Mikri Prespa). Temporal changes can be attributed to changes in prey availability and abundance and confirm this bird’s opportunistic behavior. Between-colonies, di...

Carotenoid plumage hue and chroma signal different aspects of individual and habitat quality in tits

We hypothesized that Blue Tits Cyanistes caeruleus and Great Tits Parus major from low quality habitat (small woods) would have less yellow ventral plumage than those from high quality habitat (large woods) because they moult faster and/or their diet contains fewer carotenoids. They moult faster because they moult later in the season and are subject to more rapidly shortening daylengths. We tested this using a database of the plumage coloration (chroma, hue and lightness) of birds breeding in woods of different sizes, by manipulating the speed of moult in captive Blue Tits, and by counting the abundance and size of caterpillars (the major source of dietary carotenoids) in the diet of nestlings. In accordance with our hypothesis, juveniles of both species (which moult about three weeks later than adults) were about 8% less saturated in colour (lower chroma) than adults, but there was no significant difference in chroma between habitats. However, both species did differ significantly in hue between large and small woods. Blue Tits forced to moult faster in captivity, at a rate similar to that caused by a month's delay in the start of moult, had yellow flank feathers that were 32% less saturated in colour than those allowed to moult more slowly. Blue Tit nestlings in large woods consumed 47% more caterpillar flesh (per gram of faecal material voided) than those in small woods, and Great Tit pulli 81% more. When habitat effects were controlled for in ANOVAs, Blue Tits mated assortatively on the basis of flank hue and Great Tits on the basis of flank lightness. Flank colour therefore has the capacity to provide information about the potential quality of both habitats, and individual birds, to potential colonists and sexual partners.