Ecogeographic correlates of morphometric variation in the Red-billed Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus

We estimated the magnitude of intraspecific geographic variation in the Red-billed Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus from the analysis of external measurements of museum specimens collected throughout the Palearctic ranges of the species. By means of univariate and multivariate techniques we tested the importance of climatic and geographic factors as potential agents that might have shaped Red-billed and Alpine Chough morphology, discussing the dynamics of the interplay between natural selection, gene flow and phylogenetic constraints. Both species exhibited concordance in character differentiation. Bergmann's rule offered a valid explanation of Red-billed and Alpine Chough body size variation with the largest birds being found at higher elevation, or in colder and more arid regions. Shape was also important. The extremities of the body (bill and tarsus) were longer in warmer areas, in line with Allen's rule. In the Alpine Chough, temperature seemed to be the most important cause of body trait variation, whilst in the Red-billed Chough geographic distance among populations (a measure of geographic isolation) and altitude were also significant. In this paper we critically evaluate the validity of subspecific categories quoted in the literature, given that most variation appeared to be clinal.     

Diet of the Red-billed Chough Pyrrhocorax pyrrhocorax in south-east Spain

A sample of 140 Red-billed Chough pellets (35 from each season) was collected from communal roosting sites in south-east Spain. In almost every pellet there were three distinct dietary fractions: animal, vegetable and mineral. The animal faction constituted nearly 50% of the pellet volume in each of the four seasons. Wild grains and cultivated cereals were the most important vegetable elements, while 60% of animal prey (n= 3484) were beetles (mainly Tenebrionidae). There was marked seasonal variation in the composition of both the vegetable and animal fractions, the latter associated mainly with variation in the occurrence of Orthoptera, Lepidoptera larvae and Formicidae. Mixed flocks of Choughs and Jackdaws were common in the study area though agonistic interspecific interactions were never observed. The diets of the two species differ in that Choughs eat more beetles and wild seeds, whilst Jackdaws prefer ants and cereals. These observations support the hypothesis that competition from Jackdaws is not responsible for the reduction in the Chough's range.     

A comparative analysis of the diets of the Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus coexisting in the Alps

The diets of the Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus coexisting in the western Italian Alps have been compared by faecal analyses. A total of 1581 fresh droppings (405 of the Chough and 1176 of the Alpine Chough) were collected in the pastures of the Rhêmes Valley, Aosta, Italy, from June to November 1992 and analysed in the laboratory, and a mean volume percentage for each item was calculated. Both species were omnivorous, including animal, vegetable and mineral dietary fractions. There was no overlap in the vegetable part of the diet since the Chough fed virtually exclusively on Yellow Gagea Gagea fistulosa bulbs (dug out from the soil), which were not taken at all by the Alpine Chough. Conversely, the Alpine Chough fed on berries and hips from September to November, but these were virtually ignored by the Chough. Even though animal items were collected by both species, their preferences were different. In June, Alpine Choughs largely collected cranefly (Tipula) larvae whilst Choughs mainly fed on Lepidoptera larvae. From July onward, Alpine Choughs mainly consumed grasshoppers while Choughs also collected Tipula pupae, Lepidoptera and fly (Bibionidae) larvae and beetles (Scarabaeidae and Staphylinidae). Interspecific morphological and behavioural differences may be partly responsible for the segregation observed. Chemical composition and caloric contents of the food items suggest that the balance between costs of collecting and benefits of consuming may also contribute to diet differentiation. Both species took a broad spectrum of food, and there was no clear indication that the different population densities of the two Choughs in the Alps were directly correlated with diet, even though some data suggest that during autumn the Alpine Chough might have a diet better adapted to the high mountain environment than the Chough.     

A comparative analysis of the foraging behaviour of the Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus coexisting in the Alps

The foraging behaviour of the Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus was studied during summer and autumn in the western Italian Alps. We assessed feeding times, feeding rates and foraging techniques associated with different foraging habitats. The Alpine Chough is mainly a ground surface feeder, stays for a rela-tively short time at a feeding site (on average 2.1 min) and feeds quickly (on average 9.2 items/min). In contrast, the Chough is almost exclusively an undersurface feeder (digger and prober), stays at a feeding site twice as long as the Alpine Chough (5.4 min) and feeds four times as slowly (2.2 items/min). These differences suggest that the degree of actual ecological overlap is almost as low as possible for two species using the same Alpine pastures as foraging sites. Interspecific coexistence has occurred through a clear differentiation of foraging strategies and diets. The foraging efficiency (in terms of feeding rate)of the Alpine Chough was always higher than that of the Chough in all habitats where they occurred together. The Alpine Chough was more variable in the use of foraging techniques and more diversified in the use of foraging habitats than the Chough. In both species, juveniles fed less efficiently than adults; the foraging behaviour of the Chough is probably more difficult to learn than that of the Alpine Chough. Other data have also shown that the Alpine Chough is more opportunistic than the Chough in using seasonally available food. Considering the above, we suggest that the foraging behaviour of the Alpine Chough is more flexible and, perhaps, better adapted to the high mountain Alpine environment than that of the Chough. Two hypotheses concerning the ultimate reason why the Alpine Chough and the Chough have evolved divergent beak morphology are discussed.     

Captive Husbandry and Socialization of the Red‐Billed Chough (Pyrrhocorax pyrrhocorax)

Since the 1970s, Paradise Park Wildlife Sanctuary in Cornwall, United Kingdom, has built up a captive flock of red‐billed choughs Pyrrhocorax pyrrhocorax and over 30 years has developed successful methods of keeping, breeding, and appropriately socializing them in captivity. A total of 77 nests reached the egg stage with 27 nests producing at least one young and 48 young fledging in total. Several components are important in achieving successful breeding and socialization. Provision of live food, especially ant's eggs and small mealworms and crickets, in the first days after hatching is essential, improving the condition of adults and survival of nestlings. Situating aviaries in quiet areas, away from public view, is important. Socialization in family groups during the winter months and allowing choughs to choose partners induces better compatibility. Introduction of nest cameras greatly improved young survival through early identification of health problems enabling treatment of young between hatching and 10‐days old, when mortality is otherwise highest, and enabling precautionary medication shortly after hatching. We show that clutch size increases significantly with female age and that direct intervention such as artificial egg incubation and hand rearing can be successful and worthwhile, but its requirement is reduced by closer monitoring. Red‐billed choughs provide a good model species to further develop captive management and release techniques that can then be applied to critically endangered species that show similar social and long‐learning behaviors. Captive breeding programs can play an important role in such work through provision of suitable birds and supporting avicultural expertise. Zoo Biol. 31:725‐735, 2012. © 2012 Wiley Periodicals, Inc.     

Vocalizations and morphology: interpreting the divergence among populations of Chough Pyrrhocorax pyrrhocorax and Alpine Chough P. graculus

Capsule Differences in vocalizations among populations are mostly explained on morphological bases, but historical factors may have played a significant role in differentiation processes.

Aims To investigate the relationships among vocal and morphological variation in two corvids: Chough and Alpine Chough.

Methods We used data from 11 populations of Chough and seven populations of Alpine Chough spanning the Palearctic distribution of the two species. Three data sets (morphometry, spectrotemporal parameters of trill calls and acoustic repertoire) were analysed and their variation compared with uni- and multivariate techniques.

Results In both species, morphological differences among populations were correlated to spectro-temporal variation of trills; in particular, frequencies of calls were negatively correlated to wing length (an indicator of body size). By considering only co-existing populations of the two species, the magnitude of morphological and spectrotemporal divergence was similar.

Conclusions In both species, birds from populations with similar morphology uttered similar call types and trills with close spectrotemporal features. In particular, larger-sized populations, as expressed by wing length, emitted lower pitched calls. However, the fact that dissimilarities in repertoire and morphology were correlated cannot be explained only by appealing to functional explanations, as the observed intraspecific morphological variability does not seem to be high enough to promote consistent changes in the pool of calls. In this case, historical factors might have contributed to the present pattern of differentiation.     

Influence of fine-scale habitat structure on nest-site occupancy,laying date and clutch size in Blue Tits Cyanistes caeruleus

Most birds have specific habitat requirements for breeding. The vegetation structure surrounding nest-sites is an important component of habitat quality, and can have large effects on avian breeding performance. We studied 13 years of Blue Tit Cyanistes caeruleus population data to determine whether characteristics of vegetation structure predict site occupancy, laying date and number of eggs laid. Measurements of vegetation structure included the density of English Oak Quercus robur, European Beech Fagus sylvatica, and other deciduous, coniferous and non-coniferous evergreen trees, within a 20-m radius of nest-boxes used for breeding. Trees were further sub-divided into specific classes of trunk circumferences to determine the densities for different maturity levels. Based on Principal Component Analysis (PCA), we reduced the total number of 17 measured vegetation variables to 7 main categories, which we used for further analyses. We found that the occupancy rate of sites and the number of eggs laid correlated positively with the proportion of deciduous trees and negatively with the density of coniferous trees. Laying of the first egg was advanced with a greater proportion of deciduous trees. Among deciduous trees, the English Oak appeared to be most important, as a higher density of more mature English Oak trees was associated with more frequent nest-box occupancy, a larger number of eggs laid, and an earlier laying start. Furthermore, laying started earlier and more eggs were laid in nest-boxes with higher occupancy rates. Together, these findings highlight the role of deciduous trees, particularly more mature English Oak, as important predictors of high-quality preferred habitat. These results aid in defining habitat quality and will facilitate future studies on the importance of environmental quality for breeding performance.     

The diet of a declining Red-billed Chough Pyrrhocorax pyrrhocorax population on Islay,Scotland

Capsule: We quantify Red-billed Chough Pyrrhocorax pyrrhocorax diet from faecal samples collected on Islay. Dung invertebrates formed the majority of prey biomass in dune pasture and Tipulid larvae in mixed pasture but Aphodius larvae were scarce in the diet, whereas they had been a major component in the 1980s. There are management implications from the indication of a reduction in availability of preferred food.     

Factors affecting flock size in the Alpine Chough Pyrrhocorax graculus

The Alpine Chough Pyrrhocorax graculus is a social corvid which now uses food provided by tourist activities in mountain regions (e.g. at ski stations, refuse dumps, picnic areas). Foraging flock size, flock distribution and flock structure of Alpine Choughs were studied in the northern French Alps between 1988 and 1992. Flock size varied during the year, being larger in winter than in summer. Alpine Choughs were not evenly distributed in space, and their numbers depended principally on site-specific factors, such as seasonal human presence. A significant positive correlation existed between Alpine Chough foraging flock size and the local human population. Immature birds gathered in winter in the largest flocks and principally frequented sites with the greatest food availability (e.g. refuse dump). In summer, immatures dispersed, joined small breeding groups and were more homogeneously distributed.     

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.     

The relationship between Red-Billed Chough Pyrrhocorax pyrrhocorax (L) breeding populations and grazing pressure on the Calf of Man

A link between the numbers of Loghtan Sheep Ovis aries var. and breeding pairs of Red-Billed Choughs Pyrrhocorax pyrrhocorax has been described for the Calf of Man, Isle of Man, UK, through the analysis of data from 1969 to 1982. Recent research has included further data on populations of Choughs and Sheep grazing, as well as data on brood sizes, Rabbit Oryctolagus cuniculus populations and summer rainfall. Data from 1969 to 1994 show a significant relationship between Sheep and Chough numbers, although data for the period 1983 to 1994 in isolation show no significant association. The mean (± se) brood size ringed in the nest in the period 1959–94 was 2.91 ± 0.011. Between 1972 and 1994, as Sheep numbers peaked, mean brood size decreased, only to rise again as Sheep numbers declined. High Rabbit populations correspond statistically with large Chough broods and increased fledging success. Declines in the Chough breeding population appear to be most closely linked to declines in Rabbit numbers due to outbreaks of myxomatosis, even during periods when Sheep numbers were maintained. The recovery of the Chough population after 1970 corresponds with a change in the effects of myxomatosis outbreaks. Rabbit grazing appears to be equally as important as Sheep grazing in the maintenance of the sward characteristics favoured by breeding Choughs. Combined data on Sheep and Rabbit grazing describe the fluctuations observed in Chough breeding success more fully than data for either grazer alone.     

Effect of food abundance on laying date and clutch size in the White Stork Ciconia ciconia

CapsuleFood independently affects both laying date and clutch size, suggesting that seasonal decline in clutch size is related to a decrease in food availability.

Aim To test the effect of food abundance on laying date and clutch size of the White Stork and identify the cause of seasonal decline in the number of eggs laid.

Methods During 1991 and 1996 we recorded clutch size and laying date of pairs breeding next to rubbish dumps (food abundant and constant throughout the breeding season) and birds breeding far from rubbish dumps (using natural food sources).

Results In 1991 there was no difference in mean laying date between pairs nesting at rubbish dumps and control pairs. Clutch size was significantly larger at rubbish dump nests. In contrast, mean laying date was earlier in control pairs in 1996 and there was no significant differences in clutch sizes, even when controlling for laying date effect.

Conclusion The results support the hypothesis that food availability independently affects both laying date and clutch size. The seasonal decline in clutch size close to rubbish dumps was negligible (1991) or much smaller than in the control zone (1996) suggesting that a progressive deterioration of natural food sources is the most probable reason for a decline in clutch size as the season advances.     

Fluctuating food supply affects the clutch size of Tengmalm's owl independent of laying date

Summary In western Finland, yearly median laying dates of Tengmalm's owls varied from 14 March to 27 April during 1973–1989 and were negatively correlated with the winter densities of voles. Yearly mean clutch sizes varied from 4.0 to 6.7 and were more closely related to the spring than to the winter densities of voles. The yearly mean clutch size decreased with yearly median laying date. The 3-year vole population cycle is typical of the study area. The start of egg-laying was earliest in the peak phase of the cycle (median laying date 22 March), when vole numbers are high during egg-laying, but decline rapidly to low numbers in the next autumn or winter. In the increase phase (1 April) vole abundances are moderate at the time of laying, but increase to a peak in the next autumn or winter. In the low phase (15 April) voles are scarce in spring and in the preceding winter, starting to increase in late summer. Clutch size and female body mass were independent of laying date in the low phase, decreased slowly but significantly in the increase phase, and declined abruptly in the peak phase. These trends also held when the effects of territory quality, female age and male age were ruled out. When comparing the same laying periods, clutch sizes were significantly larger in the increase than in other phases of the cycle, but there was no difference between the peak and low phases. Supplementary feeding prior to and during egg-laying increased clutch size independent of laying date. These results agreed with the income model (the rate of energy supply during laying determines clutch size). Tengmalm's owls invest most in a clutch in the increase phase, as the reproductive value of eggs is largest because of high survival of yearlings. A high reproductive effort may be adaptive during this phase, because the availability of voles is predictable during the laying period.     

Climate change, migratory connctivity and changes in laying date and clutch size of the pied flycatcher

We examined long-term (1943–2003) variability in laying dates and clutch sizes in a Finnish population of the pied flycatcher Ficedula hypoleuca Pallas, and analysed whether potential changes were explained by changes in climatic factors at the wintering area in Africa, at migration route or at breeding grounds. Among-year variation in both mean and skewness of laying dates increased, which for mean laying date appeared to be explained by variability of temperatures at the breeding grounds and for skewness by variable temperature trends along the migration route. Pied flycatchers bred earlier in warm springs, but despite a warming trend in pre-laying temperatures, the laying dates tended to delay. Laying dates became continuously later in relation to the phenology of the environment. Mean clutch size decreased with time when mean laying date was controlled for, but the climatic factors did not appear to explain the decrease. The advancement of spring phenology may have shifted some food sources needed for egg-laying, thus leading to later laying and smaller clutches. Variation in clutch size increased when wintering conditions were favourable so that clutch size distribution was skewed with a tail of small clutches when there had been lot of rainfall (more vegetation and insects) in the wintering area. We suggest that when ecological conditions during winter were good, the tail of small clutches represented low-quality individuals that were not able to breed after bad winters. Our analyses demonstrate that measures of spread and symmetry give different information about population level changes than means, and thus complement the understanding of the potential influences of climate change on populations.     

The influence of age on laying date,clutch size,and egg size of the white-fronted tern,Sterna striata

Abstract

The age at first breeding and the influence of age on laying date, clutch size, and egg size of white-fronted terns were studied at the Kaikoura Peninsula, New Zealand, between 1971 and 1976. Of the 134 banded birds recovered breeding at Kaikoura, 63% were marked as nestlings at Kaikoura; the remainder came from colonies within 104 km. The bird is extremely capricious in its choice of nesting locality, and there are indications that it is not consistently philopatric. A small number bred as 3-year-olds, but the majority did not commence breeding until after they were 6 years old. Most pairs (73%) were of partners with an age difference of 1 year or less. Laying date and egg size varied with the age of the parent, but clutch size showed no significant change in relation to age. Mean egg volume did not vary between one-egg and two-egg clutches, but in two-egg clutches the first egg laid was significantly the larger in length, breadth, and volume. Single-egg clutches were the most common, but as the season progressed the proportion of two-egg clutches increased. There was no significant seasonal change in egg size.     

Effect of habitat, date of laying and density on clutch size of the Great Tit Parus major in northern Finland

The sizes of 1034 Great Tit clutches were studied at the Oulu area (c. 65°N, 25°30'E) in northern Finland. The average size was 9.86 eggs in the first clutch and 7.51 in the second in 13 study areas. The decrease in clutch size from the first to the second laying was most pronounced in those females laying the largest first clutches.
Irrespective of habitat, the clutch size was larger in the sparsely populated areas than in the densest area (Taskila). The clutch size decreased according to the season in all the areas, but this was not as pronounced in Taskila as in the other areas.
The annual average size of the first clutches was inversely related to the breeding density and pronouncedly so to the mean dale of laying. The latter was suggested to be an adaptation to the short season in the northern areas.
An analysis of data from 27 study areas in Europe, north of the Mediterranean region, suggests that the clutch size does not vary with latitude or longitude.     

Predation risk induces changes in nest-site selection and clutch size in the Siberian jay

Life-history theory predicts that an individual should reduce its reproductive efforts by laying a smaller clutch size when high risk of nest predation reduces the value of current reproduction. Evidence in favour of this 'nest predation hypothesis', however, is scarce and based largely on correlative analyses. Here, we manipulated perceived risk of nest predation in the Siberian jay Perisoreus infaustus using playback involving a mixture of calls by corvid nest predators in the vicinity of nest sites. In response to being exposed to this acoustic cue simulating increased risk of nest predation, the jays chose a nest site offering more protective covering and reduced clutch size. This is the first experimental demonstration of clutch size adjustment and nest site selection as a result of phenotypic plasticity in an open nesting passerine reflecting a facultative response to the perceived risk of nest predation.