Azure-winged Magpie Research Articles

Evolution of host egg mimicry in a brood parasite, the great spotted cuckoo

Brood parasitism in birds is one of the best examples of coevolutionary interactions in vertebrates. Coevolution between hosts and parasites is assumed to occur because the parasite imposes strong selection pressures on its hosts, reducing their fitness and thereby favouring counter-adaptations (e.g. egg rejection) which, in turn, select for parasite resistance (e.g. egg mimicry). Great spotted cuckoos (Clamator glandarius) are usually considered a brood parasite with eggs almost perfectly mimicking those of their host, the magpie (Pica pica). However, Cl. glandarius also exploits South African hosts with very different eggs, both in colour and size, while the Cl. glandarius eggs are similar to those laid in nests of European hosts. Here, we used spectrophotometric techniques for the first time to quantify mimicry of parasitic eggs for eight different host species. We found: (1) non-significant differences in appearance of Cl. glandarius eggs laid in nests of different host species, although eggs laid in South Africa and Europe differed significantly; (2) contrary to the general assumption that Cl. glandarius eggs better mimic those of the main host in Europe (P. pica), Cl. glandarius eggs more closely resembled those of the azure-winged magpie (Cyanopica cyana), a potential host in which there is no evidence of recent parasitism; (3) the appearance of Cl. glandarius eggs was not significantly related to the appearance of host eggs. We discuss three possible reasons why Cl. glandarius eggs resemble eggs of some of their hosts. We suggest that colouration of Cl. glandarius eggs is an apomorphic trait, and that variation between eggs laid in South African and European host nests is due to genetic isolation among these populations and not due to variation in colouration of host eggs. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 551–563.

Flexible Helping Behaviour in the Azure‐Winged Magpie

AbstractHelping to rear the offspring of others may be a way for younger birds to gain access to future reproduction especially when turnover of breeding opportunities is low. However, this explanation is not applicable to cases where adults also help, or when roles shift between helpers and breeders. Over a period of 6‐yr, we studied a marked population of azure‐winged Magpie (Cyanopica cyanus) breeding in a non‐territorial, colonial system. Magpies bred in a highly flexible cooperative system, in which individuals helped at different stages of the breeding cycle, including nest building, feeding the incubating female and feeding the young and removing the faecal sacs. On average, 50% of hatched nests were assisted by helpers‐at‐the‐nest, and nest success appeared to be positively related to the presence of helpers. Helpers were predominantly males. Although juveniles were more likely to help, both juvenile and adult birds helped. Individual birds behaved as helpers either as a first‐option or after having attempted their own breeding (second‐option helpers). An individual helper may assist more than one nest during the same breeding season and in different breeding seasons. Reversals between breeder and helper roles were common in both directions, within a breeding season and between years. Helping behaviour is an option for almost any member of the colony. Therefore, hypotheses related to the enhancement of future breeding opportunities for juveniles can be discarded as general explanation of helping in this species. Although the decision to help appeared to be influenced by proximal environmental conditions hindering successful breeding, the associated benefits of helping as opposed to simply recovering for future reproduction, especially for former breeders, deserve further study.

Continental rift

The azure-winged magpie (Cyanopica cyanus), has long presented a puzzle for biologists. The naturalist Alfred Wallace was one of the first to consider it. The puzzle lies in its extraordinary distribution. It exists in two distinct locations: Iberia and eastern Asia, 9,000 kilometres apart. Two alternative theories have been put forward to explain this curious distribution. The first proposes that the Iberian population was established in the sixteenth century following the introduction of birds brought back from the Far East by Portuguese sailors. The second proposes that the species had a continuous distribution across Europe and Asia north of the Himalayas before late Pleistocene glaciation isolated the two populations. However, there was no evidence for either theory until the discovery of azure-winged magpie bones from cave deposits in Gibraltar that were 44,100 years old. Unless the bones were from an unknown species, they provided compelling evidence that the magpies were long-standing residents of Iberia, supporting the second theory of glacier-induced separation of the two populations. Now a new molecular study of mitochondrial DNA from the birds has been carried out to infer their phylogeny. Koon Wah Fok, Christopher Wade and David Parkin, at the Institute of Genetics at the Queen's Medical Centre in Nottingham, compared control sequences from birds in both populations (Proc. R. Soc. London. B 269, 1671–1679, 2002) Samples were taken both from blood samples of living birds and from the skin of museum specimens. When they compared the sequences, the results suggested that, indeed, the populations were distinct. So it seems clear that if, conceivably, Portuguese sailors had brought the odd magpie back across the 9,000 kilometres, it would have found relatives happily at home.

Inferring the phylogeny of disjunct populations of the azure-winged magpie Cyanopica cyanus from mitochondrial control region sequences.

The azure-winged magpie (AWM), Cyanopica cyanus, is found in Asia and Iberia. This remarkable disjunct distribution has been variously explained by either the sixteenth-century introduction of birds into Iberia from the Far East, or by the loss of individuals from the central part of their range as a result of Pleistocene glaciations. We have used the mitochondrial control region to undertake a molecular phylogenetic analysis of the AWM, with sequences examined from individuals collected from across the current distribution range and incorporating representatives of all currently defined subspecies. The Western birds are genetically distinct from their Asian congeners and their divergence is basal in the phylogenetic tree. This indicates that the AWM is native to Iberia and not the result of a recent introduction from Asia. In Asia, two major mitochondrial DNA lineages were identified. These correspond to an Inland Asia group and a Pacific Seaboard group, and are separated topographically by the Da Hingan Ling mountains and the Yellow Sea. Molecular clock estimates suggest that these divergences are associated with Pleistocene glaciations. Furthermore, our data do not support the current classification of the AWM into 10 subspecies, as defined based on morphology and geographical distribution.

Azure-winged magpies avoid nest predation by breeding synchronously with Japanese lesser sparrowhawks

Azure-winged magpies, Cyanopica cyana, breed most successfully when nesting near active nest sites of Japanese lesser sparrowhawks, Accipiter gularis. Magpie nests that contain nestlings after the period when sparrowhawks defend their nests suffer predation and the success of magpie breeding depends greatly upon hawk nest defence. To clarify the relationship between the timing of breeding of these two species, I compared the timing of breeding in azure-winged magpie pairs with variation in the level of nest defence by the hawk (as estimated by the nest success and the rate of nest defence of hawks). The date of onset of incubation in magpies was similar to the date that would have maximized the protection they gained from the hawk. Magpies nesting near hawk nests bred synchronously, but magpies far from them did not. The results suggest that magpies breed according to the hawks' breeding schedule in order to avoid nest predation and increase breeding success.

Karyological study of some Corvine birds (Corvidae, aves)

Karyotypes were studied in the hooded and carrion crows, their naturally occurred hybrids, the jungle crow, the azure-winged magpie (2n = 80 in all aforementioned birds), and the magpie (2n = 82). Corvine birds of Primorskii Krai were karyotyped for the first time. In addition to the similarity in the diploid chromosome sets, corvine birds were shown to have a similar structure of karyotype: in all studied birds, 14 macrochromosomes (Mchs) classified into three groups according to their size were detected. By karyotype structure, birds belonging to the same genus are similar. Some intergeneric differences are due to a change in the position of centromeres of the largest and sex chromosomes. Karyotypes of interspecific hybrids of crows are remarkable for the presence of heteromorphic (t/st) chromosome pair 2 in some individuals, which apparently does not affect their fecundity. Using differential C-banding, the sex chromosome W in female magpies was identified. In addition, heteromorphism was detected in C-bands of homologs of Mch pair 4 in the hooded crow. In the jungle crow, the azure-winged magpie, and the magpie, bright QH-bands and numerous G-bands were detected on Mchs and on some microchromosomes only. Active Ag-NOR-bands were detected on one macrochromosome pair in the magpie. In all, the karyotype structure of corvine birds is comparable to the basic structural scheme of the karyotype in the order Passeriformes, which confirms the concept of conservatism of the avian karyotype.

Seed dispersal by frugivorous birds in Nanjing Botanical Garden Mem. Sun Yat Sen in autumn and winter

Nanjing Botanical Garden Mem. Sun Yat-Sen is located in the southern foot of Zhongshan Mountain. Avian frugivores such as Turdus merula, Pycnonotus sinensis, Garrulax perspicillatus, Cyanopica cyana, Streptopelia orientalis and Turdus naumanni feed mainly on tree fruits in the garden during autumn and winter. One hundred and sixty samples of birds faeces were randomly collected within the garden from October 20, 1999 to January 20, 2000. Totally 874 intact seeds, which were generally enclosed by a hard seed coat or by hard endocarp,three pieces of insect remnants of Coleoptera and one remnant of bird were found in these birds’ faeces. Among the seeds, 842 have been identified as belonging to 26 plant species of 20 genera and 16 families. Plant species comprising the highest percentage in frequency in the 160 samples of birds’ faeces are Ilex purpurea(22.2%), Sabina chinensis(11.1%), Rhus chinensis(10.6%), Celtis sinensis(9.2%), Parthenocissus tricuspidata (7.7%) and Sabina chinensis cv. kaizuca(7.3%). Plant species with highest percentage of seed number in the samples are Ilex purpurea(23.5%), Rhus chinensis(16.2%), Sabina chinensis(13.5%),Parthenocissus tricuspidata(8.0%), Sabina chinensis cv. kaizuca(8.0%)and Rosa cymosa(5.3%). Avian frugivores may disperse from the parent trees by (i) ingesting fruits around the parent trees, then defecating or regurgitating the seeds away from it, or (ii) picking the fruits up away from the parent trees. Both fecal-borne seeds, such as Rhus chinensis and Parthenocissus tricuspidata, and regurgitated seeds, such as Cinnamomum camphora and Melia azedarach, were viable to produce seedlings based on a preliminary germination test. Seedlings of Cinnamomum camphora,Ilex purpurea, Pittosporum tobira, Taxus chinensis and some other trees cultivated in the garden have successfully invaded into a natural Pinus thunbergii - Liquidambar formosana community on a hillside at the edge of the garden and into a natural Pterocarya stenoptera - Celtis sinensis community beside a mountain stream through the garden, as a result of seed dispersal by frugivorous birds. Avian seed dispersers have spread the distribution of some cultivated fleshy-fruiting species in the botanical garden and have promoted their natural regeneration.

First fossil record of Azure‐winged Magpie Cyanopica cyanus in Europe

First fossil record of Azure‐winged Magpie Cyanopica cyanus in Europe

Cost of Nest Defense in Azure-Winged Magpies

I studied costs of nest defense in Azure-winged Magpies Cyanopica cyana in Tokyo, Japan in 1994 and 1995. I compared time devoted to nest defense, frequency of nestling feeding, and number of fledglings of magpies breeding near nests of Japanese Lesser Sparrowhawk Accipiter gularis and magpies breeding far from such nests. Because the hawks attack potential predators, magpies near a hawk's nest did not defend their nest, whereas magpies breeding far from a hawk's nest defended their nest. Feeding frequencies and number of fledglings were greater near a hawk's nest than far from it. Because nest defense incurs a cost in the form of decreased feeding time, Azure-winged Magpies far from a hawk's nest probably provided less food to their chicks and therefore raised fewer fledglings than those breeding close to a hawk.

Reproductive skew and the threat of eviction: a new perspective

Most recent models of the partitioning of reproduction attempt to explain patterns of skew on the assumption that dominant individuals have complete control over breeding opportunities within the group, but may nevertheless concede a share of direct reproduction to subordinates as an incentive to remain peacefully in the association. Although these models may be applicable to some animal societies, we argue that they fail to provide a comprehensive theory of skew. Instead, we suggest that subordinates may often be able to claim unsanctioned reproduction for themselves, but will be forced to exercise a degree of reproductive restraint lest they incite ejection by the dominant. Reproductive skew, in other words, may reflect the threat of ejection (inducing subordinate restraint) rather than the threat of subordinate departure (inducing reproductive concessions by dominants). We present a simple ESS model of reproductive skew under these circumstances, which demonstrates that a shift in emphasis from reproductive concessions by dominants to reproductive restraint on the part of subordinates, radically alters the predictions of skew models. High group productivity, high relatedness and (when group members are related) strong ecological constraints are all expected to lead to reduced skew (the opposite conclusions to those of previous, concession-based analyses). The reason is that these factors reduce the benefits (or increase the costs) of ejection to the dominant, who therefore does best to tolerate more subordinate reproduction.

Azure-Winged Magpies Avoid Nest Predation by Nesting near a Japanese Lesser Sparrowhawk's Nest

Nest site selection of Azure-winged Magpies (Cyanopica cyana) was studied in relation to their proximity to the nests of Japanese Lesser Sparrowhawks (Accipiter gularis). Magpies used nest sites that were more concealed when not nesting in association with the hawk, and nests with a higher rate of leaf cover were less frequently depredated. Magpies preferred to nest close to hawk nests, and such sites had higher breeding success. However, Azure-winged Magpies nested in places with less leaf cover near hawk nests. Despite the lack of cover, the magpie nests were more successful when located near a hawk nest. Magpies effectively avoid nest predation by exploiting the defending behavior of the hawks.

Preferences and apparent digestibilities of sugars by fruit damaging birds in Japan

SummaryGray starlings Sturnus cineraceus, azure‐winged magpies Cyanopica cyana and brown‐eared bulbuls Hypsipetes amaurotis are among the main bird pests in commercial fruit orchards in central Japan. Recently Brugger & Nelms (1991) suggested that developing high‐sucrose fruit cultivars could reduce crop damage, because some pest birds lack the enzyme sucrase and can develop an aversion to sucrose. Preferences for, and digestibilities of, the monosaccharides glucose and fructose and the disaccharide sucrose by these pests species were therefore studied to assess whether this idea would be applicable in central Japan. Gray starlings and brown‐eared bulbuls were able to detect glucose, fructose, a mixture of glucose and fructose, and sucrose at a concentration of 12% w/v. Azure‐winged magpies also detected glucose and fructose, but failed to detect sucrose at the same concentration. In pairwise preference trials gray starlings and azure‐winged magpies selected the monosaccharides over sucrose, but brown‐eared bulbuls did not. To estimate the digestibility of the sugars the apparent assimilated mass coefficient, AMC*, was calculated for each species eating each sugar by measuring intake and faecal output. Monosaccharides had mean AMC*s of 0.77, 0.96 and 0.92 when consumed by gray starlings, azure‐winged magpies and brown‐earned bulbuls respectively. AMC* values for sucrose were 0.82 and 0.49 for brown‐eared bulbuls and azure‐winged magpies respectively, but gray starlings were shown to be unable to digest sucrose. As AMC* values varied from 0.75 to 0.97, consumption rates of sugars increased as digestibility decreased. Although increasing sucrose contents of commercial fruits may deter sucrase‐deficient birds such as gray starlings from depredating fruits, it may also lead to increased crop damage by species such as the azure‐winged magpie and brown‐eared bulbul which may have to consume more of the less digestible fruit in order to meet their energy requirements.

Movements, Space Use and Social Organization of Radio-tracked Common Cuckoos during the Breeeding Season in Japan

The movements, space use, and social organization of a colour-marked Common Cuckoo Cuculus canorus population were investigated during the 1984-1993 breeding seasons in central Japan. Of 333 captured cuckoos, 81 had radio transmitters attached to them. Excluding unknown birds (8.7%), the male : female ratio was 1.25 : 1.00. Radio-tracking showed that each cuckoo had a distinct breeding area and a distinct feeding area, and commuted between them every day. Birds spent most early mornings in host-rich habitats such as the Chikuma River, and then visited neighboring mountains or suburbs for foraging. The average time spent in the breeding area was 9.0 ± 0.8 hours per day (58.2 % of the daytime hours) for males and 8.7 ± 0.7 hours (56.3 %) for females. All males visited their breeding areas just after dawn, but the peak time for females was one hour later. After the early morning peak, the rate decreased gradually until early afternoon and increased again in the late afternoon with both sexes. The main activity of males in the breeding area was singing, and they sang between 19.8 % and 40.2 % of the total time they spent there. Each male sang in a restricted area and the average size of the song area was 40.9 ± 4.9 ha. However, male song areas had a large overlap, especially at the groves of acacia trees around which were many host nests. Males sometimes made short visits outside their song areas. The average size of males' breeding area, including these short visits, was 67.5 ± 8.9 ha. There were three types of females corresponding to three major hosts: the Great Reed-warbler Acrocephalus arundinaceus, the Bull-headed Shrike Lanius bucephalus and the Azure-winged Magpie Cyanopica cyana. Each female cuckoo in this study specialized on a single host species. The breeding areas of females overlapped considerably both "inter" and "intra" between different female groups. The average size of the females' breeding areas was 63.6 ± 8.5 ha. However, magpie-cuckoo females had significantly larger areas than warber-cuckoo females. The cuckoos rarely fed in their breeding areas. During their absence from the breeding area, most cuckoos visited nearby mountains, but some cuckoos, breeding at sites far from the mountains, visited suburbs for feeding. The average size of a feeding area in the mountains was 23.7 ± 5.7 ha for males and 27.6 ± 6.8 ha for females. By contrast, a female which foraged in the suburbs had a large feeding area (327.0 ha). The number of visits per day was related to the distance between the breeding area and feeding area. Cuckoos foraging at more distant sites visited these sites only once per day, while cuckoos foraging at closer sites visited them more frequently. There was a positive relationship between distance to feeding area and mean times spent per visit. There was a negative relationship between distance to feeding area and total feeding time per day. Cuckoos roosted solitarily in both their breeding and feeding areas. Roosting sites in the mountains changed almost every day, but some cuckoos roosting at the river or in the suburbs often used the same sites repeatedly. Roosting in the breeding area was more commons with males than with females, but it decreased in both sexes as the season progressed. The average size of a home range was 3.02 ± 0.28 km2 for males and 3.26 ± 0.40 km2 for females. In this paper, we discuss the following three points: (1) The separation of the breeding area and the feeding area is a common characteristic of the cuckoo and it is closely related both to the cuckoo's parasitic breeding and to its special feeding habits; (2) There are costs attendant with leaving the breeding area in order to visit a feeding area.

Effects of chlorinated hydrocarbons on bald eagle chicks

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were determined in eggs of eight avian species collected from Dongting Lake of China to assess residue levels, accumulation patterns, and toxic potential in different avian species. Concentrations of total 2,3,7,8-substituted PCDD/Fs were in the range of 10.8–182 pg g−1 lipid weight. Eggs of great egret and lesser pied kingfisher contained higher levels of PCDD/Fs than eggs of other species, indicating the specific exposure and accumulation of PCDD/Fs relating to feeding habits and the life span. PCDD/Fs congener patterns varied among species. The patterns of PCDD/Fs in the eggs may be influenced by feeding habits, specific elimination, and metabolism. In general, concentrations of PCDDs were higher than those of PCDFs in avian eggs. On basis of lipid weight, total 2,3,7,8-TCDD toxic equivalents (TEQs) calculated based on the WHO TEFs for birds ranged from 2.04 to 42.0 pg g−1; and on basis of wet weight, total WHO-TEQs ranged from 0.19 to 1.59 pg g−1. 2,3,7,8-TCDF, 2,3,4,7,8-PeCDF, 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD were the major contributors to TEQ concentration in most avian eggs, whereas 1,2,3,4,7,8-HxCDD also accounted for a major portion of TEQs in eggs of azure-winged magpie. Values of TEQs in avian eggs were lower than toxic threshold values, implying risk reduction and natural restoration of PCDD/Fs contamination in Dongting Lake region.

Factors involved in the distribution of forest birds in the Iberian Peninsula

The relationships between a series of environmental variables and the abundance of individual species of forest birds were examined in 58 large woodlands along a band crossing the Iberian Peninsula from north to south. The variables were mean annual rainfall, mean annual temperature, density of trees <20 cm in diameter, density of trees >30 cm in diameter, floristic composition (conifer or broadleaved trees) and geographical situation (distance from northern extreme of study band). The variable most highly correlated with bird density was mean annual rainfall (40% of the species had significant partial correlations with this parameter). The northern species (Chiffchaff, Goldcrest, Robin, Song Thrush, Bullfinch, etc.) generally correlated positively with mean annual rainfall, while the Mediterranean species (Sardinian Warbler, Bonelli's Warbler, Black-eared Wheatear, Rock Sparrow, Spotless Starling, Azurewinged Magpie, etc.) exhibited an inverse pattern. Mean annual temperature (36%) was also closely associated with bird distribution, but did not show clear tendencies according to biogeographic groups. Floristic composition (26%) was a strong determinant of the abundance of species distributed throughout the whole Iberian Peninsula and geographical situation (22%) largely determined the distribution of the northern and Mediterranean species. Finally, density of trees <20 cm in diameter (20%) and >¸30 cm in diameter (14%) generally showed a negative association with the majority of the species, particularly the Mediterranean species.

Azure-winged magpies, Cyanopica cyana, 'parasitize' nest defence provided by Japanese lesser sparrowhawks, Accipiter gularis

Abstract. A field experiment with simulated nests of azure-winged magpies was carried out to test the hypothesis that this species nests in association with Japanese lesser sparrowhawks in order to reduce nest predation while paying few costs. The predation rate on nests was lower within 50 m of a hawk's nest during the incubation to nestling period than it was further away or at other stages of the breeding cycle. In addition, there was an inverse relationship between nest predation rate and hawk defence effort. Observations of natural nests showed that magpies did not defend their nests when nesting close to a hawk, and that hawks rarely preyed on magpies. Thus, magpies benefited from nesting close to hawks, while paying few or no costs.

The caching behaviour of Japanese Lesser Sparrowhawks Accipiter gularis during the breeding season

We investigated the caching behaviour of Japanese Lesser Sparrowhawks Accipiter gularis during the breeding season in Tokyo and Utsunomiya, central Japan. Observations were made from April to July 1987-1993 in Tokyo and 1991-1993 in Utsunomiya. A total of 46 caching behaviours were observed. All of the prey items cached were small and medium-sized birds, especially Tree Sparrows Passer montanus (65.2%, 30 of 46). Hawks cached prey that were half eaten by females, and prey which was not taken by the female in attempted prey exchanges initiated by the male. Many caches were carried out in the incubation and early nestling periods. Hawks stored prey on gnarled, broken twigs and leaf clumps on horizontal branches 7-8m in height and within a few meter to 50m apart from the food exchange site. Some birds used a few definite sites, and others used many places within a range of 50 × 30 m as caching sites. When hawks flew to caching sites with prey, they placed the prey carefully, and push it several times with their legs and beak. At least 11 stored items were retrieved within 3-247 min. (mean ±S.D., 78.5 min. ±73.2) after caching. Although 8 stored items were stolen by Azure-winged magpies Cyanopica cyana, most cached prey may be retrieved.

Note on stealing cached prey of a Japanese Lesser Sparrowhawk Accipiter gularts by Azure-winged Magpies Cyanopica cyan

I observed that Azure-winged Magpies Cyanopica cyana stole cached prey of a Japanese Lesser Sparrowhawk Accipiter gularis at a small wooded park in Utsunomiya, central Honshu in late May 1992. The breeding stage of this hawk's pair was during 1 to 5 days after hatching. A male hawk cached the surplus prey that had been caught more frequently than female was needed. The caching behavior was observed 7 times during the observation period of a total 440 minutes, and all of them were stolen by magpies. All the prey items were Tree Sparrows Passer montanus. Azure-winged Magpies took away the sparrows as soon as the hawk flew away from caching sites. Because the hawk's foods are plentiful in this area and the magpies did not rob the prey directly from the hawk, it is unlikely that Azure-winged Magpies have a serious effect on breeding success of Japanese Lesser Sparrowhaks.

Nest-site selection and nesting success in the Azure-winged Magpie in Central Spain

Nest-site selection and nesting success in Azure-winged Magpies Cyanopica cyana were studied in 1986 in central Spain. Preferred nest sites were a nonrandom subset of the available habitat. Nests built on evergreen trees had significantly earlier clutch initiation dates than those built on deciduous trees. Birds selected larger trees of each species for nesting, but nests built on very high trees had significantly lower nesting success. Birds tended to locate their nests in a central position relative to the canopy height and as far from the main trunk as possible, without being of the periphery. This may minimize nest accessibility and maximize concealment. Nesting success was higher in the preferred regions of the tree canopy. Predation and inclement weather were probably the factors selecting for the observed patterns in nest-site distribution.

Breeding success of Azure-winged MagpiesCyanopica cyanain Central Spain

The breeding success of Azure-winged Magpies was studied in Central Spain during 1986. Nesting density was 1.01 nests/ha, but nests were clumped. Breeding season was short and synchronized. Clutches were initiated between 10 April and 25 May. Clutches were started in 69% and completed in 60% of 136 nests built. Mean clutch size was 6.2 eggs. Only 32% of nesting attempts were successful, with an average 5.1 young fledged. Success declined as the season advanced.