Circus Pygargus Research Articles

APalaearctic migratory raptor species tracks shifting prey availability within its wintering range in theSahel

Mid-winter movements of up to several hundreds of kilometres are typical for many migratory bird species wintering in Africa. Unpredictable temporary food concentrations are thought to result in random movements of such birds, whereas resightings and recoveries of marked birds suggest some degree of site fidelity. Only detailed (e.g. satellite) tracking of individual migrants can reveal the relative importance and the causes of site choice flexibility and fidelity. The present study investigates how mid-winter movements of a Palaearctic-African migratory raptor, Montagu's harrier Circus pygargus, in the Sahel of West Africa are related to the availability of food resources. Thirty harriers breeding or hatched in northern Europe were satellite tracked (2005-2009). On average, four home ranges, each separated by c. 200 km, were visited during one overwinter stay in the Sahel. Wintering home ranges were similar in size to breeding season home ranges (average over wintering and breeding home range size c. 200 km(2) ), and harriers showed high site fidelity between years. Most preferred habitat types in the Sahel were mosaics of grass- and cropland, indicating similar habitat preferences in both the breeding- and wintering seasons. The main prey of Montagu's harriers in the Sahel were grasshoppers Acrididae. Highest grasshopper numbers in the field occurred at relatively low vegetation greenness [normalized difference vegetation index (NDVI) values 0.17-0.27]. We used NDVI as a proxy of food availability for harriers. During their overwinter stay, Montagu's harriers moved in a South-South-western direction between consecutive home ranges. The birds selected areas within the range of NDVI values associated with high grasshopper numbers, thus tracking a 'green belt' of predictable changes in highest grasshopper availability. Contrary to earlier hypotheses of random movements in the Sahelian-wintering quarters, the present study shows that Montagu's harriers visited distinct home ranges, they were site-faithful and tracked seasonal changes in food availability related to previous rainfall patterns, caused by the shifting Intertropical Convergence Zone. Itinerancy may be the rule rather than an exception among insectivorous birds wintering in African savannahs.

Breeding biology of the Montagu’s Harrier (Circus pygargus) in east-central Poland and implications for its conservation

In 2005–2011 active conservation and study on the population of the Montagu’s Harrier was conducted in the farmland areas of east-central Poland. The population was estimated at 240–270 breeding pairs and its size was stable. The mean clutch size was estimated at 3.71 eggs per breeding pair. The number of fledglings was 1.24 per nest and 2.6 per successful breeding pair. There were no significant differences in sex ratio. The birds nested mainly in winter cereal and rape (70%). Population productivity positively correlated with a high number of nests located in late harvested crops. The pairs breeding in early harvested crops had significantly lower breeding success (10%) than the pairs nesting in winter cereal (>70%), due to losses during farming activities. Protection of broods with fencing had a positive effect on the breeding success of pairs nesting on arable fields. An important factor that had a negative impact on the breeding success of Montagu’s Harriers was adverse weather conditions. 2005–2011 metais buvo vykdoma pievinių lingių intensyvi apsauga ir rūšies populiacijos tyrimai rytų centrinės Lenkijos dirbamuose laukuose. Pievinių lingių populiaciją sudarė 240–270 perinčių porų, vidutinis dėties dydis – 3,71 kiaušiniai vienai perinčiai porai, jauniklių skaičius – 1,24 jaunikliai vienam lizdui ir 2,6 jaunikliai vienai sėkmingai perėjusiai porai. Ryškaus skirtumo tarp patinų ir patelių skaičiaus nepastebėta. Paukščiai daugiausiai perėjo žieminių kultūrų ir rapso laukuose (70%). Populiacijos produktyvumas teigiamai koreliavo su dideliu lizdų skaičiumi laukuose, kur derlius nuimamas vėlai. Dėl aktyvios žemės ūkio veiklos perėjimo sėkmė buvo žymiai mažesnė laukuose, kur derlius nuimamas anksti (10%), nei žieminėse kultūrose (>70%). Lizdų aptvėrimas turėjo teigiamos įtakos dirbamuose plotuose perėjusių porų perėjimo sėkmei. Nepalankios oro sąlygos darė didelę neigiamą įtaką pievinių lingių perėjimo sėkmei.

Standing out from the crowd: are patagial wing tags a potential predator attraction for harriers (Circus spp.)?

Wing tags have been used on many bird species to facilitate individual recognition, although tags are not only conspicuous for humans but may also attract the attention of potential predators. During a Peregrine Falcon Falco peregrinus monitoring program (1997–2011) we collected prey remains from the nests of 37 Peregrine territories in the Basque Country, Northern Spain. We identified 3,127 prey items representing 132 bird species. In the 2009 breeding season, we found, for the first time, four Hen Harrier Circus cyaneus remains and the two wings with orange wing tags of a Montagu’s Harrier Circus pygargus in one nest, 1 year later we found in the same nest eight Montagu’s Harrier remains, one of them with wing tags, and in 2011 we found eight more Montagu’s Harriers, one of them marked. Simultaneously, in the breeding season of 2010, the remains of another Montagu’s Harrier were found in other Peregrine nest and two wings with orange and blue wing tags in the perch of a third pair. Our data thus shows an increase of predation rate of harriers by Peregrines; we discuss whether this could be related to the increasing use of wing tags in this species, and thus whether wing tags may have potential negative effects on the birds. We argue that further studies about the impact of identification techniques, and wing-tags in particular, on the survival of target species should be carried out.

Diet of the Montagu's Harrier Circus pygargus nesting in natural habitat in Eastern Spain

We describe the diet of the Montagu's Harrier (Circus pygargus) population breeding in inland Castellón province (eastern Spain), which exhibits among the highest breeding productivity of European populations of this species. We assessed diet using pellets col-lected at nests at the end of the breeding season. We recorded the minimum number of items in every pellet for six prey classes (lizards, passerines, small mammals, cole-opterans, orthopterans and other insects). We also analyzed between-year relationships in diet diversity and breeding output at the nest level. The most frequently eaten prey were insects, particularly large orthopterans of the family Acrididae. Passerines were also abundant in the diet and contributed more than 50% of the consumed biomass. We found no significant between-year relationship in breeding output and diet diversity at the nest level. Further studies on prey availability in different habitat types would be needed in or-der to understand how land-use changes affect the Montagu's Harrier population.

Philopatry and natal dispersal of Montagu's harriers (Circus pygargus) breeding in Spain: a review of existing data

Natal dispersal is an important component of bird ecology, plays a key role in many ecological and evolutionary processes, and has important conservation implications. Nevertheless, detailed knowledge on natal dispersal is still lacking in many bird species, especially raptors. We review and compile existing information from five tagging programmes of juvenile Montagu's harriers (Circus pygargus) in different Spanish regions, with PVC rings or wing tags, to provide an assessment of philopatry and natal dispersal of the species in Spain. Only 7% of all tagged harriers were observed as breeders in subsequent years. The percentage of philopatric (i.e. breeding within 10 km of the natal site) males and females was lower that 5%. Overall, there were no sexual differences in percentage of philopatric birds or dispersal distances, but we found study area differences. The low philopatry observed suggests a high capacity for natal dispersal in this species, for both sexes, and therefore high genetic mixing between populations. Differences in philopatry between study areas may be influenced by the different observation effort or detectability, or else reflect different philopatric strategies among populations. Finally, we found no significant differences in philopatry rate or dispersal distances related to tagging method, suggesting that tagging technique has a smaller effect than monitoring effort or observation ease on observation probability. Developing tagging programmes at a small scale and without procuring very large-scale and intensive subsequent monitoring is not worthwhile for evaluating philopatry and natal dispersal in this species.

Autumn migration of soaring birds through the Gebel El Zeit Important Bird Area (IBA), Egypt, threatened by wind farm projects

SummarySystematic bird observations were performed during autumn 2006 in the migration bottleneck area of Zeit Bay, Egypt (27.73°N, 33.51°E), situated on the coast of the Gulf of Suez, opposite southern Sinai. Owing to the strong northerly winds in that area, considerable pressure exists to construct wind farms. A total of 145,432 soaring birds, including 134,599 storks and 9,376 raptors over a period of 453.6 hours were observed between 20 August and 29 October by two teams working daily in two shifts. White Stork Ciconia ciconia and European Honey Buzzard Pernis apivorus were the most numerous species (91.4% and 5.7% respectively) of all soaring birds observed. As both species migrate early, relatively few birds were recorded passing through in October. A total of 57,179 soaring birds were observed within a range of 2.5 km from the observers, and of these 32,248 were flying at heights up to 200 m. Few individuals of the rapidly declining breeding populations of Egyptian Vulture Neophron percnotperus (‘Endangered’) and Lesser Kestrel Falco naumanni (‘Vulnerable’) passed (8 and 33 respectively). Pallid Harriers Circus macrourus (‘Near Threatened’) however, were more numerous (100) than at other migration sites along the East African-West Asian Flyway (Israel, southern tip of Sinai, Suez and Bab-el-Mandeb). Western Marsh Harrier Circus aeruginosus and Montagu’s Harrier Circus pygargus were also more numerous than at these sites. Some other large migrant species, observed at Suez, Bab el-Mandeb or in Israel, were seen only in small numbers or not at all at Zeit Bay in autumn. Among them, the Steppe Eagle Aquila nipalensis being the best known example of loop migration, entering Africa at Suez and Bab el-Mandeb, is for this reason not expected in autumn at Zeit Bay, while in spring it is a regular migrant. The number of Black Storks Ciconia nigra observed accounted for 4.8% of the flyway population, that of White Storks for 33.3%, Great White Pelicans Pelecanus onocrotalus for a further 3.5% and European Honey Buzzards for 0.8%. The extrapolation of the number of birds passing through the study area during the migration season, suggests that it was used by 92% of the White Stork, 12% of the Black Stork, 5% of the Great White Pelican, 4% of the European Honey Buzzard and 2% of the Pallid Harrier flyway populations in autumn 2006.

Carotenoid limitation and allocation priorities in asynchronous raptor nestlings

The evolution and maintenance of conspicuous animal traits and communication signals have long fascinated biologists. Many yellow–red conspicuous traits are coloured by carotenoid pigments, and in some species they are displayed at a very young age. In nestling birds, the functions and proximate mechanisms of carotenoid-pigmented traits are probably different and not as well known as those of adults. Here we investigated how Montagu’s harrier (Circus pygargus) nestlings within structured families used a limited resource, carotenoid pigments, and whether they used these for increasing coloration (deposition in integuments) or for mounting a response to a phytohaemagglutinin (PHA) challenge, which measures pro-inflammatory potential and aspects of cellular immune responsiveness. We manipulated carotenoid availability, using dietary carotenoid supplementations, and show that when supplemented, nestlings primarily allocated supplemental carotenoids to increase their coloration, irrespective of their sex, but depending of their position within the brood. Responses to PHA challenge were condition-dependent, but depending on carotenoid availability. Moreover, how nestlings allocated carotenoids depended on their rank within the brood, which in turn influenced their level of carotenoid limitation (first-hatched nestlings being less constrained than later-hatched nestlings). We discuss why nestlings would use supplemental carotenoids for increasing bare parts coloration rather than for responding to a PHA challenge, and the potential benefits for doing so in a parent–offspring communication context. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 13–24.

South West Georgia: An Important Bottleneck for Raptor Migration during Autumn

Counts of migrating raptors at Batumi, Georgia, revealed the eastern Black Sea coast to form one of the most important bottlenecks for raptor migration during autumn in the Eurasian-African migration system. Totals for 10 species (European Honey-buzzard Pernis apivorus, Steppe Buzzard Buteo buteo vulpinus, Black Kite Milvus migrans, Eurasian Sparrowhawk Accipiter nisus, Levant Sparrowhawk Accipiter brevipes, Montagu's Harrier Circus pygargus, Pallid Harrier Circus macrourus, Lesser Spotted Eagle Aquila pomarina, Greater Spotted Eagle Aquila clanga, Booted Eagle Aquila pennata) exceeded 1% of their estimated world population. We compare the observed abundance of each species to estimates of the presumed source populations in European Russia. Counts of most species involved only a limited subset of these source populations, except for European Honey-buzzard and Lesser Spotted Eagle, which were more numerous than predicted. This could be due to inaccurate population estimates or because birds from NE Europe or W Asia are also using this migration route.

Factors influencing diet variation in a generalist predator across its range distribution

Factors linked with intraspecific variation in trophic diversity are still poorly understood in generalist species like the Montagu’s harrier (Circus pygargus) but may have important implications for conservation management at a wide scale. We described geographic patterns of Montagu’s harrier diet across Eurasia, gathering diet data from 30 studies in 41 areas from 11 countries. We grouped prey as invertebrates, reptiles, small mammals, large mammals, eggs, small birds and large birds, and calculated the contribution of each prey type to the diet (as % biomass) and Shannon’s Diversity Index for each study site. We analysed qualitative estimates of prey abundance in relation to latitude and longitude, then diet composition in relation to habitat of the study area and prey abundance estimates. Diet diversity of Montagu’s harriers increased from north to south, while abundance of all prey groups other than small mammals showed the opposite trends. Agricultural areas in northern latitudes seemed to hold high densities of small mammals, but low densities of alternative prey. Overall, birds were the main prey in most of Montagu’s harrier’s distribution range, although the relative importance of each prey type in the diet was significantly explained by its local abundance and habitat, confirming the opportunistic foraging strategy of this raptor species. Consumption of mammals was an exception to this trend, being negatively associated with the abundance of alternative prey, suggesting that this prey is not preferred. Trophic diversity in this species could be influenced by land-use changes through variations in the abundance and availability of prey, which could impact its population dynamics. This may be particularly important for northern populations of Montagu’s harriers breeding in agricultural habitats, where trophic diversity is already low.

Migration and wintering areas of adult Montagu’s Harriers (Circus pygargus) breeding in Spain

Between 2006 and 2008, 14 Montagu's Harri- ers (Circus pygargus) were tagged with satellite transmit- ters at their breeding grounds in NE Spain, recording a total of 18 autumn and 10 spring journeys. In both autumn and spring migrations, harriers migrated between Europe and West Africa along a relatively narrow corridor between the coast of Morocco and Western Sahara and the western border of Algeria. Birds tended to follow a slightly more westerly track during spring migration compared to autumn migration. Harriers started autumn migration in late August-early September, arriving at their wintering grounds in early-mid-September, after travelling between 8 and 25 days, and covering a mean of 187 km a day. Spring migration started in mid-March, with birds arriving at the breeding grounds in mid-April after covering a mean of 114 km a day. On average, spring migration lasted longer, with birds covering longer distances than during autumn migration, and distances travelled in a day tended to be shorter. Significant differences in the routes followed by harriers were observed among seasons and individuals, with the same individuals following different routes in different years. Wintering areas were located in northern Senegal and the southern border of Mauritania with Mali, with some birds breeding in the same colony in Europe separated more than 1,200 km during the wintering season. Birds showed a relatively high fidelity to their wintering areas. Several birds moved from one area to another during the wintering period, which resulted in larger wintering areas, whereas others remained in the same area during the whole wintering season.

Demographic history, genetic structure and gene flow in a steppe-associated raptor species

BackgroundEnvironmental preferences and past climatic changes may determine the length of time during which a species range has contracted or expanded from refugia, thereby influencing levels of genetic diversification. Connectivity among populations of steppe-associated taxa might have been maximal during the long glacial periods, and interrupted only during the shorter interglacial phases, potentially resulting in low levels of genetic differentiation among populations. We investigated this hypothesis by exploring patterns of genetic diversity, past demography and gene flow in a raptor species characteristic of steppes, the Montagu's harrier (Circus pygargus), using mitochondrial DNA data from 13 breeding populations and two wintering populations.ResultsConsistent with our hypothesis, Montagu's harrier has relatively low genetic variation at the mitochondrial DNA. The highest levels of genetic diversity were found in coastal Spain, France and central Asia. These areas, which were open landscapes during the Holocene, may have acted as refugia when most of the European continent was covered by forests. We found significant genetic differentiation between two population groups, at the SW and NE parts of the species' range. Two events of past population growth were detected, and occurred ca. 7500-5500 and ca. 3500-1000 years BP in the SW and NE part of the range respectively. These events were likely associated with vegetation shifts caused by climate and human-induced changes during the Holocene.ConclusionsThe relative genetic homogeneity observed across populations of this steppe raptor may be explained by a short isolation time, relatively recent population expansions and a relaxed philopatry. We highlight the importance of considering the consequence of isolation and colonization processes in order to better understand the evolutionary history of steppe species.

Influence of habitat on nest location and reproductive output of Montagu’s Harriers breeding in natural vegetation

We examined distribution and breeding success of semi-colonial Montagu’s Harriers (Circus pygargus) in relation to habitat in Castellon province (eastern Spain). Breeding areas used by harriers at a 1-km2 scale were characterised by having intermediate percentages of scrub cover, their nesting habitat, and also had intermediate coverage of herbaceous crops and non-irrigated orchards. Out of all habitat variables considered, only the percentage of herbaceous crops within 500 m from individual nests had a positive and significant effect on breeding output of the species, suggesting that this habitat may be efficiently used by harriers to forage. Breeding output was also related to laying date and number of breeding neighbours within 500 m around nests, with pairs laying later and having a higher number of breeding neighbours showing lower fledged brood sizes. Number of neighbours (but not laying date) was positively related to scrub cover within 500 m and to cover of herbaceous crops within 2,000 m. Conservation actions for Montagu’s Harrier in the study area should be aimed at preserving areas of scrub with nearby presence of herbaceous crops or natural grasslands. However, habitat improvement for semi-colonial species such as Montagu’s Harrier may not result in a change of species distribution area, and good habitat areas may remain unoccupied, as social factors like presence of conspecifics play an important role in breeding area selection for these species.

Predators and nest success of Sky Larks Alauda arvensis in large arable fields in the Czech Republic

Capsule Nest failure owing to a range of predators was high, but the level and specificity of nest depredation cannot be generalised. Aims To determine fates and predators of Sky Lark nests in conventionally managed arable fields in the Czech Republic. Methods Sky Lark nests in large fields (mainly Maize, Sugar Beet and Opium Poppy) were monitored by means of continuous video surveillance. Results Primary nest fates of 42 active nests were fledging (13), depredation (22), desertion (5), nestling death (1), and flooding (1). The overall nest success (Mayfield estimate) was 17% (all mortality factors considered) or 27% (only depredation). Depredation events were caused by Marsh Harrier Circus aeruginosus (11), Hooded Crow Corvus cornix (4), Stone Marten Martes foina (3), Montagu’s Harrier Circus pygargus (2), Red Fox Vulpes vulpes (2), Hedgehog Erinaceus sp. (2) and Eurasian Jackdaw Corvus monedula (1). Successful nests were only slightly more away from field edge than depredated nests; nests taken by birds tended to be closer to field edge than those depredated by mammals. The possible reasons for the absence of a clear edge effect include comparatively large field parcels (about 50 ha) and location of nests far from field edge (median = 195 m). Conclusion Nest survival and composition of nest predators are site‐specific and contingent upon the study method and may not be simply generalised.

Does Bird Predation Enhance the Impact of Green Muscle® (Metarhizium acridum) used for Grasshopper Control?*

A study at Khelcom, Central Senegal, from September 2008 till June 2009 tested two different dose rates (25 and 50 g conidia/ha) of the mycoinsecticide Green Muscle® (Metarhizium acridum) and an untreated control, against grasshoppers in a field trial on nine 400-ha plots in three blocks. The study area was a deforested sylvo-pastoral reserve, 12.5% cultivated, whereas the remainder was fallow or grassland in succession. Grasshopper densities were calculated by executing transect and quadrat counts on plots. The grasshopper community structure was assessed by systematic sweep-net sampling on plots. From these data grasshopper biomass on plots was calculated for each sampling date. Bird numbers were counted on the same transects by the Distance Sampling technique and their densities calculated from Effective Strip Widths (ESW). Energetic requirements of individual bird species were calculated from digestibility-corrected Field Metabolic Rates (FMRs) and for acridivorous species their daily intake of grasshoppers was calculated. Grasshopper densities were very high, with up to 90 ind./m2 in September and 30–35 ind./m2 in October. Numbers and biomass decreased on treated plots as grasshoppers became infected, and remained significantly different from control plots for three months (until January). The relative importance of grasshopper consumption by birds increased between October (high grasshopper densities) and December (medium densities) from an initial 0.06 (±0.03) %/day to a ceiling of 1.6 (±0.9)% per day. Total grasshopper removal during the dry season was 70 %, whereas during the rainy season this was < 1%. Birds specifically captured large and medium-bodied grasshoppers, but rarely small-bodied species, whose numbers initially increased. These findings were corroborated by field observations and by analysis of regurgitated pellet contents of Montagu's Harriers, i.e., small-bodied grasshoppers were only 1.4 – 2.6% of all grasshoppers taken, whereas they constituted 61 – 68% of random samples from the field. Densities of acridivorous Palaearctic migratory birds, in particular White Stork, Ciconia ciconia, Montagu's Harrier, Circus pygargus and Lesser Kestrel, Falco naumanni, were very high and unprecedented elsewhere. Their numbers largely exceeded the 1% criterion for international importance.

Breeding biology of Montagu’s Harrier Circus pygargus in north-central Kazakhstan

The ecology and conservation status of Central Asian populations of Montagu’s Harriers Circus pygargus are poorly known. We studied the breeding biology of this species during 3 years in the Naurzum region, north-central Kazakhstan. Most Montagu’s Harriers in the study area nested in the forest-steppe transition area, in bushy areas dominated by dogrose Rosa canina, which was apparently the nesting vegetation type providing highest and densest nest cover in the study area. Laying occurred from 26 April to 7 June (average 13 May, n = 49) and, although it varied significantly between years, was earlier than in western European populations of similar latitude. Mean (±SD) clutch size was 4.44 ± 0.86 (range 2–6; n = 50), in the higher range observed for the species. There was no significant interannual variation in clutch size, despite large variations in the abundance of small mammals in the area. Diet was mainly composed of lizards (54.2%, n = 533 identified prey in all 3 years), with small mammals (17.1%), passerine birds (14.3%) and insects (13.6%) also being consumed. Mean brood size at the last visit was 2.55 ± 2.10 (range 0–6; n = 51). Failure rate was relatively high; the main identified cause of nest failure was predation. We compare the data obtained in this population breeding in natural steppes with breeding parameters from the well-studied western European populations, and discuss the implications for the conservation of this species.

Mixed roosts in the Montagu’s harrier Circus pygargus during courtship

Mixed communal roosting of Montagu’s harrier Circus pygargus in the pre-laying period was observed on Calcareous Marshes in Eastern Poland from 1992 to 1995. To my knowledge, this behaviour was described in literature for the first time. The communal roosting in Montagu’s harrier during courtship can help in estimation of mate attraction and finally in mate choice. Harriers from communal roosts start egg laying earlier when compared to the outside roosts. Communal roosting as anti-predator behaviour can help with predator detection and provides benefits to all members of the group. The pair formation process has led to disintegration of communal roosting. Males were more common in the roosting places than females. The time of roosting was correlated with the photoperiod. The weather and predators impact delayed the formation of mixed roosting places.

Semicolonial nesting and conservation of the Montagu's harrier Circus pygargus in rapeseed fields in Southern Podlasie (eastern Poland)

Semicolonial nesting and conservation of the Montagu's harrier Circus pygargus in rapeseed fields in Southern Podlasie (eastern Poland) Agrocoenosis are important nest sites for Montagu's harriers. In 2009, a large semicolony of 14 Montagu's harrier pairs was recorded in a rapeseed field in eastern Poland. The breeding colony arose due to a shortage of crops of suitable height in the period of nest building, caused by unfavourable weather conditions and a delayed onset of vegetation growth. The mean clutch size and hatchling number was 3.62, and the mean number of chicks in pairs that bred successfully was 2.00. Losses in broods due to predation and farming treatments were low (2% and 6%, respectively).

Blood Chemistry and Hematologic Values in Free-Living Nestlings of Montagu's Harriers (Circus pygargus) in a Natural Habitat

The establishment of reference intervals for hematologic and blood chemistry values in a given species is essential for subsequent diagnosis of disease at rehabilitation facilities and in captive breeding programs. In this study, blood samples were obtained from nestlings (18 males and 22 females) of a natural-vegetation breeding population of Montagu's harrier (Circus pygargus) in eastern Spain in order to establish reference intervals for blood values. This is the first study documenting hematologic and biochemical reference intervals for free-living Montagu's harriers. The studied population may reflect typical blood values for the species, since it is a free-living population that seems not to be constrained by food availability, as it is the population of Montagu's harriers with the highest productivity within Europe. Differences related to sex, year, clutch size, brood size, and number of fledglings were analyzed. Packed cell volume and hemoglobin were significantly lower from nests with five chicks compared to values from nests with fewer chicks, indicating that the cost of rearing more than four chicks in this species may be excessive. Total protein, calcium (Ca), and phosphorus (P) were significantly lower in the year with lowest mean rainfall, which correlates with the worst breeding success rate since the population has been monitored. No gender differences were found; this is likely a result of the prepubertal age of the animals sampled.

Carotenoids in nestling Montagu’s harriers: variations according to age, sex, body condition and evidence for diet-related limitations

Carotenoids are colored pigments forming the basis of many avian social traits. Before their utilization carotenoids must be acquired through diet and mobilized for specific uses. The relationships between carotenoid-based coloration, circulating carotenoids and body condition have been well studied in adult birds, but little is known in nestlings. Here, we investigated variations in carotenoid-based coloration in a raptor nestling, the Montagu's harrier (Circus pygargus), both in captivity and in natural conditions, and within a vole (poor-carotenoid source and cyclic prey) specialist population. We studied these variations according to nestling age and sex, and possible limitations in carotenoid availability by comparing years of contrasted prey abundance and using carotenoid supplementation experiments. Captive nestlings, fed only with mice, were strongly carotenoid limited. Wild nestlings were also carotenoid limited, especially in a year of high vole abundance. Nestlings were in better condition but less colored during a peak vole abundance year than during a low vole abundance year, when harriers targeted more alternative preys (birds, insects). Thus, variation in vole abundance resulted in a de-coupling of body condition and carotenoid-based coloration in this population. This suggested that the positive relation between the body condition and carotenoid-based traits, typically found in adult birds, could be restricted to adults or nestlings of species that feed on carotenoid-rich food. Our results should stimulate more work on the functions and mechanisms of carotenoid-based traits in nestlings, which deserve more attention and most likely differ from those of adult birds.

Long-Term Change in Population Size and Reproductive Parameters of Montagu's Harriers (Circus pygargus) in Italy

Circus pygargus es bastante abundante en el sudoeste de Europa (península ibérica y Francia), pero es raro en la península italiana, donde ha sido clasificado como “amenazado.” En este estudio, documentamos 241 intentos reproductivos de individuos de C. pygargus de la población del este y centro de Italia desde 1987 a 2005. Medimos el tamaño de la nidada, la tasa de eclosión, la tasa de emplumamiento y el éxito reproductivo. También investigamos el hábitat de anidación y la distribución agregada de los nidos. Encontramos que esta población de C. pygargus ha disminuido en términos de parámetros reproductivos y de abundancia, incluyendo el éxito reproductivo y la tasa de emplumamiento. Más aún, observamos una disminución en la fracción de parejas que anidan en las áreas agrícolas (cultivos). Estas disminuciones pueden estar relacionadas a una escasez general de recursos alimenticios y a una alta mortalidad durante la cosecha de los cultivos. Nuestros resultados destacan la importancia de proteger los ambientes naturales para conservar esta especie a escala nacional.