Montagu's Harrier Circus Pygargus Research Articles

Variable but predictable prey availability affects predator breeding success: natural versus experimental evidence

AbstractFood supply is a major source of variation in breeding success for predators, and to what extent individuals are able to cope with temporal variability in food availability remains an outstanding question in life‐history studies. We confronted the natural variation in clutch size and breeding success with results from a food supplementation experiment during egg formation, conducted over several contrasted years of natural food supply in an avian specialist predator, the Montagu's harrier Circus pygargus. This raptor mainly preys on common vole Microtus arvalis a cyclic microtine under temperate latitudes. Vole abundance together with timing of breeding accounted for most of the variance in clutch size and number of fledglings. Results from empirical and experimental data were overall in agreement. Fed pairs consistently increased clutch size compared with controls in all experimental years, whereas no effect of food supplementation on egg volume was detected. Supplemented pairs, however, did not fledge significantly more chicks than controls. The costs entailed by the increase in clutch size appear nevertheless to be limited compared with previous studies. Food supply seemed therefore to display sufficient predictability throughout a breeding season to afford individuals the opportunity to adjust their breeding effort to an optimal number of offspring, in agreement with Lack's anticipation hypothesis.

Post-fledging dependence and dispersal in hacked and wild Montagu's Harriers Circus pygargus

We compared the post-fledging dependence period, dispersal patterns and resighting rates of captive-raised and hacked Montagu's Harriers Circus pygargus with those of wild reared and naturally fledged Montagu's Harriers, in order to assess the validity of haclung as a release technique for this species. Among hacked birds, we found significant relationships between the length of the dependence period and both hatching date and body condition (birds hatched later in the season had shorter periods of dependence; birds in poorer condition had longer periods of dependence). The condition index increased with the amount of time spent in captivity. The length of the dependence period did not differ significantly between released and naturally fledged birds, when hatching dates were accounted for. Observation rates of wing-tagged fledglings in years after marlung were higher for released birds (1 5.5-20.9°/~) than for naturally fledged birds (9.4-9.9940). Released birds also tended to be resighted closer to their released location than did the naturally fledged birds. We suggest that the differences in resighting data are related to the better condition of the released birds, compared with their wild counterparts. We conclude that hacking is apparently a good release technique for captive-reared Montagu's Harriers, and that comparisons of behaviour at the post-fledging period may be a valid method for evaluating the success of release techniques.

Pre-Migratory Movements of Adult Montagu's HarriersCircus pygargus

Pre-migratory and migratory movements of Montagu's Harrier Circus pygargus, a long-distance migrant, are poorly documented by ring recoveries and observations. In the present study, we tagged 10 adult Montagu's Harriers in NE Spain with satellite transmitters and tracked their movements until their arrival on the wintering grounds. To identify the end of the breeding season and the onset of the migration based on our satellite-telemetry data we developed and applied a statistical approach, defining the time period between these two events as the pre-migratory stage. We then compared habitat preferences during the breeding season and the pre-migratory stage. The duration of the pre-migratory stage averaged 42 days, with harriers leaving the breeding areas between 4 June and 27 July, and the onset of the migration taking place between 25 July and 4 September. Staging areas used during pre-migration were located at higher altitudes than the breeding grounds, and were characterized by the presence of shrublands and cultivated areas, mainly cereals. Montagu's Harriers' use of these sites is likely to be related to food availability: at higher altitudes, peak abundance of Orthoptera, their main prey source, occurs later in the season than in the lowland breeding area. Pre-migratory movements may also play an important role in the search for suitable breeding sites for future use.

Selection of nesting habitat by Montagu's Harriers Circus pygargus and Hen Harriers Circus cyaneus in managed heaths

Capsule Montagu's Harriers avoided tree plantations and selected plots with dense heath of intermediate height, while sympatric Hen Harriers preferred afforested or taller plots of heath. Aims To investigate relationships between vegetation structure and nest selection by Montagu's and Hen Harriers. Methods We defined three vegetation strata: upper, intermediate and lower. Height and cover of plant species in each stratum were recorded in a 9-m2 area centred on nests or unused random points. Statistical analysis was performed to reveal predictors for classifying plots (i) with a Montagu's Harrier nest, (ii) with a Hen Harrier nest and (iii) without a nest. Results Montagu's Harriers selected places where tree cover was less than 25%, the maximum height of the upper stratum was 1.87 m, and the cover of the intermediate stratum was greater than 75%. Hen Harriers nested either in plots where the upper stratum was higher than 1.87 m, or where tree coverage was greater than 25%. Conclusions To encourage the breeding of Montagu's Harriers, the planting of pine should be avoided and the heath should be rejuvenated before it reaches 1.80 m in height. For Hen Harriers, certain plots of heath higher than 2 m should be kept. In agricultural landscapes, patches of managed shrubland or heathland could help conservation of both species.

Interactive effects of food and age on breeding in the Montagu's Harrier Circus pygargus

We evaluated the direct and interactive effects of food and age on reproduction in the Montagu's Harrier Circus pygargus, to test whether variation in food supply was likely to affect age‐specific breeding probability or success. Younger females were more frequently non‐breeders than older females. When breeding, older females laid earlier, produced larger clutches, failed less often and had higher number of fledglings than younger females. Probability of breeding was higher, laying was earlier, and clutch size and number of fledglings per pair increased with increasing food abundance. A significant interaction between food and age was observed in both breeding probability and breeding performance: older females were more likely to breed than younger females when food abundance was low, and younger females performed less well in good food conditions than older females. Overall, differences between age groups were most marked in extreme food conditions, regardless of the quality of the conditions.

Do voles make agricultural habitat attractive to Montagu's HarrierCircus pygargus?

Loss and degradation of habitat threatens many bird populations. Recent rural land‐use changes in the Netherlands have led to a shift in habitat use by breeding Montagu's HarriersCircus pygargus. Since the 1990s, unprecedented numbers of this species have bred in farmland compared with numbers in natural habitat. Destruction of nests by agricultural operations, however, compromises breeding success. Between 1992 and 2005, the number of breeding pairs in the northeastern Netherlands was positively, though weakly, correlated with previous‐year estimated abundance of voles, mostlyMicrotus arvalis. In good vole years, the onset of laying was earlier and mean clutch size was larger. Vole abundance was relatively higher in set‐aside land and in high and dense vegetation. We suggest that agri‐environmental schemes aimed at increasing the availability of voles in agricultural breeding areas may be an effective management tool for the conservation of Montagu's Harriers in the northeastern Netherlands.

Population trend and breeding biology of Montagu's Harrier Circus pygargus in a natural vegetation site in northeast Spain

Capsule Reproductive output in a natural habitat was higher than in birds breeding in cereal crops, highlighting the importance of natural habitats for the species. Aims To evaluate breeding in a natural habitat in inland Castellon province, Spain, and compare breeding parameters with other European populations. Methods Breeding population size in inland Castellon was recorded between 1981 and 2003. A logistic growth model was used to describe population increase. We also calculated clutch size, brood size, productivity, percentage of successful nests and fledging success for the period 1989–2003. Results Population size increased from three pairs in 1981 to 98 pairs in 2003. During 1989–2003, productivity (2.74 ± 1.49 fledglings/pair) and percentage of successful nests (84.%) were higher than observed in other European populations. Conclusions Our results show the importance of our study area for the conservation of this species in the Iberian Peninsula, as it might act as a source of colonists for other areas. Food and protection against predators might explain the high breeding output, which may in turn explain the rapid population growth in the area. The study also suggests that natural habitats might be important for the species elsewhere.

Diet composition influences annual breeding success of Montagu's Harriers Circus pygargus feeding on diverse prey

Capsule Diet diversity was positively related to nest failure in Montagu's Harriers. Aims To evaluate whether breeding density, age structure and breeding success of Montagu's Harriers were related to variations in diet composition. Methods Breeding data were collected over an eight-year period (1991–98) in Madrid, central Spain. Diet was evaluated through pellets and remains collected near nests. Diet diversity was calculated using Shannon's index. Results Diet diversity was negatively correlated to the proportion of hares Lepus granatensis in the diet, positively to the proportion of insects, and not significantly to other prey types. Breeding parameters varied significantly between years, although annual variation in breeding parameters in Madrid was lower than in populations where diet is less diverse. Nest failure was the most important variable explaining variation in productivity, and was primarily caused by food-related factors (abandonment and starvation). Nest failure was less frequent in years where diet diversity was lower. Conclusion Hares appear to be the preferred prey for Montagu's Harriers in Madrid, and other prey were used mainly when hares were less abundant or less available (with insects being the main alternative prey). Years when diet was less diverse (i.e. when hares were dominant in the diet) were associated with a higher productivity, and with a lower between-pair variation in this parameter.

Are simple plumage traits sufficient for species discrimination by harrier males?

I investigated whether plumage features are sufficient for species recognition in two sibling sympatric raptor species: the Montagu's harrier Circus pygargus and the hen harrier C. cyaneus. These species are similar in body size and differ slightly in plumage. During prelaying and laying periods, I placed artificial models close to nests of both species, simulating a conspecific male harrier (male of the same species), a heterospecific male harrier (male of the other species) or a wood pigeon Columba palumbus (acting as a control of the same size and colour). All of them represented birds perched in a neutral posture, so that they could only be recognised by their plumage differences. The use of plumage traits during this period would be particularly relevant in discriminating between their own and other species, offering the opportunity to avoid unnecessary fights, and therefore maximising the benefits of defence. I measured male responsiveness by recording aggressive behaviour towards each model (aggressive rate and time spent close to the female). Male presence time was significantly longer during conspecific decoy presentation than during heterospecific decoy presentation. Furthermore, males of both species were more aggressive towards the conspecific decoy than towards the heterospecific one, and no attacks towards the control were recorded. These results provide evidence that these birds are able to recognise plumage features of their own and the sibling species.

Age-related differences in foraging behavior of Montagu's harrier Circus pygargus males in south-east Poland

The hunting behaviour and habitat use of second-calendar-year males (subadult) and grey (adult) males of Montagu's harrier Circus pygargus were compared in south-east Poland. Subadult males performed cruising flights less frequently than did adult males. In contrast, subadult males more frequently soared thermals and were harassed more often by other birds. Overall, adult males were more frequently engaged in hunting activities than subadult males. Additionally, adult males were more successful in trapping prey than were subadult males. Only 7% (n=92) of trapping attempts by subadult males were successful, compared with 17% (n=126) by grey males. Both adult and subadult males tried to catch prey flushed by foxes Vulpes vulpes. Subadult males were seen begging and pirating from prey-carrying raptors.

Sex‐biased nestling mortality in the Montagu's harrier Circus pygargus

I evaluate causes and patterns of nestling mortality in a sexually dimorphic species, the Montagu's harrier Circus pygargus, and their relationship with sex and condition. Starvation was apparently the main reason for nestling death. Condition of birds that died was lower than those that survived. Both probability of nestling death and the proportion of nestlings that died within a brood increased with the number of hatched nestlings in a brood, and with increasing hatching date. For the nestlings that died after being sexed, when controlling for brood effects, probability of death was significantly related to nestling sex, with smaller males having a higher probability of dying. The probability of nestling death if hatched late in the season was relatively greater for males than for females. There was also a significant interaction between sex and hatching date on nestling condition: the decline in condition if hatched late in the season was steeper for males than for females. Males did not have a higher probability of death when having more sisters: neither the probability of brood reduction nor the proportion of nestlings that died were significantly related to within‐brood sex ratio. Results suggest that mortality may partly result from sibling competition: females, being the larger sex, might be better able to compete for food within a brood than their male siblings. Additionally, smaller males may be less able to recover from periods of declining body weight.

Effect of abiotic factors on reproduction in the centre and periphery of breeding ranges: a comparative analysis in sympatric harriers

Variables such as weather or other abiotic factors should have a higher influence on demographic rates in border areas than in central areas, given that climatic adaptation might be important in determining range borders. Similarly, for a given area, the relationship between weather and reproduction should be dissimilar for species which are in the centre of their breeding range and those that are near the edge. We tested this hypothesis on two sympatric ground‐nesting raptors, the hen harrier Circus cyaneus and the Montagu's harrier Circus pygargus in Madrid, central Spain, where the hen harrier is at the southern edge of its breeding range in the western Palearctic and the Montagu's harrier is central in its distribution. We examined the reproductive success of both species during an 8‐yr period, and looked at the influence of the most stressful abiotic factors in the study area (between‐year variation in rainfall and within‐year variation in temperature) on reproductive parameters.In the hen harrier, low levels of rainfall during the breeding season had a negative influence on annual fledging success and thus on population fledgling production. The relationship between rainfall and reproduction was probably mediated through food abundance, which in Mediterranean habitat depends directly on rainfall levels. In the Montagu's harrier, no negative effect of dry seasons on productivity was found. Additionally, in the hen harrier, the proportion of eggs that did not hatch in each clutch increased with higher temperatures during the incubation period. No such relationship was found in the Montagu's harrier. We interpret these between‐species differences in terms of differences of breeding range and adaptations to the average conditions existing there. Hen harriers, commonest at northern latitudes, are probably best adapted to the most typical conditions at those latitudes, and have probably not developed thermoregulatory or behavioural mechanisms to cope with drought and high temperatures in Mediterranean habitats, in contrast to Montagu's harrier. Thus hen harrier distribution might be constrained by these variables, due to lower reproductive success or higher reproductive costs. Accordingly, a logistic regression analysis of the presence or absence of both species in 289 random points throughout the western Palearctic showed that the distribution of both species was related to temperature, but the relationship was in opposite directions for the two species: hen harriers had lower probability of breeding in areas with higher temperature (as expected in a species with a more northerly distribution).

Effect of diet on the reproductive success of Montagu's Harrier Circus pygargus

Effect of diet on the reproductive success of Montagu's Harrier Circus pygargus

Migratory movements of western European Montagu's Harrier Circus pygargus: a review

We review the migratory movements of European Montagu's Harriers, based on 152 ringing recoveries (from data published up to 1993) and published data on counts at migratory convergence points. Data were analysed according to age groups and time of the year (pre- and post-breeding migration). Results showed two main migratory routes across the Mediterranean for the western European Montagu's Harriers (Gibraltar and the Sicily Channel). Passage frequency was higher in the post-breeding than the pre-breeding migration in the Gibraltar Strait, but the opposite occurred in the Sicily Channel. We discuss the possibility that Montagu's Harriers present a partially circular migration, maybe as a result of movements within the wintering areas. Recovery frequency varied according to age group, being lower for first-year birds than expected from random, which suggests that some first-year birds do not return to the breeding areas during their first summer.

Diet of Montagu's Harrier Circus pygargus in central Spain: analysis of temporal and geographic variation

The diet of Montagu's Harrier Circus pygargus was studied for 4 years near Madrid, Spain, with the use of pellets and prey remains collected during the breeding season. The diet of the study birds included a wide variety of prey categories, the most important one by weight being lagomorphs (mainly Hares Lepus granatensis). The diet varied seasonally, with Hares predominating early in the breeding season, while birds increased in importance later. The shift was partly a result of variation in availability (with fledgling birds being more abundant late in the season), but statistical analysis suggested that lagomorphs and then birds were actively chosen in the prelaying and nestling periods, respectively. Montagu's Harrier seemed to be an opportunistic species, hunting a wider range of prey types in more southern latitudes, but specialized in each region in the prey species that was most profitable. This was the only study on Montagu's Harriers to date which found lagomorphs to be the most important part of the diet throughout the season.

Breeding biology of Montagu's Harrier Circus pygargus L. in agricultural environments of southwest Spain; comparison with other populations in the western Palearctic

We studied the breeding biology of Montagu's Harrier in an agricultural habitat at various breeding sites in Extremadura (southwest Spain). Clear latitudinal trends were observed on laying date and clutch size compared to other Western Palearctic populations: as laying starts earlier, clutch size declines in southern populations. Climate and feeding could be the main factors involved. In addition to natural factors, the species' use of cultivated areas as nesting habitat at Southern latitudes is the major determinant of breeding success. Artificial nest management at harvest time has been shown to be effective in reducing losses due to farming activities. Such conservation measures reduce the mortality rate of nestlings and consequently increase the reproductive success of breeding pairs. Nevertheless, endogenous factors related to individual breeding condition limit the effect of artificial nest management. Mediterranean populations of Montagu's Harrier seem to be highly dependent on conservation measures because of the high failure rates for breeding in the absence of such intervention.

Flight strategies of migrating raptors; a comparative study of interspecific variation in flight characteristics

The comparison of flight styles and flight parameters of migrating raptors in Israel revealed the following. (1) Climbing rate in thermal circling did not differ between species, indicating that chiefly the strength of thermal updrafts determined the climbing rate and that morphological features were less relevant. (2) In interthermal gliding, air speed was positively and gliding angle negatively related to the species' average body mass. Heavier species glided faster and had smaller gliding angles. (3) In soaring and gliding flight, cross‐country speed relative to the air was positively related to the species' body mass; it was obviously the result of the gliding ability increasing with body mass. (4) Eagles and buzzards used soaring and gliding flight for more than 95% of the observation time. Additional soaring in a straight line whilst gliding was extensively used by the Steppe Eagle Aquila nipalensis, Lesser Spotted Eagle Aquila pomarina and Booted Eagle Hieraætus pennatus and even more frequently by the resident species, the Griffon Vulture Gyps fulvus and Shorttoed Eagle Circaetus gallicus. Smaller species, such as the Levant Sparrowhawk Accipiter brevipes, harriers (Circus sp.) and small falcons (Falco sp.). showed the highest proportion of flapping and gliding flight (9–33%). (5) In a comparison of the flight parameters and proportions of flight styles, a cluster analysis distinguished two main groups: The first consisted of Montagu's Harrier Circus pygargus, Pallid Harrier Circus macrourus, Levant Sparrowhawk and small falcons; their flight behaviour was characterized by both the high proportion of flapping and the low gliding performance. The second group comprised the typical soaring migrants: Steppe Eagle, Lesser Spotted Eagle, Booted Eagle, Steppe Buzzard Buteo buteo vulpinus, Honey Buzzard Pernis apivorus and Egyptian Vulture Neophron percnopterus, and they had very similar flight behaviour and were closely clustered. The Black Kite Milvus migrans and Marsh Harrier Circus aeruginosus were intermediate between typical soarers and flappers. The two resident species, Griffon Vulture and Short‐toed Eagle, were grouped separately from the soaring migrants.

Differential Timing of Autumn Migration between Sex and Age Groups in Raptors at Falsterbo, Sweden

The migration of raptors at Falsterbo, Sweden was studied during five autumns, 1986-1990, to investigate the intraspecific temporal sequence of migration for different age and sex classes. The analysis is based on counts of between 45 and 72 321 individuals of 14 species. The percentage of juveniles varied among species and to some extent between years. This reflects a variable tendency of different migrants to concentrate at Falsterbo and fluctuating breeding success from year to year. Most species showed an even sex ratio. Marked exceptions were Marsh Harrier Circus aeruginosus and Hen Harrier C. cyaneus in which females constituted 60 and 61% respectively of adult migrants. This biassed sex ratio agrees with the tendency towards polygyny in these species. In tropical (long-distance) migrants adults migrated ahead of juveniles (Honey Buzzard Pernis apivorus, Montagu's Harrier Circus pygargus, Osprey Pandion haliaetus, and Hobby Falco subbuteo). It is suggested that it is advantageous for adults to arrive early on the wintering grounds, finish moult and accumulate energy reserves before spring migration and the next breeding season. Those short-distance migrants in which adults migrated before juveniles at Falsterbo are species whose majority leave Scandinavia in the winter (Hen Harrier, Common Buzzard Buteo buteo, Roughlegged Buzzard B. lagopus, Merlin Falco columbarius and Peregrine F peregrinus). Adults leaving first have a greater possibility to secure a good winter territory forcing the juveniles, migrating later, to settle in less suitable habitat or to winter further south. In species where juveniles migrated ahead of adults a large proportion of the adults spend the winter close to the breeding grounds (Red Kite Milvus milvus, Goshawk Accipiter gentilis and Sparrowhawk A. nisus). The presumably subdominant juveniles may be excluded from the breeding territories by the adults and therefore migrate south, followed by a varying proportion of adults. Females generally migrated before males at Falsterbo due to different moult strategies; females starting and finishing moult of the flight feathers before males. This difference in timing of moult and migration is ultimately dependent on a marked role division between the sexes during the breeding cycle. In Honey Buzzard where both sexes share the breeding duties equally no difference in timing of migration was found. Social dominance, importance of early arrival at the winter quarters and moult strategies are the factors best explaining the observed differential timing in migrating raptors at Falsterbo.

Aggressive behaviour in Montagu's harrier (Circus pygargus) during the breeding season

Abstract Intra and interspecific aggressive behaviour of Montagu's harrier was studied during the breeding seasons 1987–1990. Of the intraspecific aggressive interactions the most frequent one is the ≪attack≫, mainly in relation to territory defence. The area defended by nesters against conspecifics averaged 4.0 hectares and aggressivity was more intense near the nest. Female resulted always more aggressive than males. In the defence of pair bond and of territory intruders of the other sex are widely tolerated while females are always more attacked than males. In the interspecific interactions Montagu's harrier was relatively tolerant against other species, even if raptors, present in the breeding area, while also against potential predators of eggs and nestlings, like carrion crow, it seems quite very tolerant. A non aggressivedisplay, ≪communal soaring≫, has been described in Montagu's harriers for the first time.