Food habits and the survival and growth of nestlings in two sympatric kites (Milvus milvus and Milvus migrans)

A comparative study of the Red Kite and Black Kite was conducted in the Doana National Park in southwestern Spain. Although the diets of both kites were similar, the Red Kite captured significantly more prey items from scrub habitats close to nesting areas than from marsh habitats, which were further away. Habitat differences in prey abundance and distance from breeding areas suggest that the Red Kite depended on a less abundant but more stable food supply. Nestling mortality from starvation was highest for the last hatched nestlings in both species. The growth rate of Black Kite nestlings was markedly higher than that of Red Kite nestlings. Moreover, growth rates increased with clutch size in the Red Kite, whereas they were constant in the Black Kite. Differences between species in reproductive traits are discussed mainly with regard to their feeding ecology. The slower growth and greater effect of sibling asymmetry on mortality of the Red Kite are consistent with our interpretation that the Red Kite's food supply is less abundant than the Black Kite's.     

Age of first breeding, dispersal and survival of Red Kites Milvus milvus in Wales

Twenty-nine Red Kites, that were tagged as nestlings in Wales, bred for the first time at 2–7 years old (mean 3–6). A minimum of 41% of tagged young had entered the breeding population by the 7th year. Individuals moved up to 22 km between birthplace and breeding place and, having bred, most stayed in the same locality from year to year. No differences in these various respects were found between the sexes, though two long movements by territorial birds both involved females. Annual survival of adult breeders was estimated at around 95%.     

Successful breeding at one year of age by Red Kites Milvus milvus in southern England

This paper presents the first data on individually tagged male and female Red Kites Milvus milvus breeding at 1 year old and is validated by genetic fingerprinting. The data were collected during 1989 to 1994 when Red Kite nestlings were translocated to, and released in, southern England as part of a re-establishment project. A total of 23 1-year-old Red Kites attempted to breed in southern England from 1991 to 1994, of which three pairs, each composed of at least one yearling bird, reared five young. We conclude that habitat quality is ultimately the main influence that determines whether Red Kites can breed and how well they breed. However, individual experience, climate and competition with other Red Kites for nesting territories probably influence the age at which an individual can breed in a particular habitat.     

The function of aggressive chases by breeding Black and Red Kites Milvus migrans and M. milvus during the post-fledging dependence period

Black and Red Kites Milvus migrans and M. milvus chase other raptors approaching their nests. The study of this behaviour during the post-fledging period suggested that it reflects mainly, but not only, anti-predator behaviour. The frequency of vigilance and aggressive chases decreased through the post-fledging period as predicted by theoretical models of nest defence. Although predation risks were similar, Black Kites invested more time chasing intruders than did Red Kites. Black Kites, unlike Red Kites, chased away intruding juveniles, which may be interpreted as a behaviour to avoid investment in unrelated fledglings. Black Kites usually nest in loose colonies where the risk of, and selection pressures against, accidental investment in unrelated fledglings is likely to be greater than for Red Kites. Differences in aggressive chases by Black and Red Kites are better related to this than to different predation risks.     

Growth of nestling black kites Milvus migrans: effects of hatching order, weather and season

The growth of black kites Milvus migrans was studied in 1981, 1982 and 1984 at the Doñana Biological Reserve (south-west Spain). Fifteen variables were submitted to a principal component analysis in order to characterize the growth pattern of the young. In general, in the nestlings that fledged, rapid weight gain corresponded to rapid growth of the tarsus and feathers. For nestlings that starved, tarsus growth took priority over weight gain. Within the same brood, the last-hatched sibling grew more slowly than its older sibling and the differences between them increased in proportion to the hatching asynchrony. Brood size did not affect growth as clearly as hatching order and hatching asynchrony. Increased rainfall and lower maximum temperature, factors that seem to make the search for food more difficult, had negative effects on the youngest sibling in a multiple brood and on single nestlings. The only environmental variable that had an effect on all of the nestlings was the hatching date.     

Poisoning of reintroduced red kites (<Emphasis Type="Italic">Milvus Milvus</Emphasis>) in England

Programmes to reintroduce predatory birds are resource intensive and expensive, yet there are few long-term studies on the health of these reintroduced birds following release. A total of 326 red kites (Milvus milvus) were released at four sites in England between 1989 and 2006 as part of efforts to reintroduce this species to England and Scotland, resulting in the establishment of several rapidly expanding populations in the wild. Detailed post-mortem examinations were carried out on 162 individuals found dead between 1989 and 2007, involving both released and wild-fledged birds. Toxicological analysis of one or more compounds was performed on 110 of the 162 birds. Poisoning was diagnosed in 32 of these 110 kites, 19 from second-generation anticoagulant rodenticides, 9 from other pesticides and 6 from lead. Criteria for diagnosing anticoagulant rodenticide poisoning included visible haemorrhage on gross post-mortem examination and levels of anticoagulant rodenticide exceeding 100 ng/g, but levels were elevated above 100 ng/g in a further eight red kites without visible haemorrhages, suggesting poisoning may have occurred in more birds. The anticoagulant rodenticides difenacoum and bromadiolone were the most common vertebrate control agents involved during this period. Poisoning of red kites may be slowing their rate of population recovery and range expansion in England. Simple modifications of human activity, such as best practice in rodent control campaigns, tackling the illegal use of pesticides and the use of non-toxic alternatives to lead ammunition, can reduce our impact on red kites and probably other populations of predatory and scavenging species.     

Year-to-year patterns of circulating levels of testosterone and corticosterone in relation to breeding density, experience, and reproductive success of the polygynous red-winged blackbird.

To determine across-year patterns in plasma testosterone (T) and corticosterone (B) levels in free-living birds, we took blood samples in the same 2-week breeding period during 4 consecutive years from territorial male red-winged blackbirds. We used our data to test predictions of the "challenge hypothesis" of T secretion and also to examine hormonal correlations with age, breeding experience, breeding density, and reproductive success. Average T and B levels across years were not significantly different. Within individuals, T levels between years were, in general, highly variable. T levels of males with territories in high-density breeding areas were significantly higher than those of males with territories in low-density areas. T levels were positively correlated with harem size and there was a trend for males with high T levels to fledge more offspring. We found no relationships between T and B levels and male age or breeding experience. Some results of the study were consistent with the predictions of the challenge hypothesis. This study constitutes one of the few examinations of across-year patterns in circulating hormone levels in wild populations.     

Territorial occupancy and breeding performance in a migratory raptor do not follow ideal despotic distribution patterns

It has commonly been argued that many territorial species select their breeding sites following an ideal despotic distribution model, in which the most productive, high-quality territories are more frequently occupied. Theoretical and empirical studies have shown that this occupancy pattern may have population regulatory consequences, leading to density dependence in heterogeneous habitats. During a 9-year research project in a forested area of south-eastern Spain, we tested some of the predictions of the ideal despotic distribution model and the site-dependent population regulation theory in a migratory raptor species, the booted eagle Hieraaetus pennatus . Contrary to the predictions of the despotic model, our results showed that the temporal pattern of territorial occupation did not differ from randomness, and that the territory occupancy rate was not significantly related to the reproductive parameters considered. At population level, the breeding variables were density independent, suggesting the absence of site-dependent regulation. In addition, we were unable to find significant differences in the habitat characteristics between high-quality and low-quality territories, classified according to the criteria of both occupancy frequency and average productivity. Overall, our results suggest that booted eagles select their territories at random, probably due to the lack of strong environmental heterogeneity, and that occupancy rate is not a good measure of territory quality for the population studied.     

From individual behaviour to population pattern: weather-dependent foraging and breeding performance in black kites

The links between weather and animal behaviour in population processes have received relatively little attention. I studied the effect of weather conditions on foraging and breeding performance of a medium-sized raptor, the black kite, Milvus migrans. The frequency of prey capture attempts and their likelihood of success increased with temperature and declined with rainfall. Kites used flight styles involving a higher energy expenditure in less favourable weather. Nestling provisioning rates declined during rain spells. More kites hunted during periods of favourable weather and after periods with a high frequency of successful prey capture attempts by conspecifics; this result suggested that individuals may fine-tune their foraging effort to the expected foraging reward. Such compensatory behavioural adjustments may increase species resilience to climate change. The behaviourally mediated effects of weather on prey availability translated into population effects. Yearly weather conditions during the last stage of the prelaying period affected population-level productivity, probably through an effect on female body condition mediated by male provisioning capability and hunting yield. The predicted effects of climate change on kites may already be occurring, with progressively earlier laying and northward range expansion. These results confirm the need to pay greater attention to behaviourally mediated effects of climate on populations, particularly when individuals make compensatory adjustments that may enhance resilience to climate change. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Effects of territorial intrusions, courtship feedings and mate fidelity on the copulation behaviour of the osprey

We studied copulation behaviour of the osprey, Pandion haliaetus, a semicolonial, fish-eating raptor, in Corsica (Mediterranean). Pairs copulated over a long period (45 days) and at a high rate, with, on average, 288 within-pair copulations (WPCs) for a clutch. Pairs breeding at higher density faced more frequent territorial intrusions than others and were potentially at an increased cuckoldry risk. However, and contrary to predictions of the ‘paternity assurance’ hypothesis for frequent copulations, we found that WPC rate decreased with increasing frequency of territorial intrusions. Male territory attendance increased with territorial intrusion frequency, to the detriment of the food provisioning of the female. Both attempted and successful WPC rates were positively related to the amount of food delivered by the male. Thus, the more frequent the territorial intrusions, the more time the male spent within his territory, the less he courtship fed and the smaller the fish he delivered, and the less the pair copulated successfully. WPC rate was also higher in newly formed pairs than in established pairs, and decreased with increasing pair bond length. The results suggest that males rely on mate guarding rather than frequent copulations to ensure paternity, and do not support the idea that sperm competition is the main cause of frequent WPCs. Nonfertilization functions of frequent copulations, such as pair bonding, mate assessment and mate retention, were likely early in the prelaying period. The findings that WPC rate decreased with mate fidelity and that females traded copulations for food suggest that mate retention was a possible function of frequent copulations in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Home-range use, activity, and density of caracal in relation to prey density

Two male and three female caracal Felis caracal were radio-tracked over a 1-year period in arid shrub on the west coast of South Africa, by day and night over at least 130 days for each caracal, and uninterrupted for up to 120 h at a time. These results, on short-term use of space, were related to concurrent availability of prey. The use by caracal of specific plant communities showed a significant positive correlation to prey biomass of rodents. Males had much larger home-ranges (26.9±0.75 km²) than females (7.39±1.68 km²). Male home-ranges overlapped completely with those of females, whereas female ranges overlapped between 0 and 19%. Caracal were active by night and day; onset of activity was affected more by ambient temperature (T_A) than photoperiod. Caracal were active significantly longer on nights colder than 20°C. Females ceased activity at T_A > 20°C, males at T_A > 22°C. Males foraged faster than females (667 vs. 312 m h⁻¹) and moved more than twice the distance of females during an active period. Calculated density of caracal was between 0.23 and 0.47 km⁻².     

Reproductive patterns in mantled howler monkeys: Estrus,mate choice and copulation

The present study was undertaken to evaluate non-random mating patterns in two groups of mantled howler monkeys in two tropical dry forest habitats. Sexual dimorphism, female estrus stage, male dominance rank, sexual solicitations and copulations were assessed. Males are significantly larger than females, but female weight varies more than male weight. The length of female estrus cycles is comparable in both habitats, but females in the more strongly seasonal habitat demonstrate greater estrus synchrony relative to their numbers. Males solicit potential mates more frequently than females, a pattern explained by the relatively high rate of sexual solicitation by high-ranking males. Females in “peak” estrus solicit “alpha” males, while females in other stages of estrus solicit males equally by rank. Intersexual aggression occurs rarely, and “forced copulations” are attempted but, apparently, are unsuccessful. Sexual solicitations by “alpha” males and “peak” estrus females are most likely to lead to copulation, and “alpha” males are more likely to copulate than “gamma” males. In general, latencies from first solicitation to copulation are expensive in time, especially for high-ranking males. Estimated annual reproduction success favors high-ranking males, and results indicate that male and female mating behavior is mutually coordinated and controlled.     

Factor analysis in relation to breeding system

The forces of divergence in the cultivated populations of crops belonging to different breeding systems,Sorghum, Pennisetum, Brassica, linseed and wheat, have been examined utilising the centroid method of factor analysis. The populations consisted of mostly elite material of high productivity.Three factors were found to be adequate to account for most of the total communality although upto fourteen variables have been included. The results confirmed that the use of genetic correlation matrices in populations under intensive human selection would change the factor loadings to a considerable degree as compared to environmental correlation matrices.The factor loadings inSorghum indicated the important role of the reproductive factor and the growth factor in the evolution of this genus. In the case ofPennisetum, ear girth, ear length and height were important in the first factor, while early vigour and flowering time were predominant for the second foctor. InBrassica, the data have also indicated that disruptive selection for flowering time had substantially modified factor loadings in ease of the genotypic correlation matrix and had, therefore, substantially modified the course of evolution. In the case of linseed, the inclusion of F₁ hybrids did not change the major conclusions drawn about factor loadings for factors from the genotypic correlation matrix.The number of factors and the loadings did not appear to be directly related to the breeding system but were found to be influenced by the past history of selection. The first factor which contributed the most to the total communality was concerned with reproductive capacity and characters influencing major components of fitness under both human and natural selection.Presented at the 21st annual general conference of the Indian Society of Agricultural Statistics held at Lucknow in February, 1968.     

Repeat breeding in dairy heifers: follicular dynamics and estrous cycle characteristics in relation to sexual hormone patterns

Repeat breeding occurs at an incidence of 10% in the Swedish dairy cow population.Evidence is available for a hormonal asynchrony around estrus in repeat-breeder heifers (RBH). This asynchrony seems to be the underlying cause for a series of dysfunctions such as prolonged standing estrus and delayed ovulation, leading to fertilization failure. For further determinations of repeat-breeder estrous cycle characteristics, seven strictly selected RBH and six virgin heifers (VH) were studied during 3-7 consecutive cycles, with particular attention paid to the estrous period. Follicular dynamics were studied by ultrasonography and related to estrous behavior and pattern of sexual hormones (progesterone, estradiol-17beta, and LH) in peripheral circulation. Mean group data were compared and a classification model was designed. The most prominent findings for RBH were prolonged duration of estrus, delayed LH peak, prolonged lifespan of the preovulatory follicle, and a late postovulatory rise in plasma progesterone. There was also a strong tendency for peri-ovulatory suprabasal progesterone levels in RBH. It is suspected that these deviations cause changes in the microenvironment of the preovulatory follicle, negatively affecting the final maturation of the oocyte. The heterogeneity of the RBH group underlines the multifactorial cause of the repeat-breeder syndrome. The VH formed a homogenous group with data varying within physiological limits. A classification model based on three characteristic variables managed to identify 81% of the VH and 79% of the RBH correctly. Results from this study propose that some heifers have general, consistent problems in synchronizing estrous events, displayed as varying symptoms in the course of consecutive estrous cycles. These subfertile animals could be classified as repeat-breeders.     

Variation in the diet composition of a generalist predator, the red fox, in relation to season and density of main prey

Diet composition of a generalist predator, the red fox (Vulpes vulpes) in relation to season (winter or summer) and abundance of multi-annually cyclic voles was studied in western Finland from 1983 to 1995. The proportion of scats (PS; a total of 58 scats) including each food category was calculated for each prey group. Microtus voles (the field vole M. agrestis and the sibling vole M. rossiaemeridionalis) were the main prey group of foxes (PS = 0.55) and they frequently occurred in the scats both in the winter and summer (PSs 0.50 and 0.62, respectively). There was a positive correlation between the PSs of Microtus voles in the winter diet of foxes and the density indices of these voles in the previous autumn. Other microtine rodents (the bank vole Clethrionomys glareolus, the water vole Arvicola terrestris and the muskrat Ondatra zibethicus) were consumed more in winter than in summer. The unusually high small mustelid predation by red foxes (PS = approx. 0.10) in our study area gives qualitative support for the hypothesis on the limiting impact of mammalian predators on least weasel and stoat populations. None of the important prey groups was preyed upon more at low than at high densities of main prey (Microtus voles). This is consistent with the notion that red foxes are generalist predators that tend to opportunistically subsist on many prey groups. Among these prey groups, particularly hares and birds (including grouse), were frequently used as food by foxes.     

Castle, W. E. Heredity, in relation to evolution and animal breeding

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Castle, W. E. Heredity, in relation to evolution and animal breeding