High Breeding Density Research Articles

Breeding density of exotic Red-billed Leiothrix and native bird species on Mt. Tsukuba, central Japan

Exotic Red-billed Leiothrix Leiothrix lutea numbers have increased in southern, western and central part of Japan since the early 1980's. Unlike most naturalized birds, this species mainly breeds in natural deciduous forests. We researched the breeding bird density in a deciduous forest on Mt. Tsukuba (877 m), a major breeding area of leiothrix in central Japan, in 1994 and 1995. Leiothrix bred at very high density (350-400 pairs per 100 ha) and was the most dominant species in both years. In 1995, six complete nests were found in a 1 ha area. In spite of the high breeding density of leiothrix, native avifauna showed species diversity, total breeding density and total biomass, similar to other Japanese deciduous forests. Therefore, we suggest that leiothrix have invaded Mt. Tsukuba without severe competition with native bird species.

Effects of traffic noise on paserine populations in Mediterranean wooded pastures

The effect of traffic noise on the breeding density of 20 passerine species was examined over a 2-year period in three different road types passing through pasture-woodlands in western-central Spain. No statistically significant differences were observed during the 2 years studied. An average of 19.6 birds/10 ha was recorded for the low-traffic road (LT), 21.7 birds/10 ha for the medium-traffic road (MT) and 19.1 birds/10 ha for the high-traffic road (HT). A total of 11 species (55%) did not show any statistically significant differences in breeding density among the different types of roads. By contrast, other species, such as the Blackbird, the Iberian Shrike and the Linnet, did point to differences between the MT and HT roads. House and Rock Sparrows, as well as the Corn Bunting, showed higher breeding densities near the HT road. The opposite effect was observed for the Wheatear, the Iberian chiffchaff and the Woodlark, for which high breeding densities were recorded in the vicinity of the LT road. Our results suggest that traffic noise constitutes a serious problem for at least 15% of the breeding bird community.

FEMALE SONG IN THE HOODED WARBLER

One female Hooded Warbler (Wilsonia citrina) was discovered singing in July 1993, and another in May 1996 among a color-banded breeding population under investigation. The first female's song structurally resembled the typical male Hooded Warbler mixed-mode song in duration, frequency range, and number of syllables, although it had an atypical raspy quality. Males responded similarly to playbacks of the female song and a male song from the same population. We suggest that age and high breeding density may be explanatory factors for this rare behavior.

Chlorinated hydrocarbon contamination in osprey eggs and nestlings from the Canadian Great Lakes basin, 1991-1995.

Populations of osprey (Pandion haliaetus) in the Great Lakes basin declined dramatically during the 1950s-1970s due largely to adverse effects of persistent chlorinated hydrocarbons, ingested in their fish prey, on eggshell thickness and adult survival. Nevertheless, these contaminants were not measured in osprey tissues during the decades of decline on the Canadian Great Lakes. Between 1991 and 1995, we monitored recovering osprey populations on the Great Lakes, including Georgian Bay and the St. Marys River area on Lake Huron and the St. Lawrence Islands National Park, as well as at two inland sites within the basin. Current OC levels, even from the most contaminated lakes, were typically lower than those associated with reproductive effects. DDE levels in fresh eggs averaged 1.2-2.9 microg/g, well below the 4.2 microg/g level associated with significant eggshell thinning and shell breakage. Nevertheless, a proportion of eggs from all study areas did exceed this level. PCB levels in eggs seldom exceeded 5 microg/g except in one lake of high breeding density in the Kawartha Lakes inland study area, where the mean sum PCB level was 7.1 microg/g and the maximum concentration measured was 26.5 microg/g. On average, mean reproductive output (0.78-2.75 young per occupied nest) of breeding populations in Great Lakes basin study areas exceeded the threshold of 0.8 young thought necessary to maintain stable populations. We concluded that, although eggs and especially nestling plasma, are useful in reflecting local contaminant levels, ospreys are relatively insensitive, at least at the population level, to health effects of current levels of chlorinated hydrocarbons on the Canadian Great Lakes.

Conspecific Food Competition Explains Variability in Colony Size: A Test in Magellanic Penguins

Food availability has been proposed as one of the main factors regulating population sizes in birds. Seabirds have provided evidence for the hypothesis that food depletion due to intraspecific competition explains variability in colony size. However, the predictions derived from this hypothesis have not been fully tested due mainly to the difficulties in measuring food availability in marine environments. We measured stable isotopes of nitrogen (δ15N) and carbon (δ13C) in the blood of Magellanic Penguins (Spheniscus magellanicus), which reveal information about their consumed prey and foraging habits. We tested if conspecific competition causes food depletion, affecting penguin breeding performance and, ultimately, the size of the colonies. Blood δ15N values of adults and chicks significantly decreased with increasing size of their colonies and with the number of conspecifics breeding within the parental foraging ranges. This suggests that high breeding densities provoke the depletion of high-quality prey (mainly anchovy). We also found positive relationships between δ13C values and density of conspecifics within the parental foraging ranges, indicating that when competition for food is high, individuals tend to feed closer to the colony on prey of lower quality. Adult δ15N values were positively correlated with breeding success at the colonies, which was negatively correlated with the density of conspecifics within foraging ranges. Moreover, δ15N values of fledglings were positively correlated with their body condition but not with their T-cell mediated immune response considered as two measures of their survival prospects. This decreased breeding output was translated to the colony-size structure of the population, since colony size was negatively correlated with the number of conspecifics breeding within the parental foraging ranges. Therefore, we provide strong evidence suggesting that density-dependent food depletion determines the distribution of colony sizes in birds.

CONSPECIFIC FOOD COMPETITION EXPLAINS VARIABILITY IN COLONY SIZE: A TEST IN MAGELLANIC PENGUINS

Food availability has been proposed as one of the main factors regulating population sizes in birds. Seabirds have provided evidence for the hypothesis that food depletion due to intraspecific competition explains variability in colony size. However, the predictions derived from this hypothesis have not been fully tested due mainly to the difficulties in measuring food availability in marine environments. We measured stable isotopes of nitrogen (δ15N) and carbon (δ13C) in the blood of Magellanic Penguins (Spheniscus magellanicus), which reveal information about their consumed prey and foraging habits. We tested if conspecific competition causes food depletion, affecting penguin breeding performance and, ultimately, the size of the colonies. Blood δ15N values of adults and chicks significantly decreased with increasing size of their colonies and with the number of conspecifics breeding within the parental foraging ranges. This suggests that high breeding densities provoke the depletion of high-quality prey (mainly anchovy). We also found positive relationships between δ13C values and density of conspecifics within the parental foraging ranges, indicating that when competition for food is high, individuals tend to feed closer to the colony on prey of lower quality. Adult δ15N values were positively correlated with breeding success at the colonies, which was negatively correlated with the density of conspecifics within foraging ranges. Moreover, δ15N values of fledglings were positively correlated with their body condition but not with their T-cell mediated immune response considered as two measures of their survival prospects. This decreased breeding output was translated to the colony-size structure of the population, since colony size was negatively correlated with the number of conspecifics breeding within the parental foraging ranges. Therefore, we provide strong evidence suggesting that density-dependent food depletion determines the distribution of colony sizes in birds.

A case of infanticide in the Spot-billed Duck in circumstances of high breeding density

The first observations of infanticide by a precocial avian species, Spot-billed Duck (Anas poecilorhyncha), were recorded on a small pond at Yatsu tidal flat, central Japan, from May to June 2000, where six families of conspecific and one Gadwall A. strepera family, respectively, occupied territories. A female Spot-billed Duck with 11 ducklings attacked ducklings of all the other families killing eight conspecifics and three of the Gadwall. High breeding density (15.0 families/ha) may have increased the aggression of the female.

CAUSES AND FITNESS CONSEQUENCES OF NATAL DISPERSAL IN A POPULATION OF BLACK KITES

Natal dispersal is of central interest when determining demography and genetic structure of populations and managing endangered species with fragmented distributions. However, methodological limitations linked to spatial and temporal constraints have prevented studies of natal dispersal in long-lived birds. Moreover, the consequences of natal dispersal have mainly been related to the first breeding attempt rather than to lifetime reproductive success. We studied the causes and fitness consequences of natal dispersal in a population of Black Kites at Donana National Park (southern Spain). From 1986 to 1995 we marked 2929 nestlings with plastic numbered bands. We annually monitored marked birds in breeding territories, their breeding success, and the survival of nonbreeding birds. Additionally, we searched for marked birds in broad areas of the Iberian Peninsula and North Africa. Median natal dispersal distance was 4.8 km (N = 285), with males more often dispersing shorter distances and females dispersing at all distance categories equally. Density of conspecifics negatively affected dispersal distances of both males and females. In addition, single and first-hatched males born in areas with high breeding density dispersed shorter distances. Dispersal distances tended to be correlated between siblings, possibly a result of sharing similar environmental conditions. We did not find evidence that dispersal was an active mechanism aimed to prevent close inbreeding. Patterns of dispersal in this population are probably driven by intraspecific competition. Males that dispersed shorter distances showed higher lifetime reproductive success (LRS). LRS did not differ among females dispersing different distances, but females that dispersed farther mated with more experienced males. These sex differences in dispersal patterns and their consequences may be explained by the inequality between sexes in breeding roles in this species. Familiarity with the natal area could be important for males, which defend territories and resources, while females may increase their fitness through mate choice and breeding dispersal. High levels of philopatry in Donana National Park may be a result of a surplus of food resources and the effects of conspecific attraction in densely populated areas. However, the degree of philopatry may vary between populations and with time, subject to differences in ecological pressures.

Effects of competition and season on survival and maturation of young bank vole females

In territorial microtines intra-specific density dependent processes can limit the maturation of individuals during the summer of their birth. This may have demographic consequences by affecting the number and the age distribution of breeding individuals in the population. Little is known about this process on a community level, though populations of many northern microtine species fluctuate in synchrony and are known to interfere socially with each other. We experimentally studied the influence of the field vole Microtus agrestis on maturation, breeding, space use and survival of weanling bank voles, Clethrionomys glareolus. Two additive competition experiments on bank vole populations were conducted in large outdoor enclosures, half of them additionally housing a field vole population. In a mid-summer experiment low population density and absence of older breeding females minimised intra-specific competition. Survival was not affected by the presence of field voles. Season had a significant effect on both the probability of maturation and breeding of the weanlings. Competition with field voles significantly delayed breeding, and coupled with seasonal effects decreased the probability of breeding. In a late-summer experiment breeding and survival of bank vole weanlings were studied for three weeks as part of a high density breeding bank vole population. Weanlings did not mature at all nor were their space use and survival affected by the presence of field voles. Our results show that competition with other species can also have an impact on breeding of immatures. In an extreme seasonal environment, even a short delay of breeding may decrease survival chances of offspring. Seasonal and competition effects together may thus limit the contribution of year born females to reproductive output of the population. Other studies have shown that adult breeding bank voles suffer lower survival in the presence of field voles, but this study showed no survival effects on the weanlings. Thus it might be beneficial for weanlings to stay immature especially in the end of the breeding season and postpone reproduction to the next breeding season if densities of competing species are high.

NO EXTRA-PAIR FERTILIZATION IN FLAMMULATED OWLS DESPITE AGGREGATED NESTING

We used DNA fingerprinting to estimate the frequency of extra-pair fertilization in the Flammulated Owl (Otus flammeolus), a socially monogamous species often found nesting in aggregations. We observed owls on 44 territories, 42 of which were located in aggregations of 3 to 10 territories with a mean nearest-neighbor distance of 539 m (± 160 m). We sampled a subset of these nests and compared band sharing and numbers of novel fragments among 17 social pairs and 37 offspring. Like other socially monogamous raptors, the Flammulated Owls we studied were genetically monogamous despite their relatively high breeding density. We suggest that the necessity of male parental care may be an important factor contributing to genetic monogamy in this species. Ausencia de Fertilización Extra-Pareja en Otus flammeolus a pesar de Nidificación Agregada Resumen. Usamos huellas dactilares genéticas (i.e., DNA fingerprinting) para estimar la frecuencia de fertilización extra-pareja en Otus flammeolus, una especie social monógama frecuentemente hallada nidificando en agregaciones. Observamos lechuzas en 44 territorios, 42 de los cuales se encontraron en agregaciones de entre 3 a 10 territorios, con una distancia media al territorio vecino más cercano de 539 m (± 160 m). Muestreamos un subconjunto de los nidos localizados y comparamos las bandas compartidas y el número de fragmentos nuevos entre 17 pares sociales y 37 hijos. Al igual que otras rapaces sociales monógamas, los individuos de O. flammeolus que estudiamos fueron genéticamente monógamos, a pesar de la relativamente alta densidad de individuos presentes en la época de cría. Sugerimos que la necesidad de cuidado parental masculino puede ser un factor importante que contribuye a la monogamia genética en esta especie.

Correlates of Common Buzzard Buteo buteo density and breeding success in the West Midlands

Buzzard density and breeding success in relation to habitat and Rabbit Oryctolagus cuniculus abundance was studied in the West Midlands from 1994 to 1996. We found densities of 81 and 22 territorial pairs per 100 km2 in two areas 40 km apart; the former is the highest density yet recorded in Europe. High Buzzard breeding densities were associated with high proportions of unimproved pasture and mature woodland within estimated territories. Buzzards laid earlier clutches at lower altitudes and with high proportions of unimproved pasture close to nests. Large clutches and high numbers of fledged young were associated with high Rabbit abundance close to nests. Most nest failures occurred during incubation and were probably mainly due to corvid predation. Brood reduction was associated with low proportions of deciduous woodland close to nests and small clutch sizes, although the causes of chick mortality were uncertain. Rabbits were the main prey item found at nests with passerines, especially young corvids, also appearing frequently.

Tree size and growth history predict breeding densities of Douglas-fir beetles in fallen trees

AbstractFor bark beetles (Coleoptera: Scolytidae) breeding in fallen trees, the tree characteristics that are associated with higher breeding densities are poorly known. The breeding densities of Douglas-fir beetles, Dendroctonus pseudotsugae Hopkins, in freshly felled Douglas-fir, Pseudotsugae menziesii (Mirb.) Franco, were examined with respect to tree diameter, phloem thickness, and several measures of tree growth rate over the past year to 10 years prior to tree death. Trees were felled in 8 decks of 3–12 trees to provide a range of tree qualities in a given location. Stepwise regression revealed that of the tree characteristics measured, only diameter was needed to explain the density of beetle attacks on trees within decks. Because diameter, phloem thickness, and growth-increment measures were all highly correlated, attack density also increased with phloem thickness and growth rate prior to felling when these measures were analyzed individually. The apparent preference for larger trees with thicker phloem is consistent with published results for live trees, but the positive effect of tree growth rate prior to death is contrary to results for beetles attacking live trees. Thus, assessments of stand susceptibility to bark beetles based on tree growth rate may differ depending on whether beetles are initially breeding in live or dead trees.

Reproduction and Spacing of Piping Plovers Breeding at High Density at Appam Lake, North Dakota

Abstract Knowledge of potential breeding density and associated reproduction is critical for conserving Piping Plovers (Charadrius melodus) in the northern Great Plains. Each year during 1995–1998 we observed 34–50 plover pairs nesting on Appam Lake, an isolated 1.9-km2 alkali lake in northwestern North Dakota. During peak abundance in 1996 and 1997, there were 4.2 and 5.3 pairs/km of available beach, respectively; mean distances between nest sites of nearest neighbor pairs were 99.4 m and 79.5 m. We detected no relationship between spacing and numbers of fledglings produced by individual breeding pairs. Mean production was 1.2 fledglings/pair (0.9 during 1996 and 1.5 during 1997, n = 25 and 29 pairs, respectively). Our observations suggest Piping Plovers may reproduce adequately at high breeding densities on prairie alkali lakes, but further study of the relationship between breeding density and reproductive success is needed.

Extrapair paternity and variance in reproductive success related to breeding density in Bullock's orioles

Breeding density is predicted to influence the use of alternative reproductive strategies and may account for some of the variation in extrapair paternity rates found within and between avian species. By exploiting the extreme range of breeding densities occurring in a single, semicolonial population of Bullock's oriole, Icterus galbula bullockii, this study showed that, as predicted, both the number of nests containing extrapair nestlings and the mean proportion of extrapair nestlings in a brood increased with breeding density (high versus low breeding density: broods with extrapair nestlings: 62 versus 27%; mean: 48 versus 16%). As found in some other studies, extrapair paternity (both exclusion and assignment) significantly increased the variance in reproductive success among males. No difference was found in the mean reproductive success of males at different breeding densities. However, as predicted, the variance in reproductive success among males increased with breeding density. This study indicates that the distribution of individuals within a single population can lead to significant differences in the opportunity for sexual selection, and that density may be an important factor affecting variance in male reproductive success among populations.

Offspring body condition and immunocompetence are negatively affected by high breeding densities in a colonial seabird: a multiscale approach.

Why avian colonies vary in size and how food competition among nearby colonies affects offspring quality are still not completely understood. We simultaneously examined the effects of four scales of breeding density on two measures of offspring viability (body condition and T-cell-mediated immunity) in the colonial Magellanic penguin. Body condition of fledglings was inversely correlated with breeding density within 100 m(2) of nests, and decreased with increasing numbers of breeding pairs competing within the parental foraging ranges (100 km), probably as a result of density-dependent food depletion. The T-cell-mediated immune response was positively correlated with body condition, reflecting, to some extent, the previous breeding-density effects, and was negatively correlated with colony size, which may be related to social stress. However, given the effect of protein intake on cell immunity, this result could also indicate a thus far neglected cost of coloniality, namely the consumption of low-protein food to compensate for the depletion of optimal prey. These results were not influenced by other traits, nor by the current exposure of birds to parasites and diseases, as measured by serological variables. Since body condition and the T-cell-mediated immune response of fledgling birds are indicators of their survival and recruitment prospects, the costs we have identified can explain variability in colony size in relation to food competition with surrounding colonies, as well as the skewed distribution toward small colonies in this species.

Are goose nesting success and lemming cycles linked? Interplay between nest density and predators

The suggested link between lemming cycles and reproductive success of arctic birds is caused by potential effects of varying predation pressure (the Alternative Prey Hypothesis, APH) and protective association with birds of prey (the Nesting Association Hypothesis, NAH). We used data collected over two complete lemming cycles to investigate how fluctuations in lemming density were associated with nesting success of greater snow geese (Anser caerulescens atlanticus) in the Canadian High Arctic. We tested predictions of the APH and NAH for geese breeding at low and high densities. Goose nesting success varied from 22% to 91% between years and the main egg predator was the arctic fox (Alopex lagopus). Nesting associations with snowy owls (Nyctea scandiaca) were observed but only during peak lemming years for geese nesting at low density. Goose nesting success declined as distance from owls increased and reached a plateau at 550 m. Artificial nest experiments indicated that owls can exclude predators from the vicinity of their nests and thus reduce goose egg predation rate. Annual nest failure rate was negatively associated with rodent abundance and was generally highest in low lemming years. This relationship was present even after excluding goose nests under the protective influence of owls. However, nest failure was inversely density‐dependent at high breeding density. Thus, annual variations in nest density influenced the synchrony between lemming cycles and oscillations in nesting success. Our results suggest that APH is the main mechanism linking lemming cycles and goose nesting success and that nesting associations during peak lemming years (NAH) can enhance this positive link at the local level. The study also shows that breeding strategies used by birds (the alternative prey) could affect the synchrony between oscillations in avian reproductive success and rodent cycles.

Genetic paternity analyses in Little Owls (Athene noctua): does the high rate of paternal care select against extra-pair young?

Previous studies have shown that extra-pair fertilizations are much less frequent in Non-Passeriformes, especially in raptors, than in Passeriformes. Low breeding densities, high breeding synchrony and high rates of paternal effort have been discussed as possible causes of these low extra-pair fertilization rates. Using DNA fingerprinting, we studied the mating system of Little Owls (Athene noctua) in a population of relatively high breeding density and comparatively low breeding synchrony. We found no cases of extra-pair fertilization among 53 nestlings of 16 breeding pairs. We conclude that paternal effort is probably the most important factor in preventing extra-pair fertilizations in Little Owls.

Biology of Frances's Sparrowhawk, Accipiter francesiae, on the Comoro Islands

Throughout their range on Madagascar and in the Comoros Frances's Sparrowhawks, Accipiter francesiae, breed from October to December, in the late dry/early wet season, resulting in young leaving the nest before or when the heavy rains start in January/February. In contrast to Madagascar, nests on Mayotte (Comoros) are placed in exposed positions, and are maintained and enlarged after the young fledge, possibly as a form of territorial advertisement. On average, two young fledged per successful nest, and 1.5 fledged per nesting attempt. During the breeding season, sparrowhawks on Mayotte consume more reptiles than do those on Madagascar. On Mayotte, second-year birds can be recognized by plumage type. Recruitment into the breeding population does not occur during the first year, but possibly only from the third year. Frances's Sparrowhawks are unevenly distributed on Mayotte and post-breeding dispersal may take place from the wettest zone, where the highest breeding densities occur, to the drier southeastern parts.

PARENTAL CARE AND PARENTAGE IN MONOGAMOUS GREAT SPOTTED WOODPECKERS (PICOIDES MAJOR) AND MIDDLE SPOTTED WOODPECKERS (PICOIDES MEDIUS)

Abstract Paternal effort is high in some monogamous mating systems. Trivers' (1972) model predicts that high male investment in brood care should evolve only when males have a high certainty of paternity. For this study, we chose two woodpecker species: the great spotted woodpecker (Picoides major) and the middle spotted woodpecker (Picoides medius). Both species were socially monogamous despite a very high breeding density in the study area. We used DNA fingerprinting to determine whether these two species were also genetically monogamous. We found that in great spotted and middle spotted woodpeckers paternal effort was high. Multi-locus DNA-fingerprinting showed that its actual paternity was also very high. In P. major all 161 young from 36 broods and in P. medius all 61 young from 13 broods were sired by the male feeding at the nest hole. There were also no cases of intraspecific brood parasitism or quasi parasitism (P. major: 114 chicks from 24 broods; P.medius: 33 chicks from 8 broods). We further found no case of mate switching during the fertile period of the female. Great spotted and middle spotted woodpeckers are typical of a group of monogamous nonpasserine birds with high male investment in brood care having low frequencies of EPP. We did not find efficient paternity guards. High certainty of paternity may be explained by paternal care being essential for female reproductive success, as in many seabirds and birds of prey. Females rarely engage in extra-pair copulations probably because they are constrained by male care. Males in both species spend little effort in acquiring mates as well as in extrapair copulations. They expend their reproductive effort in defending territories and in parental care. Females compete intensely with members of their own sex for pair formation before the time of frequent copulation. Choosing and securing a high quality partner is the only possibility to achieve high reproductive success for both sexes.

NO EVIDENCE FOR EFFECTS OF BREEDING DENSITY AND MALE REMOVAL ON EXTRAPAIR PATERNITY IN THE PIED FLYCATCHER

Abstract Molecular methods have brought new insight to the study of mating patterns. Extrapair fertilizations (EPF) have proven to be widespread among bird species irrespective of social relationships. Ecological factors, such as breeding density and synchrony, have been suggested as contributors to variation in EPF rates. Absence of a male during the female fertile period may also increase the probability of EPFs. In this study, we examined experimentally whether breeding density and male absence before egg-laying influence the EPF rate in Pied Flycatchers (Ficedula hypoleuca). DNA fingerprinting revealed that 4.4% (10/225) of nestlings were the result of EPFs and 7.0% (3/43) of broods included at least one offspring sired by a male other than that attending the nest. We did not find any evidence of higher EPF rate with higher breeding density as stated by the density hypothesis. Contrary to expectation, EPFs were more frequent, though not quite statistically significantly, at low breeding density: all t...