Proportion Of Broods Research Articles

Low level of extra-pair paternity in an urban population of blackbirds

We studied extra-pair paternity in a socially monogamous bird, the European Blackbird (Turdus merula). The research was conducted in an urban park in Poland. We obtained genetic samples from 36 broods (123 nestlings) of 21 unique pairs. The proportion of broods with some extra-pair nestlings was 17.1% (6 broods), and overall, 13.1% (16 nestlings) of all nestlings were sired by extra-pair males. In one brood (2.8% of all the investigated broods), we found one egg laid by a female which did not have her own territory in the study area (brood parasitism). These figures are relatively low compared to other closely related passerines. We suggest that mate guarding in the studied population may effectively prevent females from engaging in extra-pair activity, and in the case of females, divorce and serial polygamy are better strategies for enhancing the genetic quality and genetic diversity of their offspring than infidelity.

Extra-pair paternity as a strategy to reduce the costs of heterospecific reproduction? Insights from the crow hybrid zone.

Within hybrid zones of socially monogamous species, the number of mating opportunities with a conspecific can be limited. As a consequence, individuals may mate with a heterospecific (social) partner despite possible fitness costs to their hybrid offspring. Extra-pair copulations with a conspecific may thus arise as a possible post hoc strategy to reduce the costs of hybridization. We here assessed the rate of extra-pair paternity in the hybrid zone between all-black carrion crows (Corvus (corone) corone) and grey hooded crows (C. (c.) cornix) and tested whether extra-pair paternity (EPP) was more likely in broods where parents differed in plumage colour. The proportion of broods with at least one extra-pair offspring and the proportion of extra-pair offspring were low overall (6.98% and 2.90%, respectively) with no evidence of hybrid broods having higher EPP rates than purebred nests.

Assessing the impact of mowing on Common Redshanks Tringa totanus breeding on saltmarshes: lessons for conservation management

SummaryInformed application of habitat management measures is crucial, especially in saltmarshes that function as last refuges for breeding waders in Europe. Despite a reduction in agricultural use of saltmarshes since the establishment of the Wadden Sea National Parks at the end of the 1980s, there remains controversy regarding management measures such as the timing of mowing. We modelled the proportion of nests and chicks that would be jeopardised by mowing at different dates, using long-term breeding data of the Common Redshank Tringa totanus – an endangered and widespread indicator species of saltmarshes – from four study sites in the German Wadden Sea. At two study sites in the western Jadebusen, the proportion of broods that were at risk of being killed when mowing began on 1 July ranged between 78% in early, to 96% in late, breeding years, averaging 87%. Although Common Redshanks in the eastern Jadebusen started breeding one week earlier, the model still predicted a loss of 73% of chicks; while 97% of broods were at risk on the island of Wangerooge. Postponement of mowing to 1 August reduced these proportions to 21%, 11% and 32%, respectively. This study is the first to model the positive effects of delayed mowing of saltmarshes on ground-nesting birds. By implementing adjusted mowing dates in addition to previously suggested reductions in artificial drainage, direct and indirect adverse effects caused by mowing and drainage, such as an increased predation risk, are likely to be reduced, such that a ’favourable conservation status’ according to the EC Habitats Directive may be achieved.

Sex ratios, virginity, and local resource enhancement in a quasisocial parasitoid

AbstractSclerodermus harmandi (Buysson) (Hymenoptera: Bethylidae) is an economically beneficial species of parasitoid wasp that has an unusual level of sociality: groups of female foundresses reproduce on a single host and exhibit cooperative post‐ovipositional brood care. The beneficial effects females have on each other's reproductive success provide, via the theory of local resource enhancement (LRE), an explanation for their female‐biased progeny sex ratios, which is part of the same framework for understanding sex‐ratio evolution as the more often invoked theory of local mate competition (LMC). Here, we show that S. harmandi sex ratios are overdispersed, with high variance largely attributable to the common occurrence (60%) of developmental mortality. Developmental mortality is also positively associated with the proportion of broods which contain only females at emergence (virgin broods). Virginity is more common when broods are produced by fewer foundresses. Virginity is expected to be disadvantageous under LRE, as it is under LMC, but theory for LRE is less extensively developed. We suggest approaches for the development of LRE theory, in particular using models of ‘population elasticity’ in which the intensity of kin competition is reduced because extra resources are available to local populations that are more cooperative. For S. harmandi, such extra resources may include large hosts that can only be successfully utilised if multiple foundresses cooperate.

Food Supplementation and Extrapair Paternity in House Sparrows

Abstract We tested whether food availability affects extrapair paternity in House Sparrows (Passer domesticus) by providing supplemental food at their nests during some fertile periods but not others. When comparing broods produced by the same pair, a higher proportion of broods contained at least one extrapair young when food supplements were present, although the difference was not significant, and the proportion of extrapair young per brood was higher when food supplements were present, although again the difference was not significant. There was also little evidence that the presence of food supplements affected the amount of time spent at the nest by males, females, or both sexes at the same time. We also conducted two smaller experiments designed to either increase or decrease the rate at which individuals encountered one another but found no concomitant increase or decrease in the rate of extrapair paternity. Overall, we found little evidence food distribution affects extrapair paternity in House S...

Extra-pair paternity in two sympatric Aegithalos tits: patterns and implications

The explanation for extra-pair paternity (EPP) variation continues to attract research interest in the area of avian breeding systems. Comparisons among closely related species are recommended to explore factors that affect EPP rate variations. We utilised microsatellite markers to investigate extra-pair paternity in two sympatric populations of congeneric Black-throated Tits, Aegithalos concinnus, and Silver-throated Tits, A. glaucogularis. The two species share a similar breeding period at our study site and have helpers during breeding at some nests. The results suggest that the two species had low levels of extra-pair paternity: 5.7 % of the offspring in the Black-throated Tits and 6.8 % of the offspring in the Silver-throated Tits. The proportion of broods with extra-pair paternity in the Silver-throated Tits (33.3 %) was higher overall than the Black-throated Tits (17.2 %). This difference is consistent with the prediction by their different male attendance of incubation, but failed to be explained by major ecological factors. On the one hand, we conducted the study at the same site during the same time, which therefore limited the potential effect of different environmental conditions and habitat on their EPP incidence. On the other hand, other factors such as the inter-nest distances failed to explain the observed pattern. Current results also could not rule out an effect of evolutionary history on the EPP patterns of these two related species. Our research on their cooperative breeding system found a low proportion of cooperative breeding nests with offspring sired by helpers (Black-throated Tit, 8.3 % and Silver-throated Tit, 25.0 %), indicating that a direct reproductive benefit is not a likely major reason for the existence of the helpers in these two species.

Extrapair Copulations Predict Extrapair Fertilizations in the American Crow

Abstract. The general relationship between extrapair copulations (EPC) and extrapair paternity (EPP) in wild birds is unclear because relatively few studies have collected both types of information from a single population. I compared observed copulatory behavior with genetic paternity in a population of the American Crow (Corvus brachyrhynchos). For each group of nesting crows, the proportion of extrapair young in a brood was higher when EPC attempts were observed in the group that year. The overall proportion of broods with extrapair young was identical to the proportion of focal group-years in which EPC attempts were observed (32%). In a given brood, however, observed EPC attempts did not always predict EPP, and failure to observe EPCs did not always predict monogamy. Furthermore, males observed attempting EPCs often differed from the males gaining EPP, suggesting that EPCs were attempted by multiple males with certain females in certain years. Observed EPC attempts were initiated by males, and most ap...

Is female promiscuity constrained by the presence of her social mate? An experiment with bluethroats Luscinia svecica

Extra-pair paternity is common in birds and much research has focussed on the selective advantage of extra-pair matings for both sexes. In contrast, little attention has been given to the fact that in most species the majority of offspring are sired by the social male. We investigated whether extra-pair matings of female bluethroats (Luscinia svecica) are constrained by the presence of the pair male, by detaining males in cages on their territories for one morning during the peak of female fertility. The proportion of offspring sired by extra-pair males was higher in broods where males had been detained (35%) than in control broods (16%), while the proportion of broods that had at least one extra-pair offspring did not differ significantly between experimental (65%) and control broods (44%). Within the experimental group, levels of extra-pair paternity were not related to the day of experiment in relation to start of egg laying, but males caught early in the morning lost more paternity than males caught later on. Our results show that pair males exert constraints on the frequency of extra-pair paternity by being present during the period of peak fertility, which could be a direct effect of their mate guarding effort and/or due to an advantage in sperm competition for pair males.

A Bayesian model for assessing the frequency of multiple mating in nature.

Many breeding systems have multiple mating, in which males or females mate with multiple partners. With the advent of molecular markers, it is now possible to detect multiple mating in nature. However, no model yet exists to effectively assess the frequency of multiple mating (f(mm))--the proportion of broods with at least two males (or females) genetically contributing--from limited genetic data. We present a single-sex model based on Bayes' rule that incorporates the numbers of loci, alleles, offspring, and genetic parents. Two genetic criteria for calculating f(mm) are considered: the proportion of broods with three or more paternal (or maternal) alleles at any one locus and the total number of haplotypes observed in each brood. The former criterion provides the most precise estimates of f(mm). The model enables the calculation of confidence intervals and allows mutations (or typing errors) to be incorporated into the calculation. Failure to account for mutations can result in overestimates of f(mm). The model can also utilize other biological data, such as behavioral observations during mating, thereby increasing the accuracy of the calculation as compared to previous models. For example, when two sires contribute equally to multiply mated broods, only three loci with five equally common alleles are required to provide estimates of f(mm) with high precision. We demonstrate the model with an example addressing the frequency of multiple paternity in small versus large clutches of the endangered Kemp's Ridley sea turtle (Lepidochelys kempi) and show that females that lay large clutches are more likely to have multiply mated.

Extra‐pair fertilizations in Tree Sparrows Passer montanus

Females of socially monogamous bird species frequently accept or solicit copulations from males other than their social mates. At the interspecific level, it has been proposed that species with few or no sexual plumage differences have lower levels of extra‐pair fertilizations (EPFs) than more dichromatic species. This is because it is easier for females to assess the quality of extra‐pair mates in dichromatic than monochromatic species. To test this, by using genetic profiling, we compared the occurrence of extra‐pair young in nests of Tree Sparrows Passer montanus, a monochromatic species, in Switzerland and Spain, with published estimates for the House Sparrow Passer domesticus, a closely related dichromatic species. We found that 25% (10/40) of Tree Sparrow broods in Spain and 23% (8/35) in Switzerland had at least one extra‐pair offspring, and that 8% (12/151) of nestlings in Spain and 10% (12/114) in Switzerland were sired by extra‐pair mates. These proportions did not differ significantly between the two populations. Tree Sparrow EPF rates did not differ significantly from available data for the House Sparrow, either in the proportion of broods with EPF young (24%, 18/75 in Tree vs. 26%, 92/359 in House Sparrows) or the overall proportion of extra‐pair young (9%, 24/265 in Tree vs. 11%, 142/1110 in House Sparrows). Our results suggest that a close taxonomic relationship and similarities in behaviour and ecology may be more important in determining levels of EPF in these species than sexual phenotypic differences.

Smålommens Gavia stellata häckningsframgång i artens svenska kärnområde

We investigated the breeding success of a Red-throated Diver Gavia stellata population of approximately 70 pairs during ten seasons, 1991–2000, in a 1820 km2 study area, dominated by coniferous forests and mires in Malung, Dalarna in Central Sweden. The majority of the pairs bred in tarns smaller than 1.0 ha and foraged in larger freshwater lakes or rivers up to a distance of 4.6 km. Average breeding success was 0.76 “large” chicks per pair and year, with a declining trend over the study period accompanied by a decline in the proportion of broods with two “large” chicks. Breeding success was higher in seasons with an average early start of incubation and could be related to higher hatching success and survival of chicks. Predation during incubation was probably an important reason for breeding failures, and abandoning or change of breeding tarns were related to breeding failures. The annual variation of the percentage of broods with two “large” chicks was synchronised between pairs foraging at different fishing lakes, which indicates the influence of some large-scale regional factors linked to the availability of food. Chick survival in two-chicks broods was significantly lower than in one-chick broods. The declining trend in breeding success is an incitement for future monitoring, and any link to impaired foraging conditions needs to be more closely addressed.

High levels of extra-pair paternity in an isolated, low-density, island population of tree swallows (Tachycineta bicolor).

Molecular genetic studies have suggested that apparently nonbreeding males ('floaters') may account for a significant proportion of extra-pair paternity (EPP) in avian populations. Attempts to determine the influence of breeding density on EPP are therefore confounded by the presence of a subpopulation of floaters whose numbers are difficult to estimate. To study EPP in a tree swallow (Tachycineta bicolor) population with few floaters, we chose a nestbox grid on an island with an excess of available breeding sites and very few floaters. We obtained DNA samples from 13 complete families and performed DNA profiling on them using four microsatellite loci. For comparison, we also obtained a sample of 58 extra-pair young (EPY) from a mainland population typed at five microsatellite loci. Paternity assignments among resident males in both populations were made using the microsatellite profiles and a likelihood-based statistical method. Of the 67 island nestlings typed, we found 37 (55%) nestlings from 11 (85%) different nests that were EPY. The proportion of nestlings that were EPY and the proportion of broods containing EPY did not differ significantly between island and mainland populations studied previously. There was no significant difference between island and mainland populations in the proportion of extra-pair paternities assigned among neighbouring resident males. Male breeding density does not appear to affect the ability of female tree swallows to obtain extra-pair fertilizations, at least over the range of densities studied so far. The rate of EPP has remained remarkably consistent over many years, studies and populations implying an important role of active female choice in determining EPP.

Breeding synchrony best explains variation in extra-pair mating system among avian species

Stutchbury (1998) used new data and a comparative pairwise test to confirm that there is a strong correlation between breeding synchrony and extra-pair fertilization (EPF) frequency in passerines, as first reported by Stutchbury and Morton (1995). Although a pairwise test is a legitimate and powerful comparative method, Weatherhead and Yezerinac (1998) call for "better analyses to assess the correlation between synchrony and EPFs." There is a strong correlation between breeding synchrony and EPF frequency regardless of the comparative method used (Stutchbury and Morton 1995; Stutchbury 1998). Here I present a linear contrasts analysis on the 34 species given in Stutchbury (1998) using the phylogeny shown in Westneat and Sherman (1997) with other species added using the phylogeny in Sibley and Ahlquist (1990). I used version 2.0 of the Comparative Analysis by Independent Contrasts (CAIC) program (Purvis and Rambaut 1995), and assumed equal branch lengths. As expected, there was a strong positive correlation between contrasts in arcsinetransformed EPF frequency (proportion of broods with EPFs) and the synchrony index (r = 0.52, n = 33 contrasts, P < 0.002). The results for breeding density were similar to Westneat and Sherman (1997), with no correlation between contrasts of arcsine-transformed EPF frequency and nearest-neighbor distance (r -0.10, n 28 contrasts, P = 0.60). The relationship between breeding synchrony and EPFs across species demands explanation; either synchrony causally affects the evolution of extra-pair mating systems as argued by Stutchbury and Morton (1995), or both synchrony and EPF frequency are correlated with some unidentified causal factor. Weatherhead and Yezerinac (1998) favor the explanation that "both breeding synchrony and extra-pair mating [are] corre-

The effects of temperature and food on the growth of laboratory colonies ofAphaenogaster rudis Emery (Hymenoptera: Formicidae)

Laboratory colonies of the scavenging ant,Aphaenogaster rudis Emery, were maintained for 150 days at different temperatures and food levels. While pupation was successful in all high temperature colonies (25° C), low temperature colonies (15° C) produced brood, but no new workers. Deaths of original workers were significantly greater in the high temperature colonies, suggesting that low temperatures may slow the onset of senescence in workers. The low efficiency of biomass conversion at the highest food level, indicates that the optimal amount of food for a small colony (50–100 workers) may be about 50 mg/d. Across food levels, variation in the proportion of brood versus workers produced showed a trend toward relatively greater investment in new eggs with greater food consumption. Total production of brood and new workers, as measured either by ant numbers or biomass, was significantly greater at the higher food levels, suggesting that food intake can regulate colony growth inA. rudis if insolated nest sites are abundant.