European starlings: nestling condition, parasites and green nest material during the breeding season

Male European starlings (Sturnus vulgaris) intermingle fresh herbs, preferably species rich in volatile compounds, into their dry nest material. In a field study, we investigated whether these herbs affect the mite and bacteria load of the nests and the condition of the nestlings either directly or via parasite control. We examined the amount of herbs and the number of plant species males carried into their nests, the variation of volatile compounds in the headspace air of the nest boxes and mite/bacteria load of the nests throughout the season. The amount of herb material and the number of plant species, the number of substances emanated by these plants and the infestation of the nests with bacteria and mites (Dermanyssus gallinae) increased with season. In a field experiment, we exchanged natural starling nests with experimental nests with or without herbs. We found that the herbs had no effect on the mites but fewer bacteria were sampled in nests with herbs than in nests without herbs. The body mass of the fledging was not related to the season or the mite/bacteria load of the nests. However, nestlings from nests with herbs fledged with higher body mass than nestlings from nests without herbs. Both bacteria and mite load were related to nestling mortality. In nests containing no herbs, the numbers of fledglings declined significantly with the increasing mite load while the mites had no effect on the number of fledglings in nests with herbs. Thus, the nest herbs counteracted the effect of the mites. In conclusion, it seems that volatile herbs can reduce bacterial but not mite infestation of the starling nests. The positive influence of herbs on nestling growth indicates that herbs either directly (perhaps as immunostimulants) improve the condition of the nestlings and help them cope with the harmful effects of mites, or they provide a nest environment beneficial for the nestlings‘ development by the reduction of germs.     

Brood‐parasite‐induced female‐biased mortality affects songbird demography: negative implications for conservation

Parasites, of all sorts, can profoundly affect host population dynamics. Parasites commonly cause sex‐biased mortality and this can add to their impact. Female‐biased mortality in particular can destabilize dynamics and promote population collapse. We previously reported in a correlative study that brown‐headed cowbird Molothrus ater brood parasitism of song sparrows Melospiza melodia appears to cause female‐biased host nestling mortality. Here, we report results from ‘infestation’ and ‘de‐infestation’ experiments designed to test whether brood parasitism causes female‐biased mortality, and we document the resulting demographic impact using a simulation model. Experimental cowbird infestation of song sparrow nests halved the proportion of female host nestlings (0.31±0.07 vs 0.59±0.06; infested vs unparasitized nests at day 6) replicating the halving reported in naturally cowbird‐parasitized nests (0.28±0.01 vs 0.57±0.05; parasitized vs unparasitized). De‐infestation of naturally cowbird‐parasitized nests in turn wholly eliminated any effect on the proportion of female host nestlings (0.53±0.13 vs 0.54±0.06; de‐infested vs unparasitized) confirming that brood parasitism is the cause. This halving of the proportion of females fledging is likely to be as significant as nest predation in affecting population dynamics, based on the elasticities derived from our demographic model (–0.50 vs –0.59). Experimental infestation reduced the testosterone levels, begging behaviour, and body mass of six day old female host nestlings, whereas males were largely unaffected, suggesting that it is the exacerbation of intra‐brood competition that may be primarily responsible for the resulting female‐biased mortality. The brown‐headed cowbird is invasive in most of North America and has been implicated in regional population declines of many native species. We suggest that female‐biased host offspring mortality is likely to be commonplace among the 144 host species the cowbird successfully parasitizes, and we discuss the negative implications for songbird conservation, given the projected demographic impact.     

Philornis infection in blue‐black grassquits: impact on nestlings and risk factors involved

Parasitic botfly larvae (Philornis ssp., Diptera: Muscidae) are found in nests of several bird taxa, although prevalence and impact on nestling survival vary considerably among species. Here we describe patterns of botfly infestation in blue‐black grassquit Volatinia jacarina nestlings. We identified the most typically affected nestling body parts and assessed parasite prevalence, impact on nestling survival, and changes in nestling body shape. Additionally, we tested whether climatic conditions, nest morphology and habitat characteristics are associated with larvae abundance. Blue‐black grassquits had low breeding success (16% of eggs/nestlings survived to fledged; 19% of the nests fledged at least one), but most failures resulted from predation by vertebrate predators. We estimated that 1% of nestlings died due to botfly infestation, and the number of subcutaneous larvae (range 1–18) in a nestling's body did not predict fledging success. Infected chicks exhibited higher tarsus asymmetry. Thus, we argue that although botflies had a small impact on offspring survival, they may reduce fitness in adulthood. There was no evidence that environmental conditions and nest morphology are linked to the number of larvae on nestlings. Nesting areas with higher food supply had lower infestation rates. Possibly, food‐rich habitats allow parents to invest more time in offspring care (brooding nestlings), thus protecting them from fly attacks. Alternatively, vegetation composition could influence local invertebrate diversity, which could provide a natural trophic buffer against adult Philornis. The present study brings to light new perspectives concerning bird–botfly interaction.     

Intraseasonal variation in immune defence,body mass and hematocrit in adult house martins Delichon urbica

The intensity of parasite infections often increases during the reproductive season of the host as a result of parasite reproduction, increased parasite transmission and increased host susceptibility. We report within‐individual variation in immune parameters, hematocrit and body mass in adult house martins Delichon urbica rearing nestlings in nests experimentally infested with house martin bugs Oeciacus hirundinis and birds rearing nestlings in initially parasite‐free nests. From first to second broods body mass and hematocrit of breeding adult house martins decreased. In contrast leucocytes and immunoglobulins became more abundant. When their nests were infested with ectoparasites adults lost more weight compared with birds raising nestlings in nests treated with pyrethrin, whereas the decrease in hematocrit was more pronounced during infection with blood parasites. Neither experimental infestation with house martin bugs nor blood parasites had a significant effect on the amount of immune defences.     

EDITORIAL

Olver, M. D. &; Kuyper, M. A. 1978. Breeding biology of the Whitebreasted Cormorant in Natal. Ostrich 49:25-30.

From 1972–1975 Whitebreasted Cormorants Phalacrocorax carbo bred at the Cedara Dam, Natal, South Africa (29 32S, 30 17E), and from 1973 they fished for food at Midmar Dam, 5 km away and carried the food back to the nestlings. Breeding occurred from April to October and was preceded by a period of courtship. Nesting material was collected by the males and the nests built by the females. The mean clutch size for 1972–1973 was 3,1. Both parents incubated the eggs and guarded the nest and chicks. Growth of the chicks was studied in 1972–1973. The mean number of chicks reared was 1,6 per nest although seven nests contained three nestlings. At 28 days they left the nest when alarmed, but could not fly until 49 days old. The average flying age appeared to be about 53 days. The height of the nests above the ground seemed to determine the nest leaving age. Of the 186 eggs laid in the 60 nests observed over two years, 74% hatched. Fledging success was 52% of eggs laid and 69% of eggs hatched. Chick mortality seemed to be caused mainly by falling from the nests and dying of starvation.     

Invertebrate infestation on eggs and hatchlings of the loggerhead turtle, Caretta caretta, in Dalaman, Turkey

The damage caused by some invertebrates to the eggs and hatchlings of loggerhead turtles, Caretta caretta, was investigated during the summer of 2002 on Dalaman beach, Turkey. The specimens, identified to family or genus levels, from nine families representing seven orders were recorded as infesting nests of loggerhead turtles. The heaviest impacts on loggerhead turtle nests was made by Pimelia sp. (Tenebrionidae, Coleoptera). Twenty-four (36.3%) out of 66 intact loggerhead hatched nests were affected by these larvae. Larval damage by Pimelia sp. was recorded in 188 (10.6%) out of 1773 eggs, but only in two (0.28%) hatchlings. The results show that fewer insects were in the nest the further from vegetation and therefore the relocation of nests from the water's edge to further inland close to vegetation may increase the infestation rate of the eggs.     

The price of insulation: costs and benefits of feather delivery to nests for male tree swallows Tachycineta bicolor

Many species of birds line their nests with feathers, and it has been hypothesized that this functions to provide a thermally stable microenvironment for the development of eggs and nestlings. Feathers in the nest may also function as a mechanism for parasite control, providing a physical barrier that protects nestlings from ectoparasites. We tested these hypotheses by performing a feather removal and addition experiment in tree swallows Tachycineta bicolor, a species well‐known for lining their nests with feathers. While we found no evidence that quantity of feathers in nests influenced the ability of females to produce and incubate eggs, offspring in well‐feathered nests had longer flight feathers and were structurally larger just prior to fledging that those in nests with fewer feathers. Furthermore, we also demonstrated a positive correlation between feathers and the abundance of larval blow flies Protocalliphora spp. in nests, a result opposite to that predicted by the anti‐parasite hypothesis. While our study provides strong support for the insulation hypothesis, we also discuss the possibility that devoting time to feather gathering may result in males losing paternity in their nests, although manipulative studies will be necessary to fully evaluate this idea.     

Effects of intraclutch variation in egg size and hatching asynchrony on nestling development and survival in semi‐precocial Herring Gulls

Intraclutch egg size variation may non‐adaptively result from nutritional/energetic constraints acting on laying females or may reflect adaptive differential investment in offspring in relation to laying/hatching order. This variation may contribute to size hierarchies among siblings already established due to hatching asynchrony, and resultant competitive asymmetries often lead to starvation of the weakest nestling within a brood. The costs in terms of chick mortality can be high. However, the extent to which this mortality is egg size‐mediated remains unclear, especially in relation to hatching asynchrony which may operate concomitantly. I assessed effects of egg size and hatching asynchrony on nestling development and survival of Herring Gulls (Larus argentatus), where the smaller size and later hatching of c‐eggs may represent a brood‐reduction strategy. To analyze variation in egg size, I recorded the laying order and laying date of 870 eggs in 290 three‐egg clutches over a 3‐yr period (2010–2012). I measured hatchlings and monitored growth and survival of 130 chicks from enclosed nests in 2011 and 2012. The negative effect of laying date (β = ?0.18 ± SE 0.06, P = 0.002) on c‐egg size possibly reflected the fact that late breeders were either low quality or inexperienced females. The mass, size, and condition of hatchling Herring Gulls were positively related to egg size (all P < 0.0001). C‐chicks suffered from increased mortality risk during the first 12 d, identified as the brood‐reduction period in my study population. Although intraclutch variation in egg size was not directly related to patterns of chick mortality, I found that smaller relative egg size interactively increased differences in relative body condition of nestlings, primarily brought about by the degree of hatching asynchrony during this brood‐reduction period. Thus, the value of relatively small c‐eggs in Herring Gulls may lie in reinforcing brood reduction through effects on nestling body condition. A reproductive strategy Herring Gulls might have adopted to maintain a three‐egg clutch, but that also enables them to adjust the number of chicks they rear relative to the prevailing environmental conditions and to their own condition during the nestling stage.     

Great Spotted Cuckoo Nestlings but not Magpie Nestlings Starve in Experimental Age‐Matched Broods

Nestlings of non‐evicting avian brood‐parasites have to compete for food with foster parents' own nestlings. The outcome of these competitive contests is determined mainly by body size differences between parasitic and host nestlings. As part of the coevolutionary arms race between brood parasites and their hosts at the nestling stage, it has been reported that some host foster parents discriminate against parasitic chicks and are reluctant to feed them. Here, by experimentally creating size‐matched broods of different composition (only magpie Pica pica chicks, only great spotted cuckoo Clamator glandarius chicks or mixed broods), we show that great spotted cuckoo chicks starved in 20.2 per cent (17 of 84) of the parasitized magpie nests even in absence of size asymmetries, while in none (0 of 72) of the nests a magpie chick starved. As far as we know, this is the first record of non‐evictor brood parasitic nestlings starving without being smaller than their host nestmates in a frequently used host species. Nest composition had no effect on chick starvation. The cuckoo nestling starved even in two of the nests occupied by only one cuckoo chick. Our results could be explained by (1) magpies being reluctant to feed cuckoo chicks; (2) parasitic chicks receiving lower‐quality food items or cuckoo nestlings being sensitive to some particular component of the diet (e.g. cereal grains); and (3) the existence of cuckoo chick discrimination ability by magpie foster parents.     

Behavioural responses to ectoparasites in pied flycatchers Ficedula hypoleuca: an experimental study

Nests of cavity‐nesting birds usually harbor some species of haematophagous ectoparasites that feed on the incubating adults and nestlings. Given the negative impact of ectoparasites on nestlings there will be selection on hosts to reduce parasite infestations through behavioural means. We have experimentally reduced the abundance of all ectoparasites in nests of pied flycatchers Ficedula hypoleuca to explore both whether there are changes in the frequency and duration of putative anti‐parasite behaviours by tending adults, as well as whether such anti‐parasite behaviours are able to compensate for the deleterious effects that parasites may have on nestlings. Heat treatment of nests substantially decreased the density of ectoparasites, and thereby positively affected nestling growth. The frequency and intensity of female grooming and nest sanitation behaviours during the incubation and nestling periods decreased as a consequence of the experimental reduction of ectoparasite infestation. Although nestlings begged more intensely in infested nests, the experiment had no significant effect on parental provisioning effort. Reduction of parasites resulted in larger nestlings shortly before fledging and increased fledging success. This study shows a clear effect of a complete natural nest ectoparasite fauna on parental behaviour at the nest and nestling growth in a cavity‐nesting bird. Although ectoparasites induce anti‐parasite behaviours in females, these behaviours are not able to fully remove parasite's deleterious effects on nestling growth and survival.     

Multiple effects of brood parasitism reduce the reproductive success of prothonotary warblers, Protonotaria citrea

Avian brood parasitism often has multiple negative effects on the reproductive success of the host. Most studies have focused on one or two of these effects, but rarely have they all been studied simultaneously for one species. I studied prothonotary warblers to quantify the effects of different intensities of (i.e. multiple) brood parasitism by brown-headed cowbirds, Molothrus ater, on the production of host and cowbird young and on the between-year returns of adult warblers. Host clutch size decreased with an increase in the number of cowbird eggs laid in nests. The hatching success of warbler and cowbird eggs decreased with increased cowbird eggs in nests, but was always higher for cowbird eggs than warbler eggs. The survival of warbler nestlings, but not cowbird nestlings, decreased with increased cowbird nestlings in the brood. An increase in the number of cowbird nestlings in broods resulted in a reduction in the average mass of warbler nestlings but not cowbird nestlings. The number of cowbird eggs or nestlings present did not affect nest predation, and the fledging of cowbirds did not influence the renesting interval of female warblers. In addition, the between-year returns of adult warblers were not negatively affected by brood parasitism. Decreased hatching success and nestling survival reduced the reproductive output of the warblers the most. These effects were substantial and appear to favour the evolution of behavioural responses that reduce the effects of brood parasitism on prothonotary warblers. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour      

Low breeding success of the little egret (Egretta garzetta) near residential areas and in colonies exposed to gales: a comparison of colony in Sichuan,Southwest China,with literature

The breeding biology of the little egret (Egretta garzetta) was studied in 20 nests within the mixed-species breeding colonies at Nanchong, Sichuan, Southwest China, in 2006. By measuring a set of physical characteristics of vegetation at the nests and at a set of 20 randomly chosen sites we showed that birds preferentially used taller trees in areas with fewer shrubs of higher species diversity. Nests at lower locations in trees had marginally lower hatching success due to their destruction by humans; this destruction contributed marginally significantly to lowering of the total nesting success in all studied nests. Although gale winds also had a negative effect on breeding success, the anthropogenic influences were a greater factor in reproductive failure. We found similar effects in our review of literature on breeding success of the little egret from various geographical areas. Our results may be of use by conservation organizations in their actions to protect colonies of the little egret.     

广西防城7种鹭类混群繁殖的空间生态位研究

2002年3~8月对广西防城万鹤山营巢的鹭类繁殖种群进行了调查研究,结果表明:万鹤山栖息有大白鹭(Egretta alba)、中白鹭(Egretta intermedia)、白鹭(Egretta garzetta)、黄嘴白鹭(Egretta eulophotes)、牛背鹭(Bubulcus ibis)、池鹭(Ardeda bacchus)、夜鹭(Nycticorax nycticorax)7种鹭类种群。除黄嘴白鹭为均匀分布之外,其他6种均为成群分布。鹭类在万鹤山上营巢繁殖具有明显的水平分布和垂直分布现象。对影响鹭类混群繁殖时空间分布的因素及各种群间的相互关系进行了探讨。     

Variable effects of the Hen Flea Ceratophyllus gallinae on the breeding success of the Great Tit Parus major in relation to weather conditions

We investigated the effect of an ectoparasite, the Hen Flea Ceratophyllus gallinae (Siphonaptera), on the reproductive success of the Great Tit Parus major, a hole-nesting passerine bird. Parasite levels of cleaned nesting boxes were experimentally manipulated during the egg-laying period of the birds either by spraying nests with pyrethrin or by introducing c. 100 adult fleas, while other nests were left as controls. Only in 2 out of 5 years did hen fleas significantly affect reproductive success. Nestlings from parasitized nests showed reduced body-mass, tarsus-length and condition, whereas wing-length did not differ between nestlings reared with or without fleas. The impact of the fleas on the growth performance of host nestlings was more noticeable in years with lower temperatures and higher precipitation.     

Nest position,breeding success and diet of the Black-crowned Night Heron,Nycticorax nycticorax in the Anzali Wetland,Northern Iran (Aves: Ardeidae)

Breeding ecology of the Black-crowned Night Heron (Nycticorax nycticorax) was studied in a mono-specific colony in the Anzali wetland, Northern Iran during the breeding season of 2016. The breeding period lasted from mid-May to late July. The average clutch size was 3.1±0.6 eggs and the breeding success 77.6%. No significant differences were found between nests built on trunks and those built on branches of trees. The clutch size and breeding success appeared to be independent of the structural variables of the nesting site (diameter of trees, height from the ground, height of nests from the canopy, nest number per tree, location of nests on trunks and branches). No significant difference was found between the timing of the start of incubation and the height of nests above the ground. The average vertical and horizontal distances between nests was one metre. Fish, particularly Carassius gibelio, dominated the diet of the nestlings.     

Sex ratio comparisons between nestlings and dead embryos of the Sparrowhawk Accipiter nisus

Sex ratios that differ from unity have been reported for several bird species, but are poorly understood. Skewed sex ratios may originate at ovulation (primary sex ratio) or arise through differential mortality between the sexes (secondary sex ratio). To estimate the primary sex ratio from nestlings is difficult because in some nests not all the offspring can be sexed. Both when including and excluding such nests, there is a risk of overestimating the proportion of the better-surviving sex. Here we sexed dead Sparrowhawk embryos to determine whether unhatched eggs affect primary sex ratio estimates that are based on nestling data. In nests in which embryo mortality occurred, there was up to a 9% discrepancy in the primary sex ratio estimates based on nestlings alone compared to nestlings and dead embryos together. There was no evidence that these differences were based on sex-specific causes of mortality of embryos.     

Aromatic plants in nests of the blue tit <Emphasis Type="Italic">Cyanistes caeruleus</Emphasis> protect chicks from bacteria

Several bird species add fresh fragments of plants which are rich in volatile secondary compounds to their nests. It has been suggested, although never tested, that birds use fresh plants to limit the growth of nest microorganisms. On Corsica, blue tits (Cyanistes caeruleus) incorporate fresh fragments of aromatic plants into their nests. These plants do not reduce infestation by nest ectoparasites, but have been shown to improve growth and condition of chicks at fledging. To understand the mechanisms underlying such benefits, we experimentally tested the effects of these plants on the bacteria living on blue tits. Aromatic plants significantly affected the structure of bacterial communities, in particular reducing bacterial richness on nestlings. In addition, in this population where there is a strong association between bacterial density and infestation by blood-sucking Protocalliphora blow fly larvae, these plants reduced bacterial density on the most infested chicks. Aromatic plants had no significant effect on the bacteria living on adult blue tits. This study provides the first evidence that fresh plants brought to the nests by adult birds limit bacterial richness and density on their chicks.     

Chick survival in relation to nest site: is the Antarctic petrel hiding from its predator?

In birds, the characteristics of the nest site may affect reproductive success. We found that shelter is an important characteristic of the Antarctic petrel (Thalassoica antarctica) nests because shelter prevents chick predation. However, the benefit of shelter was countervailed by melt water which mainly entered well-sheltered nests. Chick survival was monitored until the chick was left unattended for the first time. Late-hatched chicks had a higher survival probability than early-hatched chicks, possibly because late hatchers swamp the predator, the south polar skua (Catharacta maccormicki). Poorly sheltered nests tended to be occupied by parents with low body mass and late-hatched eggs. The results suggest that both shelter per se and parental characteristics may explain the relationship between predation risk and shelter. We need experiments to study the influence of nest site on reproductive success, and we need to map the frequency of melt water as a cause of reproductive failure.     

Phosphorus and nitrogen in wetlands with and without egret colonies

Abstract Colonially nesting birds have been implicated in the destruction of their nest site vegetation, the most likely mechanism being through an overload or imbalance of soil nutrients. The numbers of egrets in coastal New South Wales colonies have increased rapidly in the second half of this century since cattle egrets (Ardeola ibis) were introduced. This species now nests colonially with three native species: great (Egretta alba), intermediate (Egretta intermedia) and little egrets (Egretta garzetta). Thus there is potential for more rapid degradation of the colony site. We measured the levels of phosphorus in surface sediments, and phosphorus and nitrogen in water at eight colony site wetlands, and compared each to four other wetlands in the same region where there were no egret colonies. We conclude that levels of both nutrients were elevated in colony wetlands. The implications of this result for death of colony site vegetation and the conservation of the three native egret species are briefly discussed.     

Aromatic plants in blue tit Cyanistes caeruleus nests: no negative effect on blood-sucking Protocalliphora blow fly larvae

Nesting birds use several behavioural or physiological defence mechanisms against parasites. On Corsica, female blue tits Cyanistes caeruleus incorporate fresh fragments of a limited number of aromatic plants in the nest cup, from the end of nest construction until fledging. Some of these plants negatively affect bacterial growth and host location by blood-sucking mosquitoes in laboratory conditions. In natural populations, Corsican blue tit chicks are exposed to the highest levels of blood-sucking ectoparasitic blow flies Protocalliphora spp. reported in Europe. These ectoparasites can have severe negative effects on chick development and survival probabilities, especially when food constraints are elevated. Here we investigated in several natural Corsican blue tit populations the hypothesis that aromatic plants brought to the nest have anti-blow fly effects during the chick-rearing stage. We predicted that: 1) the amount of aromatic plants should be negatively related to blow fly infestation intensity across nests, 2) experimental addition of aromatic plants in nests should reduce blow fly infestation intensity, and 3) nestlings should be in better physical condition in nests where aromatic plants were experimentally added. No significant relation was found between amount of aromatic plants in nests and blow fly infestation intensity. Experimental addition of aromatic plants did not reduce blow fly infestation intensity and did not affect the chick phenotypic parameters we measured. We conclude that aromatic plants in blue tit nests are not used as a defence against ectoparasitic Protocalliphora blow flies in our study population.