Helga Gwinner

Green plants in starling nests : effects on nestlings

European starlings, Sturnus vulgaris, intermingle fresh herbs, especially species rich in volatile compounds, with their otherwise dry nest material. In this field study we investigated whether these herbs reduce ectoparasites and thereby protect nestlings (the nest protection hypothesis). We also considered whether volatile compounds in herbs improve the condition of nestlings (the drug hypothesis). As measures of condition we used body mass, haematocrit levels and immunological parameters. We replaced 148 natural starling nests with artificial ones: half contained herbs and half (controls) contained grass. The ectoparasite loads (mites, lice, fleas) in herb and control nests were indistinguishable. However, nestlings in herb nests weighed more and had higher haematocrit levels at fledging than nestlings in control nests. Fledging success was similar in herb and control nests, but more yearlings from herb nests were identified in the colony the year after hatching. The response of the immune system when challenged with phytohaemagglutinin did not differ in nestlings from herb and control nests. Nestlings from herb nests had more basophils and fewer lymphocytes in their blood than those from control nests, while the eosinophil and heterophil counts did not differ. We conclude that herbs do not reduce the number of ectoparasites, but they improve the condition of nestlings, perhaps by stimulating elements of the immune system that help them to cope better with the harmful activities of ectoparasites. Copyright 2000 The Association for the Study of Animal Behaviour.

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.

Effects of nestboxes on LH, testosterone, testicular size, and the reproductive behavior on male European starlings in spring

The effect of nestboxes on the vernal increase and decrease in reproductive activity was investigated in male European starlings (Sturnus vulgaris), held in outdoor aviaries. Male-only groups with (group 1) and without (group 2) availability of nestboxes were compared for the amount of song, for testicular size and plasma titers of luteinizing hormone (LH) and testosterone. Testicular size and LH differed significantly between the 2 groups, being higher in males with nestboxes. Similar differences, as well as differences in nestbox-related behaviors (sitting in front of a nestbox, inspecting it, and nestbuilding) were also found when individuals of group 1, in possession of a nestbox, were compared to those without. In another group (2), the seasonal dependence of nestboxes as a modifying factor was investigated. These males were given access to nestboxes later in the season, than the males of group 1, after April 7. The effects on physiological parameters at this time of year were negligible in that only a transient increase in LH was seen compared to group 3. Nestbox-oriented behaviors did not reach the same intensities as in group 1. These results demonstrate the importance of nest-site availability in modifying behavioral and physiological functions during the vernal reproductive cycle. At the same time they indicate a seasonal dependence in these modifying effects.

Evidence for sexy sons in European starlings (Sturnus vulgaris)

The “sexy son” hypothesis suggests that females obtain future fitness benefits from mating with polygynous males through the inheritance by their sons of traits contributing to mating success. We tested this hypothesis in the facultatively polygynous European starling (Sturnus vulgaris) in two ways. We first compared sons of monogynous and polygynous free-living males for their abilities in nest site acquisition and female-directed behaviors in controlled aviary tests. We then investigated eggs laid in monogynous and polygynous matings for concentrations of maternal steroid hormones that could affect behavioral differentiation of sons. Sons of polygynous fathers defended more nest boxes and produced more courtship song than sons of monogynous fathers. Mean concentrations of maternal androstenedione (A4), 5α-dihydrotestosterone (DHT), testosterone (T), and 17β-estradiol (E) in yolks were not affected by mating status. However, the within-clutch pattern of A4 depended on mating status, with higher concentrations in last than in first eggs of clutches of monogynous but not polygynous matings. These results suggest that (1) sons may inherit from their fathers behavioral qualities for the successful acquisition of nest sites and attraction of mates; (2) differential exposure to maternal steroid hormones during development in the egg is unlikely the cause of the behavioral differences between adult sons of monogynous and polygynous fathers; and (3) females adjust the within-clutch pattern of androgen to mating status, possibly in response to the expected contribution of their mate to nestling care.

Effects of testosterone on nest-box occupation and associated behaviours by male European starlings (Sturnus vulgaris)

In an aviary experiment carried out at the beginning of the breeding season in March and April, nest-box occupation and associated behaviours were observed in a group of 18 adult and 18 first-year male European starlings. Nine birds of each group carried a testosterone implant (T-males) and the other 9 an empty implant (C-males). When analyzed for effects of age, first year birds were significantly more active with regard to nest-box inspection and nest-building than adults. When analyzed for effects of treatment, T-males occupied more nest-boxes and visited their nest-boxes more often than C-males. Other activities like singing, nest-box inspection, nest-building and aggressive behaviour were not significantly different between T-males and C-males. We suggest that the absence of a significant effect of T on aggression may be related to the colonial nesting habits of the starling. Since T-males tended to be more active with regard to all behaviours studied testosterone may have led to a general increase in frequency and persistence of behaviour which in turn facilitated nest-box occupation.

Postjuvenile molt in East African and Central European stonechats (Saxicola torquata axillaris, S. t. rubicola) and its modification by photoperiod

SummaryTwenty-eight stonechats of the European race (Saxicola torquata rubicula) from Austria and thirty-one stonechats of the Central African race (S.t. axillaris) from equatorial Kenya were handraised and subsequently investigated with regard to the temporal pattern of their postjuvenile molt. About one half of the birds of each race were held under their own native photoperiod and the other half under the photoperiodic conditions of the other race. The results demonstrated clear differences in the postjuvenile molt between the two races when birds were kept in the photoperiod under which they normally live. The African birds began to molt earlier and molted longer than their European conspecifics. The time course of postjuvenile molt was affected by photoperiod in both races as molt began and ended earlier under the equatorial photoperiod than under the European photoperiodic simulation. The question why the African birds showed strong photoperiodic reactions under these experimental conditions although in their natural environment they experience only minute photoperiodic variations, is critically evaluated: Three possible explanations are discussed: (1) the photoperiodic reaction may represent a relict from a time when ancestors of the tropical populations still lived in more temperate zones; (2) it may be due to the occasional immigration of conspecifics from populations living further north or south; (3) it may result from effects on a (possibly circadian) submechanism of the system controlling annual cycles which is normally affected by other environmental cues but can also be influenced by photoperiodic variations.

Bacteria in starling nests@@@Bakterien in Nestern von Staren

We investigated the bacterial frequency and identified 11 genera of bacteria in starling-nests of a nest box colony in southern Germany. We sampled bacteria with a new method: agar paddles, developed for the food industry, were pressed against the naked belly of nestlings at an age of 14 days for 5 seconds. The bacteria colonies on the paddle surface were counted after incubation and their numbers served as an estimate of bacterial infestation of a nest. Bacteria numbers increased with season and precipitation. No relationship between bacteria load of the nests and hatching and fledging success, nestling mortality and body mass close to fledging was detected. The reason for this may be that a high bacteria load is not necessarily harmful but may even act in a beneficial way on the digestive and immune system. Nevertheless we consider it possible that the higher load of bacteria of late nests may under certain conditions be one of the factors responsible for the frequently observed lower quality of second brood nestlings. Wir untersuchten Häufigkeit und Gattungszugehörigkeit von Bakterien in Starennestern in einer Nistkastenkolonie in Süddeutschland. Wir fanden Bakterien aus 11 verschiedenen Gattungen. Die Bakterienproben gewannen wir mit einer neuen Methode: Agarpaddeln, die in der Nahrungsmittelindustrie Verwendung finden, wurden 5 Sekunden lang auf den nackten Bauch von 14 Tage alten Nestlingen gepresst. Die sich auf dem Paddel nach 48stündiger Inkubation entwickelnden Bakterienkulturen wurden gezählt und dienten als Maß für den Bakterienbefall eines Nests. Wir fanden einen signifikanten saisonalen Anstieg von Bakterien in den Nestern, der auch mit dem Niederschlag korrelierte. Es gab keine Beziehung zwischen Bakteriendichte und dem Schlüpf- und Ausfliegeerfolg, der Nestlingsmortalität oder dem Gewicht der Nestlinge. Der Grund hierfür könnte sein, dass Bakterien nicht unbedingt schädlich sein müssen, sondern auch einen günstigen Einfluss auf die Verdauung und das Immunsystem der Nestlinge haben können. Wir halten es aber dennoch für möglich, dass unter bestimmten Bedingungen der stärkere bakterielle Befall von späten Nestern mit einer der Gründe für die häufig beobachtete schlechtere Qualität von Jungvögeln aus zweiten Bruten ist.

Assessing the effects of climate on host-parasite interactions: a comparative study of European birds and their parasites.

Background Climate change potentially has important effects on distribution, abundance, transmission and virulence of parasites in wild populations of animals. Methodology/Principal Finding Here we analyzed paired information on 89 parasite populations for 24 species of bird hosts some years ago and again in 2010 with an average interval of 10 years. The parasite taxa included protozoa, feather parasites, diptera, ticks, mites and fleas. We investigated whether change in abundance and prevalence of parasites was related to change in body condition, reproduction and population size of hosts. We conducted analyses based on the entire dataset, but also on a restricted dataset with intervals between study years being 5–15 years. Parasite abundance increased over time when restricting the analyses to datasets with an interval of 5–15 years, with no significant effect of changes in temperature at the time of breeding among study sites. Changes in host body condition and clutch size were related to change in temperature between first and second study year. In addition, changes in clutch size, brood size and body condition of hosts were correlated with change in abundance of parasites. Finally, changes in population size of hosts were not significantly related to changes in abundance of parasites or their prevalence. Conclusions/Significance Climate change is associated with a general increase in parasite abundance. Variation in laying date depended on locality and was associated with latitude while body condition of hosts was associated with a change in temperature. Because clutch size, brood size and body condition were associated with change in parasitism, these results suggest that parasites, perhaps mediated through the indirect effects of temperature, may affect fecundity and condition of their hosts. The conclusions were particularly in accordance with predictions when the restricted dataset with intervals of 5–15 years was used, suggesting that short intervals may bias findings.

Male European Starlings Use Odorous Herbs as Nest Material to Attract Females and Benefit Nestlings

Male European starlings (Sturnus vulgaris) use odorous herbs as green nest material. They show these plants to females to catch their attention before they incorporate them into their nests. Nestlings reared in nests containing herbs carry fewer bacteria, have higher haematocrit levels and more basophile leucocytes, and have a higher fledging weight than those reared in nests without herbs. The incubation temperature is higher in nests with herbs than in herbless nests. Females are attracted by herb nests and herb nests provide energy-saving benefits to incubating females. In choice experiments, starlings employed olfaction to select nest herbs, using innate information and experience acquired as nestlings to identify odours. Measures of head space air in starling nest boxes revealed an increase of volatile substances during the nestlings phase. Manganese-enhanced resonance imaging of the olfactory bulb of starling showed that the neural correlates of olfactory sensitivity change seasonally. Starlings can only discriminate odours during the reproductive season. The association between odour perception and reproductive behaviour suggests that increased testosterone production, related to the increasing photoperiod in spring, may guide these seasonal changes. The size of the olfactory bulb but not its ability to discriminate was affected by testosterone implants in the non-reproductive season.

'Green incubation' : avian offspring benefit from aromatic nest herbs through improved parental incubation behaviour

Development of avian embryos requires thermal energy, usually from parents. Parents may, however, trade off catering for embryonic requirements against their own need to forage through intermittent incubation. This dynamically adjusted behaviour can be affected by properties of the nest. Here, we experimentally show a novel mechanism by which parents, through incorporation of aromatic herbs into nests, effectively modify their incubation behaviour to the benefit of their offspring. Our study species, the European starling, includes in its nest aromatic herbs which promote offspring fitness. We provided wild starlings with artificial nests including or excluding the typically selected fresh herbs and found strong support for our prediction of facilitated incubation. Herb effects were not explained by thermal changes of the nests per se, but by modified parental behaviours. Egg temperatures and nest attendance were higher in herb than herbless nests, egg temperatures dropped less frequently below critical thresholds and parents started their active day earlier. These effects were dynamic over time and particularly strong during early incubation. Incubation period was shorter in herb nests, and nestlings were heavier one week after hatching. Aromatic herbs hence influenced incubation in beneficial ways for offspring, possibly through pharmacological effects on incubating parents.