Avian Incubation Research Articles

Assessing avian incubation behavior in response to environmental pollution with temperature-humidity loggers

The negative impact of environmental pollution on avian physiology and breeding success is well documented. However, pollution-related behavioral changes during reproduction remain underexplored, despite behavior often being one of the earliest indicators of environmental disturbances and having significant life-history consequences. For example, altered food availability in a polluted environment could potentially perturb the incubation behavior of income breeders. These birds typically alternate between staying in the nest and heating eggs (on-bout) and taking foraging trips (off-bout). In this two-year study (2020 and 2022), we investigated how the incubation behavior of an insectivorous passerine, the pied flycatcher (Ficedula hypoleuca), varied with environmental pollution levels around a Cu-Ni smelter. Additionally, we compared two different metrics – temperature and humidity within the nest – to evaluate their use as indicators of incubation rhythm. We found that temperature- and humidity-based incubation rhythm parameters correlated, but those based on humidity matched better the true incubation behavior documented by simultaneous video recording. This was because the humidity curve showed a more immediate and intensive response to the female's incubation behavior. Birds in the polluted area took slightly more (11%) but shorter (11%) off-bouts, possibly reflecting smaller energetic constraints or better food availability in the polluted area. However, we found no difference in total incubation intensity between polluted and control areas, with F. hypoleuca females incubating their eggs 75% of the daytime in both environments. Hence, incubating females in the polluted area did not allocate more time for gathering their energy reserves than the birds in the control area, and there was also no difference in the hatching success. Our study is the first to use humidity variation to record incubation rhythm, and our results indicate that measuring humidity inside the nest is a promising technique to test and develop further. For example, further studies are needed to test if this method would work in different types of nests. From an environmental protection standpoint, our results also contribute valuable insights to the relatively limited information on pollution-related behavioral changes.

Effects of the temperature during embryonic development on adult reproduction and the phenotype of the second generation in zebra finches

Across taxa, the temperature experienced by individuals early in life can have large effects on their development. However, comparatively little is known about whether the effects of this thermal developmental environment can be long-lasting or transgenerational. In birds, one important aspect of the developmental environment is incubation and, in general, eggs incubated at low temperatures produce offspring with smaller morphology, suboptimal physiology, and even lower long-term survival. Yet, little is known about whether incubation temperature may affect avian reproduction in adulthood, and nothing is known about whether the effects of avian incubation temperature may be transgenerational. To investigate this, we incubated zebra finch (Taeniopygia guttata) eggs at two different temperatures: 37.5 °C (‘control’) and 36.3 °C (‘low’), raised nestlings until adulthood, and allowed same-temperature treatment pairs to reproduce. We found that F1 individuals incubated at the low temperature had shorter beaks at the start of reproduction than those incubated at the control temperature. Further, compared to those from control parents, F2 offspring from parents incubated at the low temperature had lighter body masses at 5 days-old and had shorter beaks at 30 days-old. However, we found little evidence that incubation temperature affected other aspects of reproduction, with no effect on latency to lay, clutch size, egg mass, incubation period, hatching success/asynchrony, fledging, or the number of offspring that ultimately survived until independence. Overall, we found some evidence that a difference in the early thermal developmental environment can have lasting morphological effects into the next generation. However, future work is needed to determine whether the incubation temperature that birds experience as embryos may influence parental care behaviors or lifetime reproductive success.

Intraspecific variation in incubation behaviours along a latitudinal gradient is driven by nest microclimate and selection on neonate quality

Abstract The strategies by which animals allocate reproductive effort across their lifetimes vary, and the causes of variation in those strategies are actively debated. In birds, most research has focused heavily on variation in clutch size and fecundity, but incubation behaviour and other functionally related traits have received less attention. Variation in incubation period duration is notable because time‐dependent sources of clutch mortality should impose strong directional selection to minimize the incubation period. However, life‐history theory predicts multiple mechanisms by which inter‐ and intraspecific variation in incubation behaviours may be adaptive. We conducted one of the first studies of intraspecific latitudinal variation in avian incubation behaviours across a large portion of a single species’ range. We placed motion‐activated nest cameras inside burrowing owl nests at five study sites to quantify variation in daily nest attentiveness, cumulative nest attendance and incubation period duration. We tested predictions of two alterative hypotheses that have been proposed to explain variation in incubation periods: the parental risk tolerance hypothesis and the neonate quality hypothesis. Daily nest attentiveness, cumulative nest attendance and incubation period duration in burrowing owls were all positively correlated with latitude. Burrowing owls reduced their daily nest attentiveness at low latitudes and on days when the average nest temperature was within the range that is optimal for embryo development. Further, longer incubation periods were most strongly associated with greater cumulative nest attendance instead of reduced daily nest attentiveness. These results support predictions of the neonate quality hypothesis: longer incubation periods result from stronger selection on neonate quality rather than selection to reduce reproductive effort in response to low extrinsic mortality risk. However, some owls facultatively reduced their daily nest attentiveness, and this result supports the general hypothesis that incubation decisions reflect a trade‐off between reproduction and self‐maintenance, and that the optimal solution to that trade‐off varies systematically in response to latitudinal gradients in adult mortality. A free Plain Language Summary can be found within the Supporting Information of this article.

Evidence of incubation trade‐offs in Leach's Storm‐Petrel (Oceanodroma leucorhoa): ptilochronology as a measure of reproductive investment in a long‐lived seabird

Avian incubation investment represents a trade‐off between the energetic demands of the parent and the thermal needs of the embryo. Parental energy balance and investment in somatic maintenance relative to incubation investment can be indexed by the rate of feather growth. Feather growth rates, or ptilochronology, of adult Leach's Storm‐Petrels Oceanodroma leucorhoa were used to assess parental investment to (1) determine whether individuals that invest heavily in current reproduction pay a cost for future reproduction as indicated by a cost for somatic maintenance and (2) assess whether this trade‐off is detected using ptilochronology, which may be a more direct measure of reproductive investment compared with body mass in seabirds. We found positive relationships between duration of the incubation period and both egg neglect and a mated pair's mean rate of induced feather growth, although we did not find a relationship between either egg neglect and feather growth or hatching success and feather growth. Our results suggest that during the incubation period a trade‐off exists between energy allocated to self‐maintenance and reproduction in this species, although egg neglect does not appear to be the mechanism that extends the incubation period in response to increased energetic demands of somatic maintenance. The lack of correlation between feather growth and egg neglect further suggests that some pairs may be better able to manage competing demands of self‐maintenance and incubation, possibly due to individual quality, coordination of incubation effort, burrow quality or some other factor.

Water Vapour Conductance of Passerine Nest Walls

Avian incubation relies on maintenance of the appropriate temperature and humidity within the nest. Previous studies suggested that conductance of the nest wall to water vapour was relatively low, albeit greater than the conductance of the eggshell, but no empirical studies confirmed this. In this study hygrometer loggers were used to measure water vapour inside and outside nest cups to determine conductance of the nest wall. Average water vapour conductance values for nine species of passerine ranged from 479 mgH2O·day-1·Torr-1 for Common Chaffinch Fringilla coelebs nests to 712 mgH2O·d-1·Torr-1 for Eurasian Reed Warbler Acrocephalus scirpaceus nests. Generally, water vapour conductance values were two orders of magnitude higher than that of published values for the eggshell for these species, although humidity in the nest cup were comparable to published data for passerine nests. These results indicate that in the study species the nest wall was not an effective barrier to water vapour loss. Reconsideration of high values for nest wall conductance, nest attentiveness and sources of water to create humidity, have led to a new approach that deals with nest humidity as part of the water budget during the incubation period. Over time the amount of water vapour required to raise nest humidity far exceeds that released by the eggs. It is proposed that nest humidity is driven by cutaneous water loss from the incubating bird, rather than water vapour lost from the eggs, in order to counter loss of humidity through the nest wall and during incubation recesses.

Haemosporidian parasites of Neotropical birds: Causes and consequences of infection

Abstract Haemosporidian parasites of the genera Plasmodium, Haemoproteus, and Leucocytozoon are among the best studied parasites of Neotropical birds. Here, we describe variation in haemosporidian prevalence (i.e. the proportion of infected individuals in a sampled population) in Neotropical birds. We review correlates of haemosporidian prevalence (including several avian life-history traits, climate, and season) and the population and evolutionary consequences of infection for Neotropical birds. We find that prevalence varies among avian taxonomic families, genera, and even among species within the same genus, suggesting that prevalence reflects multiple factors, some of which (e.g., avian incubation period) are associated with avian family-level variation in prevalence while others (e.g., avian abundance) are associated with variation in prevalence among closely related host species. We find few correlates of prevalence that have been consistently demonstrated across studies. Prevalence in populations of many Neotropical birds has been estimated by microscopic examination of blood smears, which affords limited opportunity for comparison with data generated by molecular methods. However, at one site in the Brazilian Cerrado for which we have data, prevalence determined by microscopy does not correlate with prevalence determined by molecular methods for Plasmodium, but the 2 data types are positively correlated for Haemoproteus. Haemosporidians have been hypothesized to play a role in avian sexual selection, and we find the prevalence of Haemoproteus to be lower in polygynous species than in socially monogamous species in the Neotropics, confirming a pattern shown previously among Nearctic birds.

Applications of machine learning in behavioral ecology: Quantifying avian incubation behavior and nest conditions in relation to environmental temperature.

In the age of machine learning, building programs that take advantage of the speed and specificity of algorithm development can greatly aid efforts to quantify and interpret changes in animal behavior in response to abiotic environmental factors, like temperature. For both endotherms and ectotherms, temperature can affect everything from daily energy budgets to nesting behaviors. For instance, in birds environmental temperature plays a key role in shaping parental incubation behavior and temperatures experienced by embryos. Recent research indicates that temperatures experienced by embryos affect viability and are important in shaping fitness-related traits in young birds, sparking renewed interest in relationships among environmental factors, parental incubation behavior, and incubation temperature. Incubation behavior of birds can be monitored non-invasively by placing thermal probes into the nest and analyzing temperature fluctuations that occur as parents attend and leave the nest (on- and off-bouts, respectively). When other measures of temperature (e.g., ambient air or operative temperature) are collected simultaneously with incubation temperature it is possible to compare shifts in behavior with environmental changes. To improve analysis of incubation behavior using these large thermal data sets we developed a program, NestIQ, that uses machine learning to guide parameter optimization allowing it to track the behavior of diverse species. NestIQ's algorithm was tested using six species incubating in lab or field scenarios, that exhibit unique incubation patterns. This stand-alone and open source software is operated through a graphical user interface (i.e., no user programming is required) that provides important behavioral and thermal output statistics. Further, measures of environmental temperature can be imported alongside nest temperature into the program, which then reports various attributes of environmental temperature during shifts in parental behavior. This program will improve the ability of avian ecologists to interpret a critical parental care behavior that can be used across diverse incubation scenarios and species. Although specifically designed for quantifying avian incubation, NestIQ has the potential for broader applications, including basking and nesting behaviors of non-avian reptiles in relation to ambient temperature.

The importance of nighttime length to latitudinal variation in avian incubation attentiveness

Avian incubation provides an opportunity to test how parental behavior and ecological conditions interact to shape variation in offspring traits along geographic gradients. In particular, the duration of the incubation period is shorter at higher latitudes, but the degree to which this pattern arises from genetic divergence in rates of growth and development versus from parentally‐mediated variation in egg temperatures is controversial. At higher latitudes parents have higher daytime incubation attentiveness, i.e. they spend a greater proportion of the day on the nest. However, interpreting latitudinal variation in behavior is complicated by latitudinal patterns in ambient temperature and day length. Here, we use 24‐h video recordings to compare the incubation behavior of orange‐crowned warblers Leiothlypis celata in California and Alaska and test how attentiveness varies between populations and as a function of temperature. Birds in Alaska had higher nest attentiveness during the day, despite experiencing similar ambient temperatures. However, when analyzed over 24‐h, the longer nighttime period in California almost entirely canceled out daytime attentiveness differences between populations, and differences in 24‐h attentiveness were small. Our work highlights how incorporating nighttime incubation behavior qualitatively alters latitudinal patterns of attentiveness, and how lower ambient temperatures cannot account for the higher attentiveness in a high latitude population. These populations differ in their incubation period lengths, and differentiating between evolved versus environmentally‐induced variation in offspring growth and development will help understand the fitness consequences of variation in developmental periods.

Consequences of hatching deviations for breeding success: a long-term study on blue tits Cyanistes caeruleus

The causes and consequences of variation in the incubation regimes of oviparous animals remain unclear, despite having important fitness consequences. Avian incubation regimes can be shortened by parents initiating incubation prior to clutch completion or prolonged when there are gaps in the laying sequence. Here, we begin by quantifying variation in the incubation regimes of three populations of blue tits Cyanistes caeruleus from the UK and Poland before examining the consequences of such variation for their hatching and fledging success. We then investigate the mechanism causing such variation by exploring the impact of local weather conditions on incubation regimes. The difference between the expected and actual hatching dates of clutches was termed the “hatching deviation” and this showed considerable variation. Hatching deviation was negatively related to local temperature and clutch size. Hatching deviation affected hatching success and hatching deviation, temperature, wind speed and clutch size affected fledging success. Deviating from the expected laying and incubation regime caused lowered reproductive success. The most successful birds were those that were able to lay one egg per day and begin incubation upon clutch completion.

Incubation Temperature Affects Duckling Body Size and Food Consumption Despite No Effect on Associated Feeding Behaviors.

SynopsisDevelopmental conditions can have consequences for offspring fitness. For example, small changes (<1°C) in average avian incubation temperature have large effects on important post-hatch offspring phenotypes, including growth rate, thermoregulation, and behavior. Furthermore, average incubation temperatures differ among eggs within the same nest, to the extent (i.e., >1°C) that differences in offspring phenotypes within broods should result. A potential consequence of within-nest incubation temperature variation is inequality in behaviors that could cause differences in resource acquisition within broods. To investigate this, we incubated wood duck (Aix sponsa) eggs at one of two ecologically-relevant incubation temperatures (35°C or 36°C), formed mixed-incubation temperature broods after ducklings hatched, and conducted trials to measure duckling behaviors associated with acquisition of heat (one trial) or food (three trials). Contrary to our predictions, we found no effect of incubation temperature on duckling behaviors (e.g., time spent occupying heat source, frequency of feeding bouts). However, we found evidence that ducklings incubated at the higher temperature consumed more food during the 1-h feeding trials, and grew faster in body mass and structural size (culmen and tarsus) throughout the study, than those incubated at the lower temperature. Apparent food consumption during the trials was positively related to culmen length, suggesting that differences in food consumption may be driven by structural size. This could result in positive feedback, which would amplify size differences between offspring incubated at different temperatures. Thus, our study identifies incubation temperature as a mechanism by which fitness-related phenotypic differences can be generated and even amplified within avian broods.

Parental Effects and Climate Change: Will Avian Incubation Behavior Shield Embryos from Increasing Environmental Temperatures?

A major driver of wildlife responses to climate change will include non-genomic effects, like those mediated through parental behavior and physiology (i.e., parental effects). Parental effects can influence lifetime reproductive success and survival, and thus population-level processes. However, the extent to which parental effects will contribute to population persistence or declines in response to climate change is not well understood. These effects may be substantial for species that exhibit extensive parental care behaviors, like birds. Environmental temperature is important in shaping avian incubation behavior, and these factors interact to determine the thermal conditions embryos are exposed to during development, and subsequently avian phenotypes and secondary sex ratios. In this article, we argue that incubation behavior may be an important mediator of avian responses to climate change, we compare incubation strategies of two species adapted to different thermal environments nesting in extreme heat, and we present a simple model that estimates changes in egg temperature based on these incubation patterns and predicted increases in maximum daily air temperature. We demonstrate that the predicted increase in air temperature by 2100 in the central USA will increase temperatures that eggs experience during afternoon off-bouts and the proportion of nests exposed to lethal temperatures. To better understand how species and local adaptations and behavioral-plasticity of incubation behavior will contribute to population responses to climate change comparisons are needed across more avian populations, species, and thermal landscapes.

Serum prolactin and testosterone levels in captive and wild brown kiwi (Apteryx mantelli) during the prebreeding, breeding, and incubation periods.

In brown kiwi (Apteryx mantelli), the male is the primary incubator, a trait that is relatively rare among birds. The maintenance of avian incubation behavior is controlled by the protein hormone prolactin (PRL). Although steroid hormone concentrations in both wild and captive kiwi have previously been reported, this study is the first to report levels of PRL in captive and wild male and female kiwi through the prebreeding and breeding seasons, and to directly compare testosterone (T) concentrations between captive and wild males during the breeding and incubation periods. Female PRL concentrations increased at the time of oviposition, whereas male PRL concentrations rose gradually between the prebreeding and incubation periods. Although males are considered the main incubator, an increase in PRL levels could help females maintain behaviors such as nest guarding, or to take over incubation the event of mate loss. A gradual increase in PRL allows the male to be ready for incubation during the long breeding season. Interestingly, T concentrations in captive males did not decrease during incubation and was significantly higher than in wild males. Continual elevated T could have an impact on sperm production through negative feedback, thereby contributing to the low egg fertility seen in captive kiwi. Therefore, determining the underlying reason for the differences in hormone levels could be significant, if not vital, for improving the success of captive kiwi breeding programs.

Temperature, wind, vegetation, and roads influence incubation patterns of Greater Prairie-Chickens (Tympanuchus cupido pinnatus) in the Nebraska Sandhills, USA

Avian incubation involves behavioral decisions that must balance trade-offs between the incubating bird’s survival and current and future reproductive success. We evaluated variation in incubation off-bout duration and frequency among Greater Prairie-Chickens (Tympanuchus cupido pinnatus (Brewster, 1885)) in the Nebraska Sandhills, USA. Greater Prairie-Chicken life history favors incubation behaviors that prioritize success of the current breeding attempt over adult survival. Previous observations suggest incubating females make these behavioral decisions based on ambient temperature conditions, their own body condition, and predation risk. We monitored nest attendance by females at 30 Greater Prairie-Chicken nests to identify proximate cues used to make behavioral decisions regarding incubation. We recorded 930 incubation off-bouts. Females took 1.9 ± 0.7 off-bouts/day (mean ± SD), each with a mean (±SD) duration of 43.3 ± 24.1 min. Off-bouts were shorter in duration at higher wind speeds, at lower ambient temperatures, at nests with less cover, and at nests closer to roads. Females were most likely to leave the nest during mid-morning and evening, as are most gallinaceous birds, and incubation off-bouts became less frequent later in the season. We did not observe differences in incubation behavior between nests that failed and those that successfully hatched one or more chicks.

IncR: a new R package to analyse incubation behaviour

Incubation represents a life stage of crucial importance for the optimal development of avian embryos. For most birds, incubation poses a trade‐off between investing in self‐maintenance and offspring care. Furthermore, incubation is affected by environmental temperatures and, therefore, will be likely impacted by climate change. Despite its relevance and readily available temperature logging methods, avian incubation research is hindered by recognised limitations in available software. In this paper, a new quantitative approach to analyse incubation behaviour is presented. This new approach is embedded in a free R package, incR. The flexibility of the R environment eases the analysis, validation and visualisation of incubation temperature data. The core algorithm in incR is validated here and it is shown that the method extracts accurate metrics of incubation behaviour (e.g. number and duration of incubation bouts). This paper also presents a suggested workflow along with detailed R code to aid the practical implementation of incR.

The adaptive significance of variation in avian incubation periods

ABSTRACT In spite of strong selection by time-dependent mortality on the length of the embryo development (incubation) period, time to hatching varies substantially among species, independently of body size. One view, strongly supported by the work of Thomas Martin and his colleagues, maintains that this variation reflects parental strategies to minimize their own mortality risk at the nest—strategies that influence egg temperature and embryo growth rate. A second, not incompatible, view maintains that variation in the incubation period reflects a trade-off between the growth rate of the embryo and its subsequent quality as a free-living individual. We evaluate several lines of evidence relating nest attendance by adults and the quality of the immune system to the length of the incubation period. Particularly important is the role of sibling competition in selecting for rapid embryo growth and early hatching, and the fact that many species with prolonged incubation periods are raised either as single chic...

Is embryonic hypothermia tolerance common in birds?

Avian incubation temperatures oscillate within narrow limits to ensure proper embryonic development. However, field observations and experimental studies have found that some species can tolerate very low incubation temperatures, either regularly or occasionally. We artificially incubated eggs from five domestic species, which represent a range of egg sizes, to examine whether a diversity of avian species could exhibit an unusual hypothermia tolerance, as observed in the field. We found that eggs of the chicken (Gallus gallus domesticus), pigeon (Columba livia domestica), Japanese quail (Coturnix japonica) and budgerigar (Melopsittacus undulatus) survived the incubation period and hatched after experiencing 10°C hypothermia for 6 h each day. However, embryos of white-rumped munia (Lonchura striata) died after 10 days of hypothermia. Our results showed that unusual hypothermia tolerance occurs in several avian species. This phenomenon might have been selected through the evolutionary history of birds. Future research should identify the importance of phylogeny, egg size and embryonic stage in tolerance to hypothermia.

The effect of ambient temperature, habitat quality and individual age on incubation behaviour and incubation feeding in a socially monogamous songbird.

Incubation is an important aspect of avian life history. The behaviour is energetically costly, and investment in incubation strategies within species, like female nest attentiveness and the feeding by the non-incubating partner during incubation, can therefore vary depending on environmental and individual characteristics. However, little is known about the combined effect of these characteristics. We investigated the importance of ambient temperature, habitat quality, and bird age on female incubation behaviour and male feeding of the incubating female (incubation feeding) in blue tits Cyanistes caeruleus, a socially monogamous songbird. An increase in ambient temperature resulted in a higher nest temperature, and this enabled females to increase the time off the nest for self-maintenance activities. Probably as a consequence of this, an increase in ambient temperature was associated with fewer incubation feedings by the male. Moreover, in areas with more food available (more deciduous trees), females had shorter incubation recesses and males fed females less often. Additionally, males fed young females more, presumably to increase such females’ investment in their eggs, which were colder on average (despite the length of recesses and female nest attentiveness being independent of female age). Male age did not affect incubation feeding rate. In conclusion, the patterns of incubation behaviour were related to both environmental and individual characteristics, and male incubation feeding was adjusted to females’ need for food according these characteristics, which can facilitate new insights to the study of avian incubation energetics.Significance statementParents often invest a substantial amount of energy in raising offspring. How much they do so depends on several environmental factors and on the extent they cooperate to raise the offspring. In birds, males can feed incubating females, which may allow females to stay longer on the nest, which, in turn, may ultimately improve reproductive success. The interplay between environmental factors and such incubation feeding on incubation attendance has, however, received little attention. Here, we show that favourable circumstances (higher ambient temperature and food availability) allowed incubating blue tit females to increase the time off the nest to improve self-maintenance and males to feed them less, whereas males also fed inexperienced partners more often. Thus, we show a concerted effect of several environmental and intrinsic factors on parental effort during incubation, which will help to improve the general understanding of avian incubation and parental care.

Incubation Attentiveness and Nest Insulatory Values Correlate in Songbirds

The behaviour of the incubating bird should be linked with the functional characteristics of its nest because they could minimise the incubation period that will reduce the risk of predation. Incubation attentiveness (percentage of daylight hours) in small passerines is a highly variable behaviour that is unrelated to egg mass. The thermal characteristics of nests are known to vary but whether they correlate with attentiveness, i.e. high attentiveness could reflect poorly insulated nests, has yet to be investigated. In this study, insulatory values were determined using temperature loggers for five species of British songbird in order to supplement equivalent data for six species from published sources. Attentiveness values for each species were determined from the literature. There was a significant negative correlation between attentiveness and insulatory values, which was unaffected by phylogeny. By contrast, attentiveness did not correlate with female body mass. That the avian incubation behaviour correlates with the functional properties of bird nests supports the concept of a bird–nest incubation unit, where reproductive success depends on both the bird and the nest structure. Further research should be directed towards a better understanding of this relationship for more species and, given the observed plasticity exhibited in nest composition and function, within species.

Nest Surface Temperature Predicts Fledging Success of Blue TitsCyanistes caeruleusBut Not Great TitsParus major

Abstract. Studies investigating nest function in birds show that individual preferences and environmental temperature can affect the type and amount of materials used in their construction and, thus, how well insulated they are. Levels of insulation of bird nests may be important because this could impact on heat loss by adults and eggs during incubation, and by nestlings during rearing, which may in turn affect individual fitness. Here we used infrared (IR) thermography to measure the surface temperature of nests of Great Tits Parus major and Blue Tits Cyanistes caeruleus in situ during incubation to test the hypothesis that nest insulation predicts reproductive success. Previous studies of thermodynamics during incubation have focussed on factors, e.g. egg temperature, which do not directly measure the thermal conditions in the nest itself. Rarely applied to studies of avian incubation, IR thermography has yet to be used to quantify the thermal properties of nests with the incubating bird in situ. The r...

Effect of incubation on bacterial communities of eggshells in a temperate bird, the Eurasian Magpie (Pica pica).

Inhibitory effect of incubation on microbial growth has extensively been studied in wild bird populations using culture-based methods and conflicting results exist on whether incubation selectively affects the growth of microbes on the egg surface. In this study, we employed culture-independent methods, quantitative PCR and 16S rRNA gene pyrosequencing, to elucidate the effect of incubation on the bacterial abundance and bacterial community composition on the eggshells of the Eurasian Magpie (Pica pica). We found that total bacterial abundance increased and diversity decreased on incubated eggs while there were no changes on non-incubated eggs. Interestingly, Gram-positive Bacillus, which include mostly harmless species, became dominant and genus Pseudomonas, which include opportunistic avian egg pathogens, were significantly reduced after incubation. These results suggest that avian incubation in temperate regions may promote the growth of harmless (or benevolent) bacteria and suppress the growth of pathogenic bacterial taxa and consequently reduce the diversity of microbes on the egg surface. We hypothesize that this may occur due to difference in sensitivity to dehydration on the egg surface among microbes, combined with the introduction of Bacillus from bird feathers and due to the presence of antibiotics that certain bacteria produce.