Haemosporidian parasites of Neotropical birds: Causes and consequences of infection

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.

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

Synopsis Developmental 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.

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.

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.