Population monitoring and conservation implications of intra- and interspecific nest occupation rates in swallows.

With the exception of a few groups of birds, such as large raptors and colonial seabirds, direct counts of nests cannot be conducted over very large areas for most of the abundant and widely distributed species, and thus indirect methods are used to estimate their relative abundances and population sizes. However, many species of the Family Hirundinidae (swallows and martins) build their mud nests in discrete, predictable and accessible sites, which are reused across years. Therefore, the direct count of active nests could constitute a reliable method for estimating breeding population sizes and their changes at large spatial and temporal scales. We illustrate the feasibility of this monitoring approach through a single year survey of >2700 nests of three coexisting Old-World species, the barn swallow (Hirundo rustica), the red-rumped swallow (Cecropis daurica), and the crag martin (Ptyonoprogne rupestris), distributed across Portugal and Spain. Our results revealed changes in the use of nesting substrates and increases in interspecific nest usurpation rates over recent decades. While 56% of the nests of C. daurica were located in rocks five decades ago, almost 100% are nowadays located in anthropogenic substrates such as bridges, road culverts, and abandoned buildings, which could have favored the range expansion of this species. Nest occupation rates were surprisingly low (12% in C. daurica, 21% in H. rustica, and 37% in P. rupestris), and the proportion of abandoned nesting sites was very high (65% in C. daurica, 50% in H. rustica, and 27% in P. rupestris). Abandonment rates reflect the population decline reported for H. rustica. Notably, the usurpation of nests of C. daurica by house sparrows Passer domesticus, which is the main cause of breeding failure, has increased from 2.4% in 1976-1979 to 34.7% of the nests nowadays. The long-term monitoring of nests may constitute a reliable and affordable method, with the help of citizen science, for assessing changes in breeding population sizes and conservation threats of these and other mud-nest building hirundines worldwide.

Rainfall decrease and red deer rutting behaviour: Weaker and delayed rutting activity though higher opportunity for sexual selection.

In the last decades, climate change has caused an increase in mean temperatures and a reduction in average rainfall in southern Europe, which is expected to reduce resource availability for herbivores. Resource availability can influence animals' physical condition and population growth. However, much less is known on its effects on reproductive performance and sexual selection. In this study, we assessed the impact of three environmental factors related to climate change (rainfall, temperature and vegetation index) on Iberian red deer Cervus elaphus hispanicus reproductive timing and sexual behaviour, and their effects on the opportunity for sexual selection in the population. We measured rutting phenology as rut peak date, the intensity of male rutting activity as roaring rate, and the opportunity for sexual selection from the distribution of females among harem holding males in Doñana Biological Reserve (Southwest Spain), from data of daily observations collected during the rut over a period of 25 years. For this study period, we found a trend for less raining and hence poorer environmental conditions, which associated with delayed rutting season and decreased rutting intensity, but that appeared to favour a higher degree of polygyny and opportunity for sexual selection, all these relationships being modulated by population density and sex ratio. This study highlights how climate change (mainly rainfall reduction in this area) can alter the conditions for mating and the opportunity for sexual selection in a large terrestrial mammal.

Social environment modulates investment in sex trait versus lifespan: red deer produce bigger antlers when facing more rivalry.

Theory predicts that the plastic expression of sex-traits should be modulated not only by their production costs but also by the benefits derived from the presence of rivals and mates, yet there is a paucity of evidence for an adaptive response of sex-trait expression to social environment. We studied antler size, a costly and plastic sex trait, and tooth wear, a trait related to food intake and longevity, in over 4,000 male Iberian red deer (Cervus elaphus hispanicus) from 56 wild populations characterized by two contrasting management practices that affect male age structure and adult sex-ratio. As a consequence, these populations exhibit high and low levels of male-male competition for mating opportunities. We hypothesized that males under conditions of low intra-sexual competition would develop smaller antlers, after controlling for body size and age, than males under conditions of high intra-sexual competition, thus reducing energy demands (i.e. reducing intake and food comminution), and as a consequence, leading to less tooth wear and a concomitant longer potential lifespan. Our results supported these predictions. To reject possible uncontrolled factors that may have occurred in the wild populations, we carried out an experimental design on red deer in captivity, placing males in separate plots with females or with rival males during the period of antler growth. Males living with rivals grew larger antlers than males living in a female environment, which corroborates the results found in the wild populations. As far as we know, these results show, for the first time, the modulation of a sexual trait and its costs on longevity conditional upon the level of intra-sexual competition.

Disposable-soma senescence mediated by sexual selection in an ungulate.

Senescence may result from an optimal balance between current reproductive investment and bodily repair processes required for future reproduction, a theoretical prediction difficult to prove especially in large, long-lived animals. Here we propose that teeth that have fixed dimensions early in life, but that wear during chewing, can be taken as a measure of total lifetime 'repair', and their wear rate as a measure of current expenditure in performance. Our approach also considers the sexual selection process to investigate the advance of senescence in males compared with females, when selection favouring competition over mates reduces the reproductive lifespan of males. We studied carcasses of 2,141 male and 739 female red deer (Cervus elaphus) of different ages, finding that male molariform teeth emerged at a far smaller size than expected from body size dimorphism. This led to higher workload, steeper wear rate and earlier depletion of male teeth than in females, in concordance with sex-specific patterns of lifetime performance and reproduction. These findings provide the empirical support for the disposable-soma hypothesis of senescence, which predicts that investment in bodily repair will decrease when the return from this investment may not be realized as a result of other causes that limit survival or reproduction.