Does urbanization cause stress in wild birds during development? Insights from feather corticosterone levels in juvenile house sparrows (Passer domesticus)

Urban landscapes are associated with abiotic and biotic environmental changes that may result in potential stressors for wild vertebrates. Urban exploiters have physiological, morphological, and behavioral adaptations to live in cities. However, there is increasing evidence that urban exploiters themselves can suffer from urban conditions, especially during specific life‐history stages. We looked for a link between the degree of urbanization and the level of developmental stress in an urban exploiter (the house sparrow, Passer domesticus), which has recently been declining in multiple European cities (e.g., London, UK). Specifically, we conducted a large‐scale study and sampled juvenile sparrows in 11 urban and rural sites to evaluate their feather corticosterone (CORT) levels. We found that juvenile feather CORT levels were positively correlated with the degree of urbanization, supporting the idea that developing house sparrows may suffer from urban environmental conditions. However, we did not find any correlation between juvenile feather CORT levels and body size, mass, or body condition. This suggests either that the growth and condition of urban sparrows are not impacted by elevated developmental CORT levels, or that urban sparrows may compensate for developmental constraints once they have left the nest. Although feather CORT levels were not correlated with baseline CORT levels, we found that feather CORT levels were slightly and positively correlated with the CORT stress response in juveniles. This suggests that urban developmental conditions may potentially have long‐lasting effects on stress physiology and stress sensitivity in this urban exploiter.     

Biparental care in house sparrows: negotiation or sealed bid?

We explored the responses of monogamous house sparrow parentsto deviations in their mates' contributions to nestling provisioning.Following 1-2 days of baseline measurement of parental fooddelivery rates, we applied small lead fishing weights to thetail feathers of either male or female parents. Weighting hadmuch greater immediate impact on male parental care than on female care, but the handicapping had little long-term effecton either male or female provisioning behavior. When parentalperformance of handicapped males was most impaired, their matesdid not show significant increases in parental care as compensation,nor did females mated to handicapped males reduce their provisioningas their mates recovered from weighting. Similarly, males matedto handicapped females did not respond to their partners' recovery with declines in their own efforts; paradoxically, these malesshowed a sustained elevation of provisioning throughout thepost-treatment interval, despite no significant reduction inprovisioning by weighted females. The apparent insensitivityof both males and females to changes in their mates' parentalbehavior, and the ineffectiveness of current partner behaviorat predicting an individual's provisioning effort, fail toconform to assumptions of biparental care models that requirefacultative responses to partner deviations in effort. Instead,the remarkable consistency of each individual's behavior supportsthe notion of "sealed bids" and suggests that variation innestling provisioning is largely attributable to factors thatare independent of the mate's current behavior, such as differencesin individual quality.     

Does the badge of status influence parental care and investment in house sparrows? An experimental test

Theory predicts that traits which signal parental quality might evolve in males of species with biparental care. In avian species, male ornaments may be the most likely candidates for such signals. Male house sparrows (Passer domesticus) possess a black throat patch often referred to as a “badge” or a “badge of status”. By assuming a trade-off between male attractiveness (reflected in male ornaments) and parental care under the differential allocation hypothesis, we predicted that badge size would be negatively correlated with male parental investment. An experiment in which the badge was enlarged in one group and unchanged in a control group was conducted. Our manipulation was predicted to affect female as well as male parental investment. However, we found that eight variables associated with parental investment—the start date for breeding, clutch size, male and female incubation time, male and female food provisioning rate, and average chick weight and the number of fledglings—barely differed between treatments. Also, little evidence for correlations between natural variation in badge size and any of these eight variables was found. Instead, the start date for breeding and the number of fledglings were significantly correlated with both male and female age, while clutch size increased with female age. Female condition was a positive predictor of clutch size and number of fledglings. Female tarsus length, unexpectedly, is related to both male and female incubation time. Badge size was also positively correlated with male age. However, parental age (male or female) was not related to parental care. We conclude that badge size does not signal parental quality, but that the ages of both sexes and the condition of the female play significant roles in the reproductive performance of this species.     

Does multiple infection select for raised virulence?

Classical models of virulence evolution conclude that the increased competition favoured by multiple infection will select for increasing consumption and deterioration of the host resource, or 'virulence'. However, recent empirical and theoretical studies suggest that this view of virulence has some shortcomings. Here, we argue that the evolutionary consequences of multiple infection depend critically on whether the exploitation rate of an individual parasite is governed directly by the behaviour of the individual, or whether it is limited by the collective behaviour of the coinfecting group. We illustrate that, depending on the mechanistic details of exploitation, multiple infection can select for reduced virulence.     

What do mice select for in seeds?

Summary Knowledge of the basis upon which granivores select seeds is crucial to the understanding of granivory. In this study the preferences of three rodent granivores among seeds of 11 plants from the semi-arid Karoo of South Africa were estimated, and related to the physical and chemical attributes of the seeds. Seed weights and calorific, moisture, protein, polyphenol, ash, lipid and silica contents were estimated and cell contents, soluble ash and soluble carbohydrate contents were derived from these values. These attributes were determined for both the intact seeds and the portion of the seed that is ingested by the mice. The efficiency with which mice ingested the seeds (in terms of time and mass) was recorded. All three mouse species ranked the seeds similarly, and the two species for which handling efficiency was measured did not differ in this regard. Preference hierachies were highly correlated with the rate of energy intake, as predicted by optimal foraging theory. There was no correlation between rodent preferences and the gross energy content of the seeds, emphasising the importance of measuring relevant parameters. The energy yield of the seeds calculated here, in conjunction with rodent population energy requirements and dietary data, may be used to estimate potential granivore impact on the seed production of the plant community.     

Does fluctuating asymmetry constitute a sensitive biomarker of nutritional stress in house sparrows (Passer domesticus)?

Small random deviations from left–right symmetry in bilateral traits, termed fluctuating asymmetry (FA), are theoretically predicted to increase with environmental stress and believed to constitute a potential biomarker in conservation. However, reported relationships between FA and stress are generally weak and variable among organisms, traits and stresses. Here we test if, and to what extent, FA increases with nutritional stress, estimated from independent feather growth measurements, in free-ranging house sparrows (Passer domesticus). Ptilochronological feather marks showed significant heterogeneity among study plots, indicating that house sparrow populations were exposed to variable levels of nutritional stress during development. However, individuals from more stressed populations did not show increased levels of fluctuating asymmetry in tarsus or rectrix length, nor was there evidence for significant between-trait concordance in FA at the individual or the population level. Lack of support for FA in tarsus and rectrix length as estimator of nutritional stress in house sparrows may indicate that developmental instability is insensitive to nutritional stress in this species, poorly reflected in patterns of fluctuating asymmetry due to ecological or statistical reasons, or highly context-specific. Such uncertainty continues to hamper the use of FA as a biomarker tool in conservation planning.     

Can house sparrows recognize familiar or kin-related individuals by scent?

In the last decades, higher attention has been paid to olfactory perception in birds. As a consequence, a handful of avian species have been discovered to use olfaction in different contexts. Nevertheless, we still have a very limited knowledge about the use of odor cues in avian social life, particularly, in the case of songbirds. Here, we investigate if female house sparrows Passer domesticus show any preference for the odor of kin and nonkin conspecifics and we also test a possible role of familiarity based on male see nt in female choice. We performed the experiment with captive birds twice, duri ng the non breeding and breedi ng seas ons. Our results show that female house sparrows strongly avoided the odor of unrelated familiar (UF) males, both in the breeding and nonbreeding seasons. Our results suggest recognition for olfactory stimuli related to familiarity and kin ship. We suggest that avoidance for UF males is associated with previous experie nee in this species. Also, we provided further evidenee to the use of olfaction in passerine species by using a new experimental setup.     

Infanticide by male house sparrows: gaining time or manipulating females?

The killing of genetically unrelated young by males has been viewed as a strategy that forces victimized females to advance the onset of their next fertile period, thus infanticidal males gain a time advantage that may be crucial to maximize reproductive success. Among females that may raise several broods in a year, a failure occurring relatively earlier in the time-course of the previous breeding attempt may result in an increased investment in the next breeding attempt. This female strategy may be exploited by males in their own interest, and may strongly select for male infanticidal behaviour. I demonstrate that, in the house sparrow, females mated with infanticidal males re-laid earlier, initiated more breeding attempts and fledged more offspring than females mated with non-infanticidal males. These results suggest that both the time saving and the manipulation of female investment are independent mechanisms conferring advantages that may have selected for male infanticide in the studied population.     

Does 8-Azaguanine induce or select for chromosome number instability in human cell hybrids?

Segregant clones resistant to 8-Azaguanine (8AG) obtained from hybrids between clonal derivatives of the EUE line were analysed for chromosome number distribution. In almost all cases the 8AG^R clones show chromosome losses and a greater variability in chromosome numbers than that of the parental hybrids and their non-selected subclones. A study of the karyotypic evolution of 8AG^R segregant clones maintained for a prolonged period either in 8AG or in drug-free medium did not reveal any correlation between chromosome variability and the presence of 8AG. The preadaptive nature of the segregation to 8AG resistance is also indicated by the results of a fluctuation test.     

Does predation select for or against avian coloniality? A comparative analysis

Some studies have supported predation as a selective pressure contributing to the evolution of coloniality. However, evidence also exists that colonies attract predators, selecting against colonial breeding. Using comparative analyses, we tested the reduced predation hypothesis that individuals aggregate into colonies for protection, and the opposite hypothesis, that breeding aggregations increase predation risk. We used locational and physical characteristics of nests to estimate levels of species' vulnerability to predation. We analysed the Ciconiiformes, a large avian order with the highest prevalence of coloniality, using Pagel's general method of comparative analysis for discrete variables. A common requirement of both hypotheses, that there is correlated evolution between coloniality and vulnerability to predation, was fulfilled in our data set of 363 species. The main predictions of the reduced predation hypothesis were not supported, namely that (1) solitary/vulnerable species are more prone to become colonial than solitary/protected species and (2) colonial/protected species are more likely to evolve towards vulnerability than solitary/protected species. In contrast, the main predictions of the increased predation hypothesis were supported, namely that colonial/vulnerable species are more prone (1) to become protected than solitary/vulnerable species and/or (2) to become solitary than colonial/protected species. This suggests that the colonial/vulnerable state is especially exposed to predation as coloniality may often attract predators rather than provide safety.     

Does urbanization decrease diversity in ground beetle (Carabidae) assemblages?

Aim We wanted to test whether urbanization has similar effects on biodiversity in different locations, comparing the responses of ground beetle (Coleoptera, Carabidae) assemblages with an urbanization gradient. We also wanted to see if urbanization had a homogenizing effect on ground beetle assemblages. Locations Nine forested temperate locations in Europe, Canada and Japan. Methods Published results of the Globenet Project were used. At all locations, three stages were identified: (1) a forested (rural) area, (2) a suburban area where the original forest was fragmented and isolated, and (3) remnants of the original forest in urban parks. These habitats formed an urbanization series. Study arrangements (number and operation of traps) and methods (pitfall trapping) were identical, conforming to the Globenet protocol. Assemblage composition and diversity patterns were evaluated. Diversity relationships were analysed by the Rényi diversity ordering method considering all ground beetles and – separately – the forest specialist species. Taxonomic homogenization was examined by multivariate methods using assemblage similarities. Results Overall biodiversity (compared by species richness and diversity ordering) showed inconsistent trends by either urbanization intensity or by geographic position. However, when only forest species were compared, diversity was higher in the original rural (forested) areas than in urban forest fragments. Within‐country similarities of carabid assemblages were always higher than within‐urbanization stage similarities. Main conclusions Urbanization does not appear to cause a decrease in ground beetle diversity per se. Forest species decline as urbanization intensifies but this trend is masked by an influx of non‐forest species. The rural faunas were more similar to the urban ones within the same location than similar urbanization stages were to each other, indicating that urbanization did not homogenize the taxonomic composition of ground beetle faunas across the studied locations.     

Does urbanization ameliorate the effect of endoparasite infection in kangaroo rats?

Urban development can fragment and degrade remnant habitat. Such habitat alterations can have profound impacts on wildlife, including effects on population density, parasite infection status, parasite prevalence, and body condition. We investigated the influence of urbanization on populations of Merriam''s kangaroo rat (Dipodomys merriami) and their parasites. We predicted that urban development would lead to reduced abundance, increased parasite prevalence in urban populations, increased probability of parasite infection for individual animals, and decreased body condition of kangaroo rats in urban versus wildland areas. We live trapped kangaroo rats at 5 urban and 5 wildland sites in and around Las Cruces, NM, USA from 2013 to 2015, collected fecal samples from 209 kangaroo rats, and detected endoparasites using fecal flotation and molecular barcoding. Seven parasite species were detected, although only two parasitic worms, Mastophorus dipodomis and Pterygodermatites dipodomis, occurred frequently enough to allow for statistical analysis. We found no effects of urbanization on population density or probability of parasite infection. However, wildland animals infected with P. dipodomis had lower body condition scores than infected animals in urban areas or uninfected animals in either habitat. Our results suggest that urban environments may buffer Merriam''s kangaroo rats from the detrimental impacts to body condition that P. dipodomis infections can cause.     

Whom do the sparrows follow? The effect of kinship on social preference in house sparrow flocks

Non-aggressive social interactions between group-mates, e.g. maintenance of spatial proximity or activity synchrony are basic elements of a species’ social structure, and were found to be associated with important fitness consequences in group-living animals. In the establishment of such affiliative relationships, kinship has often been identified as one of the key predictors, but this has rarely been studied in simple social groups such as flocks of gregarious birds. In this study we investigated whether kinship affects social preference, as measured by the tendency to associate with others during various social activities, in captive house sparrow (Passer domesticus) flocks where birds could interact with differently related flock-mates. We found that preference between flock-mates was correlated with familiarity from early nestling period: same-brood siblings followed their sib initiating new activities more often than non-sib birds. The strength of association between birds also tended to correlate with genetic relatedness, but this was mainly due to the effect of siblings’ affiliation. Thus we concluded that house sparrows prefer the company of their siblings during social activities even well after fledging, which may facilitate kin-biased behaviours.     

Hybrid speciation in sparrows II: a role for sex chromosomes?

Homoploid hybrid speciation in animals is poorly understood, mainly because of the scarcity of well‐documented cases. Here, we present the results of a multilocus sequence analysis on the house sparrow (Passer domesticus), Spanish sparrow (P. hispaniolensis) and their proposed hybrid descendant, the Italian sparrow (P. italiae). The Italian sparrow is shown to be genetically intermediate between the house sparrow and Spanish sparrow, exhibiting genealogical discordance and a mosaic pattern of alleles derived from either of the putative parental species. The average variation on the Z chromosome was significantly reduced compared with autosomal variation in the putative parental species, the house sparrow and Spanish sparrow. Additionally, divergence between the two species was elevated on the Z chromosome relative to the autosomes. This pattern of variation and divergence is consistent with reduced introgression of Z‐linked genes and/or a faster‐Z effect (increased rate of adaptive divergence on the Z). F_ST‐outlier tests were consistent with the faster‐Z hypothesis: two of five Z‐linked loci (CHD1Z and PLAA) were identified as candidates for being subject to positive, divergent selection in the putative parental species. Interestingly, the two latter genes showed a mosaic pattern in the (hybrid) Italian sparrow; that is, the Italian sparrow was found to be fixed for Spanish sparrow alleles at CHD1Z and to mainly have house sparrow alleles at PLAA. Preliminary evidence presented in this study thus suggests that sex chromosomes may play a significant role in this case of homoploid hybrid speciation.     

Can experienced birds select for Mullerian mimicry?

Field experiments have shown that avian predators in the wildcan select for similarity of warning signals in aposematic prey(Müllerian mimicry) because a common signal is better protectedthan a signal that is novel and rare. The original theory ofMüllerian mimicry assumes that the mechanism promotingmimicry is predator learning; by sharing a signal, the comimicspecies share the mortality that is due to sampling by inexperiencedpredators. Predation events have not been observed in the wild,and learning experiments with naive bird predators in a laboratoryhave not unambiguously shown a benefit of a uniform signal comparedwith different signals. As predators in the field experimentsare likely to be more experienced compared with previous laboratoryexperiments, we studied selection by experienced predators ona novel imperfect mimic. We trained great tits Parus major toavoid artificial aposematic models and subsequently introducedperfect and imperfect mimics at different frequencies. Birdswith prior experience on the models selected against the imperfectmimics that were at a disadvantage also in a memory test conducteda week after their introduction. Selection against the imperfectmimics was antiapostatic. However, the imperfect mimics alsobenefited from some signal generalization to the models andpossibly gained protection because the birds were familiar withthe alternative cryptic prey that was also present. Our resultssuggest that experienced predators might be more important tothe evolution of mimicry than the learning-based theory assumes.     

Does the house mouse self-regulate its density in maturing sorghum and wheat crops?

1. One of the central questions in population ecology and management is: what regulates population growth? House mouse Mus domesticus L. populations erupt occasionally in grain-growing regions in Australia. This study aimed to determine whether mouse populations are self-regulated in maturing sorghum and wheat crops. This was assessed by examining food supply to mice (i.e. yield) and the relationship between initial mouse density (D(I)) and density at harvest (D(H)). Eight levels of D(I) ranging from 89 to 5555 mice ha(-1) were introduced to sorghum at the hard dough stage and to wheat crops at the milky stage in mouse-proofed pens. D(H) was measured by trapping out mice 49 days after the introduction. 2. There were at least 3.11 tonnes ha(-1) of wheat and 1.85 tonnes ha(-1) of sorghum grain available for mice at harvest. The estimated relationship between D(I) and D(H) was asymptotic exponential, with D(H) initially increasing almost linearly with D(I). When D(I) was above c. 500 mice ha(-1), D(H) increased asymptotically with D(I) and then saturated at c. 3100 mice ha(-1). The asymptotic increases in and saturation of D(H) was due partly to more young mice being born and recruited in pens treated with lower levels of D(I). 3. Our findings indicated that mouse densities in maturing cereal crops were driven by a numerical response of mice to the abundant supply of grain, modified by some unknown self-regulation mechanism that reduced this numerical response of mice at higher mouse densities. The mechanism was possibly spacing behaviours. Although the nature of this self-regulation mechanism is not known our model is, nevertheless, useful for predicting increases and eruptions in mouse population density in sorghum and wheat crops. Understanding the nature of this mechanism may provide insights into population processes that can be exploited in controlling mice in cereal crops.