Female House Sparrows Research Articles

Immune gene expression and epigenetic potential affect the consumption of risky food by female house sparrows

When organisms move into new areas, they are likely to encounter novel food resources. Even if they are nutritious, these foods can also be risky, as they might be contaminated by parasites. The behavioural immune system of animals could help them avoid the negative effects of contaminated resources, but our understanding of behavioural immunity is limited, particularly whether and how behavioural immunity interacts with physiological immunity. Here, we asked about the potential for interplay between these two traits, specifically how the propensity of an individual house sparrow (Passer domesticus) to take foraging risks was related to its ability to regulate a key facet of its immune response to bacterial pathogens. Previously, we found that sparrows at expanding geographic range edges were more exploratory and less risk-averse to novel foods; in those same populations, birds tended to over-express Toll-like receptor 4 (TLR4), a pattern-recognition receptor that distinguishes cell-wall components of Gram-negative bacteria, making it the major sensor of potentially lethal gut microbial infections including salmonellosis. When we investigated how birds would respond to a typical diet (i.e., mixed seeds) spiked with domesticated chicken faeces, birds that expressed more TLR4 or had higher epigenetic potential for TLR4 (more CpG dinucleotides in the putative gene promoter) ate more food, spiked or not. Females expressing abundant TLR4 were also willing to take more foraging risks and ate more spiked food. In males, TLR4 expression was not associated with risk-taking. Altogether, our results indicate that behaviour and immunity covary among individual house sparrows, particularly in females where those birds that maintain more immune surveillance also are more disposed to take foraging risks.

Effect of estradiol and predator cues on behavior and brain responses of captive female house sparrows (Passer domesticus).

The presence of predators can cause major changes in animal behavior, but how this interacts with hormonal state and brain activity is poorly understood. We gave female house sparrows (Passer domesticus) in post-molt condition an estradiol (n = 17) or empty implant (n = 16) for 1week. Four weeks after implant removal, a time when female sparrows show large differences in neuronal activity to conspecific vs. heterospecific song, we exposed birds to either 30min of conspecific song or predator calls, and video recorded their behavior. Females were then euthanized, and we examined neuronal activity using the expression of the immediate early gene (IEG) ZENK to identify how the acoustic stimuli affected neuronal activation. We predicted that if female sparrows with estradiol implants reduce neuronal activity in response to predator calls as they do to neutral tones and non-predatory heterospecifics, they would show less fear behavior and a decreased ZENK response in brain regions involved in auditory (e.g., caudomedial mesopallium) and threat perception functions (e.g., medial ventral arcopallium) compared to controls. Conversely, we predicted that if females maintain auditory and/or brain sensitivity towards predator calls, then female sparrows exposed to estradiol would not show any differences in ZENK response regardless of playback type. We found that female sparrows were less active during predator playbacks independent of hormone treatment and spent more time feeding during conspecific playback if they had previously been exposed to estradiol. We observed no effect of hormone or sound treatment on ZENK response in any region of interest. Our results suggest that female songbirds maintain vigilance towards predators even when in breeding condition.

Experimental evidence for clothianidin deposition in feathers of house sparrows after ingestion of sublethal doses treated seeds.

Bird feathers are commonly used to assess environmental contamination by chemical pollutants. However, although neonicotinoid insecticides are widely applied worldwide, feathers have rarely been used to survey the contamination by neonicotinoids in birds. To investigate whether clothianidin, one compound of the neonicotinoid class, is deposited into birds’ feathers, we conducted an experiment with 56 wild male and female house sparrows dispatched in 7 aviaries. During this experiment, house sparrows were fed with certified organic seeds treated with clothianidin at an estimated concentration of 0.25 μg/g BW per day and per individual. We collected blood samples and plucked four tail feathers at the onset of the experiment to confirm that no birds were previously exposed to clothianidin. 35 days later, we collected blood samples and the newly grown feathers. Before exposure, a small number of birds showed very low clothianidin concentrations in plasma and feathers. After exposure, the plasma and the newly grown feathers of all birds contained clothianidin. Clothianidin concentrations in feathers were similar in both sexes, but the plasma of males contained clothianidin at higher concentrations than that of females. Our results confirm that ingested clothianidin transits in the plasma and is deposited in feathers during their growth. They also suggest substantial individual variation in the amounts of clothianidin transiting in the plasma and being deposited in feathers that may reflect variation in metabolism and/or access to food in relation to sex, social hierarchy and group dynamics. Whether increasing levels of exposure translate linearly or non-linearly (e.g. saturation process) into increasing clothianidin concentrations in bird plasma and feathers remains to be investigated. To conclude, these results confirm the relevance of using feathers to biomonitor the presence of neonicotinoids, but the relationship between the level of exposure and the concentrations found in feathers remains to be established.

House sparrows do not exhibit a preference for the scent of potential partners with different MHC-I diversity and genetic distances.

MHC genes play a fundamental role in immune recognition of pathogens and parasites. Therefore, females may increase offspring heterozygosity and genetic diversity by selecting males with genetically compatible or heterozygous MHC. In birds, several studies suggest that MHC genes play a role in mate choice, and recent evidence suggests that olfaction may play a role in the MHC-II discrimination. However, whether olfaction is involved in MHC-I discrimination in birds remains unknown. Previous studies indicate that house sparrow females with low allelic diversity prefer males with higher diversity in MHC-I alleles. Here, we directly explored whether female and male house sparrows (Passer domesticus) could estimate by scent MHC-I diversity and/or dissimilarity of potential partners. Our results show that neither females nor males exhibit a preference related to MHC-I diversity or dissimilarity of potential partners, suggesting that MHC-I is not detected through olfaction. Further studies are needed to understand the mechanisms responsible for mate discrimination based on MHC-I in birds.

Mate choice is affected by parasite infestation rate of the choosing individual as well as of potential mating partners.

Parasites are known to be a key driving force in mate choice and are important for the expression and evolution of ornaments and behavioral traits being used. However, there is little experimental evidence on how the parasite's burden of the choosing individual is integrated into the mate-choice process and how it affects decision-making, especially in relation to parasite infestation of potential mates. Thus, the aim of our study was to determine whether female house sparrows Passer domesticus adjust their mate preference according to their own as well as the parasite load of prospective partners. To do this, we experimentally manipulated female parasite load and determined their mate preferences prior to and after parasite treatment. We manipulated the chronic coccidian parasite burden of females either by initiating the acute infection phase via re-infecting them with coccidian or by temporally reducing the parasite load of coccidia. We then measured the effect of this manipulation on mate preference by presenting females with a choice of four stimuli: three males with similar ornaments, but unmanipulated, naturally varying chronic coccidiosis levels, and an unmanipulated control female. Additionally, we recorded some males' behavior in relation to their infection status pointing toward an increased or reduced interest in mating. We found that females preferred highly infested males prior to manipulation, regardless of their own infestation level. However, after manipulation, infested females avoided highly infested males probably in response to the deterioration of their health condition by parasites. Our study suggests that mate-choice decisions are more complex when they are mediated by parasites. The implications of parasites for evolutionary theories of sexual signaling and mate choice are discussed.

Estradiol and Predator Cues Affect Behavior and Brain Responses of Captive Female House Sparrows (Passer Domesticus)

Estradiol and Predator Cues Affect Behavior and Brain Responses of Captive Female House Sparrows (Passer Domesticus)

FKBP5 expression is related to HPA flexibility and the capacity to cope with stressors in female and male house sparrows

The hypothalamic-pituitary-adrenal (HPA) axis and its end products, the glucocorticoids, are critical to responding appropriately to stressors. Subsequently, many studies have sought relationships between glucocorticoids and measures of health or fitness, but such relationships are at best highly context dependent. Recently, some endocrinologists have started to suggest that a focus on HPA flexibility, the ability of an individual to mount appropriate responses to different stressors, could be useful. Here, we tested the hypothesis that expression of FKBP5, a cochaperone in the glucocorticoid receptor complex, is a simple and reliable proxy of HPA flexibility in a wild songbird, the house sparrow (Passer domesticus). We quantified HPA flexibility in a novel way, using guidance from research on heart rhythm regulation. As predicted, we found that adult sparrows with low stress-induced FKBP5 expression in the hypothalamus exhibited high HPA flexibility. Moreover, low FKBP5 expression was associated with greater exploratory disposition and were better at maintaining body mass under stressful conditions. Altogether, these results suggest that FKBP5 may be important in the regulation of HPA flexibility, potentially affecting how individuals cope with natural and anthropogenic adversity.

On the meat scavenging behavior of House Sparrows (Passer domesticus)

Behavioral plasticity can drive feeding innovations, a frequent trait of urban exploiter species. The House Sparrow (Passer domesticus) is a widespread and abundant urban dweller whose success has often been related to its dietary breadth. Although both formal and informal sources (e.g., internet videos, news, and blogs) have shown meat scavenging behaviors of this sparrow, it has been overlooked in the literature. While it is recognized that this sparrow has a diverse diet in urban settings, quantitative sources report only 3 types of foods (i.e., seeds, plant origin, and invertebrates). Our field observation of a female House Sparrow feeding on a chicken “drumstick” (presumably fibula/tibia) leftover at a greenspace of Manhattan (i.e., High Line), USA, adds to the available formal and informal information regarding the opportunistic scavenging of dressed and cooked meat by these sparrows when available. Thus, our observation adds to the feeding plasticity knowledge of this urban-related invasive bird and suggests the importance of the role of pedestrians in molding House Sparrow diet.

Captivity alters neuroendocrine regulators of stress and reproduction in the hypothalamus in response to acute stress

Wild animals are brought into captivity for many reasons. However, unlike laboratory-bred animals, wild caught animals often respond to the dramatic shift in their environment with physiological changes in the stress and reproductive pathways. Using wild-caught male and female house sparrows (Passer domesticus) we examined how time in captivity affects the expression of reproductive and stress-associated genes in the brain, specifically, the hypothalamus. We quantified relative mRNA expression of a neurohormone involved in the stress response (corticotropin releasing hormone [CRH]), a hypothalamic inhibitor of reproduction (gonadotropin inhibitory hormone [GnIH]), and the glucocorticoid receptor (GR), which is important in terminating the stress response. To understand potential shifts at the cellular level, we also examined the presence of hypothalamic GnIH (GnIH-ir) using immunohistochemistry. We hypothesized that expression of these genes and the abundance of cells immunoreactive for GnIH would change in response to time in captivity as compared to free-living individuals. We found that GR mRNA expression and GnIH-ir cell abundance increased after 24 and 45 days in captivity, as compared to wild-caught birds. At 66 days in captivity, GR expression and GnIH cell abundance did not differ from wild-caught birds, suggesting birds had acclimated to captivity. Evaluation of CRH and GnIH mRNA expression yielded similar trends, though they were not statistically significant. In addition, although neuroendocrine factors appeared to acclimate to captivity, a previous study indicated that corticosterone release and immune responses of these same birds did not acclimate to captivity, suggesting that neuroendocrine endpoints may adapt more rapidly to captivity than downstream physiological measures. These data expand our understanding of the physiological shifts occurring when wild animals are brought into captivity.

Male and female House Sparrow <i>Passer domesticus</i>, on Tamana-shi, Kumamoto Prefecture — the first record for Kyushu, Japan

Male and female House Sparrow <i>Passer domesticus</i>, on Tamana-shi, Kumamoto Prefecture — the first record for Kyushu, Japan

Developmental programming of the adrenocortical stress response by yolk testosterone depends on sex and life history stage.

Developmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus-pituitary-adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific and life history stage-dependent manner. Compared with controls, males from testosterone-treated eggs had higher baseline corticosterone levels, whereas females from testosterone-treated eggs showed prolonged stress-induced corticosterone secretion during the reproductive but not the non-reproductive phase. Adult RMR was unaffected by in ovo testosterone treatment but correlated with integrated corticosterone stress secretion levels. We conclude that exposure of the embryo to testosterone programs the hypothalamus-pituitary-adrenal axis in a sex-specific manner that in females depends, in expression, on reproductive state. The modified baseline corticosterone levels in males and stress-induced corticosterone levels in females may explain some of the long-lasting effects of maternal testosterone in the egg on behavior and could be linked to previously observed reduced mortality of testosterone-treated females.

House sparrow uropygial gland secretions do not attract ornithophilic nor mammophilic mosquitoes.

Mosquito feeding preferences determine host-vector contact rates and represent a key factor in the transmission of vector-borne pathogens. The semiochemical compounds of which vertebrate odours are composed probably play a role in mosquito host choice. Birds spread secretions from uropygial gland over their feathers to protect their plumage, comprising behaviour that may in turn affect odour profiles. Although uropygial secretions are expected to modify the attractiveness of birds to mosquitoes, contradictory findings have been reported. Mosquito species differ in their feeding preferences, with some species feeding mainly on birds (ornithophilic species) and others on mammals (mammophilic species). Consequently, it is possible that ornithophilic and mammophilic species differ in their response to uropygial gland secretions. Using a dual-choice olfactometer, the present study tests this hypothesis by comparing the behavioural response to uropygial gland secretions from juvenile male and female house sparrows (Passer domesticus) in the ornithophilic Culex pipiens and the mammophilic Aedes (Ochlerotatus) caspius mosquitoes. No differences were found in the response of either mosquito species to the uropygial gland secretions. Therefore, the preference of ornithophilic mosquitoes for avian hosts is apparently not explained by a greater attraction of mosquitoes to the uropygial gland secretion odour when presented in combination with a CO2 -enriched airflow.

Post-natal glucocorticoid elevation affects GnRH-induced luteinizing hormone concentration in female house sparrows

Most non-mammalian studies investigating the long-term effects of early-life stressor exposure on endocrine regulation have focused on the hypothalamic-pituitaryadrenal (HPA) axis. However, the hypothalamic-pituitary-gonadal (HPG) axis may more directly affect fitness by regulating reproduction. Changes in HPG axis regulation could allow vertebrates to adaptively mitigate negative effects of early-life stressor exposure. However, only a few studies have examined long-term effects of early-life stressor experience on the HPG axis, and these have found mixed results. Here, we evaluate long-term effects of post-natal corticosterone exposure on the HPG axis in adult female house sparrows (Passer domesticus). We elevated circulating corticosterone non-invasively in wild nestling house sparrows between 8 and 11 days post-hatching, and then brought birds into captivity at fledging. Early in their first breeding season (ages 285-353d post-hatching), females were given a gonadotropin releasing hormone (GnRH) challenge. We found that early-life corticosterone exposure interacted with current condition such that females exposed to elevated post-natal corticosterone had higher baseline and GnRH-induced luteinizing hormone (LH) concentration than control females, but only if they had a high mass. Our results suggest that female house sparrows may mitigate negative impacts of early-life corticosterone exposure by investing in early reproduction, but only when current energetic condition allows.

House sparrows\u2019 (Passer domesticus) behaviour in a novel environment is modulated by social context and familiarity in a sex-specific manner

BackgroundExploratory behaviour is one of the best-investigated behavioural traits. However, little is known about how differences in familiarity, i.e. in the knowledge and previous experience with a companion can influence the exploration of a novel environment. However, to our knowledge, such a critical feature of the social environment has never been the target of a study relating it to exploratory behaviour in birds. Here we examined if familiarity with a conspecific could affect behavioural responses of individuals confronted with a novel environment. We recorded the latency to land on the ground, latency to feed, time spent feeding and number of sectors visited of 48 female and 48 male house sparrows (Passer domesticus) in an indoor aviary in three contexts: alone (individual context), with an unfamiliar and with a familiar same-sex companion.ResultsHouse sparrows landed sooner on the ground when in the familiar context than when in the individual context. Birds in unfamiliar pairs followed each other less than familiar birds, but this difference diminished with time spent exploring. Moreover, males and females differed in their behavioural responses in the unfamiliar context. Females with a familiar companion landed sooner than when they were paired with an unfamiliar conspecific, whereas only the presence of a companion but not familiarity reduced males latency to land on the ground. Finally, when considering the unfamiliar context males had shorter latencies to forage and thus spent more time eating than females.ConclusionsThe presence or absence of a companion and its familiarity with the focal individual influenced differently the behavioural responses of male and female house sparrows in a novel environment. As house sparrows are strongly sociable, the influence of the social environment is likely to be of paramount importance to understand the selective pressures acting on them, particularly in recently colonized areas with ephemeral food sources. Our results shed light on the complex influence that the social environment has on the behavioural responses of a cosmopolitan bird.

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 scent in female choice. We performed the experiment with captive birds twice, during the nonbreeding and breeding seasons. 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 kinship. We suggest that avoidance for UF males is associated with previous experience in this species. Also, we provided further evidence to the use of olfaction in passerine species by using a new experimental setup.

Estradiol modulates neural response to conspecific and heterospecific song in female house sparrows: An in vivo positron emission tomography study.

Although there is growing evidence that estradiol modulates female perception of male sexual signals, relatively little research has focused on female auditory processing. We used in vivo 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) imaging to examine the neuronal effects of estradiol and conspecific song in female house sparrows (Passer domesticus). We assessed brain glucose metabolism, a measure of neuronal activity, in females with empty implants, estradiol implants, and empty implants ~1 month after estradiol implant removal. Females were exposed to conspecific or heterospecific songs immediately prior to imaging. The activity of brain regions involved in auditory perception did not differ between females with empty implants exposed to conspecific vs. heterospecific song, but neuronal activity was significantly reduced in females with estradiol implants exposed to heterospecific song. Furthermore, our within-individual design revealed that changes in brain activity due to high estradiol were actually greater several weeks after peak hormone exposure. Overall, this study demonstrates that PET imaging is a powerful tool for assessing large-scale changes in brain activity in living songbirds, and suggests that after breeding is done, specific environmental and physiological cues are necessary for estradiol-stimulated females to lose the selectivity they display in neural response to conspecific song.

Antioxidant allocation modulates sperm quality across changing social environments.

In promiscuous species, male reproductive success depends on their ability to mate with fertile females and on the fertilizing ability of their sperm. In such species, theory predicts that, owing to a trade-off between pre- and post-copulatory reproductive traits, males with lesser access to females should increase resource investment into those sperm traits that enhance fertilization success–usually referred to as ejaculate quality. This prediction has been validated in several taxa, yet studies on the physiological mechanisms modulating ejaculate quality are lacking. Sperm cells are highly vulnerable to oxidative stress, which impairs male fertility. Therefore, males that better protect their sperm from oxidative stress are expected to achieve higher ejaculate quality. Based on theoretical expectations, and since social dominance is a major determinant of mating opportunity, we predicted that subordinate males should invest more into the antioxidant protection of their sperm in order to achieve higher ejaculate quality. We maintained 60 male and 60 female wild-caught house sparrows Passer domesticus in outdoor aviaries, where we experimentally manipulated male social status to test our predictions. We measured cellular oxidative stress and enzymatic antioxidant activity in blood and sperm both before and after manipulating social ranks. Before manipulating the social status, we found that ejaculate viability correlated with oxidative stress level in sperm, with dominant males producing more oxidized and less viable ejaculates. Further, males at the lower end of the hierarchy produced ejaculates of similar quality to those of dominant males, suggesting that restricted access to resources might limit male reproductive strategies. After experimentally manipulating the social status, males matched their ejaculate quality to their new rank, while increases in antioxidant investment into ejaculates paralleled increases in ejaculate viability. Oxidative stress has been proposed as a general constraint to the evolution of life histories. Our results highlight oxidative stress and strategic antioxidant allocation as important proximate physiological mechanisms underlying male reproductive strategies.

Experimentally reducing corticosterone mitigates rapid captivity effects on behavior, but not body composition, in a wild bird

Wild animals and captives display physiological and behavioral differences, and it has been hypothesized, but rarely tested, that these differences are caused by sustained elevation of the hormone corticosterone. We used repeated computed tomography (CT) imaging to examine body composition changes in breeding male and female wild house sparrows (Passer domesticus; n=20) in response to two weeks of captivity, and assessed behavioral changes using video recordings. Half of the birds received the drug mitotane, which significantly decreased stress-induced corticosterone titers compared to controls. Based on the CT images, fat volumes increased, and pectoralis muscle density and heart and testes volumes decreased, over the two weeks of captivity in both groups of birds. However, beak-wiping, a behavior that can indicate anxiety and aggression, showed increased occurrence in controls compared to mitotane-treated birds. While our results do not support the hypothesis that these body composition changes were primarily driven by stress-induced corticosterone, our data suggest that experimentally reducing stress-induced corticosterone may mitigate some captivity-induced behavioral changes. Broadly, our results emphasize that researchers should take behavioral and physiological differences between free-living animals and captives into consideration when designing studies and interpreting results. Further, time in captivity should be minimized when birds will be reintroduced back to the wild.

Volume and antimicrobial activity of secretions of the uropygial gland are correlated with malaria infection in house sparrows.

BackgroundAnimals have developed a wide range of defensive mechanisms against parasites to reduce the likelihood of infection and its negative fitness costs. The uropygial gland is an exocrine gland that produces antimicrobial and antifungal secretions with properties used as a defensive barrier on skin and plumage. This secretion has been proposed to affect the interaction between avian hosts and their ectoparasites. Because uropygial secretions may constitute a defense mechanism against ectoparasites, this may result in a reduction in prevalence of blood parasites that are transmitted by ectoparasitic vectors. Furthermore, other studies pointed out that vectors could be attracted by uropygial secretions and hence increase the probability of becoming infected. Here we explored the relationship between uropygial gland size, antimicrobial activity of uropygial secretions and malaria infection in house sparrows Passer domesticus.MethodsA nested-PCR was used to identify blood parasites infection. Flow cytometry detecting absolute cell counting assessed antimicrobial activity of the uropygial gland secretionResultsUninfected house sparrows had larger uropygial glands and higher antimicrobial activity in uropygial secretions than infected individuals. We found a positive association between uropygial gland size and scaled body mass index, but only in uninfected sparrows. Female house sparrows had larger uropygial glands and higher antimicrobial activity of gland secretions than males.ConclusionThese findings suggest that uropygial gland secretions may play an important role as a defensive mechanism against malaria infection.

Steroids in house sparrows (Passer domesticus): Effects of POPs and male quality signalling

At high trophic levels, environmental contaminants have been found to affect endocrinological processes. Less attention has been paid to species at lower trophic levels. The house sparrow (Passer domesticus) may be a useful model for investigating effects of POPs in mid-range trophic level species. In male house sparrows, ornamental traits involved in male quality signalling are important for female selection. These traits are governed by endocrinological systems, and POPs may therefore interfere with male quality signalling. The aim of the present study was to use the house sparrow as a mid-range trophic level model species to study the effects of environmental contaminants on endocrinology and male quality signalling. We analysed the levels of selected PCBs, PBDEs and OCPs and investigated the possible effects of these contaminants on circulating levels of steroid hormones (4 progestagens, 4 androgens and 3 estrogens) in male and female adult house sparrows from a population on the island Leka, Norway. Plasma samples were analysed for steroid hormones by GC–MS and liver samples were analysed for environmental contaminants by GC-ECD and GC-MS. In males, we also quantified ornament traits. It was hypothesised that POPs may have endocrine disrupting effects on the local house sparrow population and can thus interfere with the steroid hormone homeostasis. Among female house sparrows, bivariate correlations revealed negative relationships between POPs and estrogens. Among male sparrows, positive relationships between dihydrotestosterone levels and PCBs were observed. In males, positive relationships were also found between steroids and beak length, and between steroids and ornamental traits such as total badge size. This was confirmed by a significant OPLS model between beak length and steroids. Although sparrows are in the mid-range trophic levels, the present study indicates that POPs may affect steroid homeostasis in house sparrows, in particular for females. For males, circulating steroid levels appears to be more associated with biometric parameters related to ornamental traits.