Social factors affect the singing rates of female northern cardinals Cardinalis cardinalis

Social factors, such as the duration of territorial occupancy or of time paired with a mate can affect the rate at which individual birds sing. This study examined the influence of duration of pair-bond and territory occupancy as well as date on the rate of singing by male and female northern cardinals Cardinalis cardinalis . When differences in breeding status were controlled, female cardinals sang at higher rates earlier in the season. Females in newly formed pairs sang at significantly higher rates than those in pairs that had previously bred together. In contrast, male cardinals did not show significant variation in the rate of singing throughout the season. The song rates of males in newly formed and established pairs did not differ significantly. Song rates for males and females in mated pairs were not significantly correlated. This study suggests that social factors have a strong effect on the rate at which female cardinals sing. It is possible that increased intra-sexual aggression by females when they are establishing a new territory with a new mate leads to this higher level of song output. Once females have established a territory and acquired a mate, dear-enemy effects might diminish the need for acoustic territorial defence. Differences in the constraints of nesting or the attraction of extra-pair mates might explain the sexual differences in male and female singing behaviour.     

Assortative mating by multiple ornaments in northern cardinals (Cardinalis cardinalis)

In positive assortative mating, individuals of similar phenotypemate together more frequently than expected by chance. Assortativemating by a variety of qualities, including ornamentation, iswell documented in birds. Studies of assortative mating by ornamentshave focused on single, highly conspicuous ornaments, but manyspecies of birds possess multiple ornaments in both sexes. Wecompared ornament expressions between mates of northern cardinals(Cardinalis cardinalis) to determine if assortative mating occurredby one or more of the four ornaments displayed by both sexes.All cardinals possess tall head crests and red-orange bills.In addition, males have black face masks and entirely red bodyplumage, whereas females have blackish face masks and red underwingcoverts. We predicted that cardinals mate assortatively by plumagecolor because red plumage expression has been shown to indicatequality in both sexes. We found that cardinals mate assortativelyby plumage and bill color, the two ornaments colored by carotenoidpigments, but not by mask expression or crest length. Whetherthis mating pattern arises by mutual mate choice or intrasexualselection is not known.     

Nest predation reduces benefits to early clutch initiation in northern cardinals Cardinalis cardinalis

Life history theory and empirical studies suggest that early breeding confers higher reproductive success, but the extent to which this advantage can be generalized to human‐dominated systems and across species is less well understood. We studied the fitness consequences of clutch initiation for 181 female northern cardinals Cardinalis cardinalis and 1228 nests in forests within urban and rural landscapes of Ohio, USA between 2004–2007. Cardinals that bred earlier made significantly more nesting attempts, but cumulative number of young fledged was similar to that of later‐breeding individuals. The expected number of fledglings produced per successful nest was unrelated to date and remained ~1.8 fledglings across the season, despite the fact that nest survival rates improved dramatically as the season progressed. Because the probability of resighting breeding individuals in subsequent years was unrelated to first clutch initiation date, we have no evidence that clutch initiation affected adult survival. The absence of a clear benefit to early breeding appears to be a consequence of high rates of nest predation early in the breeding season.     

Snake behavior and seasonal variation in nest survival of northern cardinals Cardinalis cardinalis

Seasonal variation in nest success is well documented for many bird species. Predator behavior has been suggested as a mechanism behind these seasonal patterns, but this hypothesis has received little attention. Here we test the hypothesis that predator behavior produces seasonal patterns of nest success by relating nest success of northern cardinals Cardinalis cardinalis to the activity of Texas rat snakes Elaphe obsoleta. Cardinal nest survival varied over the season and was lower when rat snakes were more active. The probability that a nest survived was associated both with when cardinals nested and with nest height, indicating that both temporal and habitat factors affected predation risk. The increased success of higher nests could be associated with some aspect of rat snakes’ climbing ability. In combination with results for two other species studied previously at the same location, our results for cardinals suggest that the specific seasonal pattern of nest success expected for a given bird species will depend on how its nesting season coincides with predator activity. Determining the generality of seasonal variation in predator behavior as a mechanism for producing seasonal patterns of avian nest success will require additional studies that investigate birds and their nest predators simultaneously.     

Testosterone elevation and response to gonadotropin-releasing hormone challenge by male northern cardinals (Cardinalis cardinalis) following aggressive behavior

There is much discrepancy about the relationship between testosterone (T) and male aggressive behavior. For example, in birds, males of many species significantly elevate T levels during inter-male conflict. However, this is not universal, and in species where males typically do not elevate T during aggressive interactions, concentrations of the hormone are often assumed to be circulating at maximum levels. We examined if male northern cardinals (Cardinalis cardinalis) significantly elevated T during simulated territorial intrusions (STIs). We also examined if individuals had the capacity to further elevate T levels in response to gonadotropin-releasing hormone (GnRH) injections immediately after an aggressive encounter. Our results indicate that male cardinals do not significantly elevate T levels in response to STIs, but have the physiological capacity to significantly elevate T in response to GnRH injections following aggressive interactions. This implies that T levels of individuals captured during STIs were not at maximum concentrations. However, additional findings in this study also suggest the possibility that prolonged social instability could elicit significant elevations in T in males of this species, warranting further investigation.     

The influence of carotenoid acquisition and utilization on the maintenance of species-typical plumage pigmentation in male American goldfinches (Carduelis tristis) and northern cardinals (Cardinalis cardinalis).

Birds display a tremendous variety of carotenoid-based colors in their plumage, but the mechanisms underlying interspecific variability in carotenoid pigmentation remain poorly understood. Because vertebrates cannot synthesize carotenoids de novo, access to pigments in the diet is one proximate factor that may shape species differences in carotenoid-based plumage coloration. However, some birds metabolize ingested carotenoids and deposit pigments that differ in color from their dietary precursors, indicating that metabolic capabilities may also contribute to the diversity of plumage colors we see in nature. In this study, we investigated how the acquisition and utilization of carotenoids influence the maintenance of species-typical plumage pigmentation in male American goldfinches (Carduelis tristis) and northern cardinals (Cardinalis cardinalis). We supplemented the diet of captive goldfinches with red carotenoids to determine whether males, which are typically yellow in color, were capable of growing red plumage. We also deprived cardinals of red dietary pigments to determine whether they could manufacture red carotenoids from yellow precursors to grow species-typical red plumage. We found that American goldfinches were able to deposit novel pigments in their plumage and develop a striking orange appearance. Thus, dietary access to pigments plays a role in determining the degree to which goldfinches express carotenoid-based plumage coloration. We also found that northern cardinals grew pale red feathers in the absence of red dietary pigments, indicating that their ability to metabolize yellow carotenoids in the diet contributes to the bright red plumage that they display.     

Multiple Ornaments in Male Northern Cardinals, Cardinalis cardinalis, as Indicators of Condition

Investigations of male ornaments in the context of sexual selection have tended to focus on single ornaments, although many species of birds possess multiple ornaments. Understanding the evolution of multiple ornaments requires knowledge of correlations among ornaments in the same individual and the extent to which ornament expression reflects individual condition and behavior. Variation in four male ornaments in socially monogamous, biparental northern cardinals (Cardinalis cardinalis) was related to body size, indices of condition, level of paternal care, and reproductive success. Redness of breast plumage positively predicted body size and negatively predicted nestling feeding rate. Bill color predicted current body condition, with birds with redder bills in better condition. Birds with smaller black face masks had greater reproductive success. These results are consistent with the hypothesis that different ornaments in male cardinals provide information on different aspects of condition and behavior.     

Carotenoid-Based Plumage Coloration Predicts Leukocyte Parameters during the Breeding Season in Northern Cardinals (Cardinalis cardinalis)

Dichromatism in songbirds is often associated with polygyny and dimorphic parental investment, and is thought to arise via sexual selection. Northern cardinals (Cardinalis cardinalis) are not only dichromatic but also monogamous and biparental, suggesting that plumage coloration in this species may serve different functions than in more typical dichromatic species. In order to explore the role of sexual selection in the evolution of plumage coloration in cardinals, we used reflectance spectrophotometry to investigate whether two carotenoid‐based ornaments, the male’s red breast and the female’s underwing coverts, contain information that potential mates or competitors could use to assess condition. We found that whereas coloration was not related to body condition (measured as the residual body mass from a regression of body mass on wing chord), more saturated carotenoid coloration was associated with higher heterophil to lymphocyte ratios in males, and with higher white blood cell counts in females. Thus, in both sexes, carotenoid coloration was positively linked to immune measures normally associated with higher levels of stress and infection. These results do not indicate that carotenoid‐based coloration functions as a signal of low levels of stress or disease in this species. We propose instead that because plumage coloration may be related to competitiveness, the more saturated individuals increase their risk of injury, stress, and infection by engaging in more competitive behavior or by secreting more testosterone, or both. Our finding that carotenoid pigmentation is positively associated in males with the size of the cloacal protuberance, an androgen‐sensitive sex character, supports this hypothesis.     

Multiple ornaments correlate with aspects of condition and behaviour in female northern cardinals, Cardinalis cardinalis

Male ornamentation in socially monogamous birds has been shown to provide information to potential mates on aspects of condition and behaviour. We studied female ornamentation in the socially monogamous, biparental northern cardinal to determine whether expressions of multiple ornaments correlate with aspects of female condition and behaviour. Expressions of the ornamental red-orange bill, red underwing feathers, head crest and blackish face mask were compared to several measures of condition, parental behaviour and intrasexual aggression. Red-orange bill colour of females was correlated with both body size and an index of body condition. Redness of the underwing feathers was correlated with body size, body condition, date of first nest produced and reproductive success. Face mask expression was correlated with both nestling feeding rate and level of intrasexual aggression. The length of head crest feathers did not correlate with any measured aspect of condition or behaviour. These results are consistent with the hypothesis that ornaments in female cardinals provide redundant information to prospective mates on aspects of female condition and behaviour.     

Red coloration of male northern cardinals correlates with mate quality and territory quality

I investigated how mate quality and territory quality influencean extravagant ornament in a socially monogamous species thatdefends multipurpose territories. Northern cardinals (Cardinaliscardinalis) are a highly dichromatic, socially monogamous species,and males are a brilliant red. I conducted a 3-year field studyof northern cardinals and found that redder males produced moreoffspring in a breeding season. Two selective factors mediatedthis fitness gain. Redder males were paired with earlier breedingfemales, an established measure of mate quality in birds. Second,redder males obtained territories of higher quality, as measuredby vegetation density. Interactions among these factors werealso important in explaining variance in male reproductive success.Multivariate analysis indicated that earlier breeding increasedreproductive success independent of territory quality. In turn,territory quality contributed to male reproductive success throughits effect on nest survival and possibly through its role in attractingan earlier breeding female.     

Male singing behaviour and female presence in the territory in whitethroats Sylvia communis

Unmated male songbirds usually change their vocal behaviour when females enter their territories. Either the males court the females by changing the rate or pattern with which their normal long-ranging full songs are emitted, or they shift to special displays and long- or short-ranging vocalisations. In this study we quantified how female presence and behaviour affect the singing behaviour of male whitethroats. In the presence of a female the male frequently performed song flights, maybe to locate the female before it was courted, with sequences of diving-song displays. The courtship was interrupted by periods of perch songs. Female dscharp calls and short movements made the males initiate or resume courtship, whereas short horizontal jumps made the males intensify their courtship. Overall, the males changed their dual-function song activity in females' presence by emitting fewer perch songs and more flight songs. The quiet diving songs were only emitted during direct courtship of a female. The song types emitted immediately before, during, and after courtship are all highly variable, thus allowing for a quick assessment of the male's song repertoire. The courtship was also interrupted by periods of male woid calling, a call that is known to have a deterring effect on rival males. Bouts of woid calls were usually followed by song flights, again probably to locate the female that might have moved out of sight, or maybe to locate potential rival intruders. The latter was supported by an increased intrusion rate during female presence. Communicated by P. McGregor     

Evaluating recipient and embryo factors that affect pregnancy rates of embryo transfer in beef cattle

The objectives of this experiment were to determine the effects of corpus luteum characteristics, progesterone concentration, donor-recipient synchrony, embryo quality, type, and developmental stage on pregnancy rates after embryo transfer. We synchronized 763 potential recipients for estrus using one of two synchronization protocols: two doses of PGF2alpha (25 mg i.m.) given 11 d apart (Location 1); and, a single norgestomet implant for 7 d with one dose of PGF2alpha (25 mg i.m.) 24 h before implant removal (Location 2). At embryo transfer, ovaries were examined by rectal palpation and ultrasonography. Of the 526 recipients presented for embryo transfer, 122 received a fresh embryo and 326 received a frozen embryo. Pregnancy rates were greater (P < 0.05) with fresh embryos (83%) than frozen-thawed embryos (69%). Pregnancy rates were not affected by embryo grade, embryo stage, donor-recipient synchrony, or the palpated integrity of the CL. Corpus luteum diameter and luteal tissue volume increased as days post-estrus for the recipients increased. However, pregnancy rates did not differ among recipients receiving embryos 6.5 to 8.5 days after estrus (P > 0.1). There was a significant, positive simple correlation between CL diameter or luteal tissue volume and plasma progesterone concentration (r = 0.15, P < 0.01 and r = 0.18, P < 0.01, respectively). There were no significant differences in mean CL diameter, luteal volume or plasma progesterone concentration among recipients that did or did not become pregnant after embryo transfer. We conclude that suitability of a potential embryo transfer recipient is determined by observed estrus and a palpable corpus luteum, regardless of size or quality.     

Annual cycle of the black-capped chickadee: seasonality of singing rates and vocal-control brain regions

Black-capped chickadees have a rich vocal repertoire including learned calls and the learned fee-bee song. However, the neural regions underlying these vocalizations, such as HVC, area X, and RA (robust nucleus of arcopallium), remain understudied. Here, we document seasonal changes in fee-bee song production and show a marked peak in singing rate during March through May. Despite this, we found only minimal seasonal plasticity in vocal control regions of the brain in males. There was no significant effect of time of year on the size of HVC, X, or RA in birds collected in January, April, July, and October. We then pooled birds into two groups, those with large testes (breeding condition) and those with small testes (nonbreeding), regardless of time of year. Breeding birds had slightly larger RA, but not HVC or X, than nonbreeding birds. Breeding birds had slightly larger HVC and RA, but not X, as a proportion of telencephalon volume than did nonbreeding birds. Birds collected in July had heavier brains than birds at other times of year, and had the greatest loss in brain mass during cryoprotection. The absence of any overall seasonal change in the vocal-control regions of chickadees likely results from a combination of individual differences in the timing of breeding phenology and demands on the vocal-control regions to produce learned calls year-round.     

Risk factors for elevated HIV incidence rates among female injection drug users in Vancouver

Background

In 1997, we found a higher prevalence of HIV among female than among male injection drug users in Vancouver. Factors associated with HIV incidence among women in this setting were unknown. In the present study, we sought to compare HIV incidence rates among male and female injection drug users in Vancouver and to compare factors associated with HIV seroconversion.

Methods

This analysis was based on 939 participants recruited between May 1996 and December 2000 who were seronegative at enrolment with at least one follow-up visit completed, and who were studied prospectively until March 2001. Incidence rates were calculated using the Kaplan–Meier method. The Cox proportional hazards regression model was used to identify independent predictors of time to HIV seroconversion.

Results

As of March 2001, seroconversion had occurred in 110 of 939 participants (64 men, 46 women), yielding a cumulative incidence rate of HIV at 48 months of 13.4% (95% confidence interval [CI] 11.0%–15.8%). Incidence was higher among women than among men (16.6% v. 11.7%, p = 0.074). Multivariate analysis of the female participants'' practices revealed injecting cocaine once or more per day compared with injecting less than once per day (adjusted relative risk [RR] 2.6, 95% CI 1.4–4.8), requiring help injecting compared with not requiring such assistance (adjusted RR 2.1, 95% CI 1.1–3.8), having unsafe sex with a regular partner compared with not having unsafe sex with a regular partner (adjusted RR 2.9, 95% CI 0.9–9.5) and having an HIV-positive sex partner compared with not having an HIV-positive sex partner (adjusted RR 2.7, 95% CI 1.0–7.7) to be independent predictors of time to HIV seroconversion. Among male participants, injecting cocaine once or more per day compared with injecting less than once per day (adjusted RR 3.3, 95% CI 1.9–5.6), self-reporting identification as an Aboriginal compared with not self-reporting identification as an Aboriginal (adjusted RR 2.5, 95% CI 1.4–4.2) and borrowing needles compared with not borrowing needles (adjusted RR 2.0, 95% CI 1.1–3.4) were independent predictors of HIV infection.

Interpretation

HIV incidence rates among female injection drug users in Vancouver are about 40% higher than those of male injection drug users. Different risk factors for seroconversion for women as opposed to men suggest that sex-specific prevention initiatives are urgently required.Recent reports in Canada and numerous other countries indicate that HIV is increasingly affecting women.¹ Before 1995, adult women in Canada had 9.6% of all positive HIV tests for which the age and sex of the person being tested were known. By 1995, this proportion had increased to 18.5% and reached 23.9% in 2000. In addition, 39% of all new HIV infections among women in 2000 were attributed to injection drug use.² These data are consistent with findings in the United States where, in 1999, women accounted for 23% of all reported AIDS cases in adults, of which 42% were attributed to injection drug use.³These data clearly indicate that the face of the epidemic is changing. Whereas some factors unique to the transmission of HIV to women are known, basic and behavioural research efforts addressing sex-related and drug-related vulnerabilities among female injection drug users (IDUs) are lacking.⁴ At a time when women''s vulnerability to HIV infection is becoming increasingly apparent worldwide,^5,6 a better understanding of the processes and factors that cause drug-related harm among women in industrialized countries is urgently required.Since the mid-1990s, the Downtown Eastside of Vancouver, British Columbia, has experienced an explosive and ongoing HIV epidemic among IDUs with annual HIV incidence rates reaching as high as 19% in 1997.^7,8 When subjects were enrolled in the Vancouver Injection Drug User Study (VIDUS), it was found that the baseline HIV prevalence was higher among women than men (35.2% v. 25.8%).⁷ Follow-up of this cohort now allows an investigation aimed at identifying the predictors of HIV seroconversion among female and male IDUs. Therefore, we sought to compare HIV incidence rates among male and female IDUs in Vancouver and to compare risk factors associated with HIV seroconversion.     

Lesions to the medial preoptic area affect singing in the male European starling (Sturnus vulgaris)

The aromatization of testosterone (T) in the medial preoptic nucleus (POM) is known to regulate male courtship and sexual behaviors expressed prior to, and in anticipation of, copulation. Singing in male European starlings is used to attract mates prior to physical sexual contact, suggesting that the POM might be involved. The present study was performed to examine the effects of lesions targeting the POM on singing and courtship behavior in reproductively active male starlings. A significant decrease in song output and the gathering of green nest materials was observed in males with lesions to the POM compared to males with damage to brain areas outside of the POM. Lesions did not affect a male's tendency to remain near a female or to occupy a nestbox, suggesting that the effects of POM lesions were specific to courtship behaviors. Behavioral differences were not related to testis mass or volume, and GnRH immunoreactivity was observed within the hypothalamus and median eminence for each male, suggesting that the effects of POM lesions were related specifically to POM involvement in song expression rather than to a disruption of the GnRH axis. These results suggest a general role for the POM in the expression of behaviors related to sexual arousal or anticipation, including song.     

成年雌性短尾猴的社会联系强度及影响因素

灵长类动物社会中,个体间的社会关系是维系群体稳定的重要基础,也影响个体的寿命和繁殖成功。本研究以栖息于安徽黄山的短尾猴YA1群为对象,采用焦点动物取样法和行为取样法采集成年雌性个体在交配期（2015.9 - 2015.12）和非交配期（2016.3 - 2016.5）的社会行为,通过理毛和近距行为计算社会联系强度,探讨群体成员之间的社会关系及影响因素。结果表明：在交配期和非交配期,雌性短尾猴的社会联系强度无显著差异（t = 0.181,P = 0.857）;亲缘关系和社会联系强度呈显著正相关（交配期：r = 0.534, P = 0.001; 非交配期：r = 0.469, P= 0.001）;个体间的等级距离和社会联系强度呈显著负相关（交配期：r = -0.288, P= 0.014; 非交配期：r = -0.238, P= 0.048）;年龄差异和社会联系强度无显著相关性（交配期：r = -0.176, P = 0.181; 非交配期：r = -0.192, P = 0.151）。本研究提示成年雌性短尾猴个体间会形成稳定的社会关系,亲缘关系和等级顺位是影响个体之间社会关系的重要因素。     

Social stimulation of dawn singing in Dusky Flycatchers: a serendipitous experiment

Hypotheses regarding dawn singing in birds remain largely unsupported by quantitative data, especially for suboscine passerines (suborder Tyranni). During a study of the singing behavior of a suboscine, the Dusky Flycatcher (Empidonax oberholseri), in Alberta, Canada, spring storms in 2002 caused the disappearance and presumed mortality of several territorial males and some of their replacements, creating a serendipitous experiment. Overall, 15 males disappeared and, as a result, the number of territorial males in our study area declined from 13 prior to the storms to six afterward. Only one male maintained the same territory throughout the breeding season. During the period of inclement weather and social instability (20 May to 9 June), males sang at high rates during the predawn period. From 10 to 19 June, following this period of unstable weather and turnover in territorial males, males began dawn singing later in the morning, and sang shorter bouts at lower rates. The proportion of males engaging in dawn singing also decreased between the two periods. In contrast, daytime singing activity of paired males was low during both time periods. Playback of dawn songs to territorial males between 20 June and 21 July caused a resumption of some dawn singing. Singing rates were higher on the day of playback than on the day before playback, and the times when dawn singing was initiated were earlier on each of 2 d after playback than on the day before playback. In addition, the proportion of males engaging in dawn singing increased between the day before and the day after playback. Both the decrease in dawn singing when population density was reduced and its partial restoration by playback suggest that dawn singing in this species functions in male–male interactions and support the social‐dynamics hypothesis as an explanation for the dawn chorus in this species.