Glycated hemoglobin and albumin reflect nestling growth and condition in American kestrels

Blood chemistry can be used to assess physiological state and condition. Levels of glycated hemoglobin (GHb), which integrates blood glucose levels over a period of weeks, may provide a way to assess resource intake. I tested whether GHb reflects offspring quality by comparing growth rates of nestling American kestrels (Falco sparverius) with GHb levels at 24 days of age. Nestlings that gained structural size faster had higher levels of GHb than did slower growing nestlings. There was no difference in GHb levels between males and females, although females are larger. In addition, I tested whether albumin levels, a measure of protein storage, were correlated with nestling growth and body condition (reflected in residual body mass). Larger individuals, measured by both absolute body mass and by residual body mass, had larger levels of albumin. This was due in part to females having higher albumin levels. Interestingly, there was no correlation between GHb and albumin, suggesting that both measures are necessary to assess physical condition in nestling kestrels. These results suggest that blood chemistry can reflect offspring condition measures and may provide a way to assess offspring quality that reflects conditions experienced by offspring over longer periods through measurements at a single time point.     

Seasonality in song behaviour revisited: seasonal and annual variants and invariants in the song of the domesticated canary (Serinus canaria)

The song of the domesticated canary (Serinus canaria) is one of the most widely used models to study the neural correlates of behavioural plasticity and the mechanisms of female mate choice. However, only few studies have described the song behaviour in detail and monitored their changes throughout the year, and these data are restricted to the “Waterslager” strain. Here, we studied the song characteristics of the male common domesticated canary at different times of the year, the spring breeding and autumnal non-breeding season, and monitored the birds' songs up to the following breeding season. During breeding, males have increased plasma levels of testosterone, and songs are on average longer and consist of fewer non-repeated syllable types compared to the non-breeding season. When subsequent seasons are compared, song duration and the proportion of non-repeated syllable types change seasonally but not across years. Repertoire size remains constant throughout seasons although syllable types are exchanged. Syllable carry-over is significantly higher from one breeding season to the next than between the breeding and non-breeding season. Further, the repertoire of the breeding season contains more potentially sexually attractive syllable types than that of the non-breeding season. These data show that overall song structure is retained throughout the year while seasonality occurs in the temporal pattern and in repertoire composition.     

Song correlates with social context,testosterone and body condition in male barn swallows

Bird song, like many other male secondary sexual characters, may have evolved as intra- or inter-sexual signals of male phenotypic quality. The hypotheses that song rate and song features reflect androgen levels and body condition, qualities useful in male–male competition, and that they are also influenced by social context, was tested for the first time in the present correlational study. The relationships between song rate and 14 variables describing song structure, respectively, and absolute plasma testosterone levels, body mass, body condition, number of neighbouring males and distances between nest sites in male barn swallows,Hirundo rustica, were analysed. Song rate was not correlated with any of the song features nor with male or social context characteristics. By contrast, a harsh song syllable, the ‘rattle’, was positively related to plasma testosterone levels, and its peak amplitude frequency varied inversely with male body mass and condition. In addition, eight features of song varied according to the social environment of each male. In particular, males sang longer and more varied songs when they had few or no neighbours, whereas males in highly competitive contexts uttered short songs, interrupted them more frequently, and emphasized the rattle. Neighbouring males also sang more similar songs than distant males, and this resulted in matched countersinging. The quality of song output therefore reflects aspects of male competitive potential, and relationships between song structure and social context suggest that some features, such as the rattle, might have originally evolved to serve in male–male interactions; a female preference may have further promoted song evolution leading to complex syllable repertoires.     

Influences of landscape composition on hunter-harvested mallard body mass and condition in eastern Arkansas

Waterfowl with more body mass and a greater body condition during the non-breeding season are thought to be more likely to survive and have increased productivity during the following breeding season. Body mass and body condition in waterfowl should reflect the resources available to them locally. We analyzed the relationship of landscape composition on mallard (Anas platyrhynchos) body mass and body condition (mass-wing length index) among age and sex groups. We calculated these variables from hunter-harvested mallards during the 2019–2020 and 2020–2021 duck hunting seasons in the Lower Mississippi Alluvial Valley of Arkansas, USA. We used linear mixed-effects models to analyze changes in body mass and body condition with changes in the percent landscape composition of water cover, woody wetlands, herbaceous wetlands, rice, soybeans, and disturbance. We found that body mass and condition of harvested mallards were positively associated with greater proportions of water cover and woody wetlands but negatively associated with greater proportions of herbaceous wetlands and human disturbance from human infrastructure. Management actions focused on providing flooded and woody wetland areas on the landscape that allow waterfowl to access food resources, while decreasing the disturbance around wetlands in the form of road density and human infrastructure, should increase body mass and body condition in mallards spending the non-breeding season in the Lower Mississippi Alluvial Valley.     

Time course of changes in Gambel's white-crowned sparrow song behavior following transitions in breeding condition

Seasonal changes in behavior and in its underlying neural substrate are common across animal taxa. These changes are often triggered by steroid sex hormones. Song in seasonally breeding songbirds provides an excellent example of this phenomenon. In these species, dramatic seasonal changes mediated by testosterone and its metabolites occur in adult song behavior and in the neural circuitry controlling song. While song rate can quickly change in response to seasonal breeding cues, it is unknown how quickly other aspects of song change, particularly the stereotypy of song phonology and syntax. In this study we determined whether and how quickly song rate, phonology, and syntax change in response to breeding and non-breeding physiological cues. We asked these questions using Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii), a closed-ended learner with well-characterized changes in the neural circuitry controlling song behavior. We exposed ten photosensitive sparrows to long-day photoperiod and implanted them with subcutaneous testosterone pellets (day 0) to simulate breeding conditions. We continuously recorded song and found that song rate increased quickly, reaching maximum around day 6. The stereotypy of song phonology changed more slowly, reaching maximum by day 10 or later. Song syntax changed minimally after day 6, the earliest time point examined. After 21 days, we transitioned five birds from breeding to non-breeding condition. Song rate declined precipitously. These results suggest that while song rate changes quickly, song phonology changes more slowly, generally following or in parallel with previously investigated changes in the neural substrate.     

Oestrogen regulates male aggression in the non-breeding season

Extensive research has focused on territorial aggression during the breeding season and the roles of circulating testosterone (T) and its conversion to 17beta-oestradiol (E2) in the brain. However, many species also defend territories in the non-breeding season, when circulating T-levels are low. The endocrine control of non-breeding territoriality is poorly understood. The male song sparrow of Washington State is highly territorial year-round, but plasma T is basal in the non-breeding season (autumn and winter). Castration has no effect on aggression in autumn, suggesting that autumnal territoriality is independent of gonadal hormones. However, non-gonadal sex steroids may regulate winter territoriality (e.g. oestrogen synthesis by brain aromatase). In this field experiment, we treated wild non-breeding male song sparrows with a specific aromatase inhibitor (fadrozole, FAD) using micro-osmotic pumps. FAD greatly reduced several aggressive behaviours. The effects of FAD were reversed by E2 replacement. Treatment did not affect body condition or plasma corticosterone, suggesting that all subjects were healthy These data indicate that E2 regulates male aggression in the non-breeding season and challenge the common belief that aggression in the non-breeding season is independent of sex steroids. More generally, these results raise fundamental questions about how sexual and/or aggressive behaviours are maintained in a variety of model vertebrate species despite low circulating levels of sex steroids or despite castration. Such non-classical endocrine mechanisms may be common among vertebrates and play an important role in the regulation of behaviour.     

Seasonal changes in testosterone and corticosterone levels in four social classes of a desert dwelling sociable rodent

Animals have to adjust their physiology to seasonal changes, in response to variation in food availability, social tactics and reproduction. I compared basal corticosterone and testosterone levels in free ranging striped mouse from a desert habitat, comparing between the sexes, breeding and philopatric non-breeding individuals, and between the breeding and the non-breeding season. I expected differences between breeders and non-breeders and between seasons with high and low food availability. Basal serum corticosterone was measured from 132 different individuals and serum testosterone from 176 different individuals of free living striped mice. Corticosterone and testosterone levels were independent of age, body weight and not influenced by carrying a transmitter. The levels of corticosterone and testosterone declined by approximately 50% from the breeding to the non-breeding season in breeding females as well as non-breeding males and females. In contrast, breeding males showed much lower corticosterone levels during the breeding season than all other classes, and were the only class that showed an increase of corticosterone from the breeding to the non-breeding season. As a result, breeding males had similar corticosterone levels as other social classes during the non-breeding season. During the breeding season, breeding males had much higher testosterone levels than other classes, which decreased significantly from the breeding to the non-breeding season. My results support the prediction that corticosterone decreases during periods of low food abundance. Variation in the pattern of hormonal secretion in striped mice might assist them to cope with seasonal changes in energy demand in a desert habitat.     

Determining seabird body condition using nonlethal measures

Energy stores are critical for successful breeding, and longitudinal studies require nonlethal methods to measure energy stores ("body condition"). Nonlethal techniques for measuring energy reserves are seldom verified independently. We compare body mass, size-corrected mass (SCM), plasma lipids, and isotopic dilution with extracted total body lipid content in three seabird species (thick-billed murres Uria lomvia, all four measures; northern fulmars Fulmarus glacialis, three measures; and black-legged kittiwakes Rissa tridactyla, two measures). SCM and body mass were better predictors of total body lipids for the species with high percent lipids (fulmars; R2 = 0.5-0.6) than for the species with low percent lipids (murres and kittiwakes; R2 = 0.2-0.4). The relationship between SCM and percent body lipids, which we argue is often a better measure of condition, was also poor (R2 < 0.2) for species with low lipids. In a literature comparison of 17 bird species, percent lipids was the only predictor of the strength of the relationship between mass and total body lipids; we suggest that SCM be used as an index of energy stores only when lipids exceed 15% of body mass. Across all three species we measured, SCM based on the ordinary least squares regression of mass on the first principal component outperformed other measures. Isotopic dilution was a better predictor of both total body lipids and percent body lipids than were mass, SCM, or plasma lipids in murres. Total body lipids decreased through the breeding season at both sites, while total and neutral plasma lipid concentrations increased at one site but not another, suggesting mobilization of lipid stores for breeding. A literature review showed substantial variation in the reliability of plasma markers, and we recommend isotopic dilution (oxygen-18, plateau) for determination of energy reserves in birds where lipid content is below 15%.     

Food supply controls the body condition of a migrant bird wintering in the tropics

The hypothesis that migratory bird populations are limited during the non-breeding season is increasingly supported by empirical studies that also suggest consequences that carry-over into subsequent seasons. Although variation in food supply is the best supported explanation for non-breeding season limitation, the ecological mechanisms and physiological consequences are not well understood. We both supplemented and reduced Ovenbird (Seiurus aurocapilla) food availability on replicate plots in Jamaica in each of 3 years to determine the direct role of food in limiting the physical condition of Ovenbirds. Annual variation in rainfall and food supply created a natural experiment in parallel with manipulations. Sex and age-classes of Ovenbirds did not respond differently in terms of body condition to either food manipulation or natural variation in environmental conditions, suggesting that this population is not structured by strong dominance relationships. Ovenbird body mass, fat, and pectoralis muscle shape were positively and predictably related to manipulated food availability. Feather regrowth rate also responded positively to food supplementation and negatively to food reduction in the drier of 2 years. Prior to manipulation, annual variation in body mass corresponded to annual variation in food supply and rainfall, providing additional, correlational evidence of food limitation. Since multiple intercorrelated body condition indices of Ovenbirds responded directly to food supply, and since food supply influenced body condition independently of other habitat features, we argue that food is a primary driver of non-breeding season population limitation. Moreover, since these effects were observed during the late non-breeding period, when individuals are preparing to migrate, we infer that food availability likely initiates carry-over effects.     

Context-Dependent Links between Song Production and Opioid-Mediated Analgesia in Male European Starlings (Sturnus vulgaris)

Little is known about the neural mechanisms that ensure appropriate vocal behaviors within specific social contexts. Male songbirds produce spontaneous (undirected) songs as well as female-directed courtship songs. Opioid neuropeptide activity in specific brain regions is rewarding, at least in mammals, and past studies suggest that the opioid met-enkephalin in such areas is more tightly linked to undirected than female-directed song. Recent data using a song-associated place preference paradigm further suggest that production of undirected but not directed song is tightly linked to intrinsic reward. Opioids have analgesic properties. Therefore, if production of undirected song is closely linked to opioid-mediated reward, the production of undirected but not directed song should be associated with analgesia. Consistent with this prediction, in male starlings we identified a positive correlation between analgesia (decreased reactivity to a hot water bath) and undirected song (in non-breeding season condition males in affiliative flocks) but not female-directed song (in breeding season condition males presented with females). When breeding condition males were divided according to social status, a negative correlation was found in subordinate males (i.e. males that failed to acquire a nest box). These data are consistent with the hypotheses 1) that the production of undirected song is facilitated or maintained by opioids (and/or other neuromodulators that also induce analgesia) and 2) that production of female-directed song is not linked in the same way to release of the same neuromodulators. Results also demonstrate a link between analgesia and song in subordinate individuals lacking a nesting territory within the breeding season. Overall, the findings indicate that distinct neural mechanisms regulate communication in different social contexts and support the working hypothesis that undirected but not directed song is tightly linked to opioid release.     

Body condition of shorebirds upon arrival at their Siberian breeding grounds

Arctic breeding shorebirds carry substantial body stores on their long-distance migrations from their non-breeding grounds. Upon arrival at the breeding area the remains of these stores can be used for egg formation, insurance against poor feeding conditions or rebuilding organs. We quantified body condition (body mass, total body water, lean body mass and fat mass estimated using the deuterium dilution method) in seven shorebird species caught upon arrival in the Siberian Arctic. Arrival condition was compared with incubation condition in a subset of species. After correction for structural size, body mass was significantly lower at arrival than during incubation in most of the species (but 3–18% above lean mass). Fat index (fat mass/lean mass) varied between 5.1 and 13.2%. Fat stores were estimated to enable survival for 0.6 days for the smallest and 2.5 days for the largest species. We discuss possible functions of arrival stores: insurance, egg-formation or rebuilding organs. G. H. Visser: Deceased.     

Nutritional condition and serum biochemistry for free-living Swainson's Hawks wintering in central Argentina

We assessed the nutritional condition and established reference values for serum chemistry parameters in a long distance migrant bird of prey, the Swainson's Hawk (Buteo swainsoni), wintering in central Argentina. We analyzed serum concentration of urea, uric acid, cholesterol, and triglycerides and assessed age and sex related differences in these parameters. A body condition index was obtained from the resultant residuals of the regression of body mass and a morphometric measure. No statistical differences were observed among sex and age groups for urea, uric acid and triglyceride serum concentration. However, cholesterol concentration differed among male and female hawks, which could be related to the gain of body mass in wintering grounds at differential rates. The mean values of the four parameters were in the range of those recorded in the Common Buzzard (Buteo buteo), indicating good nutritional condition of the population we studied. Forearm length was the morphometric variable that better correlated with body mass. The resultant body condition index was only correlated with triglyceride concentration, suggesting that this index could be valuable in future work dealing with the assessment of body fat storage in wintering and breeding hawks, as well as in stopover points on the migratory route.     

Body condition variation in kestrel (<Emphasis Type="Italic">Falco tinnunculus</Emphasis>) nestlings in relation to breeding conditions

The body condition index (i.e., body mass corrected for age or size differences) is commonly used to investigate offspring condition in nestling birds. The body condition index reflects different parameters related to the general nutritional state of nestlings and may predict survival prospects. Since conditions experienced during the growth period can affect the fitness of nestlings in adulthood, we investigated proximate and ultimate factors underlying body condition index variation in kestrel (Falco tinnunculus) nestlings in a 9-year field study and we carried out two cross-fostering experiments to disentangle the origin (genetics plus maternal effects) and rearing (environment effect) components of body condition index variation. In total, we sampled 2,065 nestlings from 464 broods and used 121 nestlings from 24 broods in the cross-fostering experiments. We found that nestlings from larger broods had higher body condition index than nestlings from smaller ones, but this pattern did not emerge in two of the 9 years of study; nestlings born later in the breeding season had lower body condition index in some years but not in others; the decrease of body condition index over the breeding season emerged in all but three-chick broods; males and females did not differ neither in body condition index nor in the covariation between body mass and wing length, while this result was limited to one of the nine field study years; the annual mean value of body condition index did not covary with the total rainfall; both the origin and rearing components explained body condition index variation, but their relative contributions varied from a year to another. Overall, these results suggest that the brood size is not a good predictor of body condition index; the rule “nesting early in the season is better” is less general than previously thought; the body condition index may contain origin variance, whose expression may be modulated by environmental conditions.     

Experimentally Elevated Plasma Testosterone Levels Do Not Influence Singing Behaviour of Male Blue Tits (Parus caeruleus) During the Early Breeding Season

Sexual selection theory suggests that females might prefer males on the basis of testosterone (T)‐dependent secondary sexual traits such as song. Correlational studies have linked high plasma T‐levels to high diurnal song output. This has been confirmed in experiments where T‐levels were kept high at times when natural T‐levels have decreased. However, surprisingly little is known about the relation between T‐levels during the early breeding season and song. In many passerine birds males sing at a high rate at dawn early in the breeding season, referred to as the dawn chorus. In blue tits (Parus caeruleus), the dawn chorus coincides with the fertile period of the female, whereas diurnal song occurs throughout the breeding season. Previous studies on blue tits showed that characteristics of the dawn chorus correlate with male reproductive success. We experimentally elevated plasma T‐levels in male blue tits during the pre‐fertile and fertile period. Our aim was to test whether increased plasma T‐levels affect dawn song characteristics and increase the amount of diurnal song. Although T‐implants successfully raised circulating T‐levels, we did not find any difference between T‐ and control males in temporal performance measures of dawn song or in diurnal song output. Our results suggest that either there is no direct causal link between song output or quality and individual T‐levels, or experimental manipulations of T‐levels using implants do not permit detection of such effects during the early breeding season. Although we cannot exclude that individual T‐levels are causally linked to other (e.g. structural) song parameters, our results cast doubt on T‐dependence as the mechanisms that enforces honesty on song as a sexually selected trait.     

Relationship of the parameters of body cholesterol metabolism with plasma levels of HDL cholesterol and the major HDL apoproteins

The inverse relationship between plasma levels of high density lipoprotein (HDL) and coronary heart disease rates has suggested that HDL might influence body stores of cholesterol. Therefore, we have investigated potential relationships between the parameters of body cholesterol metabolism and the plasma levels of HDL cholesterol and the major HDL apoproteins. The study involved 55 human subjects who underwent long-term cholesterol turnover studies, as well as plasma lipoprotein and apolipoprotein assays. In order to maximize the likelihood of detecting existing relationships, the subjects were selected to span a wide range of plasma levels of lipids, lipoproteins, and apolipoproteins. Single univariate correlation analyses suggested weak but statistically significant inverse relationships of HDL cholesterol and apoA-I levels with the following model parameters: production rate (PR), the mass of rapidly exchanging body cholesterol (M1), the minimum estimate of the mass of slowly exchanging body cholesterol (M3min), and of the mass of total exchangeable body cholesterol (Mtotmin). These correlations, however, were quantitatively quite small (/r/ = 0.28-0.42) in comparison to the strength of the univariate relationships between body weight and PR (r = 0.76), M1 (r = 0.61), M3min (r = 0.58), and Mtotmin (r = 0.78). Correlations for apoA-II and apoE levels were even smaller than those for apoA-I and HDL cholesterol. In additional analyses using multivariate approaches, HDL cholesterol, apoA-I, apoA-II, and apoE levels were all found not to be independent determinants of the parameters of body cholesterol metabolism (/partial r/ less than 0.17, P greater than 0.3 in all cases). Thus the weak univariate correlations reflect relationships of HDL cholesterol and apoA-I levels with physiological variables, such as body size, which are primarily related to the model parameters. We conclude that plasma levels of HDL cholesterol and apoproteins A-I, A-II, and E are not quantitatively important independent determinants of the mass of slowly exchanging body cholesterol or of other parameters of long-term cholesterol turnover in humans. These studies give no support to the hypothesis that the inverse relationship between HDL cholesterol levels and coronary heart disease rates is mediated via an influence of HDL on body stores of cholesterol.     

Undirected Song in Wild Zebra Finch Flocks: Contexts and Effects of Mate Removal

Wild zebra finches, Taeniopygia guttata, sing frequently throughout the year but the function of undirected song, the most prevalent type, is unknown. Paired males commonly sang undirected song in feeding flocks where it occurred more frequently in the non-breeding season than in the breeding season. Song rate varied greatly among males. The context of the singer and the absence of any overt responses from flock members excludes direct aggressive and mate-attracting functions. Performance of undirected song may have energetic costs and predatory risks. The finding that singers are active individuals with ‘spare time’, that are neither hungry, nor tired, nor sexually motivated, suggests that singers are advertising their ‘quality’ as potential mates and/or participants for extra-pair copulations. When the female partner in non-breeding pairs was experimentally removed, the rate of undirected song of the ‘widower’ increased significantly. Males quickly re-paired. This experiment supports the hypothesis that singing in the flock has a mate-attracting role.     

Breeding experience affects condition: blood metabolite levels over the course of incubation in a seabird

In vertebrates little is known about causes and correlates of differences in individual body condition. This is, however, essential if we are to gain an understanding of environmental influences on wild populations. To track changes in individual physiological state we analysed blood metabolite concentrations in breeding common terns Sterna hirundo. We selected birds to contrast sex, breeding experience, sampling year and nutritional state and collected repeated samples from individuals during incubation. Unlike cholesterol, triglyceride and uric acid levels strongly correlated with nutritional state. While cholesterol levels in males remained stable throughout incubation, comparatively lower levels were measured in females directly after egg-laying. In 2006, only highly experienced females showed increased cholesterol concentrations by mid-incubation, whereas less experienced females maintained reduced levels and were apparently unable to recover. In 2007, all females showed an increase in cholesterol by mid-incubation. Triglyceride levels did not differ between sexes, but concentrations were significantly higher in more experienced birds and were overall higher in 2007 than in 2006. Uric acid concentrations did not differ significantly. The variation in cholesterol and triglyceride levels can be explained by differences in foraging conditions, as food abundance, onset of breeding and mean clutch size indicate 2007 to be the superior year. Thus, environmental conditions and breeding experience play an important role for cholesterol and triglyceride levels as well as the physiological state.     

黄腹山鹪莺成鸟的秋季换羽

黄腹山鹪莺(Prinia flaviventris)具有冬羽尾羽长于繁殖羽尾羽的特点,可能意味着一种新的生存和繁殖策略。为此,从2006年9月～2007年2月,在广东省肇庆市江溪村对黄腹山鹪莺的秋季换羽进行研究。结果显示:(1)黄腹山鹪莺成鸟繁殖羽体长和尾羽长皆极显著短于冬羽(P<0.01),繁殖羽翼长显著短于冬羽(P<0.05),其余身体量度的差异均不显著(P>0.05)。(2)9月17日获得第一个黄腹山鹪莺换羽个体,初级飞羽已更换到P5,次级飞羽已更换到S6,11月20日后所获样本均已完成羽毛的更换。(3)初级飞羽的换羽模式为递降换羽,次级飞羽为递升换羽,尾羽为离心型换羽。(4)换羽期间,10月的个体平均体重最大,显著(P<0.01)重于11月的体重,其他各月无显著性差异(P>0.05)。据此,推测黄腹山鹪莺秋季种群换羽的持续时间约100d;相对其他羽毛而言,尾羽更换对黄腹山鹪莺生长发育的影响更为明显。     

Spring and autumn territoriality in song sparrows: same behavior, different mechanisms?

Vertebrates show a diverse array of social behaviors associatedwith territoriality. Field and laboratory experiments indicatethat underlying themes—including mechanisms—mayexist. For example in birds, extensive evidence over many decadeshas implicated a role for testosterone in the activation ofterritorial aggression in reproductive contexts. Territorialityat other times of the year appeared to be independent of gonadalhormone control. One obvious question is—why this diversityof control mechanisms for an apparently similar behavior? Controlof testosterone secretion during the breeding season must balancethe need to compete with other males (that tends to increasetestosterone secretion), and the need to provide parental care(that requires lower testosterone concentrations). Regulationof aggressive behaviors by testosterone in the non-breedingseason may incur substantial costs. A series of experimentson the male song sparrow, Melospiza melodia morphna, of westernWashington State have revealed possible mechanisms to avoidthese costs. Song sparrows are sedentary and defend territoriesin both breeding and non-breeding seasons. Dominance interactions,territorial aggression and song during the non-breeding seasonare essentially identical to those during the breeding season.Although in the non-breeding season plasma testosterone andestradiol levels are very low, treatment with an aromatase inhibitordecreases aggression and simultaneous implantation of estradiolrestores territorial behavior. These data suggest that the mechanismby which testosterone regulates territorial behavior at theneural level remains intact throughout the year. How the hormonalmessage to activate such behavior gets to the brain in differentseason does, however, appear to be different.     

Consequences of breeding system for body condition and survival throughout the annual cycle of tidal marsh sparrows

An individual's body condition and probability of survival can change throughout the annual cycle, based on the combined effects of many factors, including reproductive investment during breeding, colder temperatures during winter, and elevated risks during migration. We evaluated body condition and survival during breeding and non‐breeding periods in two closely related species with notably different reproductive systems. Male and female saltmarsh sparrows Ammodramus caudacutus represent extremes in parental care: males perform none, leaving females to do everything from build nests to care for fledglings. In contrast, male and female seaside sparrows A. maritimus have bi‐parental care and similar levels of reproductive investment, intermediate between male and female saltmarsh sparrows. Our results are consistent with the idea that females experience non‐lethal effects of reproduction, and that differences between the breeding season and winter affect condition. In both species, females had lower scaled mass index (SMI) values than males during both breeding and non‐breeding seasons, and female saltmarsh sparrows had lower SMI values than female seaside sparrows. Females carried more fat than males during the breeding season, and female, but not male, fat and muscle scores decreased over time, which is consistent with the adaptive mass hypothesis. In winter, all groups carried more fat and had higher muscle scores than when breeding, despite having lower SMI scores. Although we observed variation in body condition, within‐season survival was uniformly high in both seasons, suggesting that sex, species, season, body size, and body condition have little impacts on within season survival. Comparisons with previously‐published estimates of annual adult survival suggest that most mortality occurs during migration, even in these short‐distance migrants. The importance of considering multiple aspects of body condition, multiple seasons, and difficult‐to‐monitor events, such as migration, should not be ignored when thinking about the events and processes that cumulatively determine population dynamics.