Interrelationships between egg mass and adult body mass and metabolism among passerine birds

Summary The regression of egg mass of Passeriformes against female body mass (n=1244) and basal metabolic rate of Passeriformes against body mass (n=159) have similar slopes, indicating that for this group egg mass is directly proportional to basal metabolic rate and that the relative egg mass (% of body mass) is directly proportional to the weight-specific metabolism. This relationship and the average caloric density of passerine eggs (n=38) provides an estimate of the cost of egg production, which for single eggs is 41 % of the basal metabolic rate.

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Beziehungen zwischen Eigewicht, Körpergewicht und Stoffwechsel bei Sperlingsvögeln

Zusammenfassung Die Regressionsgeraden von Eigewichten der Passeriformes und weiblicher Körpergewichte (N=1244) einerseits sowie von Ruheumsatz und Körpergewichten (N=159) andererseits haben vergleichbare Steigungen. Das bedeutet, (1) daß für diese Vogelordnung das Eigewicht proportional zum Ruheumsatz und (2) daß das relative Eigewicht (% des Körpergewichtes) proportional zum gewichtspezifischen Stoffwechsel ist. Dieses Verhältnis und der durchschnittliche kalorische Wert der Eier (N=38) erlauben die Kosten der Eiproduktion zu schätzen: sie betragen für das einzelne Ei 41 % des Ruheumsatzes.

     

Global diversification rates of passerine birds

The distribution of species richness in families of passerine birds suggests that the net rate of diversification was significantly higher than average in as many as 7 out of 47 families. However, the absence of excess species richness among the 106 tribes within these families indicates that these high rates were transient, perhaps associated in some cases with tectonic movements or dispersal events that extended geographical ranges. Thus, large clade size among passerine birds need not represent intrinsic key innovations that influence the rate of diversification. Approximately 17 families and 30 tribes have too few species relative to other passerine taxa. Many of these are ecologically or geographically marginal, being especially overrepresented in the Australasian region. Observed intervals between lineage splitting suggest that extinction has occurred ca. 90% as frequently as speciation (waiting times of 1.03 and 0.93 Myr) and that the 47 modern families comprising 5712 species descended from approximately 430 passerine lineages extant 24 Myr ago. Speciation and extinction rates among small, marginal families might be 1-2 orders of magnitude lower.     

Global warming and egg size of birds

Global warming or climate change is known to have many effects on plants, but there has been relatively little research on global warming and animals, partly because too few long-term studies have been carried out. In northern areas, mean temperature is believed to be rising, and indeed during the last decades mean spring temperatures in Finnish Lapland have increased. In 1975-1993, mean air temperature during the main egg-laying period of a pied flycatcher Ficedula hypoleuca population correlated positively and significantly with mean egg volume of that population. Since larger eggs enjoy improved hatching success, global warming may alter birds' reproductive strategies, because warmer weather may allow females to invest more resources in reproduction. This in turn may help birds rapidly conquer new areas when they become available and compensate for rising mortality rates to be expected elsewhere where warming means desiccation.     

Polyterritorialitytion in passerine birds

In some birds, males defend two spatially separated territories and attract females to each one in turn. it has been proposed that this behaviour, referred to as polyterritoriality, allows males to conceal their marital status, thereby deceiving females into accepting polygyny against their best interests. The deception hypothesis has gained general acceptance as an explanation for polyterritoriality in birds, but until recently the empirical basis for the hypothesis rested almost entirely on studies of Swedish populations of the pied flycatcher (Ficedula hypoleuca). New findings, emerging from further studies of the pied flycatcher and of other species, suggest several alternative selection pressures that may have favoured polyterritoriality.     

Climate warming,ecological mismatch at arrival and population decline in migratory birds

Climate is changing at a fast pace, causing widespread, profound consequences for living organisms. Failure to adjust the timing of life-cycle events to climate may jeopardize populations by causing ecological mismatches to the life cycle of other species and abiotic factors. Population declines of some migratory birds breeding in Europe have been suggested to depend on their inability to adjust migration phenology so as to keep track of advancement of spring events at their breeding grounds. In fact, several migrants have advanced their spring arrival date, but whether such advancement has been sufficient to compensate for temporal shift in spring phenophases or, conversely, birds have become ecologically mismatched, is still an unanswered question, with very few exceptions. We used a novel approach based on accumulated winter and spring temperatures (degree-days) as a proxy for timing of spring biological events to test if the progress of spring at arrival to the breeding areas by 117 European migratory bird species has changed over the past five decades. Migrants, and particularly those wintering in sub-Saharan Africa, now arrive at higher degree-days and may have therefore accumulated a ‘thermal delay’, thus possibly becoming increasingly mismatched to spring phenology. Species with greater ‘thermal delay’ have shown larger population decline, and this evidence was not confounded by concomitant ecological factors or by phylogenetic effects. These findings provide general support to the largely untested hypotheses that migratory birds are becoming ecologically mismatched and that failure to respond to climate change can have severe negative impacts on their populations. The novel approach we adopted can be extended to the analysis of ecological consequences of phenological response to climate change by other taxa.     

Recent changes in body weight and wing length among some British passerine birds

We tested the prediction that global warming has caused recent decreases in body weight (Bergmann's rule) and increases in wing length (Allen's rule) in 14 species of passerine birds at two localities in England: Wicken Fen (1968–2003) and Treswell Wood (1973–2003).
Predicted long-term linear decreases in residual body weight occurred in four species: dunnocks (Wicken Fen), and great tits, blue tits and bullfinches (Treswell Wood). Non-linear decreases also occurred in reed warblers and blackcaps at Wicken Fen, which also had a surprising linear increase in residual body weight in blackbirds.
Residual wing lengths increased linearly, as predicted, in six of seven species at Wicken Fen. Whereas there were non-linear long-term increases in wrens, dunnocks and blackbirds in Treswell Wood. Unexpected linear decreases also occurred in residual wing lengths in willow warblers (Wicken Fen), and blue tits, great tits and chaffinches (Treswell Wood).
The most parsimonious explanation for such long-term changes in body weight is global warming, as predicted by Bergmann's rule. Greater site and species-specific effects on wing length (e.g. non-linear changes plus shorter wings in the woodland habitat) suggest a less straightforward conclusion concerning Allen's rule, probably because wing length involved variation in both bone and feather growth.
Changes in residual body weights and wing lengths often differed between species and were sometimes non-linear, perhaps reflecting short-term modifications in selection pressures. Human-induced influences are discussed, such as avian predator population densities and land-use change. Short-term variation in temperature had little effect, but rainfall did explain the unusual increase in blackbird body weight, possibly as a result of improving food (earthworm) availability.     

Phenotypic flexibility of body composition associated with seasonal acclimatization in passerine birds

Improved winter cold tolerance is widespread among small birds overwintering in cold climates and is associated with improved shivering endurance and elevated summit metabolic rate (M_sum). Phenotypic flexibility resulting in elevated M_sum could result from either increased skeletal muscle mass (perhaps with support from similar adjustments in “nutritional organs”) and/or cellular metabolic intensity. We investigated seasonal changes in body composition of three species of passerine birds resident in cold winter climates, all of which show large seasonal variations in M_sum (>25%); white-breasted nuthatch (Sitta carolinensis), black-capped chickadee (Poecile atricapillus), and house sparrow (Passer domesticus). All three species displayed significant winter increases in pectoralis and heart masses, and supracoracoideus mass also increased in winter chickadees. Gizzard mass increased in winter for all three species, but masses of other nutritional organs did not vary consistently with season. These data suggest that winter increases in pectoralis and heart masses are important contributors to elevated thermogenic capacity and cold tolerance, but seasonal variation in nutritional organ masses, other than gizzard, which is likely associated with dietary changes, are not universally associated with seasonal phenotypes. The winter increases in pectoralis and heart masses are consistent with data from other small passerines showing marked seasonal changes in cold tolerance and support the Variable Maximum Model of seasonal phenotypic flexibility, where physiological adjustments that promote improved cold tolerance, also result in elevated M_sum.     

Estimating lipid and lean body mass in small passerine birds using TOBEC,external morphology and subcutaneous fat‐scoring

To assess regression models for lipid and lean body mass in small birds, we recorded live body mass ±0.1 g, total body electrical conductivity (TOBEC; from “third generation” TOBEC machine EM‐SCAN® SA‐3000) or E‐Value, visual fat score (VisFat), and seven body measurements for 52 migratory passerine birds of 13 species (5–40 g). We determined lipid and lean mass of each bird after petroleum‐ether extraction of lipids. We obtained “net”E‐Value (NEV) for each scanned bird by subtracting the E‐Value of the empty bird‐restraining tube, because these showed an inverse temperature dependence (P<0.005). Leave‐one‐out cross validation was used to assess model selection and construct 95% confidence intervals. Although precision of TOBEC increased with bird size (CV of NEV vs. live mass: r=−0.276, P=0.002) and it explained an increasing proportion of variation in lean mass moving from small‐ to medium‐ to large‐bird classes of our data, it did no better than head length in single‐variable prediction of lean or lipid mass and was included in five of the 14 multivariate models we developed. The best multiple regression to predict lean mass included live weight, VisFat, bill length, tarsus and lnNEV (adjusted R²=99.0%); however, the same model lacking only lnNEV yielded aR²=98.9%. A parallel to the above pair of models, but predicting lipid mass, yielded aR²=90.3% and 90.0%, respectively. Subdividing the data by three size classes and three taxa (American redstart Setophaga ruticilla, ovenbird Seiurus aurocapilla, warblers), best‐subset multiple‐regression models predicted lean mass with aR² from 94.7 to 99.6% and lipid mass with aR² from 85.4 to 98.3%. Best models for the size‐ and species‐groups included VisFat and zero to five body measurements, and most included live weight. lnNEV was included only in the models for ovenbird (lipid), warblers (lipid), all birds (both), and large birds (both). Actual lipid mass of all birds was more highly correlated with multiple‐regression‐predicted lipid mass (r=0.955) than with visual subcutaneous fat‐scoring (r=0.683). These multiple‐regression models predicting lipid content using live‐bird measurements and visual fat score as independent variables represent more accurate and precise estimates of actual lipid content in small passerines than any previously published. They are particularly accurate for placing birds into percentage body‐fat classes.     

Body frontal area in passerine birds

Projected body frontal area is used when estimating the parasite drag of bird flight. We investigated the relationship between projected frontal area and body mass among passerine birds, and compared it with an equation based on waterfowl and raptors, which is used as default procedure in a widespread software package for flight performance calculations. The allometric equation based on waterfowl/raptors underestimates the frontal area compared to the passerine equation presented here. Consequently, revising the actual frontal areas of small birds will concomitantly change the values of the parasite drag coefficient. We suggest that the new equation     (m²) where m _B is body mass (kg) should be used when a value of frontal area is needed for passerines.     

Seasonality in daily body mass variation in a hoarding boreal passerine

We studied the body mass variation from autumn to winter, in a free-living population of willow tits (Parus montanus), a food-hoarding passerine living year-round in boreal forests. Our aim was to find out whether this population exhibits winter fattening as part of the annual body mass cycle. True winter fattening is considered to be a strategic response to winter conditions. The strategy includes an increase in both the morning mass and the daily mass increase, as winter approaches. A multivariate approach was used to find which predictors (year, date, age, sex, body size, temperature and snow depth) explained the mass variation in birds measured twice per day. Morning mass variation was explained by sex, age, wing length and snow depth. Independently, date explained morning mass variation only in adult males. None of the predictors explained the variation observed in daily mass increase in any age or sex class. Therefore, we failed to detect winter fattening in our study population of willow tits. Response to increasing night length is not due to higher absolute intake, but to higher energy acquisition rate and decreased night-time energy consumption. The results suggest that willow tits at high latitudes manage increasing energy demands on a short-term basis and respond flexibly to changing conditions by adjusting foraging efficiency and especially night-time energy expenditure.     

Postexercise ketosis in night-migrating passerine birds

This study investigated the postexercise metabolism of six species of free-living, night-migrating passerine birds (European robin, pied flycatcher, wheatear, redstart, blackcap, and garden warbler). The birds were caught during autumn migration out of their nocturnal flight, and their metabolism changed from a fasting, highly active state to a fasting, resting state. Concentrations of six plasma metabolites of the fat, carbohydrate, and protein metabolism were measured during up to 10 h of recovery time. The metabolic changes indicated a biphasic pattern: (a) a quick first response to the reduced energy demands during the first 20 min of recovery, suggested by an increase and subsequent decrease of free fatty acid levels, and (b) subsequently, a postexercise ketosis and a reduction of lipolysis and proteolysis, suggested by high beta-hydroxy-butyrate and low free fatty acid, glycerol, triglyceride, and uric acid levels. This metabolic pattern differs from that of humans and rats, in which ketosis starts immediately postexercise or is absent in trained subjects. Since migrating birds are naturally adapted to endurance exercise, it is hypothesized that the high and long-lasting postexercise ketosis does not evoke physiological problems (such as hypoglycemia) but, by contrast, increases the ability of birds to rely on lipids, to a very high extent, during and after flight and decreases the dependence on glucose and glucogenic amino acids. Differences between species in fat stores and metabolic pattern support this hypothesis.     

Global warming and excess nitrogen may induce butterfly decline by microclimatic cooling

Global warming may explain the current poleward shift of species distributions. However, paradoxically, climatic warming can lead to microclimatic cooling in spring by advancing plant growth, an effect worsened by excess nitrogen. We suggest that spring-developing but thermophilous organisms, such as butterflies hibernating as egg or larva, are particularly sensitive to the cooling of microclimates. Using published data on butterfly trends in distribution, we report a comparatively greater decline in egg–larva hibernators in European countries with oceanic climates and high nitrogen deposition, which supports this explanation. Furthermore, trends in abundance from a nationwide butterfly monitoring scheme reveal a 63% decrease over 13 years (1992–2004) for egg–larva hibernators in the Netherlands, contrasting with a nonsignificant trend in adult–pupa hibernators. This evidence supports the hypothesis that these environmental changes pose new threats to spring-developing, thermophilous species. We underline the threat of climate change to biodiversity, as previously suggested on the basis of mobility, habitat fragmentation and evolutionary adaptation, but we here emphasize a different ecological axis of change in habitat quality.     

Genome size and wing parameters in passerine birds

Despite their status as the most speciose group of terrestrial vertebrates, birds exhibit the smallest and least variable genome sizes among tetrapods. It has been suggested that this is because powered flight imposes metabolic constraints on cell size, and thus on genome size. This notion has been supported by analyses of genome size and cell size versus resting metabolic rate and other parameters across birds, but most previous studies suffer from one or more limitations that have left the question open. The present study provides new insights into this issue through an examination of newly measured genome sizes, nucleus and cell sizes, body masses and wing parameters for 74 species of birds in the order Passeriformes. A positive relationship was found between genome size and nucleus/cell size, as well as between genome size and wing loading index, which is interpreted as an indicator of adaptations for efficient flight. This represents the single largest dataset presented for birds to date, and is the first to analyse a distinctly flight-related parameter along with genome size using phylogenetic comparative analyses. The results lend additional support to the hypothesis that the small genomes of birds are indeed related in some manner to flight, though the mechanistic and historical bases for this association remain an interesting area of investigation.     

Sperm morphology and sperm velocity in passerine birds

Sperm velocity is one of the main determinants of the outcome of sperm competition. Since sperm vary considerably in their morphology between and within species, it seems likely that sperm morphology is associated with sperm velocity. Theory predicts that sperm velocity may be increased by enlarged midpiece (energetic component) or flagellum length (kinetic component), or by particular ratios between sperm components, such as between flagellum length and head size. However, such associations have rarely been found in empirical studies. In a comparative framework in passerine birds, we tested these theoretical predictions both across a wide range of species and within a single family, the New World blackbirds (Icteridae). In both study groups, sperm velocity was influenced by sperm morphology in the predicted direction. Consistent with theoretical models, these results show that selection on sperm morphology and velocity are likely to be concomitant evolutionary forces.     

DNA evolutionary rates in nine-primaried passerine birds

Differences in single-copy nuclear-DNA sequences among 13 species of passerine birds were measured using DNA-DNA hybridization. A matrix of pairwise dissimilarity values (delta mode distances) was constructed from analysis of fitted thermal dissociation curves. A least-squares method of phylogenetic estimation was used to construct two topologies from the distance matrix, one constraining branch lengths of sister taxa to be equal and the other permitting such lengths to vary. These topologies were identical in the pattern of branching of taxa, and the difference in their sums of squares was not statistically significant, suggesting that rates of DNA evolution in sister groups of nine- primaried oscines are equal. A nonparametric test for nonrandom variation in distances of sister groups to outgroup taxa revealed no statistically significant deviation from random variation that would be expected as a result of measurement error. However, the level of measurement error was such that rates of DNA evolution in sister taxa could vary by as much as 10% without being detected with the statistical methods used here.      

Evolution of sperm structure and energetics in passerine birds

Spermatozoa exhibit considerable interspecific variability in size and shape. Our understanding of the adaptive significance of this diversity, however, remains limited. Determining how variation in sperm structure translates into variation in sperm performance will contribute to our understanding of the evolutionary diversification of sperm form. Here, using data from passerine birds, we test the hypothesis that longer sperm swim faster because they have more available energy. We found that sperm with longer midpieces have higher levels of intracellular adenosine triphosphate (ATP), but that greater energy reserves do not translate into faster-swimming sperm. Additionally, we found that interspecific variation in sperm ATP concentration is not associated with the level of sperm competition faced by males. Finally, using Bayesian methods, we compared the evolutionary trajectories of sperm morphology and ATP content, and show that both traits have undergone directional evolutionary change. However, in contrast to recent suggestions in other taxa, we show that changes in ATP are unlikely to have preceded changes in morphology in passerine sperm. These results suggest that variable selective pressures are likely to have driven the evolution of sperm traits in different taxa, and highlight fundamental biological differences between taxa with internal and external fertilization, as well as those with and without sperm storage.     

Global warming and alternative causes of decline in arctic-alpine and boreal-montane lichens in North-Western Central Europe

Lichens are thought to be sensitive indicators of global warming, as the spread of several thermophilous epiphytes in north-western Central Europe has been attributed to late 20th century warming. In the present paper, the potential contribution of late 20th century warming to the decline of arctic-alpine and boreal-montane lichen species is analyzed. Relevant ecological groups of lichens include terricolous heathland species, saxicolous species of exposed rock outcrops and boulder fields as well as epiphytes of mountain forests. These three groups of lichens experienced significant declines before the onset of late 20th century warming in the 1970s. These declines can be attributed to the abandonment of traditional land use systems in the case of the heathland lichens, increased recreational use of the exposed summits usually inhabited by cold-tolerant saxicolous lichens, and to high atmospheric SO₂ levels in the mid-20th century, but are probably not directly connected to global warming.     

Social mating systems and extrapair fertilizations in passerine birds

Two alternative hypotheses have been proposed to explain howsocial and genetic mating systems are interrelated in birds.According to the first (male trade-off) hypothesis, socialpolygyny should increase extrapair fertilizations because whenmales concentrate on attracting additional social mates, theycannot effectively protect females with whom they have already paired from being sexually assaulted. According to the second(female choice) hypothesis, social polygyny should decreaseextrapair fertilizations because a substantial proportion offemales can pair with the male of their choice, and males caneffectively guard each mate during her fertile period. To discriminatethese alternatives, we comprehensively reviewed informationon social mating systems and extrapair fertilizations in temperatezone passerine birds. We found significant inverse relationshipsbetween proportions of socially polygynous males and frequenciesof extrapair young, whether each species was considered asan independent data point (using parametric statistics) orphylogenetically related species were treated as nonindependent (using contrasts analyses). When social mating systems weredichotomized, extrapair chicks were twice as frequent in monogamousas in polygynous species (0.23 vs. 0.11). We hypothesize thatin socially polygynous species, (1) there is less incentivefor females and males to pursue extrapair matings and (2) femalesincur higher costs for sexual infidelity (e.g., due to physical retaliation or reduction of paternal efforts) than in sociallymonogamous species.