THE SURVIVAL RATES OF SOME SOUTHERN AFRICAN PASSERINES

Yom-Tov, Y., McCleery, R. & Oatley, T. 1994. The survival rates of some southern African passerines. Ostrich 65:329-332.

Little information is available on survival rates of southern hemisphere passerines, but two recent studies indicate that Australian passerines tend to live longer than their northern hemisphere relatives. The aim of this paper is to provide data on survival of some South African passerines and compare them with Australian data. The survival rates of eleven species (eight genera) of South African passerines were calculated using recapture data provided by the South African Bird Ringing Unit for birds whose retraps occurred more than 12 months after the original ringing. Survival did not depend on either the length of the study or body mass. Mean survival rate was similar to that of 32 species of Australian passerines, which is at least 1,2 greater than that of British passerines.     

Prediction of mean adult survival rates of southern African birds from demographic and ecological covariates

Estimates of annual survival rates of birds are valuable in a wide range of studies of population ecology and conservation. These include modelling studies to assess the impacts of climatic change or anthropogenic mortality for many species for which no reliable direct estimates of survival are available. We evaluate the performance of regression models in predicting adult survival rates of birds from values of demographic and ecological covariates available from textbooks and databases. We estimated adult survival for 67 species using dead recoveries of birds ringed in southern Africa and fitted regression models using five covariates: mean clutch size, mean body mass, mean age at first breeding, diet and migratory tendency. Models including these explanatory variables performed well in predicting adult survival in this set of species, both when phylogenetic relatedness of the species was taken into account using phylogenetic generalized least squares (51% of variation in logit survival explained) and when it was not (48%). Two independent validation tests also indicated good predictive power, as indicated by high correlations of observed with expected values in a leave‐one‐out cross validation test performed using data from the 67 species (35% of variation in logit survival explained), and when annual survival rates from independent mark–recapture studies of 38 southern African species were predicted from covariates and the regression using dead recoveries (48%). Clutch size and body mass were the most influential covariates, both with and without the inclusion of phylogenetic effects, and a regression model including only these two variables performed well in both of the validation tests (39 and 48% of variation in logit survival explained). Our regression models, including the version with only clutch size and body mass, are likely to perform well in predicting adult survival rate for southern African species for which direct survival estimates are not available.     

The survival rate of Australian passerines

The Australian avifauna is composed largely of two groups–the 'old endemics', species that originated in Gondwana and radiated in Australia and New Guinea, and the 'new invaders', species that originated in Asia and invaded Australia during the Pleistocene. In addition, several species were introduced by Europeans during the last 200 years. The old endemics have clutch-sizes significantly smaller than those of the new invaders (Yom-Tov 1987). The aim of this paper was to study the survival rates of Australian passerines from the three groups.
The survival rates of 3 5 species of Australian passerines were calculated by using recapture data provided by the Australian Bird Banding Scheme for birds older than one year. Survival depends primarily on body-mass, with no difference between the old endemics and the new invaders. It is suggested that the survival rates of birds younger than one year is different between the two main groups.
Overall, the survival rates of Australian passerines is at least 1.2 greater than that of equal-sized British passerines. The survival rates of the introduced House Sparrow Passer domesticus and Blackbird Turdus merula were similar on the two continents, suggesting either that insufficient time had elapsed since their introduction to Australia for them to adapt to local conditions, or that the habitats occupied in Australia were so modified by human activities that selection did not favour long lives. The survival rate of the introduced Starling Sturnus vulgaris was lower in Australia, probably because it lives in natural habitats there.     

Similar survival of birds between wet and seasonally dry Neotropical environments

Studies in the tropics suggest a regional similarity in survival rates of adult birds; however, this literature often overlooks species in semi-arid tropical environments. Bird survival in seasonally dry environments (e.g. seasonally dry tropical forests (SDTFa)) may be lower than that in more constantly wet areas (e.g. tropical rainforests (TRFs)), especially if the birds are negatively affected by seasonal rainfall or food-limitation. However, survival could be similar across these tropical environments, as the asymmetry between young and adult mortality tends to be high in all tropical areas, and the higher risk of mortality in young animals may favour adult survival (residual reproductive investment) regardless of the local climatic conditions. To fill this knowledge gap, we tested the hypothesis that bird survival is similar between seasonally dry (SDTF) and constantly wet (TRF) Neotropical environments. We estimated the apparent survival of 27 South American bird populations from three SDTF areas and 39 populations from a TRF. Apparent survival was estimated from Cormack–Jolly–Seber (CJS) models fitted using a Bayesian structure and the resulting variation in survival rates between study areas and with body mass was explored using a Bayesian phylogenetic mixed model. Apparent annual survival of passerines did not differ between areas (geometrical mean of survival: SDTF = 0.50, 0.56, 0.64; TRF = 0.58), but body mass was positively associated with survival. The variation in bird survival was partially explained by phylogenetic relationships among species. Our results suggest that bird survival is regionally similar in Neotropical forests, despite the climatic variation. We discuss possible physiological and behavioural mechanisms adopted by birds in SDTFs to attenuate effects of environmental seasonality on survival.     

Nest predation patterns in ground-nesting passerines on the Iberian Peninsula

The idea that ground-nesting birds have a high risk of predation is widely accepted This paper analyzes the nest predation patterns of ground-nesting passerines on the Iberian Peninsula The nest predation rates are higher m open land species x= 71%) than m countryside farmland (10%) or forest birds (29%) The latter species have no differences in daily survival between ground and above-ground nests The higher nest predation in ground-nesting open land species was similar m peninsular Spain and North America We conclude that it is incorrect to generalize that all ground nesters have high nest predation rates, and we discuss the possible link of the high nest predation rates of open land birds to the decline observed in their population trends in Spain     

GROWTH RATES OF BIRDS IN THE HUMID NEW WORLD TROPICS

The growth curves of 40 species of lowland neotropical birds were fitted by logistic equation. The birds were mostly from Panama, Trinidad and Surinam. The growth constants of the fitted equations (asymptote A and growth rate K) were compared within and among species, and with previously published data on temperate species. Growth parameters of tropical passerines are about as variable within species as they are within temperate species. In both cases, variation in A and K between broods is greater than it is within broods. Panamanian birds breed during the dry-wet transition and conditions for growth apparently improve as rainfall increases. Asymptotes of growth curves are higher, and mortality within broods lower, as the breeding season progresses. Asynchronous hatching and the reduction of brood-size by selective starvation of young is a prominent phenomenon during the early part of the breeding season. Several instances are reported, however, of young persisting in nests with inadequate feeding and greatly subnormal weights. Slowed development under conditions of poor nutrition may be adaptive in the tropics if periods of low food availability are short and allow the possibility of recovery from undernourishment. As a group, neotropical lowland passerines (30 species) grow 23% more slowly than a sample of 51 temperate passerines. Variation of growth rates among these tropical species is similar to variation among temperate species, and it is related to adult body-size the length of the nestling period. Young of tropical and temperate species attain similar asymptotes, relative to adult body-weight, by the end of the nestling period. Hypotheses are advanced which might explain the slower growth rate of tropical species, and tested to the extent available data permits. (1) Because brood-size can be changed only by adding or removing whole young, changes in growth rate could provide finer adjustment of the energy requirements of the young to the feeding capacity of the parents. This model predicts different means and variances for growth rate within groups of species with different clutch-sizes, predictions not supported by available data. (2) Growth rate is shown to increase the maximum energy requirement of a nestling only if K exceeds some value determined by the energy requirement of the young, growth rate should vary in proportion to the level of basal maintenance metabolism. In a small sample of tropical species, rates of basal metabolism were 25% lower than in a comparable sample of temperate species. These data therefore support the hypothesis, although the cause of the lower metabolic rate of the tropical nestlings is not known. (3) Daily periods of hypothermia could reduce the energy requirement of the young and at the same time reduce their growth rate; but observations of body temperatures of tropical nestlings are contrary to this hypothesis. (4) The short day-length of tropical climates reduces the time during which young can assimilate energy relative to their energy expenditures. This model predicts that tropical nestlings would have less productive energy available, (consistent with their reduced growth rates), but it also predicts that arctic birds should grow faster than temperate species, which is not confirmed by available data. (5) The low nitrogen content of fruits may cause the slow growth of a few strictly frugivorous species (Oilbird and Bearded Bellbird), but among other tropical species growth rate is not correlated with the estimated proportion of fruit in the diet.     

Effect of Geolocators on Migration and Subsequent Breeding Performance of a Long-Distance Passerine Migrant

Geolocators are small light-weight data loggers used to track individual migratory routes, and their use has increased exponentially in birds. However, the effects of geolocators on individual performance are still poorly known. We studied geolocator effects on a long-distance migrating passerine bird, the northern wheatear (Oenanthe oenanthe L.). We asked the general question of whether geolocators affect migratory behaviour and subsequent reproductive performance of small passerines by comparing arrival time, breeding time, breeding success and survival of geolocator versus control birds of known identity and breeding history. During two years geolocator birds (n=37) displayed a lower apparent survival (30%) as compared to controls (45%, n=164). Furthermore, returning geolocator birds (n=12) arrived on average 3.5 days later, started laying eggs 6.3 days later, and had lower nest success (25%) than control birds (78%). Our results suggest that geolocators affect migratory performance with carry-over effects to the timing of breeding and reproductive success in the subsequent breeding season. We discuss the implications of such geolocator effects for the study of migratory strategies of small passerines in general and suggest how to identify and investigate such effects in the future.     

A survey of the prevalence of selected bacteria in wild birds

We determined the prevalence of six genera of bacteria from a sample of 387 cloacal swabs from 364 passerines and woodpeckers. The prevalence of bacteria were as follows: Escherichia coli (1%), Pseudomonas spp. (22%), Salmonella spp. (0%), Staphylococcus spp. (15%), Streptococcus spp. (18%), and Yersinia spp. (1%). The prevalence of Streptococcus spp. was higher in omnivorous species than in granivorous species (20% versus 8%). Individuals captured at feeders had a lower prevalence of both Streptococcus spp. (15% versus 33%) and Escherichia coli (0.5% versus 4%) than birds that did not have access to feeders. These differences are probably not due to the feeder per se, but instead to other site related differences. The prevalence of bacteria did not differ between male and female black-capped chickadees, Parus atricapillus. For 279 color marked black-capped chickadees, we calculated the cumulative mortality rate during 12 wk following swabbing. Although the cumulative mortality rates of infected birds were consistently higher than the rates of non-infected birds, none of these differences were significant. Infections may cause slight reductions in survival rates, but we were not able to confirm this with our data.     

Survival during the Breeding Season: Nest Stage,Parental Sex,and Season Advancement Affect Reed Warbler Survival

Avian annual survival has received much attention, yet little is known about seasonal patterns in survival, especially of migratory passerines. In order to evaluate survival rates and timing of mortality within the breeding season of adult reed warblers (Acrocephalus scirpaceus), mark-recapture data were collected in southwest Poland, between 2006 and 2012. A total of 612 individuals (304 females and 308 males) were monitored throughout the entire breeding season, and their capture-recapture histories were used to model survival rates. Males showed higher survival during the breeding season (0.985, 95% CI: 0.941–0.996) than females (0.869, 95% CI: 0.727–0.937). Survival rates of females declined with the progression of the breeding season (from May to August), while males showed constant survival during this period. We also found a clear pattern within the female (but not male) nesting cycle: survival was significantly lower during the laying, incubation, and nestling periods (0.934, 95% CI: 0.898–0.958), when birds spent much time on the nest, compared to the nest building and fledgling periods (1.000, 95% CI: 1.00–1.000), when we did not record any female mortality. These data (coupled with some direct evidence, like bird corpses or blood remains found next to/on the nest) may suggest that the main cause of adult mortality was on-nest predation. The calculated survival rates for both sexes during the breeding season were high compared to annual rates reported for this species, suggesting that a majority of mortality occurs at other times of the year, during migration or wintering. These results have implications for understanding survival variation within the reproductive period as well as general trends of avian mortality.     

Food habits and the basal rate of metabolism in birds

Summary The correlation of basal rate of metabolism with various factors is examined in birds. Chief among these is body mass. As in mammals, much of the remaining variation in basal rate among birds is associated with food habits. Birds other than passerines that feed on grass, nectar, flying insects, or vertebrates generally have basal rates that are similar to mammals of the same mass and food habits. In contrast, most invertebrate-eating birds that weigh over 100 g have higher basal rates than equally-sized, invertebrate-eating mammals. The high basal rates of small passerines equal those of small mammals that do not enter torpor and represent the minimal cost of continuous endothermy. Large passerines and small procellariiforms, charadriiforms, and psittaciforms generally have higher basal rates than mammals with the same mass and food habits. The high basal rates of passerines (in combination with altricial habits) may have significance in permitting high post-natal growth rates and the exploitation of seasonally abundant resources. These interrelations may contribute to the predominance of passerines in temperate land environments.     

Negative population trend for Chapada Flycatchers (Suiriri islerorum) despite high apparent annual survival

ABSTRACT Population size and trends are demographic parameters that can be used to help determine the threat of extirpation or extinction of bird populations and in determining management strategies. Chapada Flycatchers (Suiriri islerorum) are endemic to the Cerrado region of Brazil, dependent on open cerrado habitat, defend large territories, and their populations seem to be declining. From 2003 to 2007, we analyzed demographic parameters of a declining population of Chapada Flycatchers, using the rate at which territories became vacant and the size of the breeding population to ascertain the status of the population, and evaluated the relative contributions of apparent annual survival and recruitment rates to these trends. Territories became vacant at a mean rate of 13% per year, and 32% of all territories were vacated during our study. The current breeding population (20 pairs) was at least seven times smaller than the estimated carrying capacity of the reserve (141 territorial pairs). Estimated apparent annual survival probabilities (0.77 for breeders; 0.67 for nonbreeders) based on model averaging were comparable to those reported for other Neotropical passerines. Survival rates did not differ between the sexes and the estimated recruitment rate was 0.21. In many species, adult survival is the factor that most strongly influences population growth rates. However, the population of Chapada Flycatchers we studied is declining despite high annual survival rates, with low and variable breeding success probably causing the decline. Our results improve our understanding of the possible role of adult survival and breeding success in the decline of populations of small passerines in isolated reserves in the tropics.     

Prevalence of West Nile virus neutralizing antibodies in wild birds from the Camargue area, southern France

The Camargue area of southern France experienced the re-emergence of West Nile Virus (WNV) in the late summer of 2000 and 2004. Immediately preceding the 2004 outbreak, samples were collected from 432 birds of 32 different species captured in mist nets and from 201 Cattle Egret (Bubulcus ibis) nestlings sampled in their nests between 1 April and 12 June 2004. West Nile virus neutralizing titers of >/=40 were detected in 4.8% (95% confidence limit, 2.9-7.5%) of the adult birds and in 1.6% (0.3-4.6%) of the egret nestlings. Migratory passerines had a higher prevalence of WNV neutralizing antibodies (7.0%) than did resident and short-distance migratory passerines (0.8%), suggesting exposure to WNV or a related flavivirus during overwintering in Africa.     

Allometric scaling and Bayesian priors for annual survival of birds and mammals

Allometric theory predicts that instantaneous mortality rates scale with body mass with a negative quarter power. Such a relationship would mean that the survival rate of one species is partly predictable from the survival rate of other species. We develop allometric regression models for annual adult survival of birds and mammals, using data collected from the literature. These models conform to the predictions of the allometric theory; the value of negative one-quarter for the scaling parameter is within the 95% credible interval, which is [-0.31, -0.10] for birds and [-0.35, -0.15] for mammals. The predictions are very well supported when evaluated using an independent set of data. The regression models can be used to provide objective and informative Bayesian priors for annual adult survival rates of birds and mammals or to act as a point of comparison in new studies.     

Effect of radio transmitters on return rates of Swainson's Warblers

ABSTRACT.   Although radio telemetry can provide useful information, the possible negative effects of transmitters, including biased results and detrimental effects on the birds, must also be considered. Several investigators have examined the effects of transmitters on larger birds, but few have examined their possible long-term effects, as assessed by return rates, on small passerines. We examined the possible negative effects of transmitters on a small (15.5 g) passerine. We used glue to attach radio transmitters to 40 male Swainson's Warblers ( Limnothlypis swainsonii ) at two study sites in Arkansas in 2005 and 2006. To assess possible effects of transmitters on survival, we compared the following-year return rates of radio-tagged birds to birds that were captured and color banded, but did not receive transmitters. Least squared mean return rates for all birds ranged between 0.46 and 0.57. We found no significant difference in the following-year return rate of radio-tagged and nonradio-tagged birds. In addition, we found no significant differences in return rates between study sites or years, and no significant interactions between any combination of radio transmitter (radio tagged or not), site, and year. Our results indicate that attachment of transmitters did not affect return rates of male Swainson's Warblers and that the glue-on technique is a good option for short-term studies of small passerines.     

Ecological factors affect the level and scaling of avian BMR

The basal rate of metabolism (BMR) in 533 species of birds, when examined with ANCOVA, principally correlates with body mass, most of the residual variation correlating with food habits, climate, habitat, a volant or flightless condition, use or not of torpor, and a highland or lowland distribution. Avian BMR also correlates with migratory habits, if climate and a montane distribution is excluded from the analysis, and with an occurrence on small islands if a flightless condition and migration are excluded. Residual variation correlates with membership in avian orders and families principally because these groups are behaviorally and ecologically distinctive. However, the distinction between passerines and other birds remains a significant correlate of avian BMR, even after six ecological factors are included, with other birds having BMRs that averaged 74% of the passerine mean. This combination of factors accounts for 97.7% of the variation in avian BMR. Yet, migratory species that belong to Anseriformes, Charadriiformes, Pelecaniformes, and Procellariiformes and breed in temperate or polar environments have mass-independent basal rates equal to those found in passerines. In contrast, penguins belong to an order of polar, aquatic birds that have basal rates lower than passerines because their flightless condition depresses basal rate. Passerines dominate temperate, terrestrial environments and the four orders of aquatic birds dominate temperate and polar aquatic environments because their high BMRs facilitate reproduction and migration. The low BMRs of tropical passerines may reflect a sedentary lifestyle as much as a life in a tropical climate. Birds have BMRs that are 30-40% greater than mammals because of the commitment of birds to an expensive and expansive form of flight.     

Water and energy economy of an omnivorous bird: population differences in the Rufous-collared Sparrow (Zonotrichia capensis)

We investigated the intraspecific variation in basal metabolic rate (BMR) and total evaporative water loss (TEWL) in the omnivorous passerine Zonotrichia capensis from two populations inhabiting regions with different precipitation regimes and aridity indices. Values of TEWL in birds from the semi-arid region were significantly lower than those found in sparrows from the mesic region. TEWL in birds from the semi-arid site was 74% of the expectation based on body mass for passerines from mesic areas and similar to the allometric expectation for passerines from arid environments. In sparrows from the mesic area, TEWL was higher than predicted by their body mass for passerines from arid environments (133%), but very close (97%) to the expectation for passerines from mesic areas. BMR values were 25% lower in sparrows from the semi-arid region. The lower TEWL and BMR of birds from the semi-arid region may be a physiological adjustment that allows them to cope with fewer resources and/or water. We propose that the lower endogenous heat production in birds from the semi-arid environment may decrease their water requirements.     

Breeding Success Affects the Apparent Survival of Grassland Passerines

The apparent adult survival rate is one of the key population parameters of migratory birds. The widely used Cormack–Jolly–Seber capture–mark–recapture model has a number of disadvantages, the main one of which is the impossibility of discerning mortality and permanent emigration. The accuracy of survival estimates can be increased using a multistate capture–mark–recapture model, with the help of which it is possible to assess the survival of successful and unsuccessful birds separately. We used this model to estimate the apparent survival rates of adults in local populations of three ground-nesting passerines: Booted Warbler (Iduna caligata), Whinchat (Saxicola rubetra), and Yellow Wagtail (Motacilla flava), all breeding on abandoned agricultural lands. We studied the reproductive success of 472 marked pairs and analyzed individual capture histories of 814 birds. The previous reproductive success was found to influence significantly the apparent survival of adults. This relation was best expressed in the Yellow Wagtail (apparent survival of successful birds, φ = 0.39 ± 0.06, vs. that of unsuccessful birds, φ = 0.19 ± 0.06) and the Whinchat (apparent survival of successful birds, φ = 0.32 ± 0.05, vs. apparent survival of unsuccessful birds, φ = 0.10 ± 0.05), but a little lower in the Booted Warbler (apparent survival of successful birds, φ = 0.33 ± 0.17, vs. apparent survival of unsuccessful birds, φ = 0.16 ± 0.13). Unsuccessful individuals leave the study area for good, while most of the successful birds return there the next year. Thus, the apparent survival rate of passerines evaluated with capture–recapture models is determined to a considerable degree by the previous reproductive success within local populations.     

Monthly survival of African Sylvia warblers in a seasonally arid tropical environment

Latitudinal gradients of life-history traits in animals are thought to be shaped by environmental variables. For example, it has been suggested that the increase in avian clutch size from the tropics towards the northern temperate regions is caused by a reduced survival of adult birds in the north due to increasing environmental seasonality. However, the tropical savannahs of East Africa show pronounced seasonality in resources caused by distinct rainy and dry seasons. This raises the question of whether survival and other life-history traits of birds living in these tropical savannahs are influenced by this seasonality, making them more similar to northern temperate species. We used 2-year monthly resighting data, a multistate modelling approach and the program MARK to test whether survival, transition probabilities between breeding states and other life-history traits of two resident Kenyan Sylvia species (Aves: Passeriformes: Sylviidae) are shaped by seasonality of rainfall in their environment. Contradicting our hypotheses, the two species showed only very slight influence of seasonality of rainfall on their survival. Survival in the dry months was hardly lower than in the rainy months. The species in the more seasonal environment ( S. boehmi , annual survival 71%) survived as well as the one in the more constant environment ( S. lugens , 56%). The observed survival rates correspond well to other life-history traits of the two species and are of similar magnitude to survival rates of other tropical passerines. This implies that either seasonality is not the driving force behind the life-history traits of the two species or the birds do not experience their environment as seasonal, as might be suggested by fluctuations in rainfall.     

Handling of uncertain nest fates and variation in nest survival estimates

Researchers are moving their attention away from the Mayfield method of estimating nest success to advanced nest survival models that can be implemented within statistical software packages. In spite of this, little attention has been paid to developing formal rules for handling of ambiguous nesting data within these software-based methods. I compared the variation caused by differential handling of data between the hand-calculated Mayfield estimates and those obtained using the constant survival logistic-exposure method. Four variants of each of the two methods were applied to sets of nest records (n = 5,476) of nine open-nesting passerines. Of all nest fates, 57% (unweighted mean across species) were categorized as failed, 29% as successful and 14% as uncertain, according to either age criterion or combination of all fate evidence criteria. Different methods yielded survival estimates that differed as much as 6% over a 25-day nesting cycle. Variation in logistic-exposure survival estimates caused by the four variants of interval coding was higher (range = 4.4%) than variation in the Mayfield estimates (range = 2.7%) caused by the four variants of exposure termination. Researchers are urged to consider different handling of ambiguous nesting data as one of the many possible sources of bias when implementing any method of nest survival analysis.     

A comprehensive demographic assessment of the endangered Fiordland crested penguin Eudyptes pachyrhynchus

ABSTRACT

Many species of Eudyptes penguin have shown substantial population declines and in response, there have been efforts to identify the key demographic parameters. Here, we present the demographic parameters of one of the least well known and the least abundant species of crested penguin, the endangered Fiordland crested penguin Eudyptes pachyrhynchus. A population study incorporating mark–recapture, nest occupancy and breeding success was conducted over 16 years at several sites in the northern half of the range of the species. Survival probabilities were calculated using standard Cormack–Jolly–Seber models and the Burnham Live and Dead model. The annual probability of true survival for banded birds and apparent survival for birds with transponders were both estimated at 89% during their adult years, which is similar to that reported for Eudyptes penguin species inhabiting more southerly latitudes. Annual juvenile survival was assessed for Fiordland crested penguins until their first return at 77%. The mean breeding success (0.61?±?0.02 chicks/pair) was higher than is observed for other crested penguin species, except the southern rockhopper penguin, which may be due to having lower A-egg ejection rates and higher rates of fledging two chicks per pair. Breeding success was related to the niche of predators present.