Avian growth and development rates and age-specific mortality: the roles of nest predation and adult mortality

Previous studies have shown that avian growth and development covary with juvenile mortality. Juveniles of birds under strong nest predation pressure grow rapidly, have short incubation and nestling periods, and leave the nest at low body mass. Life-history theory predicts that parental investment increases with adult mortality rate. Thus, developmental traits that depend on the parental effort exerted (pre- and postnatal growth rate) should scale positively with adult mortality, in contrast to those that do not have a direct relationship with parental investment (timing of developmental events, e.g. nest leaving). I tested this prediction on a sample of 84 North American songbirds. Nestling growth rate scaled positively and incubation period duration negatively with annual adult mortality rates even when controlled for nest predation and other covariates, including phylogeny. On the contrary, neither the duration of the nestling period nor body mass at fledging showed any relationship. Proximate mechanisms generating the relationship of pre- and postnatal growth rates to adult mortality may include increased feeding, nest attentiveness during incubation and/or allocation of hormones, and deserve further attention.     

Nest predation and nestling growth rate of two lark species in the Negev Desert, Israel

Clutch-size, nestling growth and predation rates on eggs and nestlings in two sympatric alaudids, the Crested Lark Galerida cristata and the Desert Lark Ammomanes deserti, were studied in the Negev desert of Israel. Logistic growth constants were similar for both species, and experimental brood reduction did not accelerate the growth rate of their nestlings. It is suggested that the predation rate on nests of both species has been sufficiently high to select for maximal growth rate of nestlings. Overall probability of predation was 0.85 on a Desert Lark nest and 0.76 on a Crested Lark nest. The smaller clutch-size of the Desert Lark (3.7) may be an adaptation to a higher predation risk, as compared to that of the Crested Lark (4.6) which is more vigilant and nests in more concealed sites.     

Video nest monitoring reveals male coloration-dependant nest predation and sex differences in prey size delivery in a bird under high sexual selection

Increased predation risk should select for reduced parental activity to decrease the probability of visually hunting predators discovering the nest. Parental activity and conspicuousness are known to increase predation risk. Here, we test for sex differences in parental visitation rate (number of visits), time seen at the nest (time at the nest × adult visibility), and food delivery (prey size) using continuous video recordings at nests. We test the role of these variables for predation outcome in the Superb Fairy-wren (Malurus cyaneus). The study species is sexually dimorphic: males have iridescent blue plumage while females have brown plumage. The results showed that nest predation was predicted by male time seen at the nest (but not visitation rate), but not female time seen at the nest (or visitation rate). Contrary to our expectation that males would have lower visitation rates than females, our analysis of video images showed that male and female visitation was comparable but that males consistently brought smaller prey items to the nest than females. These findings are discussed in the light of morphological differences between male and female beak size. We conclude that sexual selection has favoured conspicuous male signalling in this system, and that natural selection should select for reduced parental care for the conspicuous sex.     

Parental care,nestling growth and diet in a Spotted Eagle Aquila clanga nest

Capsule The breeding biology of the Spotted Eagle was studied and we analysed results from direct observations at a nest in Estonia.     

Long‐term and large‐scale analyses of nest predation patterns in Australian songbirds and a global comparison of nest predation rates

Juvenile mortality is one of crucial drivers of life‐history evolution, and predation is the main cause of nest loss in birds. Thus, understanding how nest predation and failure vary in nature is important for understanding life history evolution and, moreover, for effective conservation. We used published data and unpublished records to study factors influencing nest predation and total failure in 138 populations of 90 species of Australian songbirds. Daily predation (average 2.0% d^?1) and failure rates (2.9%) increased from temperate regions to the tropics, over the last four decades, and were lowest in temperate south‐western Australia. Predation and failure were higher in smaller species, and failure rates were lower in species with closed nests than in species with open nests. There was no effect of nest height or nest site (ground, shrub, canopy) or social organization on nest predation or failure rates. Nest predation caused on average 72% of total nest failure, similar to other tropical, subtropical, and temperate areas. Our study spanning from the tropics to temperate regions and using > 10 000 nests confirmed that tropical birds faced higher nest failure rates. We identified an increase in nest depredation rates in the last four decades in Australia, suggesting that a large‐scale ecological phenomenon must be responsible. It may include increases in predator abundances and/or ranges, possibly connected with human‐caused habitat change. A global comparison of nest failure rates confirmed that predation is the main source of nest mortality in songbirds worldwide. We discuss implications of our results for the evolution of reproductive strategies and for the conservation of Australian birds.     

Artificial nest predation rates in tropical and temperate forests: a review of the effects of edge and nest site

Nest predation rates are believed to be higher in tropical than in temperate forests. This notion is central in explaining different life history traits of tropical and temperate birds, but it is not known whether this assertion is true for all nest sites, such as ground and shrub nests, and at different distances from forest edge. I reviewed 22 studies using artificial nest experiments which concurrently contrasted predation rates of ground and shrub nests in temperate and tropical forests and found, contrary to the current dogma, no overall difference in predation rates between regions. However, there was a significant interaction between region and nest site. Ground nest predation rates were significantly higher in the tropical region, while predation rates on shrub nests were similar between regions. Within the tropical region, ground nests had significantly higher predation rates than shrub nests. Elevated nest predation rates at forest edges were found in both temperate and tropical forests. The results may have great implications for expected patterns of avian life histories and for the effects of forest fragmentation in temperate and tropical regions. First, if nest predation affects avian life histories, my results predict ground-nesting species in tropical forests to have shorter nestling periods, more broods and smaller clutch sizes than shrub-nesting species. Second, vulnerability of ground- and shrub-nesting guilds is suggested to differ between regions due to differences in forest vegetation structure, and the composition of predator faunas and their specific responses to forest fragmentation. Data to test these hypotheses are limited, but agree with the results of this review.     

Romanomermis culicivorax parasitism and the development, growth, and feeding rates of two mosquito species

The dry weight, development, and feeding rates of Culex pipiens and Toxorhynchites amboinensis larvae infected with the nematode, Romanomermis culicivorax, were measured and gross conversion efficiences were calculated. The weight of C. pipiens larvae infected at two different inoculum levels did not differ significantly from controls until day 6 postinfection (PI). Infected larvae of T. amboinensis were significantly lighter than controls at days 2, 4, and 6 PI. The rate of larval mosquito development was slowed after day 3 in parasitized individuals of both mosquito species. Infection significantly retarded the interval feeding rate of the filter-feeding C. pipiens throughout development. Infected T. amboinensis larvae consumed significantly fewer prey larvae of C. pipiens than controls. Calculation of gross conversion efficiency (GCE) showed that lightly infected C. pipiens larvae had an elevated GCE early in the infection but were less efficient relative to controls after 4 days PI. Lightly parasitized T. amboinensis had a lower total GCE than controls.     

Rapid plant species loss at high rates and at low frequency of N addition in temperate steppe

Humans are both intentionally (fertilization) and unintentionally (atmospheric nutrient deposition) adding nutrients worldwide. Increasing availability of biologically reactive nitrogen (N) is one of the major drivers of plant species loss. It remains unclear, however, whether plant diversity will be equally reduced by inputs of reactive N coming from either small and frequent N deposition events or large and infrequent N fertilization events. By independently manipulating the rate and frequency of reactive N inputs, our study teases apart these potentially contrasting effects. Plant species richness decreased more quickly at high rates and at low frequency of N addition, which suggests that previous fertilization studies have likely over‐estimated the effects of N deposition on plant species loss. N‐induced species loss resulted from both acidification and ammonium toxicity. Further study of small and frequent N additions will be necessary to project future rates of plant species loss under increasing aerial N deposition.     

Developmental acquisition of a rapid calcium-regulated vesicle supply allows sustained high rates of exocytosis in auditory hair cells

Auditory hair cells (HCs) have the remarkable property to indefinitely sustain high rates of synaptic vesicle release during ongoing sound stimulation. The mechanisms of vesicle supply that allow such indefatigable exocytosis at the ribbon active zone remain largely unknown. To address this issue, we characterized the kinetics of vesicle recruitment and release in developing chick auditory HCs. Experiments were done using the intact chick basilar papilla from E10 (embryonic day 10) to P2 (two days post-hatch) by monitoring changes in membrane capacitance and Ca(2+) currents during various voltage stimulations. Compared to immature pre-hearing HCs (E10-E12), mature post-hearing HCs (E18-P2) can steadily mobilize a larger readily releasable pool (RRP) of vesicles with faster kinetics and higher Ca(2+) efficiency. As assessed by varying the inter-pulse interval of a 100 ms paired-pulse depolarization protocol, the kinetics of RRP replenishment were found much faster in mature HCs. Unlike mature HCs, exocytosis in immature HCs showed large depression during repetitive stimulations. Remarkably, when the intracellular concentration of EGTA was raised from 0.5 to 2 mM, the paired-pulse depression level remained unchanged in immature HCs but was drastically increased in mature HCs, indicating that the Ca(2+) sensitivity of the vesicle replenishment process increases during maturation. Concomitantly, the immunoreactivity of the calcium sensor otoferlin and the number of ribbons at the HC plasma membrane largely increased, reaching a maximum level at E18-P2. Our results suggest that the efficient Ca(2+)-dependent vesicle release and supply in mature HCs essentially rely on the concomitant engagement of synaptic ribbons and otoferlin at the plasma membrane.     

Resource limitation,predation risk and compensatory growth in a damselfly

Periods of poor nutrition during early development may have negative fitness consequences in subsequent periods of ontogeny. In insects, suppression of growth and developmental rate during the larval stage are likely to affect size and timing of maturity, which in turn may lead to reduced reproductive success or survivorship. In light of these costs, individuals may achieve compensatory growth via behavioural or physiological mechanisms following food limitation. In this study, we examined the effects of a temporary period of food restriction on subsequent growth and age and size at maturity in the larval damselfly Ischnura verticalis (Odonata: Coenagrionidae). We also asked whether this temporary period of reduced nutrition affected subsequent foraging behaviour under predation risk. I. verticalis larvae exposed to a temporary food shortage suffered from a reduced growth rate during this period relative to a control group that was fed ad libitum. However, increased growth rates later in development ensured that adult body size measurements (head and pronotum widths) did not differ between the treatments upon emergence. In contrast, adult dry mass did not catch up to that of the controls, indicating that the increased growth rates for size dimensions occur at the cost of similar gains in mass. Predators reduced foraging effort of larvae, but this reduction did not differ between control larvae and those previously exposed to poor nutrition.     

Effect of light on the feeding rates of pelagic and littoral mysid shrimps: a trade-off between feeding success and predation avoidance

It has been shown that freshwater pelagic mysid shrimps capture zooplankton at a higher rate in light than in darkness. This has been suggested to be due to facilitation of visual predation on evasive zooplankton prey. To test this hypothesis with Baltic mysid shrimps, and to see whether pelagic (migrating) and littoral (non-migrating) mysids differ in this respect, we compared the feeding rates of Mysis mixta and Praunus flexuosus on the copepod Acartia spp. As light conditions change radically from the beginning of summer to late autumn at the Baltic latitudes, we conducted the experiments during three different times of the year to determine if there was a seasonal response to light in mysids. The feeding rates of pelagic mysids were significantly higher in total darkness than in light. In contrast, the feeding rates of littoral mysids did not differ in the dark and the light in the three different seasons. The decreased feeding of pelagic mysids under well-lit conditions may be an adaptation to avoid visual predation by pelagic fish. In contrast, littoral mysids, which live in the well-lit layer throughout the day, do not show a similar response. The fact that light did not increase feeding in either of the mysid species indicates that these mysid species do not use vision in capturing prey, but rely mainly on mechano-reception.     

Diet and feeding of nestling Little Bitterns Ixobrychus minutus at fishponds: testing a new method for studying a difficult-to-monitor species

Capsule: The diet and feeding of nestling Little Bitterns Ixobrychus minutus was studied using trail cameras. Little Bitterns nestlings were mostly provisioned with amphibians and small fish. They were fed in the morning and evening, but not during the night, and both parents provided similar amounts of food.     

Sources of variation in predation rates at high prey densities: an analytic model and a mite example

Some mathematical techniques for the analysis of satiation-based predation models previously developed by the first author are applied in the present paper to a model by the second author for predation by the predatory miteMetaseiulus occidentalis (Nesbitt). It turns out that for this predator the predation rate should keep increasing at high prey densities as the square root of the prey density,x. This particular shape of the functional response is shown to occur if and only if the upper satiation threshold for prey capture coincides with the maximum gut capacity. The functional response predicted by the model, moreover, is in fair quantitative agreement with predation rates observed by the third author in artificial arenas. A further analysis of the model shows that the variance of the catch should also increase as the square root ofx. This prediction is consistent in a qualitative manner with the continued increase in the variance of the catch. However, quantitatively, the observed variances are even too large to be compatible with any model in which the feeding rate is subject to regulation by a negative feedback. Therefore, the difference between predicted and observed variances is hypothesized to be due to nonhomogeneities in the experimental material. The inferred additional variance component proportional tox accords fairly well with the trend apparent in the data.     

Variation in predation risk and vole feeding behaviour: a field test of the risk allocation hypothesis

Many prey animals experience temporal variation in the risk of predation and therefore face the problem of allocating their time between antipredator efforts and other activities like feeding and breeding. We investigated time allocation of prey animals that balanced predation risk and feeding opportunities. The predation risk allocation hypothesis predicts that animals should forage more in low- than in high-risk situations and that this difference should increase with an increasing attack ratio (i.e. difference between low- and high-risk situations) and proportion of time spent at high risk. To test these predictions we conducted a field test using bank voles (Clethrionomys glareolus) as a prey and the least weasel (Mustela nivalis nivalis) as a predator. The temporal pattern and intensity of predation risk were manipulated in large outdoor enclosures and the foraging effort and patch use of voles were measured by recording giving-up densities. We did not observe any variation in feeding effort due to changes in the level of risk or the proportion of time spent under high-risk conditions. The only significant effect was found when the attack ratio was altered: the foraging effort of voles was higher in the treatment with a low attack ratio than in the treatment with a high attack ratio. Thus the results did not support the predation risk allocation hypothesis and we question the applicability of the hypothesis to our study system. We argue that the deviation between the observed pattern of feeding behaviour of bank voles and that predicted by the predation risk allocation hypothesis was mostly due to the inability of voles to accurately assess the changes in the level of risk. However, we also emphasise the difficulties of testing hypotheses under outdoor conditions and with mammals capable of flexible behavioural patterns.     

Genetic correlations between basal and maximum metabolic rates in a wild rodent: consequences for evolution of endothermy

According to the aerobic capacity model, endothermy in birds and mammals evolved as a correlated response to selection for an ability of sustained locomotor activity, rather than in a response to direct selection for thermoregulatory capabilities. A key assumption of the model is that aerobic capacity is functionally linked to basal metabolic rate (BMR). The assumption has been tested in several studies at the level of phenotypic variation among individuals or species, but none has provided a clear answer whether the traits are genetically correlated. Here we present results of a genetic analysis based on measurements of the basal and the maximum swim- and cold-induced oxygen consumption in about 1000 bank voles from six generations of a laboratory colony, reared from animals captured in the field. Narrow sense heritability (h2) was about 0.5 for body mass, about 0.4 for mass-independent basal and maximum metabolic rates, and about 0.3 for factorial aerobic scopes. Dominance genetic and common environmental (= maternal) effects were not significant. Additive genetic correlation between BMR and the swim-induced aerobic capacity was high and positive, whereas correlation resulting from specific-environmental effects was negative. However, BMR was not genetically correlated with the cold-induced aerobic capacity. The results are consistent with the aerobic capacity model of the evolution of endothermy in birds and mammals.     

Effects of temperature and nest heat exposure on nestling growth,dehydration and survival in a Mediterranean hole‐nesting passerine

Variable environments impose constraints on adaptation by modifying selection gradients unpredictably. Optimal bird development requires an adequate thermal range, outside which temperatures can alter nestling physiology, condition and survival. We studied the effect of temperature and nest heat exposure on the reproductive success of a population of double‐brooded Spotless Starlings Sturnus unicolor breeding in a nestbox colony in central Spain with a marked intra‐seasonal variation in temperature. We assessed whether the effect of temperature differed between first and second broods, thus constraining optimal nest‐site choice. Ambient temperature changed greatly during the chick‐rearing period and had a strong influence on nestling mass and all body size measures we recorded, although patterns of clutch size or nestling mortality were not influenced. This effect differed between first and second broods: nestlings were found to have longer wings and bills with increasing temperature in first broods, whereas the effect was the opposite in second broods. Ambient temperature was not related to nestling body mass or tarsus‐length in first broods, but in second broods, nestlings were lighter and had smaller tarsi with higher ambient temperatures. The exposure of nestboxes to heat influenced nestling morphology: heat exposure index was negatively related to nestling body mass and wing‐length in second broods, but not in first broods. Furthermore, there was a positive relationship between nest heat exposure and nestling dehydration. Our results suggest that optimal nest choice is constrained by varying environmental conditions in birds breeding over prolonged periods, and that there should be selection for parents to switch from sun‐exposed to sun‐protected nest‐sites as the season progresses. However, nest‐site availability and competition for sites are likely to impose constraints on this choice.     

Growth rate variation among passerine species in tropical and temperate sites: an antagonistic interaction between parental food provisioning and nest predation risk

Causes of interspecific variation in growth rates within and among geographic regions remain poorly understood. Passerine birds represent an intriguing case because differing theories yield the possibility of an antagonistic interaction between nest predation risk and food delivery rates on evolution of growth rates. We test this possibility among 64 Passerine species studied on three continents, including tropical and north and south temperate latitudes. Growth rates increased strongly with nestling predation rates within, but not between, sites. The importance of nest predation was further emphasized by revealing hidden allometric scaling effects. Nestling predation risk also was associated with reduced total feeding rates and per-nestling feeding rates within each site. Consequently, faster growth rates were associated with decreased per-nestling food delivery rates across species, both within and among regions. These relationships suggest that Passerines can evolve growth strategies in response to predation risk whereby food resources are not the primary limit on growth rate differences among species. In contrast, reaction norms of growth rate relative to brood size suggest that food may limit growth rates within species in temperate, but not tropical, regions. Results here provide new insight into evolution of growth strategies relative to predation risk and food within and among species.     

Differences in growth,pigment composition and photosynthetic rates of two phenotypes Microcystis aeruginosa strains under high and low iron conditions

This paper provided insight into the influence of iron on the growth of Microcystis aeruginosa strains related to different phenotypes of this species. In this research it was intended to compare the growth, pigment composition, photosynthetic efficiency and extracellular polysaccharides production of unicellular and colonial strains of M. aeruginosa. A significantly growth inhibition under iron-limited condition on unicellular M. aeruginosa was noted, whereas the colonial strain could maintain a steady growth along with the culture time. This observation was reconfirmed by the content of chlorophyll a. Compared with unicellular strain; the colonial strain exhibited a higher PSII maximum light energy transformation, photosynthetic oxygen evolution and extracellular polysaccharides (EPS) production in iron-limited condition. Further, in order to gain more information about the accessibility of iron in the two phenotypic Microcystis, we found the two strains could produce hydroxamate-type siderophores, the content of siderophores produced by the colonial strain was more than those in unicellular strain under the iron-limited condition. It was interpreted as an adaptation to the dilute environment. Our results demonstrated that the colonial phenotypes possessed stronger ability to endure iron-limited condition than unicellular strain by higher pigment contents, higher photosynthetic activities, higher EPS production and higher siderophores secretion. It might elucidate that the colonial M. aeruginosa bloom can sustain in eutrophic reservoirs and lakes.     

Fatty-acid composition of cells and lipopolysaccharides in different Yersinia species under the conditions of growth at low temperature

Y. pestis, Y. pseudotuberculosis, Y. enterocolitica, Y. frederiksenii, Y. intermedia, Y. kristensenii and Y. ruckeri grown at 4 degrees C were characterized by fatty acid composition with a high content of C16:1 and C18:1, as well as the proportion of saturated to nonsaturated fatty acids equal to, on the average, 2.0. In Yersinia lipopolysaccharides a relatively high level of C16:1 and C12:0 was observed with the prevalence of 3-OH-C14:0. In the fatty-acid spectra of both cells and lipopolysaccharides no essential difference was noted. Thus, during growth at low temperature differences, earlier detected in the studied Yersinia species grown at 37 degrees C and making it possible to divide 7 Yersinia species into 2 groupes, were completely leveled. These results confirmed the close phylogenetic relationship between the Yersinia species under study and were indicative of more pronounced biological community of Yersinia under the conditions of growth at low temperature.