Feeding experience and relative size modify the begging strategies of nestlings

The offspring of birds and mammals use a combination of movementsand vocalizations, known as begging, to solicit food from theirparents. A widespread interpretation of begging is that itconstitutes an honest signal of offspring need. But we knowthat in the house sparrow (Passer domesticus) the intensityof begging calls reflects the past experience of offspringin addition to their need. Here we show that this result generalizesto other species. An experiment with hand-reared magpies (Pica pica) and great spotted cuckoos (Clamator glandarius) indicates that the begging strategies depend on the past experience ofchicks and the composition of their brood. In asynchronoustwo-magpie broods, both chicks begged at the same intensitywhen the large chick obtained food more easily than its sibling,but the large chick begged at higher intensity when it was easier for the smaller chick to obtain food. Cuckoo chicks beggedat higher intensity than magpies.     

Effects of feeding frequency on nestling begging and digestion

Nestling begging has the potential to provide parents with honest information about both short- and long-term nutritional needs, yet the importance of previous feeding experience remains largely untested in empirical studies. We examined the effect of two experimental feeding rates on nestling begging in Southern Grey Shrikes Lanius meridionalis using differences in load size to equalize the total volume of food received. There was variation in the pattern of begging behaviour between six pairs of siblings during a hand-feeding trial, although individuals maintained a similar begging intensity throughout a 9-h feeding period. Both treatment groups showed elevated begging responses during a terminal deprivation period, but nestlings fed small food items at frequent intervals demonstrated higher begging responses after a period of deprivation than did siblings fed large food items infrequently. As nestlings fed frequently with small food items had greater levels of undigested protein present in their faeces than birds fed large items infrequently, we suggest experimentally induced variation in digestive efficiency may account for the observed differences in begging behaviour. The possible role of learning, the adaptive significance of trade-offs between feeding rate and digestive efficiency, and a possible conflict of interests between parents and offspring are discussed.     

Food limitation in asynchronous bluethroat broods: effects on food distribution, nestling begging, and parental provisioning rules

Scramble competition models of begging predict that junior nestlingswill be more affected by food limitation than seniors. Thesemodels assume that food allocation is under offspring controland, hence, predict that this change in food distribution iscaused by a differential behavioral response by seniors andjuniors. By using the bluethroat (Luscinia svecica svecica)as our model species, we induced food limitation by removingthe male parent temporarily. We found that, as predicted, fooddistribution became more biased in disfavor of juniors whenfood was limited. However, there was no significant differencein the behavioral responses of seniors and juniors (i.e., positioningin the nest or begging postures) to food limitation that couldexplain the change in food distribution. Hence, there was noevidence that seniors controlled food distribution. As predictedif parents preferentially fed seniors, nestling rank affectedfood distribution when controlling for variation in nestlingbehaviors. Furthermore, as expected if the increased skew infood distribution under food limitation was caused by activefood allocation by parents, nestling rank had a greater effecton food distribution under food limitation than under normalconditions. The present study suggests that food distributionin passerine birds is determined not only by nestling behaviors(begging posture and positioning) alone but also by parentalpreferences for seniors based on nonsignaling cues, such asbody size.     

Some mistakes go unpunished: the evolution of "all or nothing" signalling

Many models of honest signaling, based on Zahavi's handicap principle, predict that if receivers are interested in a quality that shows continuous variation across the population of signalers, then the distribution of signal intensities will also be continuous. However, it has previously been noted that this prediction does not agree with empirical observation in many signaling systems, where signals are limited to a small number of levels despite continuous variation in the trait being signaled. Typically, there is a critical value of the trait, with all individuals with trait values on one side of the threshold using the same cheap signal, and all those with trait values on the other side of the threshold using the same expensive signal. It has already been demonstrated that these classical models naturally predict such "all-or-nothing signaling" if it is additionally assumed that receivers suffer from perceptual error in evaluating signal strength. We show that such all-or-nothing signaling is also predicted if receivers are limited to responding to the signals in one of two ways. We suggest that many ecological situations (such as the decision to attack the signaler or not, or mate with the signaler or not) involve such binary choices.     

Change in host rejection behavior mediated by the predatory behavior of its brood parasite

Passerine hosts of parasitic cuckoos usually vary in their abilityto discriminate and reject cuckoo eggs. Costs of discriminationand rejection errors have been invoked to explain the maintenanceof this within-population variability. Recently, enforcementof acceptance by parasites has been identified as a rejectioncost in the magpie (Pica pica) and its brood parasite, the greatspotted cuckoo (Clamator glandarius). Previous experimentalwork has shown that rejecter magpies suffer from increased nestpredation by the great spotted cuckoo. Cuckoo predatory behavioris supposed to confer a selective advantage to the parasitebecause magpies experiencing a reproductive failure may providea second opportunity for the cuckoo to parasitize a replacementclutch. This hypothesis implicitly assumes that magpies modulatetheir propensity to reject parasite eggs as a function of previousexperience. We tested this hypothesis in a magpie populationbreeding in study plots varying in parasitism rate. Magpie pairs thatwere experimentally parasitized and had their nests depredated,after their rejection behavior had been assessed, changed theirbehavior from rejection to acceptance. The change in host behaviorwas prominent in study plots with high levels of parasitism,but not in plots with rare or no cuckoo parasitism. We discussthree possible explanations for these differences, concludingthat in study plots with a high density of cuckoos, the probability fora rejecter magpie nest of being revisited and depredated bya cuckoo is high, particularly for replacement clutches, and,therefore, the cost for magpies of rejecting a cuckoo egg ina replacement clutch is increased. Moreover, in areas with highlevels of host defense (low parasitism rate), the probabilityof parasitism and predation of rejecter-magpie nests by thecuckoo is reduced in both first and replacement clutches. Therefore,rejecter magpies in such areas should not change their rejectionbehavior in replacement clutches.     

Nest size affects clutch size and the start of incubation in magpies: an experimental study

Nest size has been suggested to be a sexually selected traitindicating parental ability of both males and females. To testwhether a female's reproductive decisions (e.g., clutch sizeand starting incubation) change in relation to experimentalmanipulation of nest size, as would be predicted if nest sizeis a sexually selected signal reflecting the male's parental quality, we manipulated nest size in a population of monogamousmagpies before laying by adding or removing about 20 cm oflarge sticks in the roof of magpie nests. On the one hand,we found that clutch size of reduced nests was smaller thanthat of control or enlarged nests. Moreover, clutch size was significantly related to nest size after manipulation, whichindicates that females adjust clutch size to the final sizeof the nest, nest size thereby being a good candidate for asexually selected trait. On the other hand, number of eggshatched during the first day is hypothesized to be related to the expected available resources during nestling growth, andsubsequent nestlings hatched are likely to die due to broodreduction if resources are not sufficient to raise well-developednestlings. Nest size is hypothesized to inform females abouta male's willingness to invest in reproduction, and we foundthat in broods of experimentally reduced nests, females startedto incubate earlier in the laying sequence than they did inbroods of control or enlarged nests. Moreover, in experimentallyreduced nests, fewer nestlings hatched during the first day,and the difference in body mass between the first and the fourthnestling hatched increased. This result is in accordance withthe hypothesis that the female's decision of when to start incubationin the laying sequence is mediated by nest size, a sexuallyselected trait signaling parental quality. We discuss alternativeexplanations for the results such as the possibility that nestsof different treatments may differ in their thermoregulationproperties or in their protection against predators.     

Antagonistic antiparasite defenses: nest defense and egg rejection in the magpie host of the great spotted cuckoo

Brood parasites dramatically reduce the reproductive successof their hosts, which therefore have developed defenses againstbrood parasites. The first line of defense is protecting thenest against adult parasites. When the parasite has successfullyparasitized a host nest, some hosts are able to recognize andreject the eggs of the brood parasite, which constitutes the secondline of defense. Both defense tactics are costly and would be counteractedby brood parasites. While a failure in nest defense implies successfulparasitism and therefore great reduction of reproductive successof hosts, a host that recognizes parasitic eggs has the opportunityto reduce the effect of parasitism by removing the parasiticegg. We hypothesized that, when nest defense is counteractedby the brood parasite, hosts that recognize cuckoo eggs shoulddefend their nests at a lower level than nonrecognizers becausethe former also recognize adult cuckoos. Magpie (Pica pica) hoststhat rejected model eggs of the brood parasitic great spottedcuckoo (Clamator glandarius) showed lower levels of nest defensewhen exposed to a great spotted cuckoo than when exposed toa nest predator (a carrion crow Corvus corone). Moreover, magpiesrejecting cuckoo eggs showed lower levels of nest defense againstgreat spotted cuckoos than nonrecognizer magpies, whereas differencesin levels of defense disappeared when exposed to a carrion crow.These results suggest that hosts specialize in antiparasitedefense and that different kinds of defense are antagonistically expressed.We suggest that nest-defense mechanisms are ancestral, whereasegg recognition and rejection is a subsequent stage in the coevolutionaryprocess. However, host recognition ability will not be expressedwhen brood parasites break this second line of defense.     

Effects of repeated investigator handling of Leach's Storm‐Petrel chicks on growth rates and the acute stress response

Disturbance during development may have lasting effects on the growth rates and stress physiology of birds. Although repeated handling by researchers is often necessary, the possible effects of such handling on the development of semi‐altricial young are unclear. We examined the effect of daily handling on growth rates and plasma corticosterone levels of Leach's Storm‐Petrel (Oceanodroma leucorhoa) chicks on Kent Island in the Bay of Fundy, New Brunswick, Canada, during the 2011 nesting season. From post‐hatch day 7 to post‐hatch days 14–36, birds in the experimental group were extracted from burrows and measured (wing, tarsus, and mass) for ～3 min every day, whereas birds in the control group were left undisturbed. After the treatment period, blood was collected from birds in both groups within 3 min of initially reaching into burrows (baseline) and after a 30‐min restraint stress test to assess the effect of early life disturbance on programming of the hypothalamic‐pituitary‐adrenal (HPA) axis. A second acute restraint stress test was conducted three weeks after the end of the treatment period to investigate possible longer term effects of early life disturbance. Growth rates of wings and tarsi were similar for handled chicks (N = 18) and non‐handled control chicks (N = 21), as were baseline and 30‐min acute restraint stress‐induced corticosterone levels. As also reported in previous studies of other altricial and semi‐altricial species, older chicks (42–64 d old) had higher plasma corticosterone levels than younger chicks (21–43 d old) after acute restraint stress tests, reflecting delayed development of the HPA axis. The age‐related increase in HPA axis sensitivity observed prior to fledging could facilitate foraging and predator avoidance behaviors while minimizing exposure to high levels of corticosterone earlier in development. Overall, we found no evidence that repeated disturbance influenced either growth rates or HPA axis programming of Leach's Storm‐Petrel chicks.     

Brood size, sibling competition, and the cost of begging in great tits (Parus major)

Evolutionary theory of parent-offspring conflict explains beggingdisplays of nestling birds as selfish attempts to influenceparental food allocation. Models predict that this conflictmay be resolved by honest signaling of offspring need to parents,or by competition among nestmates, leading to escalated beggingscrambles. Although the former type of models has been qualitativelysupported by experimental studies, the potential for a beggingcomponent driven by scramble competition cannot be excludedby the evidence. In a brood-size manipulation experiment withgreat tits, Parus major, we explored the scramble componentin the begging activity of great tit nestlings by investigatingthe mechanisms of sibling competition in relation to brood size.While under full parental compensation, the feeding rate pernestling will remain constant over all brood sizes for bothtypes of models; the scramble begging models alone predict anincrease in begging intensity with brood size, if begging costsdo not arise exclusively through predation. Great tit parentsadjusted feeding rates to brood size and fed nestlings at similarrates and with similar prey sizes in all three brood-size categories.Despite full parental compensation, the begging and food solicitationactivities increased with experimental brood size, whereas nestlingbody condition deteriorated. These findings support a scramblecomponent in begging and suggest that the competition-inducedcosts of food solicitation behavior play an important role inthe evolution of parent-offspring communication.     

三种鹭异步孵化与雏鸟生长的比较研究

根据1996～1999年的野外工作和实验饲养,研究了池鹭、白鹭、夜鹭3种鹭的繁殖、雏鸟生长和异步孵化对雏鸟生长的影响.3种鹭于4月上、中旬迁到常山、余杭鹭保护区,9月下旬陆续迁离.孵卵期池鹭为23.0 d(n=26),白鹭23.9 d(n=32),夜鹭25.3 d(n=34);孵化率池鹭为76.32%,自鹭86.96%,夜鹭95.45%,池鹭繁殖力为3.21只,白鹭3.38只,夜鹭3.50只.雏鸟体重增长与成体体形大小呈负相关.幼雏体重增长与孵化顺序相关.在生长早期(≤8 d)全部雏鸟正常发育,之后差异显著.第1和第2孵化雏鸟生长曲线相似,但明显高于第4雏鸟,表明较早孵化者获得食物能力较强,而迟孵出雏鸟有食物不足现象.该3种鹭孵育幼雏能力的最适度估计为3只左右.     

Effects of common origin and common environment on nestling plumage coloration in the great tit (Parus major)

Abstract.— Carotenoids cannot be synthesized by birds and thus have to be ingested with food, suggesting that ca-rotenoid-based plumage coloration is environmentally determined. However signaling functions ascribed to plumage imply that plumage coloration is the outcome of an evolutionary process based on genetic variation. By means of a cross-fostering design we show significant effects of both a common rearing environment and the brood from which a nestling originally came from (common origin) on the plumage coloration of nestling great tits ( Parus major ). This demonstration of origin-related variation in carotenoid-based plumage coloration suggests that the observed variation of the trait has a partial genetic basis. Consistent with environmental determination of this trait, we also found a significant positive correlation between the color saturation of nestlings and their foster-father's plumage. There was no significant correlation between nestling plumage coloration and the food quantity provided to the nestlings by the male, the female, or both parents. This suggests that the nestling-foster father correlation arises by the carotenoid quantity ingested rather than the food quantity per se. No significant nestling-true father correlation was found, which suggests that nestling plumage coloration did not indirectly evolve due to sexual selection. Consistent with this result there was no significant correlation between the nestling's plumage color and its coloration as a breeding adult the following year, suggesting that nestling plumage color is a different trait than the first year plumage.     

Quantitative analysis of multiple forest disturbances and their compound influences on tree growth in the western U.S.

As the frequencies of extreme weather increase, forest ecosystems experience stronger influences from various disturbances. Previous research focuses on single disturbances or qualitative analysis of overlaid effects from two disturbances. Studies rarely explored the interactions between three or more disturbances, especially mechanisms behind the multiple disturbances. Our study covered four states (Idaho, Montana, Wyoming, and Utah) in the U.S. which shared similar climate patterns and vegetation distributions. We collected 241 chronologies from the International Tree-Ring Data Bank (ITRDB) and our own field expeditions. We assigned each tree ring to eight possible disturbance combinations. From the correlations between tree indices and climate (monthly temperature and total precipitation), the radial growth of tree rings showed a significant positive correlation with summer precipitation and a negative correlation with summer temperature. With three-factor ANOVA and one-way ANOVA, we ranked the impacts of each disturbance and combination of disturbances on tree growth based on tree-ring index; control (1.038) > insect (1.029) > fire (1.008) > fire & insect (0.963) > drought & insect (0.918) > drought (0.890) > drought, fire & insect (0.803) > drought & fire (0.784). We found that in most cases, the combined impact from two disturbances was larger than the impacts from single disturbances with the inclusion-exclusion principle. This research quantitatively revealed the interactions between disturbances and evaluated the effects from a combination of multiple disturbances.     

Effects of land‐use change and rainfall in Sudano‐Sahelian West Africa on the diet and nestling growth rates of an avian predator

Raptor populations in Sudano‐Sahelian West Africa are being severely affected by widespread habitat alteration which depletes prey populations, potentially aggravated by changing rainfall patterns. We studied Grasshopper Buzzards Butastur rufipennis at nests in natural and transformed habitats in the Sudano‐Sahelian region of northern Cameroon to assess the effects of habitat transformation and rainfall on nestling diet and growth. Grasshoppers and small mammals were more frequently taken in natural habitat, whereas lizards were most frequently taken in transformed habitats. These dietary differences reflected differences in prey availability around nests in natural and transformed habitats. Land use was a significant predictor of asymptotic weight: nestlings in natural habitat attained a higher mass than those in transformed habitats, when potentially confounding variables such as hatch order, gender, hatch date, rainfall or the presence of siblings were taken into consideration. These results suggest that body condition at fledging was habitat‐dependent, with potential consequences for subsequent survival. However, we recorded no differences in caloric content of food delivered to nests in natural and transformed habitat, which was possibly related to prey caught during twilight hours. There was a positive relationship between precipitation levels during the nestling phase and nestling growth rate. We predict unfavourable future conditions for nestling growth of raptors in Sudano‐Sahelian savannas as a consequence of continued widespread habitat transformation and diminished rainfall.     

Effects of pyrrol-carboxylic acid derivatives on the growth of coliphages.

Effects of 14 pyrrol-carboxylic acid derivatives and analogues (PY-compounds) on the growth of coliphage MS2 using E. coli E102 (Hfr) as the host were measured by the agar double-layer method. Enlargements of plaque size were observed with 7 PY-compounds but increase in plaque numbers was not induced. These enlargements of plaque size were specific to RNA coliphages MS2, GA and qbeta and not found with DNA coliphages delta AC and T4. Furthermore, the interaction between PY-compound PY-10 and the coliphage MS2 was dependent on the host bacterium (indicator strain). When E102 (Hfr) was used, the enlargement was marked, in the case of substrain W1895 (Hfr) it was less, while in the case of substrain W6 (F+) it was undetectable. The one-step growth of the phage MS2 and the production of intracellular phage MS2 were little affected by the PY-compound PY-10. However, the rate of one-step growth was increased in the early stage after infection. Accordingly, the enlargements of plaque size by the PY-compounds might be correlated with an increase in rate of release of phage particles.     

Effects of nestling condition on UV plumage traits in blue tits: an experimental approach

Intraspecific sexual and social communications are among themost important factors shaping costly color traits in birds.Condition capture models assume that only animals in superiorcondition can develop and maintain a colorful plumage. Althoughthere is good evidence that carotenoid-based components of plumagecolors show condition dependence, the situation is more controversialwith the underlying UV-reflecting structural component. We conducteda brood size manipulation in blue tits (Parus caeruleus) toinvestigate condition-dependent effects on plumage colorationin male and female offspring. Carotenoid chroma and UV reflectanceof the yellow breast plumage showed condition-dependent expressionin male and female fledglings. However, only males that wereraised in reduced broods had higher UV reflectance in the UV/bluetail feathers, whereas female tail coloration did not differbetween treatments. Our data suggest that there is a sex-specificeffect on the blue but not the yellow plumage and that thisis related to differences in the signaling function of bothplumage traits. Although sexual selection may already act onmale nestlings to develop colorful tail feathers for the nextbreeding season, the UV/yellow breast feathers are molted duringthe postjuvenile molt, and their signaling value is likely tobe important for both sexes during the extended postfledglingphase.     

盐胁迫对桑树幼苗生长、叶片水分状况和离子分布的影响

以黑龙江省两个桑树品种（秋雨桑和泰来桑）为试验材料,研究了不同盐浓度下桑树幼苗生长、叶片水分关系和不同器官中离子的分布.结果表明：盐胁迫明显降低了桑树幼苗的植株高度和每株干物质量,且对新生叶片干质量的影响大于老叶片.随着盐胁迫的加重,两个品种桑树的叶片水势、渗透势、压力势和相对含水量明显下降,根、茎中Na⁺浓度明显增加,当外界NaCl浓度达到或超过150 mmol·L^-1时,各器官中Na⁺浓度达到饱和.盐胁迫明显降低了两个品种桑树根、茎和叶片中K⁺ 和 Ca²⁺浓度,以及茎和叶片中Mg²⁺浓度,而对根中Mg²⁺浓度影响不大.Na⁺在根、茎和老叶中的区域化分布是两个品种桑树生长过程中表现出耐盐性的机理之一,而盐胁迫使叶片中的Ca²⁺、K⁺和Mg²⁺浓度降低,导致植株体内的离子亏缺,从而限制了植株的生长.     

马尾松的生长与气候关系的年轮分析

马尾松的生长与气候关系的年轮分析兰涛,夏冰,贺善安（江苏省－中国科学院植物研究所,南京２１００１４）ＴｒｅｅｒｉｎｇａｎａｌｙｓｉｓｏｎｒｅｌａｔｉｏｎｏｆＰｉｎｕｓｍａｓｓｏｎｉａｎａｇｒｏｗｔｈｔｏｃｌｉｍａｔｅｆａｃｔｏｒｓ．￥ＬａｎＴａｏ;Ｘ...     

Effects of short-term hunger and competitive asymmetry on facultative aggression in nestling black guillemots Cepphus grylle

Siblings in a diversity of species are facultatively aggressive,yet the proximate control of the aggressive response and theecological conditions selecting for such systems are poorlyunderstood. In this study, we investigated the effects of foodamount (food amount hypothesis) and competitive asymmetry onsibling aggression in black guillemot broods. Parental provisioningrates were experimentally manipulated in broods comprisinga range of hatching intervals over a 12-h period. Aggressionbecame evident only after parental provisioning rates wereexperimentally reduced. When parental provisioning resumed,adults did not increase their feeding rate to compensate forthe induced food deficit, and the result of sibling rivalry was a change in the allocation of parental deliveries from oneof equality to one in favor of the dominant chick. Food-deprivedchicks from synchronous broods were more aggressive than thosefrom asynchronous broods, suggesting that one benefit of hatchingasynchrony in the black guillemot is to establish an efficientcompetitive hierarchy among siblings which minimizes the needfor costly aggressive interactions. On the following day, siblingaggression ceased, and chicks regained an equal share of parentalfeeds. Our results provide the first evidence that short-termfood shortage per se acts as an initial trigger for aggressionand also show that the aggressive response is complicated byfactors associated with hatching and laying order.