Colony choice in birds: models based on temporally invariant site quality

We propose two stochastic models to explain how birds choose colonies. In the resource choice model, birds settle at each site at a rate proportional to the total resources the site contains. In the reduced resource choice model, a smaller cohort of birds enters sites at a rate determined by the total resources at each, and the remaining individuals enter sites at a rate that is linearly proportional to the total number of birds already nesting at each site. Thus, a fraction of birds chooses sites based on the resources present, and the remainder are attracted to a site by the presence of other birds. Colony site quality is assumed not to vary between years. Both models result, on average, in an ideal free distribution of colony sizes if the birds' settlement rate is linearly related to the resources in a site, if resources are distributed equally among individuals within sites, and if individuals with equal resources have equal fitness. We applied these models to long-term data on colony sizes and site usage of cliff swallows in south-western Nebraska. A test of the resource choice model suggested that the swallow population as a whole did not choose sites based strictly on site quality or the total resources contained at each site. However, a test of the reduced resource choice model suggested that a smaller fraction of the individuals in each colony may have based their choice of site on local resource availability, with the remaining birds aggregating at those sites based on the number of birds already settled there. Tests of these models may provide insight into how individuals choose colony sites and why colonies vary in size.     

Information transfer and gain in flocks: the effects of quality and quantity of social information at different neighbour distances

We assessed experimentally how the quality and quantity of social information affected foraging decisions of starlings (Sturnus vulgaris) at different neighbour distances, and how individuals gained social information as a function of head position. Our experimental set up comprised three bottomless enclosures, each housing one individual placed on a line at different distances. The birds in the extreme enclosures were labelled senders and the one in the centre receiver. We manipulated the foraging opportunities of senders (enhanced, natural, no-foraging), and recorded the behaviour of the receiver. In the first experiment, receivers responded to the condition of senders. Their searching rate and food intake increased when senders foraged in enhanced conditions, and decreased in no-foraging conditions, in relation to natural conditions. Scanning was oriented more in the direction of conspecifics when senders behaviour departed from normal. In the second experiment, responses were dose dependent: receivers increased their searching rate and orientated their gaze more towards conspecifics with the number of senders foraging in enhanced food conditions. In no-foraging conditions, receivers decreased their searching and intake rates with the number of senders, but no variation was found in scanning towards conspecifics. Differences in foraging and scanning behaviour between enhanced and no-foraging conditions were much lower when neighbours were separated farther. Overall, information transfer within starling flocks affects individual foraging and scanning behaviour, with receivers monitoring and copying senders behaviour mainly when neighbours are close. Information transfer may be related to predation information (responding to the vigilance of conspecifics) and foraging information (responding to the feeding success of conspecifics). Both sources of information, balanced by neighbour distance, may simultaneously affect the behaviour of individuals in natural conditions.Communicated by H. Kokko     

Vicarious sampling: the use of personal and public information by starlings foraging in a simple patchy environment

Group foragers may be able to assess patch quality more efficiently by paying attention to the sampling activities of conspecifics foraging in the same patch. In a previous field experiment, we showed that starlings foraging on patches of hidden food could use the successful foraging activities of others to help them assess patch quality. In order to determine whether a starling could also use another individual’s lack of foraging success to assess and depart from empty patches more quickly, we carried out two experimental studies which compared the behaviour of captive starlings sampling artificial patches both when alone and when in pairs. Solitary starlings were first trained to assess patch quality in our experimental two-patch system, and were then tested on an empty patch both alone and with two types of partner bird. One partner sampled very few holes and thus provided a low amount of public information; the other sampled numerous holes and thus provided a high amount of public information. In experiment 1, we found no evidence of vicarious sampling. Subjects sampled a similar number of empty holes when alone as when with the low and high information partners; thus they continued to rely on their own personal information to make their patch departure decisions. In experiment 2, we modified the experimental patches, increasing the ease with which a bird could watch another’s sampling activities, and increasing the difficulty of acquiring accurate personal sampling information. This time, subjects apparently did use public information, sampling fewer empty holes before departure when with the high-information partner than when with the low-information partner, and sampling fewer holes when with the low-information partner than when alone. We suggest that the degree to which personal and public information are used is likely to depend both on a forager’s ability to remember where it has already sampled and on the type of environment in which foraging takes place. Received: 31 January 1995/Accepted after revision: 11 September 1995     

Passing the buck: resource defence,lek breeding and mate choice in fallow deer

Summary Lek breeding systems, where males defend small, clustered mating territories, are thought to occur where the distribution of females is heavily clumped but males are unable to defend resources used by females. In this paper, we describe a breeding system in fallow deer where males are able to defend resources used by females but the most successful bucks instead defend small territories on a traditional mating ground; where the lek is sited in an area not heavily used by females at other times of year and is visited primarily by females in or close to oestrus; and where mating success on the lek is related to territory position and to male phenotype but not to the resources available on different lek territories. Comparisons with other ungulates suggest that lek breeding species fall into two groups: those where leks are regularly visited by herds of females many of which are not in oestrus and those, like fallow deer, where leks are visited primarily by oestrous females. In the latter species, it is unlikely that females visit the lek for ecological reasons.     

Song rate as a signal for nest site quality in blackcaps (Sylvia atricapilla)

In this study we examine male song output as a measure of nest site quality in blackcaps (Sylvia atricapilla). Song rate, breeding success, predation on nests and reaction to playbacks were investigated in individual males. Habitat features determining nest site and song post quality in terms of vegetation cover were compared between successful nests and nests that had suffered predation. We then related song rate of unmated males to habitat factors in territories and nesting sites in order to examine a possible predictor function of blackcap song for habitat quality. Several habitat features are responsible for variation in nesting success. These features also correlate with song rate of unmated males. The study indicates a potential role of song rate in the advertisement of territory quality. Furthermore, the data suggest that females use song rates rather than territory quality in mating decisions. The information females may gain about male quality in relation to territory quality are also discussed.     

Sulfur isotopes link overwinter habitat use and breeding condition in Double-crested Cormorants.

North American Double-crested Cormorant (Phalacrocorax auritus) populations have increased greatly. Both breeding and overwintering ground factors have likely contributed to these increases. However, demonstrating how overwintering conditions may affect breeding birds has not been possible because of the difficulty in linking breeding birds to their wintering grounds. Here, we demonstrate the utility of stable sulfur isotopes to elucidate overwintering habitat use by cormorants breeding on Lake Erie. Sulfur isotopes in feathers grown on overwintering grounds provided insights into the degree to which birds used freshwater vs. marine environments. The proportion of birds utilizing freshwater habitats increased through time. This change may have reflected increases in freshwater aquaculture (i.e., catfish) in the U.S. south. Examination of body condition in birds returning to breed on Lake Erie indicated that those individuals that solely used marine habitats for at least a portion of the overwintering period were in poorer condition than birds using freshwater. Enhanced foraging opportunities at aquaculture facilities may improve the fitness of individuals that have returned to breed after overwintering at such locations. This study is the first to demonstrate a linkage between overwinter habitat use and breeding ground parameters in Double-crested Cormorants. These results underscore that factors throughout the Mississippi flyway are likely acting together to regulate cormorant populations.     

Female choice and the quality of parental care in the great tit Parus major

Summary Previous work on great tits suggested that female mate choice was based on the characteristics of the male rather than the quality of his territory. The aim of this paper was to see whether females were deriving any direct benefits as a result of such choice by comparing male plumage colouration (the size of the central black breast-stripe) with the quality of parental care provided by both members of the pair. Males with large stripes were more likely to defend their broods because their nest attentiveness was higher increasing the chances of predator detection. Males with large stripes produced heavier fledglings primarily as a result of faster growth early in the nestling period. Previous work on great tits has shown that heavier fledglings have a higher survival probability than lighter ones. The results of this study can more easily be explained by differences in parental quality between males rather than as a result of variation in female or territory quality. Therefore, female great tits could increase their reproductive success by pairing with males with a large stripe because such males appear to be better quality parents. This suggests that female choice in the great tit may concern, at least in part, the quality of male parental care.     

Variance in female quality, operational sex ratio and male mate choice in a bushcricket

Male bushcrickets, Kawanaphila nartee, exercise mate choice when nutrients are limited. Male mate choice is associated with a female-biased operational sex ratio (OSR) that arises from an increased relative paternal investment under nutrient limitation. However, increased male choosiness could be attributable to the fact that females vary more in fecundity, and consequently in mate quality, when nutrient limited. Our objective was to experimentally partition the influences of OSR (male or female bias) and variance in mate quality (high or low) and to assess their relative influence on the intensity of mate choice by male bushcrickets. Female quality was manipulated by controlled feeding regimes that directly affected female fecundity. We found that males and females engaged in sexual interactions sooner under a male-biased than a female-biased OSR. Males were more likely to reject females on their first encounter when variance in female quality was high. However, the effect of quality variance on the total number of rejections during a 4-h observation period was dependent on the perceived OSR. A male's prior experience of variance in female quality did not influence male choosiness. Our observed rates of mate rejection conformed well with those predicted from recent theoretical models of sexual differences in choosiness. In conclusion, our results show that the opportunity for selection via male mate choice is influenced by an interaction between OSR and the variance in mate quality that arises within nutrient-limited populations of females. Received: 5 January 1998 / Accepted after revision: 25 October 1998     

The use of slope and visual information in sandhoppers: innateness and plasticity

Mediterranean sandhoppers of the species Talitrus saltator (Montagu) from the Tyrrhenian population of Burano (Grosseto, Italy) were tested by rearing under different conditions in order to enquire into the innateness and modifiability of orientation with respect to substrate slope and landscape features. Tests were conducted from November 1990 to November 1991. The results were as follows: the sandhoppers responsed to slope only by orienting themselves downslope on dry substrate and upward on a wet one. These responses appeared to be innate but modifiable by experience. Visual dishomogeneity (half horizon covered with a black strip), with a horizontal substrate, elicited an innate orientation towards the black shape, again modifiable by experience. When a black strip was positioned around the upper half of the inclined arena, the sandhoppers responded differently, dependent upon their prior experience: wild individuals responded to the visual stimulus, amphipods reared in optical homogeneity did not make a choice and those reared in conditions identical to those of the test arena responded to slope by orienting downwards and away from the balck strip. With a black strip around the lower half of the inclined arena and with a dry substrate identical responses were shown by wild-caught and laboratory-reared sandhoppers, i.e., downslope and towards the black strip.     

Yolk androgens in great tit eggs are related to male attractiveness,breeding density and territory quality

Females can adaptively adjust phenotype of their offspring via deposition of various compounds into eggs, including androgens and other hormones. Here, I investigated how egg yolk androgens (testosterone and androstenedione) related to environmental conditions and parental traits in the great tit (Parus major) across three breeding seasons. Male and female traits studied included age, condition and multiple feather ornaments, both carotenoid- and melanin-based (carotenoid and UV chroma of yellow breast feathers, area of black breast band and white cheek immaculateness). Yolk mass increased with laying temperature, laying date and area of male black breast band. Concentration of androgens increased with breeding density, territory quality and carotenoid chroma of male yellow breast feathers and was higher in mates of 1 year old as compared to older males. Yolk androgens were not related to any of the female traits analysed. These patterns were thus consistent with (1) social and environmental effects on yolk mass and composition and (2) both positive and negative differential allocation strategies of resource allocation in females. Overall, male traits were the most important predictors of egg yolk characteristics in this socially monogamous songbird.     

Effect of temperature on seawater desalination-water quality analyses for desalinated seawater for its use as drinking and irrigation water

The effect of feed seawater temperature on the quality of product water in a reverse osmosis process was investigated using typical seawater at Urla Bay, Izmir region, Turkey. The tests were carried out at different feed seawater temperatures (11–23°C) using two RO modules with one membrane element each. A number of variables, including pH, conductivity, total dissolved solids, salinity, rejection percentage of a number of ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, HCO₃ ⁻, and SO₄ ²⁻), and the levels of boron and turbidities in collected permeates, were measured. The suitability of these permeates as irrigation and drinking water was checked by comparison with water quality standards.     

Male choice and sperm competition as constraints on polyandry in the red-necked phalarope Phalaropus lobatus

Summary The mating system of the red-necked phalarope Phalaropus lobatus is usually classed as polyandrous, but studies show that the majority of females are monogamous. Polyandry appears to be constrained because later arriving males do not usually nest with females that have already laid a clutch that season (C1-females), despite the sexual receptiveness of these females. Rather they nest with females that have not previously laid a clutch that season (C0-females). Five potential explanations of this constraint on polyandry were tested. Two hypotheses, invoking female-female competition, were not supported as female agonistic success appeared to be unrelated to priority of access to males, and there was no apparent difference between C0- and C1-females in their ability to find unpaired males. Two hypotheses suggest that C0-females are preferred by males either because they can initiate a clutch more rapidly or because they lay larger eggs. Neither hypothesis was supported by the available data. The data upheld a third male choice hypothesis that C1-females are discriminated against because they have copulated previously with another male and this may compromise paternity. Secondary males copulated and attempted to copulate more often when paired with C1-females, suggesting that sperm competition was greater and confidence of paternity was lower. Corroborative evidence of active male choice showed that males were more aggressive towards associating C1-females than towards C0-females, although how males discriminated between the two classes of females was not determined.     

Male characteristics,parental quality and the study of mate choice in the red-winged blackbird (Agelaius phoeniceus)

Summary A demonstration of adaptive mate choice by females in resource-defence mating systems requires clear predictions as to how females should rank breeding situations (defined by the quality of both the resident male and the territory he defends) so as to maximize their fitness. Since male quality is only weakly correlated with territory quality in red-winged blackbirds (Agelaius phoeniceus), ranking breeding situations in this species will require a consideration of both those parameters independently of each other as long as both vary among males, are predictable before mating, and affect female fitness. Data from a two year study of an eastern Ontario population of this species suggested that two components of male parental quality, nest defence effort and provisioning of nestlings with food, both varied among males and were somewhat predictable. Two measures of nest defence effort were correlated with an index of epaulet size (a reliable predictor of captive dominance rank in this species) (Table 5), and provisioning appeared to be predictable on the basis of both courtship behavior and breeding experience. Our data also suggest that these two components of male parental quality do not covary. Since male provisioning tends to be restricted to the nestlings of the primary and secondary mates in this species, breeding situations must be ranked not only with respect to their manifold quality but also with respect to the mating status of individual females.     

Clutch size adjustment, information use and the evolution of gregarious development in parasitoid wasps

As larvae, solitary species of parasitoid wasps eliminate rivals, including sibs, through contest competition. In gregarious species, larvae tolerate each other and several individuals can develop from a single host. We report experiments on two congeneric braconid species aimed at understanding how gregarious development evolved in one genus, and the consequences of larval interactions for parental behavior. In the transition from solitary to gregarious development, one possible intermediate stage is if solitary species frequently lay more than one egg per host. If the risk of conspecific superparasitism (another female of the same species oviposits into a single host) is high, optimal clutch size theory predicts the laying of multiple-egg clutches, because a female will increase the probability of the surviving larva being her own. Under the same conditions, theory predicts that gregarious species should reduce their clutch size. In our experiments, the solitary Aphaereta genevensis increased their clutch size under the risk of intraspecific competition for hosts whilst the gregarious A. pallipes reduced their clutch size, as predicted. In A. genevensis, the response to the risk of competition was dependent upon body size, being greatest amongst small females. In A. pallipes, the response did not depend on female body size, but clutch size increased with body size in all treatments, unlike in A. genevensis. Under the risk of competition from the other species, the response differed relative to the intraspecific treatments and differed between species. Thus, our data suggest that: (1) competition for hosts may have contributed to the evolution of gregarious development in this genus; (2) female wasps can combine information from both external and internal cues in complex ways during clutch size adjustment; and (3) the social environment may alter the adaptive response to both external and internal cues in adult females.Communicated by M. Elgar     

Comparison of diving behavior and foraging habitat use between chinstrap and gentoo penguins breeding in the South Shetland Islands, Antarctica

Chinstrap, Pygoscelis antarctica, and gentoo, P. papua, penguins are sympatric species that inhabit the Antarctic Peninsula. To evaluate differences in the foraging habitat of these two species, we recorded their foraging locations and diving behavior using recently developed GPS-depth data loggers. The study was conducted on King George Island, Antarctica during the chick-guarding period of both species, from December 2006 to January 2007. The area used for foraging, estimated as the 95% kernel density of dive (>5 m) locations, overlapped partially between the two species (26.4 and 68.5% of the area overlapped for chinstrap and gentoo penguins, respectively). However, the core foraging area, estimated as the 50% kernel density, was mostly separate (12.8 and 25.0% of the area overlapped for chinstrap and gentoo penguins, respectively). Chinstrap penguins tended to use off-shelf (water depth > 200 m) regions (77% of the locations for dives >5 m), whereas gentoo penguins mainly used on-shelf (water depth < 200 m) areas (71% of dive locations). The data on foraging locations, diving behavior, and bathymetry indicated that gentoo penguins often performed benthic dives (28% of dives >5 m), whereas chinstrap penguins almost always used the epipelagic/mid-water layer (96% of dives >5 m). Diving parameters such as diving bottom duration or diving efficiency differed between the species, reflecting differences in the use of foraging habitat. The diving parameters also suggested that the on-shelf benthic layer was profitable foraging habitat for gentoo penguins. Conversely, the relationship between trip duration, date, and stomach content mass suggested that the chinstrap penguins went further from the colony to forage as the season progressed, possibly reflecting a reduction in prey availability near the colony. Our results suggest that chinstrap and gentoo penguins segregated their foraging habitat in the Antarctic coastal marine environment, possibly due to inter- and intra-specific competition for common prey resources.     

Using information theory as a substitute for stepwise regression in ecology and behavior

In ecological and behavioral research, drawing reliable conclusions from statistical models with multiple predictors is usually difficult if all predictors are simultaneously in the model. The traditional way of handling multiple predictors has been the use of threshold-based removal-introduction algorithms, that is, stepwise regression, which currently receives considerable criticism. A more recent and increasingly propagated modelling method for multiple predictors is the information theoretic (IT) approach that quantifies the relative suitability of multiple, potentially non-nested models based on a balance of model fit and the accuracy of estimates. Here, we examine three shortcomings of stepwise regression, subjective critical values, model uncertainty, and parameter estimation bias, which have been suggested to be avoided by applying information theory. We argue that, in certain circumstances, the IT approach may be sensitive to these issues as well. We point to areas where further testing and development could enhance the performance of IT methods and ultimately lead to robust inferences in behavioral ecology.     

Soil and plant characteristics as determining factors in site selection for surface coal mine reclamation

Four vegetative associations occur on surface mines located in Mercer County, Pennsylvania. Seventeen different species of grasses and legumes and 30 different species of trees and shrubs were evaluated for their ability to become established and control erosion on surface mines. The amount of organic matter and soil moisture are the principle factors regulating the establishment of vegetative cover on surface mines. Those species possessing a fibrous root system are better able to adapt for erosion control than tap rooted species. Likewise, shrubs such as bristley locust (Robina hispida) and Silver Bush or Autumn Olive (Elaeagnus umbellata) that will produce shoots when a root becomes exposed due to erosion are better adapted for erosion control than other species. The methods and species utilized during reclamation will determine, at least in part, the future use of the land and should establish conditions for natural succession to occur.This study was supported by funds from the National Geographical Society and the Office of Water Resources, U.S. Department of Interior.