Food Availability as a Determinant of Pairing Behaviour in the European Robin

Barrow's Goldeneye Bucephala islandica have a multi-stage territorial system, defending distinct pair, brood, and winter territories. Only paired birds defend winter territories and their territorial behaviour is similar to that observed on the breeding areas. Breeding pair territories averaged 0.44 ha (range: 0.05-1.85 ha) whereas brood territories averaged 0.91 ha (range: 0.27-2.79 ha). Breeding pair territories were not centered around the females but had well defined boundaries, and were defended even when the female was absent. Removal of two pairs suggests that territory size was determined mostly by pair density as territories expanded after the removals. Breeding pair and brood territories averaged approximately 0.35 km from the nest site (range: 0-2.9 km). Broods usually settled on the lake closest to the nest site. Philopatry to breeding pair and brood territories was strong. I suggest that the main advantage of spring and winter pair territoriality may be in providing an exclusive and undisturbed feeding area for the female. Similarly brood territories provide an exclusive feeding area for the young.

ABSTRACTCapsule: Pairs of White-throated Dippers Cinclus cinclus which defended winter territories bred earlier than non-territorial individuals, but there was no difference in reproductive success.Aims: The effect of winter territoriality on breeding ecology has rarely been studied in resident birds. We carried out a preliminary investigation of whether winter territorial behaviour and territory size affect the timing of reproduction, breeding territory size and reproductive success in a riverine bird, the White-throated Dipper.Methods: We monitored an individually marked population of White-throated Dippers in the UK. Wintering individuals were classified as either territorial or ‘floaters’ according to their patterns of occurrence and behaviour, and their nesting attempts were closely monitored in the subsequent months. Winter and breeding territory sizes were measured by gently ‘pushing’ birds along the river and recording the point at which they turned back.Results: All birds defending winter territories did so in pairs, but some individuals changed partners before breeding. Territorial pairs that were together throughout the study laid eggs significantly earlier than pairs containing floaters and those comprising territorial birds that changed partners. However, there were no significant differences in clutch size, nestling mass or the number of chicks fledged. There was no relationship between winter territory length and lay date or any measure of reproductive success, although sample sizes were small. Winter territories were found to be significantly shorter than breeding territories.Conclusion: Winter territoriality may be advantageous because breeding earlier increases the likelihood that pairs will raise a second brood, but further study is needed. Territories are shorter in winter as altitudinal migrants from upland streams increase population density on rivers, but this may also reflect seasonal changes in nutritional and energetic demands.

Abstract. Increases in atmospheric carbon dioxide drive accompanying changes in the marine carbonate system as carbon dioxide (CO2) enters seawater and alters ocean pH (termed "ocean acidification"). However, such changes do not occur in isolation, and other environmental factors have the potential to modulate the consequences of altered ocean chemistry. Given that physiological mechanisms used by organisms to confront acidification can be energetically costly, we explored the potential for food supply to influence the response of Olympia oyster (Ostrea lurida) larvae to ocean acidification. In laboratory experiments, we reared oyster larvae under a factorial combination of pCO2 and food level. Elevated pCO2 had negative effects on larval growth, total dry weight, and metamorphic success, but high food availability partially offset these influences. The combination of elevated pCO2 and low food availability led to the greatest reduction in larval performance. However, the effects of food and pCO2 interacted additively rather than synergistically, indicating that they operated independently. Despite the potential for abundant resources to counteract the consequences of ocean acidification, impacts were never completely negated, suggesting that even under conditions of enhanced primary production and elevated food availability, impacts of ocean acidification may still accrue in some consumers.

Abstract. Clutch size is an important life history trait, and factors such as nest predation and food availability can both be of crucial importance for its variation in nature. The aim of the present study was to evaluate the effects of extra food on clutch size, laying date and hatching success in the White Stork. Three different colonies of White Storks were studied in northern Algeria over a three-year period (2002–2004) that was characterised by considerable variation in both food availability and precipitation. This study demonstrated that an extra food supply during the pre-laying period had a positive effect on clutch size — nests with extra food had larger clutches. There was also an advance in laying date and a greater hatching success in nests with access to extra food. In addition to food supply, clutch size was independently affected by the year, which could have been due to differences in rainfall. Furthermore, the results of this study suggest that extra food during the incubation period co...

Vertebrate population dynamics, social organisation and space use often are closely associated with the distribution of critical resources, such as food. Tree squirrels are ideal models to study these relationships, since both key demographic parameters (reproduction, survival and dispersal) and spatio‐temporal variation in food supplies (measured as seed‐crop size) can be reliably estimated. In this paper we test the following two predictions underlying the association between annual food abundance and demography in six alpine red squirrel populations, both with and without time‐lag effects: 1) between‐season and between‐year fluctuations in survival rate, population density and increase parallel those in food availability; and 2) individuals follow a resource tracking strategy and increase in density mainly the year after a rich seed‐crop. Red squirrels occurred at higher densities in Scots pine forest, characterised by stable seed‐crops, than in Norway spruce with more abundant but more variable seed crops. Fluctuations in numbers were positively correlated with food availability, measured as annual conifer seed‐crop sizes. Overall, adult survival rates were higher than those of subadults, and survival substantially fluctuated between seasons and years. Autumn densities and rates of population increase (summer‐autumn) were strongly correlated with the same year's autumn seed‐crop, while correlations with the previous year's seed‐crop (time‐lag models) were either weak (population density) or absent (population increase). Results of this paper show that fluctuations in red squirrel densities in habitats with strong temporal variation in seed production are more closely linked with food availability than in more stable habitats. In addition, in the Alpine conifer forests squirrel population sizes, in autumn, increase in synchrony with food resources, eliminating the population lag normally present when resources are produced in pulses.

ABSTRACTModels of territorial behaviour predict a reduction in territory size when food availability and competitive pressure increase. Moreover, body size can play an important role in territorial defence. The Torrent Duck (Merganetta armata) is a river specialist that exhibits year-round territorial behaviour and long-term pair bonds. Food availability measured as biomass of invertebrates per unit area, territory and body size of Torrent Ducks were studied in the Andes in Argentina to test predictions of territoriality models. The availability of aquatic invertebrates decreased with latitude, while territory size increased. As expected, territory size of Torrent Ducks showed a negative relationship with the availability of aquatic invertebrates, a major food source for Torrent Ducks. Larger males and females paired together and occupied territories with greater food availability. Body size may be important for both males and females for the successful acquisition and defence of territories, especially during the non-breeding season when the contest winner acquires or maintains the territory and the mate. Our results suggest that Torrent Duck specialisation on fast-flowing mountain rivers leads to year-round territoriality in both sexes, a positive correlation between territorial defence and body size, and territory size proportional to food availability and population density.

We report on a series of experiments performed on a population of free—living eastern chipmunks, Tamias striatus, inhabiting a forest in northwestern Pennsylvania. The experiments were designed to examine, via pertubations of food supply and/or population density, the relationship between home range size, food availability, and population density. When food levels were increased within an area, a simultaneous effect was noted: mean home range size decreased and population density increased through recruitment from neighboring habitats. Whether the cause of the decreased patterns of movement was the increased food supply or the elevated population density was determined in subsequent experiments. When population density was held constant and food supplies were experimentally increased, there was a significant reduction in mean home range sizes when compared to the normal (control) situation. When food supplies were undistributed, put population density was greatly reduced, there was no change in the mean home range size over that determined at higher mean home range size, whereas population density, at least at the levels we examined experimentally, has no effect on movement patterns. These results are in accord with those theories relating movement patterns to resource abundance, but are not in accord with hypotheses suggesting that the home range sized and population density and inversely associated.

An accurate assessment of food security and its challenges is essential for formulating effective measures and promoting sustainable socioeconomic development. This study develops an evaluation system for China's food security, focusing on four dimensions: food supply, food access, food production stability, and food continuity. The entropy weight extended matter element model is used for quantitative processing, which ensures that the integrity of the information can be guaranteed to a greater extent while reducing the influence of subjective factors, and then, the study evaluates the food security of different functional areas in China, and finally, it diagnoses the main obstacles to food security by using the obstacle degree model. (1) From 2000 to 2020, China's food security level fluctuated, initially declining, and then increasing. The food security level in major production and marketing areas is generally higher, while the primary marketing areas exhibit the lowest security levels. (2) The level of grain yields and the total power of machinery per unit area are the key factors affecting food security; the impact of inputs of agricultural materials (fertilizers and pesticides) on food security has decreased and is constantly stabilizing. In the main marketing area, the per capita food share is significantly lower than in the other functional areas, which has the greatest impact on food security. (3) Analysis of the obstacle factors reveals that the food supply and access security subsystems are crucial for ensuring national, production, and marketing security. From 2000 to 2020, the average obstacle degrees of food supply and food access security at the national level were 46.56% and 21.17%, respectively; for the production and marketing areas, they were 58.47% and 21.45%; and for primary marketing areas, they were 37.69% and 26.59%. In major grain-producing areas, the main obstacles lay within the food supply security and food production stability subsystems, with average obstacle degrees of 53.77% and 15.67%, respectively, from 2000 to 2020. The above results provide a scientific basis for comprehensively improving the level of food security in China, optimizing the structure of food production in each functional area, and formulating regionalized policies for stabilizing and maintaining food production and supply.

Vocal performance during spontaneous song is equal in male and female European robins

Irruptions are irregular mass movements performed outside the main breeding area of a species (Svardson 1957, Bock and Lepthien 1976). These movements commonly involve juveniles or individuals with poor competitive ability (Smith and Nilsson 1987) and often are attributed to large-scale variation in food supplies or weather conditions that lead to population booms (Bock and Lepthien 1976, Perrins 1979). Irruptions may be produced after years of good food production followed by a successful breeding season (Ulfstrand 1963, Bejer and Rudemo 1987, Hussell 1996). However, anomalous seed-crop production may be interpreted only as the proximate cause for the irruptive behavior of parids (Ulfstrand 1962) and fringillids (Jenni 1987). Large seed crops increase resource availability and may lead to high population densities, which in turn may force some individuals to make long movements (Ulfstrand et al. 1974). However, some related species of parids with similar foraging behavior and habitat selection (e.g. Great Tit [Parus major] and Marsh Tit [P palustris], or Coal Tit [P ater] and Crested Tit [P cristatus]; Cramp and Perrins 1993) show very different responses to variation in food-crop size, resulting in specific irruptive tendencies. Few studies have been conducted on mechanisms of irruptive behavior (but see Bock and Lepthien 1976). In this study, I used comparative methods to examine possible links between winter territoriality and irruptive behavior in parids. Differences in nonbreeding social systems (i.e. degree of winter territoriality) can affect spacing mechanisms of individuals (Matthysen 1990). Therefore, an increase in the degree of winter territoriality likely would reduce the benefits of irruptive behavior. I also assessed the relative importance of annual fecundity in the predicted relationship between winter territoriality and irruptive behavior, because high fecundity favors offspring production and therefore may lead to irruptive episodes. Methods.-I gathered data from the literature on winter territoriality and irruptive tendency for 13 species of parids and the White-breasted Nuthatch (Sitta carolinensis), which I used as an outgroup (see Appendix). Whether a species was considered to be irruptive was based on information in Cramp and Perrins (1993) and Harrap and Quinn (1996). Al-

Regional variation in seasonality affects migratory behaviour and life-history traits of two Mediterranean passerines

The influence of food supply on postembryonic durations, egg production, and functional feeding responses (FFRs) of Tropodiaptomus cunningtoni was measured in relation to food supply under laboratory conditions at around 26.5°C. Growth and fecundity was determined in 20 μm-filtered lake water with seven levels of Cryptomonas sp. enrichment (0 to 2.5 mg C.l −1 ). FFRs were measured in GF/C-filtered lake water at six food enrichment levels (0 to 1 mg C.l −1 ). Naupliar durations (N 1 -C 1 ) showed little response to increasing food supply, whereas total (N 1 -C 6 ), and thus copepodite (C 1 -C 5 ) durations showed a continuous monotonic decline over the food range tested. Egg production continued to increase with rising food supply, although clutch size was only weakly related to food level. Individual egg volume declined markedly with clutch size, which ranged from one to eight eggs, under both laboratory and field conditions. Filtration rates of up to 8 and 28 ml.individual −1 .day −1 were measured in stage 3/4 nauplii and adult females. Maximal ingestion rates amounted to 37% and 27% body C.d −1 , and estimated metabolic maintenance demands of these stages were only met at food levels of 0.65 and 0.85 mg C.l −1 , far above those prevailing in the surface waters of L. Malawi. These experimental findings are discussed in relation to field data presented on aspects of the distribution of T. cunningtoni in L. Malawi, on which basis we suggest that naupliar development relies largely on lipid reserves, while copepodite growth and egg production by adults in situ may depend on deep chlorophyll maxima

This study represents a combination of observations on the biology of the nocturnal Sportive Lemur (Lepilemur mustelinus leucopus) living in the arid bush zone (characterised by the Family Didiereacae) of South Madagascar. Comparative data relating to nutrition, diurnal resting sites and population density in gallery forest of the same area are also presented. During its phase of nocturnal activity, this Lemur remains immobile for long periods of time, and the actual time spent in search of food is extremely limited. During daytime, it remains close to the orifice of its retreat, thus permitting constant surveillance (state of somnolence without deep sleep). The dietary regime, which is almost exclusively folivorous, represents an extreme case of specialisation within the Order Primates, as is demonstrated by quantitative analysis of the assimilable components of the diet. The digestive tract is specialised as an adaptation to this diet ; there are several peculiar features in the proportions between the different segments of the tract, in the histological structure of the mucosa and in the différenciation of the cæcum and the colon, which both possess villosities of a special type. A description is given of an organ situated at the ileo-colic junction, which is derived from a Peyer patch and which possibly plays an important part in the digestive sequence. In addition, Lepilemur exhibits reingestion of its faeces (cæcotrophy), thus presenting an apparently unique case among the Primates. This observation under natural conditions helps to explain how the animal is able to benefit from a small quantity of ingested matter which is extremely poor in directly assimilable matter. An attempt has been made to calculate the balance of energy-expenditure, and this reveals great economy in muscular expenditure relative to the total availability of energy. This ecological study was conducted during the critical period during which the availability of food (evaluated according to the mean area exploited by each individual animal) was passing a minimum. During this period, the ratio of available energy to energy consumed was 1,6 : 1 (a value quite close to those calculated by Smith, 1968 with respect to annual availability for a squirrel species in North America). Study of the social behaviour of Lepilemur was undertaken following capture, marking and release of all the individuals in a particular population. The individual territories whose limits were determined to within a matter of meters, are defended by males against other males or by females against other females. Each individual devotes the major part of the activity period to surveillance of adjacent individuals. Aggressive signals (postures and vocalisations) are predominantly associated with territorial defence. Even outside the period of reproductive activity, social relationships exist between males and females whose territories overlap. Social bonds were also identified between adult females and juvenile females ; territorial independence of the latter seems to develop progressively and relatively slowly. This type of social system is found in other nocturnal prosimians which have been studied, and it would appear to be a primitive character. An experiment conducted in the field permitted observation of rapid modifications in the territorial limits of males following the removal of one male. These modifications were associated with establishment of social links with the females whose territories coincided with that of the male eliminated in the experiment, even though this took place outside the period of reproductive activity.

Introduction: Twelve functions have been assigned to avian vocal duets (e.g., maintaining contact, mate guarding, signaling quality, or resource defense). To separate between functions of duets it is necessary to take into account who is the receiver, the information coded by the sender, and if there is a conflict between pair members. Duets used for resource defense (e.g., territory) are a more aggressive signal than solo songs because they act as a joint defense signal that encode a pairs’ strength or time together in the coordination of both individuals’ song. Therefore, interacting pairs may use duet coordination to respond according to rival information. Objective: Our main objective in this study was to test whether the coordination in time and frequency of White-eared Ground-Sparrow (Melozone leucotis) pair duets influences the territorial response of conspecific pairs. Methods: We recorded 2-5 duets from 31 territorial pairs and measured duet coordination by dividing each ground-sparrow duet into three sections (include sections here) according to each individual’s contribution. In each section we measured frequency range and duration and the difference in frequency range and duration between the introductory and middle section, and the middle and terminal section of each duet. We then used a playback experiments to test pair response to duet coordination. Each pair were exposed to two types of duets: highly coordinated duets and a poorly coordinated duets. Results: We exposed 31 pairs to these two treatments during duet playbacks and measured their territorial response according to the simulated intruders’ duet coordination. We found that pairs that produced highly coordinated duets approached faster and spent more time closer to all playbacks. By comparison, territorial pairs spent more time closer to the poorly coordinated duet stimulus. Total number of vocalization produced in response to duet stimuli were similar between stimuli and independent of the duet coordination of the territorial pairs. Conclusions: Our study indicates that, duet coordination in territorial pairs of White-eared Ground-sparrows is a good predictor of the strength in territorial defense and suggests that pairs used duet coordination to perceive the level of threat from an intruder.

The findings from previous food-addition experiments designed to examine the effects of food availability on reproductive parameters could have led to false conclusions because most experimental designs fail to take account of population parameters during periods preceding the experiments and because the studied effects of supplemental food could have been confounded by effects on age composition and pair bonds. To test this possibility, we provided a population of the Varied Tit Parus varius with extra food (sunflower seed) from February to April and compared density, survival rate and mate change of the fed population with those of an unfed population. A similar comparison is made between these populations before and after the addition of food. In the fed area, population density was stable and pair bonds from the winter were maintained. By contrast, the survival rate in the unfed area was low resulting in lower density, and many members of winter units changed their partners. Since food supply in early spring promoted the stability of pair bonds and may make age composition more stable, we propose that food-addition experiments should include not only comparisons of reproductive parameters of fed and unfed populations, but also comparisons of both age composition and pairbond stability before and after the addition of food.