Arrival-breeding interval is flexible in a songbird and is not constrained by migration carry-over effects.

As spring phenology advances with climate change, so too must the timing of life cycle events. Breeding at the right time is critical in many species as it maximizes fitness. For long-distance migratory birds, flexibility in the duration of the arrival-breeding interval (pre-breeding period) may allow populations to adjust their timing of breeding. However, whether first egg-lay dates are flexible to local environmental conditions after arrival, and if they are constrained by the time needed to replenish energy lost during migration, remains unclear. We investigated the regional flexibility of the arrival-breeding interval in an avian migrant, the purple martin, Progne subis, across their breeding range. We evaluated whether the duration of the arrival-breeding interval was flexible to temperature and precipitation at breeding sites, and if timing was limited by migration rate and stopover duration. We also tested if longer interval durations were associated with higher fledging success. To address our hypotheses, we used a combination of migration tracking, weather and breeding data collected from four regions across eastern North America (26.1° N to 52.4° N latitude). We found the arrival-breeding interval to be shortest in the north and longest in the south. Across all regions, warmer temperatures encountered at breeding grounds were associated with shorter intervals, and faster migration rates led to longer intervals. The length of the interval was not influenced by precipitation or stopover duration. Finally, longer intervals were not associated with higher fledge success. Currently, the longer arrival-breeding intervals in this study system, on average 28.3 days, may provide both early and late-arriving birds with ample time for recovery so birds can lay eggs according to temperature. Any negative effects of faster migration may have been buffered by longer arrival-breeding intervals, as interval length did not determine fledge success. With ongoing climate change, further research is needed to examine if arrival-breeding intervals become constrained by migration timing, which may limit opportunities for migrants to match the timing of breeding with key resources.

Ethogram of the Chinese Giant Salamander during the Breeding Period Based on the PAE Coding System.

The PAE (Posture-Act-Environment) coding system is a behavior coding system that divides the study of animal behavior into postures, actions, and the corresponding environmental factors, and they are coded correspondingly. It determines the analysis dimension to standardize the study of behavior. To investigate the behavior of A. davidianus during the breeding period, as well as their related postures, actions, and required environmental conditions, this study monitored the behavior of four pairs of A. davidianus in a simulated natural breeding pool using an infrared image monitoring system and recorded the changes in water quality during this process using a water quality monitoring system. The process of reproductive behaviors was observed and recorded with the random sampling method and the focal animal sampling method to classify and code the behaviors, and the ethogram of A. davidianus during the breeding period was constructed based on the PAE coding system. The result showed that 10 postures, 33 actions, 11 environments, and 45 behavioral patterns were differentiated and defined, which were classified into 9 categories of behaviors according to the behavioral function. Among these categories, five were distinguished as behaviors unique to the reproductive period, which include sand pushing, showering, courtship, oviposition, and parental care. The remaining four categories were daily behaviors: exercise, feeding, rest, and miscellaneous behaviors. The quantitative data on water quality and habitat factors that had a significant impact on the behavior of A. davidianus, such as water temperature (WT), pH, and dissolved oxygen (DO), were included in the coding framework, which more accurately expresses the environmental conditions and thresholds required for the breeding behavior.

Reproductive seasonality of hair rams under tropical conditions: an alternative for non-seasonal lamb production?

Reproductive seasonality limits the periods of breeding on the year and, therefore, productive output. However, some breeds appear as probably non-seasonal. The aim of the study was to characterize the seasonal pattern of Santa Inês rams, including an ultrasound characterization of the reproductive tract, testosterone concentrations, and semen characteristics. Fifteen Santa Inês rams remained in a grazing system with concentrate supplementation, and measurements of the reproductive tract and ultrasound evaluation (biometrics and pixel intensity) of the testicles and accessory sex glands were monthly recorded. Computerized seminal evaluations were also performed monthly, and serum testosterone concentration was measured every 15 days. Body weight and condition remained stable throughout the year. In general, reproductive traits varied along the year and reached maximum values during autumn and minimum in spring. Despite that, as fresh semen remained with enough quality to breed all along the year, seasonality does not appear as a limiting factor to breed along the year. Therefore, Santa Inês rams can be used for all-year-round breeding or for crossbreeding when rams from other breeds decrease their fertilizing ability.

Effects of environmental factors on avian communities in urban parks in small- to medium-sized city: a case study of Fuyang City, Anhui, China.

With a worldwide expansion of urbanization, the conservation of urban biodiversity is attracting growing attention; it is important to study the relationship between wildlife and urban green spaces. In this study, we selected 31 parks in the urban area of Fuyang City in the North China Plain. A total of 8795 individual birds from 69 species were recorded. The study found that (a) at the local level, tree diversity and heights are the most important factors contributing to each level of bird diversity, followed by the coverage of shrubs and herbs, and (b) at the landscape level, the proportion of woodland has a strong positive correlation with the multidimensional diversity of birds, followed by the patch diversity and percent of grassland. Our results showed that artificial greenland can effectively increase bird diversity. While considering urban planning and human well-being, the proportion of vegetation and landscape in urban parks should be properly planned, providing more habitats to enrich bird diversity.

Distance doesn't matter: migration strategy in a seabird has no effect on survival or reproduction.

Migrating animals show remarkable diversity in migration strategies, even between individuals from the same population. Migrating longer distances is usually expected to be costlier in terms of time, energy expenditure and risks with potential repercussions for subsequent stages within the annual cycle. Such costs are expected to be balanced by increased survival, for example due to higher quality wintering areas or lower energy expenditure at lower latitudes. We compared reproductive parameters and apparent survival of lesser black-backed gulls (Larus fuscus) breeding in The Netherlands, whose winter range extends from the UK to West Africa, resulting in one-way migration distances that differ by more than 4500 km. Individuals migrating furthest arrived later in the colony than shorter distance migrants, but still laid in synchrony with the colony and consequently had a shorter pre-laying period. This shorter pre-laying period affected neither egg volumes nor hatching success. We found no relationship between migration distance and apparent survival probability, corresponding with previous research showing that annual energy expenditure and distance travelled throughout the year is similar across migration strategies. Combined, our results indicate an equal fitness payoff across migration strategies, suggesting there is no strong selective pressure acting on migration strategy within this population.

Influence of prey availability on habitat selection during the non-breeding period in a resident bird of prey.

BACKGROUND: For resident birds of prey in the temperate zone, the cold non-breeding period can have strong impacts on survival and reproduction with implications for population dynamics. Therefore, the non-breeding period should receive the same attention as other parts of the annual life cycle. Birds of prey in intensively managed agricultural areas are repeatedly confronted with unpredictable, rapid changes in their habitat due to agricultural practices such as mowing, harvesting, and ploughing. Such a dynamic landscape likely affects prey distribution and availability and may even result in changes in habitat selection of the predator throughout the annual cycle. METHODS: In the present study, we (1) quantified barn owl prey availability in different habitats across the annual cycle, (2) quantified the size and location of barn owl breeding and non-breeding home ranges using GPS-data, (3) assessed habitat selection in relation to prey availability during the non-breeding period, and (4) discussed differences in habitat selection during the non-breeding period to habitat selection during the breeding period. RESULTS: The patchier prey distribution during the non-breeding period compared to the breeding period led to habitat selection towards grassland during the non-breeding period. The size of barn owl home ranges during breeding and non-breeding were similar, but there was a small shift in home range location which was more pronounced in females than males. The changes in prey availability led to a mainly grassland-oriented habitat selection during the non-breeding period. Further, our results showed the importance of biodiversity promotion areas and undisturbed field margins within the intensively managed agricultural landscape. CONCLUSIONS: We showed that different prey availability in habitat categories can lead to changes in habitat preference between the breeding and the non-breeding period. Given these results we show how important it is to maintain and enhance structural diversity in intensive agricultural landscapes, to effectively protect birds of prey specialised on small mammals.

Accelerated Genetic Gains in Early-Maturing Maize Hybrids following Three Periods of Genetic Enhancement for Grain Yield under Low and High Soil-Nitrogen Environments.

Maize (Zea mays L.) is an important staple, as well as cash crop, in sub-Saharan Africa (SSA). However, its production is severely constrained by low soil nitrogen (low N). Fifty-four early-maturing hybrids developed during three breeding periods, (2008-2010, 2011-2013 and 2014-2016) were evaluated under low (30 kg ha-1) and high (120 kg ha-1) soil nitrogen (N) in Ile-Ife and Mokwa, Nigeria, from 2017 to 2019. The study was designed to (i) determine the genetic gains in grain yield of the early-maturing maize hybrids developed during the three breeding periods, (ii) determine the relationship between grain yield and other agronomic traits and (iii) identify the highest-yielding and most stable hybrids under low- and high-N environments. The 54 hybrids were evaluated using a 6 × 9 lattice design with three replications. Mean squares for hybrids were significant for measured traits under low- and high-N environments, except the mean squares for stalk lodging and EPP under low N. Annual genetic gains in grain yield were 75 kg ha-1 year-1 (2.91%) and 55 kg ha-1 year-1 (1.33%) under low- and high-N environments, respectively, indicating that substantial gains were achieved in the genetic enhancement of the early-maturing hybrids. The hybrids TZdEI 314 × TZdEI 105, TZdEI 378 × TZdEI 173, ENT 12 × TZEI 48 and TZdEI 352 × TZdEI 315 were identified as the highest-yielding and most stable across test environments and should be tested extensively on farms and commercialized in SSA.

Individual consistency in migration strategies of a tropical seabird, the Round Island petrel.

BACKGROUND: In migratory species, the extent of within- and between-individual variation in migratory strategies can influence potential rates and directions of responses to environmental changes. Quantifying this variation requires tracking of many individuals on repeated migratory journeys. At temperate and higher latitudes, low levels of within-individual variation in migratory behaviours are common and may reflect repeated use of predictable resources in these seasonally-structured environments. However, variation in migratory behaviours in the tropics, where seasonal predictability of food resources can be weaker, remains largely unknown. METHODS: Round Island petrels (Pterodroma sp.) are tropical, pelagic seabirds that breed all year round and perform long-distance migrations. Using multi-year geolocator tracking data from 62 individuals between 2009 and 2018, we quantify levels of within- and between-individual variation in non-breeding distributions and timings. RESULTS: We found striking levels of between-individual variation in at-sea movements and timings, with non-breeding migrations to different areas occurring across much of the Indian Ocean and throughout the whole year. Despite this, repeat-tracking of individual petrels revealed remarkably high levels of spatial and temporal consistency in within-individual migratory behaviour, particularly for petrels that departed at similar times in different years and for those departing in the austral summer. However, while the same areas were used by individuals in different years, they were not necessarily used at the same times during the non-breeding period. CONCLUSIONS: Even in tropical systems with huge ranges of migratory routes and timings, our results suggest benefits of consistency in individual migratory behaviours. Identifying the factors that drive and maintain between-individual variation in migratory behaviour, and the consequences for breeding success and survival, will be key to understanding the consequences of environmental change across migratory ranges.

Seasonal changes in the milt quality of spotted scat, Scatophagus argus: Implications for artificial propagation.

The current study investigated the correlation among sperm production (milt volume, spermatocrit and sperm count), sperm motility characters and biochemical composition of seminal plasma during different seasons to estimate the quality of semen in the Spotted scat (Scatophagus argus). The sperm of 120 males were collected over a period of 2 years seasonally viz., summer, pre-monsoon, monsoon and post-monsoon. During the collection period, it was observed that there were significant (p < 0.05) seasonal variations in the semen quality including sperm motility and production more in the summer season than other seasons. The osmolality of seminal plasma varied from 343.33 to 370.33 mOsm/kg. The pH of seminal plasma elevated from 7.37 to 7.63 during monsoon and summer seasons. The motility of S. argus sperms correlated with the concentration of biochemical compounds viz., Ca2+, Mg+ and Cl- during the summer season. Based on the present observation it could be highlighted that sodium and potassium were negatively correlated (p < 0.01 and p < 0.05) effect on total protein (r = -0.826; -0.956), glucose (r = -0.819; -0.717), cholesterol (r = -0.978; -0.849), AST (r = -0.853; -0.897), ALT (r = -0.970; -0.967), calcium (r = -0.850; -0.697), magnesium (r = -0.852; -0.843) and chloride (r = -0.906; -0.926). In conclusion, many physical and biochemical compositions of S. argus semen improved during that the summer and pre-monsoon season as compared to that of monsoon and post-monsoon. Fertility tests were performed to determine the ability of spermatozoa to fertilize an egg. Highest fertilization (79.92 ± 4.60%) and hatching (80.75 ± 3.89%) rates were observed during summer, while the rates were lowest during monsoon (40.50 ± 4.52%; 53.92 ± 7.38%). This work forms a compiled data for standard semen quality, which in turn will help to select good milters for hatchery production, cryopreservation and assisted breeding programs of this fish.

The Starfish Asterina pectinifera: Collection and Maintenance of Adults and Rearing and Metamorphosis of Larvae.

Here we describe methods for (a) collecting starfish during their breeding period; (b) maintaining adults with fully grown gonads in laboratory aquaria; (c) rearing fertilized eggs to brachiolaria larvae, and (d) inducing larvae to metamorphose into juveniles under laboratory conditions. Such protocols should facilitate various analyses of starfish development throughout the entire life cycle of these model organisms.

Fast-track breeding system to introduce CTV resistance of trifoliate orange into citrus germplasm, by integrating early flowering transgenic plants with marker-assisted selection.

BACKGROUND: Global warming will expand the range of new and invasive pathogens in orchards, and subsequently increase the risk of disease epidemics and economic losses. The development of new resistant plant varieties can help to reduce the impact of pathogens, however, the breeding speed can be extremely slow, due to the growth rates of the plants, and the availability of resistance genes. Citrus trees are suffering immense damage from serious diseases such as citrus canker (XCC), huanglongbing (HLB), and citrus tristeza virus (CTV). A fast-track breeding system, that aimed at shortening the duration for disease resistance breeding by incorporating the resistance genes from related species to commercial varieties, has been developed using the integration of precocious transgenic trifoliate orange with the overexpression of CiFT and MAS. It was applied here to incorporate CTV resistance of trifoliate orange into citrus germplasm. RESULTS: One generation of backcrossed breeding, that would normally take at least 5 years, was achieved in a single year by fast-track breeding system. Linkage analysis using the corresponding DNA markers revealed that CTV resistance and T-DNA integrated regions were found in different linkage groups, and they were independently segregated in the BC progenies. The CTV resistant null segregants, in which the T-DNA integrated region was removed from their genome, were feasibly obtained by MAS in each generation of the BC progenies, and their CTV resistance was confirmed by immunological analysis. Several BC3 null segregants, whose genetic backgrounds had been substituted into citrus germplasm, except for the haplotype block of CTV resistance, were successfully obtained. CGH and NGS analyses revealed that the T-DNA integrated region was safely segregated out in null segregants. CONCLUSION: Fast-track breeding systems are expected to shorten the required breeding time by more than one-fifth in comparison with conventional cross breeding techniques. Using this system, we obtained BC3-8, whose genetic background was successfully substituted except for the CTV resistance locus, and could be a novel mandarin breeding material. The fast-track breeding system will be useful to introduce important traits from related species to citrus germplasm while also drastically reducing the time required for breeding.

Compromised liver functions during the breeding period of clinically healthy Holstein cows.

BACKGROUND: The sub-clinical carry-over effects of post-partum (PP) conditions and the problems independent of parturition may affect the cows' performance during the breeding period. AIMS: It was hypothesized that some mid-lactation cows may have compromised liver functions and calculating liver activity index (LAI; -1.5 to +1.5) may be helpful in detecting such conditions. METHODS: Plasma lipid and protein profiles, retinol and ceruloplasmin were measured in 37 Holstein cows on days 60, 90, and 120 PP. Liver activity index was calculated using the measures of cholesterol, albumin and retinol. The results were interpreted using some health and performance indices. RESULTS: The mean LAI was 0.00 ± 0.61. Sixteen cows (45.7%) were LAI‾ and 19 cows (54.3%) were LAI+. In LAI+ cows the concentrations of cholesterol and albumin were unchanged, but in LAI‾ cows both of them increased through the study (P<0.05). Greater concentrations of low density lipoproteins (LDL) (P<0.01) and lower concentrations of γ- and total globulins (P<0.05; day 60) were detected in LAI+ cows. Ceruloplasmin was not different between the LAI groups with the highest level on day 90. Cholesterol had the strongest and the most repeated correlations with LAI during the study. The correlation of albumin with LAI faded on day 120 and vitamin A had a relationship only on day 60 PP. Triglycerides (TGs), very low density lipoproteins (VLDL) (day 60) and LDL (days 60 and 90) had positive correlations with LAI. All globulin fractions showed negative correlations with LAI on day 60. Seventy percent of the cows without endometritis (day 30 PP) and 33% of the infected cows were LAI+ during the breeding period. About 79% of the cows with body condition score (BCS) loss ≤0.75 (day 60) and 38% of the cows with BCS loss >0.75 were LAI+ during the breeding period. CONCLUSION: Compromised liver functions may exist in dairy cows during the breeding period and may be detected by calculating LAI. The relationship of LAI during the progressed lactation with herd's performance needs to be investigated.

Expansion of sandhill cranes (Grus canadensis) in east Asia during the non-breeding period.

AIM: Historically, the distribution of Sandhill Cranes included much of North America and extending in summer into northeast Russia. In recent years, observations of sandhill cranes in Asia during the non-breeding period have been frequently reported. However, the distribution and abundance of sandhill cranes during the non-breeding period in Asia have rarely been summarized and studied. Our study aimed to analyze the status of sandhill cranes that have spread south into East Asia during the non-breeding period and to assess the possible impacts of their potential spread. METHODS: Based on opportunistic data collected in the field and occurrence data collected online over the past half century, we used Geographic Information System to visualize the spatial distribution changes and regression analysis to analyze and visualize the changes in the amount of individuals over time. RESULTS: In the last 50 years, the distribution of sandhill cranes during the non-breeding season in Asia spanned 31 degrees in longitude to the west and 15 degrees in latitude to the south. Their distribution in Asia has expanded to 17 provinces and municipalities in China, Japan and South Korea. The amount of cranes in the non-breeding period in Asia increased significantly from 1963 to 2017. According to the historical records in East Asia, sandhill cranes were mixed with five other species of crane groups. MAIN CONCLUSIONS: These results indicate that the range and amount of sandhill cranes have expanded. Sandhill cranes were mixed with five other crane species, which indicate their adaptability to a range of habitat types and food resources. The implications of these trends in sandhill cranes in East Asia for this and other crane species warrants further research.

A field study on glucose, non-esterified fatty acids, beta-hydroxybutyrate and thyroid hormones in dairy cows during the breeding period in Fars province, Iran.

BACKGROUND: It was hypothesized that under apparently good management practices in dairy farms, some cows may not be metabolically perfect during the breeding period and this may affect their performance. AIMS: This study was conducted to assess probable metabolic drawbacks in mid-lactation dairy cows affecting their performance. METHODS: Thirty-seven clinically healthy Holstein cows were assessed for plasma concentrations of glucose, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), thyroxin (T4), and tri-iodothyronine (T3) on days 60, 90 and 120 of lactation. The relationships of the measured analytes with some performance indices were also studied. RESULTS: Continuous declines in plasma glucose (within reference values; P<0.006), T4 (P<0.001) and T3 (0.003) were found during the study. Non-esterified fatty acids showed relatively high levels through the study with a rise at day 90 (P<0.041). Beta-hydroxybutyrate concentrations did not change significantly (P>0.05) but were higher than those reported by others in mid-lactation cows. By progress in lactation 27% of cows had glucose concentrations <2.5 mmol/L, 62% had NEFA concentrations >0.40 mmol/L and 13.5% had BHB levels above 1200 µmol/L, which are the threshold levels of peri- and post-parturient problems. Milk production had negative correlations with glucose and T4 while the correlation was positive with NEFA. The interval between calving to the 1st heat had positive correlations with BHB concentrations. The interval between calving and the 1st insemination was inversely correlated with glucose and positively correlated with NEFA levels. CONCLUSION: The changes of the studied analytes in mid-lactation cows resembled those that would happen during negative energy balance in early lactation cows and feed restriction in mid-lactation cows and may affect the general health and the performance of the cows.

What constitutes "social complexity" and "social intelligence" in birds? Lessons from ravens.

In the last decades, the assumption that complex social life is cognitively challenging, and thus can drive mental evolution, has received much support from empirical studies in nonhuman primates. While extending the scope to other mammals and birds, different views have been adopted on what constitutes social complexity and which specific cognitive skills are selected for. Notably, many avian species form "open" groups as non-breeders (i.e., seasonally and before sexual maturity) that have been largely ignored as potential sources of social complexity. Reviewing 30 years of research on ravens, we illustrate the socio-ecological conditions faced by these birds as non-breeders and discuss how these relate to their socio-cognitive skills. We argue that the non-breeding period is key to understand raven social life and, to a larger extent, avian social life in general. We furthermore emphasize how the combination of the large-scale perspective (defining social system components: e.g., social organization, mating system) and the individual-scale perspective on social systems allows to better capture the complete set of social challenges experienced by individuals throughout their life, ultimately resulting on a more comprehensive understanding of species' social complexity.

Structural study and expression of the androgen receptors during the reproductive cycle in the Harderian gland of the male Meriones libycus.

The goal of this study was to evaluate for the first time the expression of the androgen receptors (AR) in Harderian glands (HG) of the male Meriones lybicus in relation to the reproductive cycle. Six male Harderian glands of the resting period and 6 of the breeding period were collected. The animals were trapped in the desert of Béni Abbès (Algeria). The morphology of the Harderian glands was studied by light microscopy and morphometry, whereas the expression of the androgen receptors was assessed and quantified based on immunohistochemistry techniques. We have shown that the Harderian glands of Meriones libycus are tubuloalveolar glands with wide lumen. The glandular epithelium is composed of two types of cells (types I and II) in the resting season and three types of cells (types I, II and III) in the breeding season. These three types of cells differ in size and shape. Type-I cells have a prismatic shape, an acidophilic cytoplasm, and small lipidic vacuoles, whereas type-II ones are pyramidal in shape, with basophilic cytoplasm. Type-III cells resemble those of type I, and so they are prismatic in shape and have an acidophilic cytoplasm with larger lipidic vacuoles. The immunoreactivity of type-I and type-III cells was mainly cytoplasmic and the intensity of the immunostaining was significantly higher during the breeding season. Among other functions, the Harderian gland seems to be involved in the production of pheromones under the effect of androgens.

Comparative studies on testis, epididymis and serum hormone concentrations in foxes, and hybrids during the pre-breeding period.

Silver fox and blue fox belong to different genera, and the hybrid males are reproductively sterile. In the present study, there was a comparison of testicular and epididymal morphology and serum hormone concentrations among silver foxes, blue foxes, and the hybrids during the pre-breeding period, using 20 male silver foxes, 20 male blue foxes, 15 male HSBs (silver fox male × blue fox female hybrids) and 15 male HBSs (blue fox male × silver fox female hybrids), respectively. Hybrids had a smaller diameter of seminiferous tubules than pure-species males, and testes of hybrid males did not differ in mean size and relative weight from pure-species males. There were many Sertoli cells and spermatogenic cells in silver foxes and blue foxes, while numbers of spermatogonia and primary spermatocytes were less with no secondary spermatocytes in the hybrids. Furthermore, mean serum testosterone and estradiol concentrations in the hybrids were less, and FSH, LH, and PRL were greater than that in silver foxes and blue foxes (P < 0.05), suggesting that lesser concentrations of testosterone and estradiol and greater concentrations of FSH, LH and prolactin can inhibit the completion of spermatogenesis during the pre-breeding period. The results indicate that fox hybrid sterility may result from failures at the early stages of spermatogenesis.

Effects of human disturbance on cave-nesting seabirds: the case of the storm petrel.

Human disturbance is an important stress factor with potentially strong impact on breeding activity in animals. The consequences can be extinction of the breeding population, because disturbed animals might desert their breeding area and find no suitable substitute area. In this study, we investigated the effects of anthropogenic disturbance on a breeding population of Mediterranean storm petrels. Seabirds are increasingly used as bio-indicators for sea environmental parameters, because they are very sensitive to changing conditions. Burrowing or cave-nesting species may be particularly susceptible to human disturbance because their direct contact with humans is usually minimal or absent. First, we compared two different populations (exposed or not exposed to human disturbance) for their individual stress response to a standardized stressor (handling and keeping in a cloth bag). Second, we compared the two sub-colonies for their population-level stress response. Third, we tested experimentally whether sub-colonies of storm petrels exposed to tourism have physiological adaptations to anthropogenic disturbances. Our results indicate that storm petrels may be habituated to moderate disturbance associated with boat traffic close to the colony.

Pre-incubation feeding activities and energy budgets of Snow Geese: can food on the breeding grounds influence fecundity?

The potential contribution of early spring feeding conditions in the Arctic to clutch size variation was examined in a population of Lesser Snow Geese Anser caerulescens caerulescens. Behavioural observations were combined with energetic analyses of food material to derive an estimate of the energy budgets of pre-laying and laying females. Food intake of females between arrival on the breeding grounds and incubation was considerable; estimated energy gains in this period were in the same magnitude as the cost of one or several eggs. The pre-laying period spent on the breeding grounds can thus be energetically beneficial rather than costly. Accumulation of resources for reproduction in Snow Geese is a continual process including the breeding grounds, and nutrient limitation after arrival in the Arctic cannot sufficiently explain the environmental component of clutch size variation. The timing of migration and follicle development is such that clutch size decisions are sometimes made during the late stages of migration and some-times after arrival. In the latter case food conditions on the breeding grounds may greatly influence clutch size; in the former case they may still influence readjustments of clutch size after the initial decision. The universal negative correlation between clutch size and laying date in Snow Geese can be explained by negative fitness consequences of late hatching, which outweigh the benefits of delayed laying and further nutrient accumulation. Food shortage on the breeding grounds may sometimes be a secondary factor contributing to seasonal clutch size decline.