Clutch Volume Research Articles

Predation Risk, and Not Shelter or Food Availability, as the Main Determinant of Reproduction Investment in Island Lizards

Reproductive investment, including the number of offspring produced, is one of the fundamental characteristics of a species. It is particularly important for island vertebrates, which face a disproportionate number of threats to their survival, because it predicts, among other things, a species’ resilience to environmental disruption. Taxa producing more offspring recover more quickly from environmental perturbations and survive environmental change better. However, ecologists do not understand which primary drivers shape a species’ reproductive investment well. Here, we compare the reproductive efforts of 14 island populations of the Aegean Wall Lizard (Podarcis erhardii), which lives across widely diverging environmental conditions. We test three hypotheses, namely that reproductive investment (measured as clutch size, clutch volume) is (1) positively associated with predation risk [‘Predation Risk Hypothesis’]; (2) positively associated with the presence of reliable vegetation cover that provides shelter [‘Gravid Female Protection Hypothesis’]; and (3) limited by (and hence positively correlated with) food availability [‘Food Limitation Hypothesis’]. Although field data are somewhat consistent with all three hypotheses, statistical analyses provide strong support for the Predation Risk Hypothesis. The results not only shed light on which fundamental forces shape reproductive investment in island vertebrates, but can also help shape conservation priorities.

Variations in the Reproductive Strategies of Different Charadrius alexandrinus Populations in Xinjiang, China.

Due to the influence of bio-geographical and environmental factors, as well as anthropogenic landscape features, organisms show different reproductive strategies among different populations. There is a lack of detailed information on the reproductive biology of Kentish plover Charadrius alexandrinus in arid lands in Central Asia. In this study, we summarized the characteristics of the reproductive biology of three geographically distinct plover populations in Aibi Lake in northwestern Xinjiang, Taitema Lake in southern Xinjiang and artificial reservoirs around Urumqi City in northern Xinjiang, based on 440 eggs from 158 nests observed and analyzed from April to July of 2019 and 2020. We found that there was no significant difference in clutch size among the three populations. However, the egg size of the Taitema Lake population was significantly larger than those of the other two populations, whilst the egg volume and clutch volume of the artificial reservoirs' populations were significantly larger than that of Aibi Lake. With the postponement of laying dates, the northern and northwestern populations showed the characteristics of a small clutch size and a relatively small egg size, respectively, and a decrease in reproductive output. The heavier female plovers in Taitema Lake laid eggs earlier, and there was a significantly positive correlation between female body mass and clutch size and egg size. The tarsometatarsus length of the female plovers was significantly positively correlated with the reproductive output in all three populations. The model selection results show that female body size and ambient temperature restrict the egg size and reproductive output of Kentish plovers, which is consistent with the upper limit hypothesis of the maternal condition and maternal constraint. Our data support the hypothesis that Kentish plovers show distinct flexibility in their breeding strategies to cope with the harsh natural environment in the arid lands of Xinjiang, China. The results of a relatively high average clutch size and average egg size imply that the saline wetlands of Western China are important breeding habitats for Kentish plovers.

Female-dependent factors affect sex allocation in Lesser Kestrels Falco naumanni

Abstract The sex ratio of nestlings is a crucial population determinant in rare and/or endangered species. We investigated the role of female body condition and female-related traits in Lesser Kestrel (Falco naumanni) nestling sex allocation at a nest-box colony in central Greece. We used the total clutch volume and size, female weight, hatching dates, body length, wing length, tail length, tarsometatarsus, and bill length as explanatory variables of the number of male nestlings (the response variable) using CART model analysis. This analysis showed that the reproduction output was biased towards male nestlings when female parents were shorter in body length and clutch size and volume were smaller. The skewed sex ratio favoring females, 1:2.35, suggests that when female parents are in good condition, they invest most in good-quality female nestlings, providing a reproductive advantage and increased long-term fitness.

Evolution of female colours in birds: The role of female cost of reproduction and paternal care.

Female ornamentation is frequently observed in animal species and is sometimes found as more evolutionary labile than male ornamentation. A complex array of factors may explain its presence and variation. Here we assessed the role of female cost of reproduction and paternal care. Both factors have been pinpointed as important by theoretical studies but have not been investigated yet in details at the interspecific level. We worked on 133 species of North temperate Passeriformes bird species for which both the clutch volume - here taken as the proxy of female cost of reproduction - and amount of paternal care are relatively well known. Using spectrometry, we measured the whole-body coloured plumage patches and quantified three metrics corresponding to brightness (i.e. achromatic component), colour chromaticity (i.e. intensity) and colour volume (i.e. diversity). We found a strong association between male and female colour metrics. Controlling for this association, we found additional small but detectable effects of both cost of reproduction and paternal care. First, females of species with more paternal care were slightly brighter. Second, the interaction between the level of paternal care and egg volume was correlated with female colour intensity: females with more paternal care were more chromatic, with this association mostly present when their investment in reproduction was low. Together these results suggest that female cost of reproduction and paternal care are part of the multiple factors explaining variation of female coloration, besides the strong covariation between male and female coloration.

Food quantity and quality shapes reproductive strategies of Daphnia.

In freshwater environments, one of the challenges aquatic grazers face are periods of suboptimal food quantity and quality. In a life table experiment, the effects of food quantity (a gradient of algae concentration) and quality (a diet of cyanobacteria) on the life histories and resource allocation strategy in Daphnia magna were tested. Growth‐related traits were similarly affected under different food regimes while the reproductive strategies differed in animals exposed to low food quantity and quality. The per‐clutch investment (clutch volume) did not differ between Daphnia fed with cyanobacteria and underfed mothers, but resources were differently allocated; underfed mothers increased their per‐offspring investment by producing fewer, but larger eggs, whereas cyanobacteria‐fed mothers invested in a greater number of eggs of smaller size. I argue that both strategies of resource allocation (number vs. size of eggs) may be adaptive under the given food regime. The results of the study show that the cyanobacteria diet‐driven fitness losses are comparable to losses caused by food quantity, which is only slightly above the growth capability threshold for Daphnia.

Clutch size of passerines increases with latitude in China, but egg size is conserved

The size and number of eggs are important components of reproductive strategies, with implications for offspring and parental fitness. Birds typically produce larger clutches in more poleward latitudes, in response to the strong seasonal peak of food availability required to raise young. However, changes in egg size impact the interpretation of this pattern, and latitudinal variation in egg size remains poorly explored. Here we comparatively investigate this issue at both interspecific and intraspecific levels, using datasets from 298 populations of 154 passerine species breeding in mainland China. Clutch size was larger toward the north, but egg size was relatively constant and therefore total clutch volume (clutch size × egg size) increased. No negative correlation was evident between egg size and clutch size along latitudinal gradients, suggesting the lack of a direct trade‐off between the two traits. This may be explained by latitudinally increased food availability and concentrated annual reproductive investment due to seasonal time constraints on raising more broods, arising from the later onset of reproduction at higher latitudes. In addition, the latitudinal patterns of egg size and clutch size appear to be independent of parental investment in terms of the lengths of incubation and nestling periods, which were similar for lower‐ and higher‐latitude birds. Our results shed light on the evolution of avian life histories across latitudinal gradients.

Tibetan birds lay larger but fewer eggs in a clutch.

How do offspring size and number vary along elevational gradients? This is a striking but rarely addressed question in life-history evolution. Here we comparatively explore it using phylogenetically paired passerine birds of lowland China vs. the Tibetan plateau spanning an elevational range of 18-4500m. Toward the Tibetan plateau, egg size increased, clutch size decreased and total clutch volume (= clutch size × egg size) did not change, when accounting for major confounding factors. Larger eggs and smaller clutches can be a response to harsh abiotic conditions at higher elevations and the corresponding reduction in food resources required for raising young, respectively. There was a negative correlation between egg size and clutch size after controlling for elevation effect on either trait, suggesting that the trade-off contributed to the expression of these two traits across elevations, given the lack of an elevational trend in total clutch volume. Tibetan birds had a shorter breeding season, prolonged incubation and nestling period than their lowland counterparts. While fewer clutches over the short breeding season may facilitate the increase in egg size, the concentration of annual reproductive investment did not seem to act on clutch size; despite the smaller clutches, hard environments may impose greater costs of parental care on Tibetan birds. The current research provides insight into the evolution of avian life histories across elevations.

Habitat and Nest Site Selection in the Common Gull Larus canus in Southern Poland: Significance of Man-Made Habitats for Conservation of an Endangered Species

The Common Gull is a rare and endangered breeding species at inland habitats in Poland as well as in some other countries in Europe. Breeding biology, habitat and nest site selection were studied in this species in southern Poland. Almost all birds nested on industrial water bodies (gravel pits, sedimentation basins), although fishponds and reservoirs were the most abundant habitat in the study area. Birds built their nests mainly on islets, man-made constructions and dry land on the shores of water bodies. The islets occupied by birds were smaller and were covered by lower vegetation than the unoccupied ones. When occupied islets on industrial water bodies were compared with a random sample of islets on fishponds, the latter were found to be larger, with taller and denser vegetation. This may explain why Common Gulls did not breed on fishponds in southern Poland. Shore-breeding birds nested in open areas with sparse vegetation, occupying sites with less vegetation cover and closer to shrubs or trees than randomly selected points. Breeding performance (mean date of clutch initiation, clutch size, clutch volume, hatching success and breeding success) did not differ among nests built on islets, man-made constructions or on the shores of the water bodies. Breeding success was more than twice as high as in large riverine colonies. Industrial water bodies may become important alternative breeding habitats for this species in Poland.

Microalgal Diet Influences the Nutritive Quality and Reproductive Investment of the Cyclopoid Copepod Paracyclopina nana

Copepods represent an interesting alternative or a complement live food to brine shrimps and rotifers commonly used in aquaculture. They constitute the natural prey of many fish species and therefore do not require a potential nutritional enrichment. But an optimization of the microalgal diets used to feed copepods is essential to improve their mass culture. This study examined the effects of seven microalgal diets, namely single-species diets of Rhodomonas salina (R), Tisochrysis lutea (T), and Pavlova lutheri (=Diacronema lutheri) (P), two-species diets (R + T, T + P, and R + P), and a three-species diet (R + T + P), on the fatty acid and monosaccharide composition of the cyclopoid copepod Paracyclopina nana as well as its reproductive investment. Experiments were run during 15 days in 10-L beakers; starting with nauplii collected from a large 300-L batch culture. Copepods fatty acid contents were studied, particularly the relative amounts of docosahexaenoic acid (DHA) and eicosa-pentaenoic acid (EPA). The R + T, R, and T diets induced the highest total fatty acid amount in copepods. R + T and R also generated the lowest DHA/EPA ratios in copepods due to high EPA contents. The highest value of total monosaccharides was found in copepods fed with R + T + P. Diets R + T and R induced the greatest prosome volumes and clutch volumes in ovigerous females. Both prosome volume and clutch volume in P. nana ovigerous females were correlated to the individual EPA amount. The results demonstrated that all diets including R. salina enhanced the productivity of P. nana in mass culture, particularly when combined with T. lutea. R. salina, and T. lutea induced complementary fatty acid and monosaccharide profiles, confirming that R + T represents the best microalgae combination for productive culture of P. nana. Conversely, P. lutheri did not enhance the nutritional profile nor the fecundity of P. nana in the culture. This study is the first to demonstrate that R. salina is a suitable microalga for productive mass culture of P. nana for use as live food in aquaculture.

Using a 3D image-based volumetric model to estimate fecundity in Lithodes santolla: A tool for improving Lithodidae crustacean monitoring

In this study, we designed, applied and evaluated a new methodology to estimate the direct fecundity of Lithodes santolla ovigerous females that can be applied during fishing expeditions or independent monitoring. Eighty-five ovigerous females were collected from the fishery and 24 high-resolution images of each egg mass were used to estimate the egg mass volume using three dimensional (3D) modeling in the laboratory. Second, the carapace length, clutch volume, number of eggs per clutch, and egg sizes were recorded for each ovigerous female. Third, the relationship between the observed clutch volume and the estimated volume from the 3D model was evaluated, in addition to the relationship between fecundity and clutch volume using linear models. Finally, two imaging surveys were carried out on fishing boats, resulting in 46 photogrammetric surveys (representing 46 ovigerous females). In the laboratory, the 3D modeling of clutch volume was successful in 66 ovigerous females (77 %), and explained 99 % of the variance when estimating the observed clutch volume. The most informative model for estimating fecundity was a linear model which explained 88 % of the variance and included carapace length as a covariable. This could be related to egg size, which should be studied in more detail. From the images obtained on fishing boats, the 3D modeling and fecundity estimates were successful for ∼62 % of clutches. This non invasive method for estimating fecundity presents an opportunity to improve the estimation of per capita reproductive contribution in female Lithodidae crustaceans through monitoring, although the photogrammetric survey process on fishing boats needs improvement.

The allocation between egg size and clutch size depends on local nest survival rate in a mean of bet-hedging in a shorebird

BackgroundThe allocation of resources between offspring size and number is a central question of life-history theory. Although several studies have tested the existence of this trade-off, few studies have investigated how environmental variation influences the allocation of resources to offspring size and offspring number. Additionally, the relationship between population dynamics and the offspring size and number allocation is far less understood.MethodsWe investigate whether resource allocation between egg size and clutch size is influenced by the ambient temperature and whether it may be related to apparent nest survival rate. We measured 1548 eggs from 541 nests of two closely related shorebird species, the Kentish Plover (Charadrius alexandrinus) and the White-faced Plover (C. dealbatus) in China, in four populations that exhibit contrasting ambient environments. We weighed females, monitored nest survival, and calculated the variance of ambient temperature.ResultsAlthough we found that egg size and clutch size were all different between the four breeding populations, the reproductive investment (i.e. total clutch volume) was similar between populations. We also found that populations with a high survival rate had relatively larger eggs and a smaller clutch than populations with a low nest survival rate. The latter result is in line with a conservative/diversified bet-hedging strategy.ConclusionsOur findings suggest that plovers may increasing fitness by investing fewer, larger or many, small according local nest survival rate to make a similar investment in reproduction, and thereby may have an impact on population demography.

Forced nest site relocations negatively affect reproductive investment in a colonial seabird species

Species breeding in urban environments are highly prone to a wide variety of non-natural, human activities, which range from short-term disturbances to the degradation or loss of suitable habitat. The latter in turn may force individuals to relocate to new sites for foraging or breeding, both of which presumably entails fitness costs due the trade-offs of finding and exploring new habitats. Species showing a high level of spatial foraging specialisation or nest site fidelity are expected to be most vulnerable. In this study, we explored the consequences of nest site loss on the reproductive investment of lesser black-backed gulls (Larus fuscus), a site faithful seabird species breeding in an urban environment. We monitored a population of 1.173 colour-ringed gulls across 13 years, that involved several episodes of spatially restricted loss of breeding habitat. We found that birds which lost their breeding territories reduced their investment into the eggs as reflected in a decrease of the clutch volume. They relocated over larger distances compared to birds that relocated voluntarily. Moreover, the likelihood of skipping the subsequent breeding season increased after a forced relocation. These negative effects of forced relocation likely contribute to the decline in the number of breeding pairs in our urban population as observed during the last ten years, and highlights the importance of maintaining a stable breeding environment in urban areas for the conservation of this and potentially other colonial breeding seabird species.

Parental care and the evolution of terrestriality in frogs.

Frogs and toads (Anura) exhibit some of the most diverse parental strategies in vertebrates. Identifying the evolutionary origins of parenting is fundamental to understanding the relationships between sexual selection, social evolution and parental care systems of contemporary Anura. Moreover, parenting has been hypothesized to allow the invasion of terrestrial habitats by the ancestors of terrestrial vertebrates. Using comprehensive phylogenetic analyses of frogs and toads based on data from over 1000 species that represent 46 out of 55 Anura families, we test whether parental care is associated with terrestrial reproduction and several life-history traits. Here, we show that both the duration of care and offspring protection by males and females have coevolved with terrestrial reproduction. Sexual size dimorphism is also related to care, because the large male size relative to female size is associated with increased paternal care. Furthermore, increased egg size and reduced clutch volume are associated with increased care in bivariate but not in multivariate analyses, suggesting that the relationships between care, egg size and clutch volume are mediated by terrestrial reproduction. Taken together, our results suggest that parenting by males and females has coevolved, and complex parenting traits have evolved several times independently in Anura in response to breeding in terrestrial environments.

Calcium is Not a Limiting Micronutrient for Egg Production by Green-Backed Tits in a Mosaic Landscape of Mixed-Oak Forest and Cedar Plantation in Subtropical Taiwan

In many passerines, reproductively active females must forage for calcium-rich materials on a daily basis to meet exact calcium demands during egg production. Calcium availability often constrains reproductive output in birds, but is dependent on species-specific foraging traits and local calcium availability, and, thus, land use. Here, we examined whether calcium availability limits the reproductive output of Green-backed Tits Parus monticolus over a four-year period in mid-altitude subtropical forest of Taiwan. We compared soil nutrients and the availability of calcium-rich snails between mixed-oak forest and Japanese cedar Cryptomeria japonica plantation. We also provided supplementary calcium (in the form of snail shells and chicken egg-shells) in the nest boxes of half of all pre-laying pairs breeding in both habitats. The reproductive output of birds across the two treatments and two habitats was recorded. Our results showed that the soil was very acidic in both habitats. Compared to the mixed-oak forest, the litter in the cedar plantation contained marginally significantly more calcium, while the soil had significantly higher pH and exchangeable Ca2 . The cedar plantation supported similar, or even higher, snail abundance than the mixed-oak forest. We found no abnormal eggs with defective shells in either habitat. We also found no significant difference in clutch size, egg mass, egg shape index, egg volume, clutch volume, or hatching success across the two calcium-treatment groups or the two habitats. Calcium availability had a weak effect on the reproductive output of birds in the two habitats, possibly because the study area supported a high abundance of snails. Our results, combined with our calculations of the calcium demand of birds, suggest that calcium is not a limiting micronutrient for egg production by Green-backed Tits in the montane forest of subtropical Taiwan at present.

Offspring Hg exposure relates to parental feeding strategies in a generalist bird with strong individual foraging specialization

Generalist species can potentially exploit a wide variety of resources, but at the individual level they often show a certain degree of foraging specialization. Specific foraging strategies, however, may increase exposure to environmental contaminants that can alter the cost-benefit balance of consuming particular food items. The Lesser Black-backed Gull (Larus fuscus) is known to opportunistically feed on a wide range of marine and terrestrial prey that differ in contaminant load, such as mercury (Hg) that strongly biomagnifies through the aquatic food web. The hypothesis tested in this study were: i) a predominant use of marine prey by females during egg-formation and by both parents during chick rearing increases the exposure to Hg during embryonic development and chick growth, and ii) this affects parental investment in clutch volume, chick growth and body condition. Total Hg burden and isotopic signatures of carbon (δ13C) and nitrogen (δ15N) were determined for eggs, down feathers, and primary feathers of L. fuscus chicks collected at a coastal colony in Belgium. As expected, eggs and feathers of chicks from parents with a stable isotope signature that suggested a predominantly marine diet had higher levels of Hg. The use of marine resources by females during the egg-formation period positively correlated to maternal investment in egg size, though entailing the cost of increased Hg-concentrations which in turn negatively affected clutch volume. Furthermore, it is shown that the use of chick down feathers is a suitable matrix to non-lethally estimate Hg concentrations in eggs. Contrary to our expectations, no relationship between Hg exposure and chick growth or chick body condition was found, which may be due the low concentrations found. We conclude that currently Hg contamination does not constitute a risk for development and condition of L. fuscus offspring at the levels currently observed at the Belgian coast.

The Evolution of Diapsid Reproductive Strategy with Inferences about Extinct Taxa.

Diapsids show an extremely wide range of reproductive strategies. Offspring may receive no parental care, care from only one sex, care from both parents, or care under more complex regimes. Young may vary from independent, super-precocial hatchlings to altricial neonates needing much care before leaving the nest. Parents can invest heavily in a few young, or less so in a larger number. Here we examine the evolution of these traits across a composite phylogeny spanning the extant diapsids and including the limited number of extinct taxa for which reproductive strategies can be well constrained. Generalized estimating equation(GEE)-based phylogenetic comparative methods demonstrate the influences of body mass, parental care strategy and hatchling maturity on clutch volume across the diapsids. The influence of polygamous reproduction is not important despite a large sample size. Applying the results of these models to the dinosaurs supports the hypothesis of paternal care (male only) in derived non-avian theropods, previously suggested based on simpler analyses. These data also suggest that sauropodomorphs did not care for their young. The evolution of parental-care occurs in an almost linear series of transitions. Paternal care rarely gives rise to other care strategies. Where hatchling condition changes, diapsids show an almost unidirectional tendency of evolution towards increased altriciality. Transitions to social monogamy from the ancestral state in diapsids, where both sexes are polygamous, are common. In contrast, once evolved, polygyny and polyandry are very evolutionarily stable. Polygyny and maternal care correlate, as do polyandry and paternal care. Ancestral-character estimation (ACE) of these care strategies with the character transition likelihoods estimated from the original data gives good confidence at most important nodes. These analyses suggest that the basalmost diapsids had no parental care. Crocodilians independently evolved maternal care, paternal care evolved in the saurischian line, prior to derived theropod dinosaurs, and the most basal neognaths likely exhibited biparental care. Overall, the evolution of parental care among diapsids shows a persistent trend towards increased care of offspring, and more complex care strategies and behaviors with time. Reversions to reduced care are infrequent.

Factors Affecting Brood Patch Development in Magellanic PenguinsSpheniscus magellanicus

Abstract. Brood patches allow the transfer of heat to eggs for their successful embryonic development, and in many species determine egg temperature during incubation. We investigated brood patch development of Magellanic Penguins Spheniscus magellanicus in Isla Quiroga, Argentina, during 2012–2013. Here, we evaluate if brood patch development (in a narrow sense i.e. increase of the brood patch area and temperature measured with an electronic probe thermometer) varies according to laying date of the eggs, and with respect to adults' body condition and size, total clutch volume, and/or the sex of the adults. We found that brood patch temperature reaches its maximum when egg laying is finished, while brood patch area is fully developed starting from the end of the first quarter of the incubation period. The later the penguins started to breed the warmer the initial brood patches — when first egg is laid. Besides, the incubation period was shorter in penguins breeding late. Furthermore, adults in a good body...

Mismatching between nest volume and clutch volume reduces egg survival and fledgling success in black-tailed gulls.

A longstanding suggestion posits that parents prefer to match nest volume and clutch size (clutch volume), but few studies have tested this in colonial seabirds that nest in the open. Here, we demonstrate the effects of nest–clutch volume matching on egg survival, hatching, and fledgling success in black-tailed gulls Larus crassirostris on Hongdo Island, Korea. We show that the volume mismatch, defined as the difference between nest volume and total egg volume (the sum of all eggs’ volume in the clutch), was positively related to egg and chick mortality caused by predation, but was not significantly related to hatching success incurred by insulation during the incubation period. Although nest volume was negatively related to laying date, we found that the mismatch was positively related to laying date. Our results support the claim that well-matched nest–clutch volume may contribute to survival of eggs and chicks, and ultimately breeding success.

Coevolution of Body Form and Reproductive Effort in Shorebirds (Aves: Charadriiformes)

In order to test for co-evolution of reproductive life history with body form, cluster analysis applied to nine skeletal measurements was used to identify three distinctive body types within the avian order Charadriiformes: a “sandpiper” type, a “gull/plover” type, and an “auk” type. Both in conventional analyses and in phylogenetically independent contrasts, the sandpiper body type was associated with increased values of a mass-adjusted measure of clutch volume and with decreased adult survival. A hypothesis that would explain the results is that increased reproductive effort characterizes charadriiform species with morphological features such as long bills and legs that render them vulnerable to predation, consistent with the hypothesis that reproductive effort represents a trade-off between current and future reproductive opportunities.

Reproductive Parameters of Caspian GullLarus cachinnansPallas, 1811 in Different Habitats Nearby and Away Fish Ponds

Reproductive performance of gulls depends on a variety of factors, but food abundance and its availability are among the most important. Clutch and egg sizes in gulls are found to be strongly influenced by food availability, thus better reproductive performance in the colony with greater fish availability (near fish ponds) was expected in that study. We compared the reproductive traits (clutch size, volume of eggs in the full clutch, relative volume of the C-egg (the third egg in gull's clutches) and hatching success) of Caspian Gull Larus cachinnans in five inland colonies in Poland located at a gravel pit, a lake, a river and two dam reservoirs. Differences in the clutch size between sites were found, with the lowest at a lake. We found similar clutch volume in all studied colonies. C-eggs were slightly smaller than A- and B- eggs, in all colonies and all study years, but the relative volume of C-egg in colonies located near fish ponds (<10 km) was significantly greater compared to colonies located far away. This may be explained by high fish availability in fishponds in comparison to other habitats. However hatching success (the ratio of the number of hatched chick to the number of eggs laid) was highest in the colony at the lake. This indicates that both inland habitats a gravel pit and a lake offered good food conditions for large gulls when fish ponds are nearby.