Mean Clutch Size Research Articles

Long-term monitoring of dwarf eggs in clutches of Yellow-legged Gulls (Larus michahellis) breeding in a western Mediterranean colony

The present study provides data on clutches with dwarf eggs from a large sampling in a colony of Yellow-legged Gulls (Larus michahellis) over 31 years. Their occurrence was very low, with a global percentage of 0.26%. Significant variations were not detected among periods of 10 or 11 years. In all the cases, only one dwarf egg was found per clutch. Mean volume of dwarf eggs was 34% of that of non-dwarf eggs. Their content was mostly albumen and a very reduced quantity of yolk, and they were infertile. Several results of the study (the laying order of the dwarf eggs, their mean clutch size and the mean size of the non-dwarf eggs from clutches with dwarf eggs) support the hypotheses that runt eggs occur from a temporary disturbance to the reproductive tract.

Breeding parameters of a Great Tit (Parus major) population on the island of Cyprus compared to other Mediterranean populations

Many studies on the Great Tit, Parus major, have been conducted within the Mediterranean Basin, especially on its reproductive biology, forest habitat interactions, and nutritional resources. However, to date no detailed scientific research on these issues has been conducted on the island of Cyprus with a general paucity in research on this topic from the Eastern Mediterranean. Island species, through reduced gene flow and general isolation often evolve reproductive differences from their mainland relatives. As Cyprus is the third largest island in the Mediterranean and the most easterly positioned it provides an ideal opportunity compare the breeding biology of this island population with those from the wider Mediterranean region. This study aimed to gather some baseline reproductive data for Great Tits breeding in Cyprus. This data was then used to compare the reproductive outputs of Cypriot Great Tits from the sub species Parus major aphrodite with other Mediterranean island populations. This study was performed over a 3-year period during the breeding seasons of 2016-2018 in four evergreen forest areas. Mean clutch size was 7.7 eggs and hatching success 76.0%. The mean weight of the young was 16.3 g and mean tarsus length 18.7 mm. Significant differences were found between the years of the study, both in mean clutch size (p<0.0001) and the day of the first egg (p<0.0001), with 2016 producing the largest clutches and clutches being laid earlier than the subsequent two years. The start of the breeding season of the Great Tit was considerably earlier in Cyprus compared to other Mediterranean regions.

Observations on Indian Skimmer Rynchops albicollis Swainson, 1838 (Aves: Charadriiformes: Laridae) breeding colonies in Middle Ganges stretch, India

Indian Skimmer Rynchops albicollis Swainson, 1838 is a riverine habitat specialist bird and a species of significant conservation concern. In 2020 it was up-listed to the ‘Endangered’ category of the IUCN Red List. Breeding grounds of the species are known from the major rivers of India like Ganga, Chambal, Son, and Mahanadi. We monitored breeding colonies of the species in two breeding seasons (2017 and 2018) in the middle Ganges stretch. We identified nine nesting islands and monitored a total of 111 active nests during the study period. A total of 302 eggs were counted with clutch sizes ranging 1–5 and the mean clutch size of 2.7 (±1.18 SD). We observed a 10% &amp; 7% of hatching and fledgling success rate in 2017 and 10% &amp; 17% in 2018, respectively. Low breeding success was probably due to the severe anthropogenic factors such as egg collection, cattle trampling, and stochastic weather events such as flooding and sand inundation by sand storms in nests. We also recorded instances of nest abandoning because of unknown reasons. This article recommends more surveys to identify new breeding colonies of Indian Skimmer in the middle Ganges and subsequently provide adequate protection to the colonies. We also recommend sensitization programs for different stakeholders to create more awareness for the conservation of this threatened species in the middle Ganges stretch.

Zambian indigenous chicken genetic resources: phenotypic characteristics and their production systems among small-scale farmers.

Indigenous chickens are very important to households for income and protein. However, their performance is usually poor, especially under small-scale farmer management, despite their potential to perform better. The performance of these chickens can be improved by selective breeding. However, for this to be a success, there is a need to understand the phenotypic and production characteristics of these chickens fully. Hence, this study aimed to characterize the phenotypes of these chickens and their production system among small-scale farmers. A structured questionnaire was administered to 177 small-scale farmers. A total of 538 chickens whose mean weight was 1.66 kg were individually phenotyped in Luapula, Muchinga, and Northern provinces of Zambia. Ownership of the indigenous chickens was dominated by females (65.37%), with most (64.31%) having attained primary education. Most housed their chickens in family houses (42.03%). All the farmers let their chickens scavenge for their feed, with 45.58% of them providing basic supplementation. Most (84.10%) farmers bought their breed stock from within their community and had a mean flock size of 12.5 chickens/household, which they mostly (78.09%) kept as free-range. The majority (77.39%) practiced culling, with low productivity being the most common reason for culling (84.45%). Only 59.01% of farmers practiced selective breeding, while 86.22% practiced uncontrolled mating. The age at first mating for cocks and hens was 6.8 months and 6.34 months, respectively, with 6.73 months being the age at first egg. It takes 15.43 days to reach a mean clutch size of 13 eggs. The hatchability and mortality at 8 weeks were 83.44% and 67.57%, respectively. All chickens were sold as live chickens, and the majority (51.59%) of the farmers sold their chickens within the community at 7.23 months. Diseases and predators were the most common challenges affecting farmers in the study area. Consultations with veterinarians, vaccinations, and deworming were uncommon while treating sick chickens mostly using ethnoveterinary medicines was common. The most common qualitative traits were brown (27.88%) and mixed (26.77%) plumage color, white skins (91.45%) and shanks (48.70%), single comb type (91.08%), red earlobe (55.76%), and orange eyes (78.07%). All linear body measurements positively and significantly correlated with the body weight averaging 1.66kgs, an indicator that selection for any of them would result in a corresponding increase in body weight. Principal Component Analysis extracted two components with 69.38% of the total variation. The diversity in phenotypes of these chickens and their production systems indicate huge potential for improvement by implementing breeding programs.

Predation of sea turtle eggs by rats and crabs

Egg predation by invasive and native species may have severe impacts on endangered species and negatively affect species recovery. We assessed the levels of egg predation within green turtle (Chelonia mydas) clutches on the island of Diego Garcia (7.42°S, 72.45°E), Chagos Archipelago (Indian Ocean). Native coconut crabs (Birgus latro) and ghost crabs (Ocypode spp.), as well as introduced black rats (Rattus rattus), were predators of eggs, with these species entering nests via tunnels dug obliquely in the sand. Often whole eggs were removed from clutches. For example, the mean clutch size at oviposition (mean 127.8 eggs, n = 23, range = 74–176) was significantly larger than at the end of incubation (mean 110.9 hatched and unhatched eggs, n = 16, range = 9–147). In other cases, egg predation was recorded where the egg had been opened and contents were eaten in the nest. Overall, hatching success (the percentage of eggs laid leading to a hatchling emerging from the egg) was 64.9%, while 3.1% of eggs were predated within nests, 18.1% died during incubation without predation and 13.9% were removed. We reviewed evidence from 34 sites around the world identifying 36 predators that were either native (e.g., crabs, and goannas, n = 30) or invasive (e.g., rats, and pigs, n = 8). Depending on location, a predator could be identified as both native and invasive (e.g., dogs). We discuss how either nest protection and/or invasive predator eradication may be used to increase egg survival and when these approaches might be used.

Seasonal Reproductive Cycle of Wild Alligator Snapping Turtles (Macrochelys temminckii) in Southwest Georgia

We studied the reproductive cycle of wild Macrochelys temminckii (Alligator Snapping Turtle) in southwest Georgia from March 2008 to September 2010. We measured plasma testosterone (T), estradiol (E2), and corticosterone (C). Seasonal changes in T were observed in males, with maximum concentrations occurring in October. Evidence of mating and male combat were seen in April. Females displayed seasonal changes in T and E2 concentrations, with peaks occurring in March and April, respectively, (in association with mating and ovulation) and again in September and October, respectively, (in association with follicular development and vitellogenesis). We observed oviductal eggs (mean clutch size = 28.5) in April. Concentrations of C were not significantly different between months. Reproductive patterns coincided with seasonal variation in temperature and water level.

Nesting Ecology of the Alligator Snapping Turtle (Macrochelys temminckii) along the Lower Apalachicola River, Florida

We studied nesting ecology and sex determination in a population of Macrochelys temminckii (Alligator Snapping Turtle) inhabiting the lower Apalachicola River in western Florida. During 1990–1991, we located 105 nests (63 intact, 42 depredated); 83% occurred on prominent dredged spoil substrates. Coupled with data from additional years, mean clutch size of 130 nests was 35.1 (min–max = 17–52). Most nesting occurred from 20 April to 18 May, with about a week annual variation. Hatching extended throughout August. In nests that we protected from predators, hatching success averaged 78% (24 nests) in 1990 and 66% (26 nests) in 1991. Overall sex ratios were roughly 1 male: 2 females, although individual nests varied from all males to all females in conjunction with solar exposure.

Nestling Growth Pattern and Breeding Biology in the Eurasian Nuthatch Sitta europaea

Avian growth has been traditionally examined using logistic, Gompertz or von Bertalanffy non-linear equations. Although many studies have analysed nestling mass increase and the factors affecting growth rates, there is little information on nestling growth curves for several avian groups, such as Nuthatches (Sittidae). Moreover, the breeding biology of Nuthatches is still poorly studied because of their reluctance to use nest boxes. Here we examined the growth pattern in Eurasian Nuthatch Sitta europaea nestlings, in addition to studying the breeding biology of this species, in a mixed deciduous forest from Central Portugal during one year. The nestling growth was well fit by the logistic and Gompertz models, whilst the von Bertalanffy equation was less accurate, especially when predicting the asymptotic mass and the mass in the first development stages. Nestlings attained their maximum mass around the age of 18 days, while the largest daily mass increase was achieved when nestlings were 8 days old. Weather conditions did not affect nestling growth. Regarding the breeding biology, the mean date of laying of the first egg was 3 April, the mean clutch size was 5.43 ± 0.78 (±SD) eggs and the mean number of fledglings per clutch was 4.00 ± 2.09. The proportion of eggs that produced fledglings in a nest averaged 72%. Clutch size and number of fledglings were negatively correlated with the laying date. These results contribute to our understanding of Eurasian Nuthatch breeding biology and nestling development, the latter providing useful data for the standardization of ornithological practices, such as determining the appropriate fledgling ringing period.

Spatial and ontogenetic variance in local densities modify selection on demographic traits

Abstract Local density can affect individual performance by altering the strength of species interactions. Within many populations, local densities vary spatially (individuals are patchily distributed) or change across life stages, which should influence the selection and eco‐evolutionary feedback because local density variance affects mean fitness and is affected by traits of individuals. However, most studies on the evolutionary consequences of density‐dependent interactions focus on populations where local densities are relatively constant through time and space. We investigated the influence of spatial and ontogenetic variance in local densities within an insect population by comparing a model integrating both types of local density variance with models including only spatial variance, only ontogenetic variance, or no variance. We parameterized the models with experimental data, then used elasticity and invasion analyses to characterize selection on traits that affect either the local density an individual experiences (mean clutch size) or individuals' sensitivity to density (effect of larval crowding on pupal mass). Spatial and ontogenetic variance reduced population elasticity to effects of local density by 76% and 34% on average, respectively. Spatial variance modified selection and adaptive dynamics by altering the tradeoff between density‐dependent and density‐independent vital rates. In models including spatial variance, strategies that maximized density‐dependent survival were favoured over fecundity‐maximizing strategies even at low population density, counter to predictions of density‐dependent selection theory. Furthermore, only models that included spatial variance, thus linking the scales of oviposition and density‐dependent larval survival, had an evolutionarily stable clutch size. Ontogenetic variance weakened selection on mean clutch size and sensitivity to larval crowding by disrupting the relationship between trait values and performance during critical life stages. We demonstrate that local density variance can strongly modify selection at empirically observed interaction strengths and identify mechanisms for the effects of spatial and ontogenetic variance. Our findings reveal the potential for local density variance to mediate eco‐evolutionary feedback by shaping selection on demographically important traits. Read the free Plain Language Summary for this article on the Journal blog.

Molecular identification, life history description and biotic potential of Plodia interpunctella (Lepidoptera: Pyralidae) feeding on amaranth (Amaranthus sp.) products in the state of Morelos, Mexico

The flour moth Plodia interpunctella (Hübner) is considered one of the most significant pests of stored and processed products, its adaptability allowing it to settle on new food hosts. In 2020 in Mexico, the presence of larvae and adults of P. interpunctella in amaranth products stored and processed for export was reported for the first time, causing considerable damage. The objective of this study was molecular identification of the insects found in amaranth products and description of the biotic potential of these pests grown in different amaranth products under laboratory conditions. For this purpose, molecular identification of P. interpunctella was carried out using the mitochondrial gene cytochrome oxidase subunit one (COI). Three cohorts with 200 eggs each, fed with three types of amaranth products (amaranth with chocolate, amaranth with honey and natural amaranth) were implemented, with hatching rates of 75% for amaranth with chocolate, 66.5% for amaranth with honey and 71.5% for natural amaranth. The larval period consisted of five instars and one prepupa, with the shortest life expectancy in the first instar. The life cycle of the insect varied from 51 days in chocolate amaranth, 54 days in honey amaranth and 64 days in natural amaranth. This lepidopteran presented a high fecundity when fed with chocolate amaranth with a mean clutch size of 257.0435.98 eggs per female during her whole life (h/h/v), followed by honey amaranth with 177.3836.23 (h/h/v) and finally by natural amaranth with 157.643.33 (h/h/v), with a mean fertility of 71%. In the population parameters, a generation time (T) of 25.08, 26.69 and 31.41 days and a net reproduction rate (R0) of 405.10, 253.82 and 215.49 were obtained for amaranth with chocolate, with honey and natural respectively, ensuring a high replacement over a short period of time; these values make this species an important pest of stored amaranth products.

Swainson’s Hawk Nesting Population in the Antelope Valley of the Western Mojave Desert, California

The Swainson’s Hawk (Buteo swainsoni) has a long history of breeding in California, but a severe decline in the statewide breeding population was identified in 1979, when in all of southern California only two pairs were found, one in the Antelope Valley of the western Mojave Desert. That area was little studied until we began banding Swainson’s Hawks there in 1997. Over 20 breeding seasons between 1979 and 2022, we documented in the Antelope Valley 124 attempts to nest, in which the mean clutch and brood sizes were 2.49 and 2.37, respectively. From 2004 through 2006, we observed two to four breeding pairs annually; from 2009 through 2022, three to 14 breeding pairs. The rate of success of the 91 nests revisited to determine if any young fledged was 64%. Nest trees consisted of 81.5% non-native species, 13.7% native species, including Joshua trees (Yucca brevifolia), and 4.8% unidentified deciduous trees. Between 1997 and 2022, in 50 nests, we recorded 170 vertebrate prey items, of which 90 were gophers (Thomomys bottae). Though the Antelope Valley population has grown since 1980, its nesting and foraging habitat now face multiple threats. To conserve occupied nesting territories, we recommend creation of nesting and foraging habitat reserves that include both native desert and cultivated alfalfa close to existing conserved land.

Reproductive and Morphological Characteristics of Hemidactylus turcicus (Squamata: Gekkonidae) and Tarentola annularis (Squamata: Phyllodactylidae) in Southern Egypt

Hemidactylus turcicus and Tarentola annularis are occasionally sympatric and are ecologically similar in vertical wall microhabitat. For this reason, I studied their sexual, fat-body, and liver cycles for three years. All morphological variables are male-biased in T. annularis, unlike male H. turcicus, which showed significant differences in head sizes only. Females exhibited a spring to summer vitellogenic period with ovulation occurring during mid-spring to mid-summer in T. annularis and from late spring to late summer in H. turcicus. The mean clutch size of oviductal eggs (1.86) and relative clutch mass (0.188) was higher in H. turcicus than in T. annularis (1.67 and 0.132). Relative clutch mass was negatively correlated with snout–vent length in T. annularis but was not in H. turcicus. Sperm were present in the epididymis for eight months in H. turcicus while year-round in T. annularis. Post-breeding, masses of liver and fat body increased in both sexes of both species. There were significant differences in fat body and liver masses between the sexes of both species. Based on the liver-mass cycle, the energy expenditure on reproduction in male and female T. annularis was high compared with the corresponding sexes of H. turcicus. Testicular recrudescence began in late fall or early winter corresponding to lower temperatures, photoperiod, and precipitation. Testicular regression occurred at the highest temperatures in late summer and early fall.

Bioecology and breeding performance of cattle egret (Bubulcus ibis) in selected sites at Sharkia Governorate, Egypt.

Cattle egret Bubulcus ibis, feeds on insect pests in many agro-ecosystems. Thus, there is an urgent need to study the breeding chronology of cattle egret, in order to develop suitable protection programs for this beneficial bird to perform its role as abiological control agent in Egyptian agro-ecosystems. The study was conducted at Sharkia Governorate, Egypt, from December 2018 to December 2020; in different habitats (irrigation canals, drainage canals, garbage collection areas and Abbasa ponds). The mean clutch size ranged from 2-5 eggs/nest with an incubation period ranging between 21-25 days. The mean percentage of hatching success was 90.21%, while the total number of mortality eggs was 47 and the total egg hatching was 433. Also the total number of nests located nearby tree trunks were 73, while nests located in the core of the tree were 47 nests, and nests located at the peripherals were 15 nests.

Breeding Biology of the White-Throated Cacholote Pseudoseisura gutturalis ochroleuca, an Endemic Bird of the Monte Desert

The White-throated Cacholote Pseudoseisura gutturalis is a little studied, socially monogamous furnariid, endemic to arid Argentina. Here we provide novel information to characterize the breeding biology of the northern subspecies ochroleuca in the Monte Desert, Argentina, and discuss the similarities and differences with other Pseudoseisura species. Nests were bulky enclosed structures constructed with thorny sticks and twigs of native plant species (n = 15) and 47% of them had objects used as external decorations. Nests had an entrance tube oriented preferentially towards the northeast, probably to avoid the prevailing south-southeast winds at the study site, and were placed at a mean height of 2.1 m above the ground (n = 13). Most of the active nests (93%) were built in columnar cacti Trichocereus atacamensis that were healthier and with fewer branches than nearby available conspecifics. Mean clutch size was 3.2 white eggs (n = 9) and the incubation period was c. 18–20 days. Brood size ranged from one to three hatchlings (n = 12) and nestlings remained in the nest for 24–26 days until fledgling. Nests with complete clutches were found between 29 October and 1 February and nestlings were found between 1 November and 5 February. Nestlings were attended by both parents and were fed with arthropods (n = 63) and vertebrates (n = 7). Nest visitation rate per nestling was similar among nests with three and two nestlings and lower than for a nest with one nestling. The breeding success was high during the incubation (73%) and nestling rearing (82%) stages. Our data show that Pseudoseisura species are similar in some aspects of their breeding biology (e.g. nest dimensions, nest decorations, mating system, clutch size), whereas other aspects, such as nest-site selection, nestling period and nest attendance rate, are more variable among species.

Fecundity, Female Maturation, and Nesting Season of Western Chicken Turtles (Deirochelys reticularia miaria) in Texas

The reproductive lifespans of turtles are consistently long, but reproductive cycles are under environmental control and thus can vary within species, populations, and individuals over time and space. Knowledge of turtle species' reproductive traits and their associated variances over time and space are critical to understanding the dynamics of turtle populations, especially those requiring management or conservation. Deirochelys reticularia is a species being considered for protection by the US Fish and Wildlife Service and contains 3 subspecies with some differences in reproductive characteristics of nesting season, annual nesting frequency, and egg retention. We collected ultrasound and x-radiograph data in Texas to identify the maturation size, nesting season, annual nesting frequency, and clutch size of female D. r. miaria in Texas. We observed no reproductive activity in individuals from 101 to 146 mm in plastron length (PL) and detected either unshelled eggs, shelled eggs, or both in individuals from 150 to 197 mm PL. Maturation sizes were similar to those in other regions and for other subspecies. We observed shelled clutches or nesting events from April to July, confirming a spring–summer nesting season in Texas consistent with other D. r. miaria sites and supporting the paradigm that the western subspecies does not follow the autumn–winter nesting season of the other subspecies. We found no evidence that individuals retain shelled eggs while aestivating or overwintering. Individuals nested up to 3 times/yr in Texas. Individuals laid 7–11 eggs and the mean clutch size was 9.2 eggs, similar to other regions and other subspecies. Nesting phenology is regionally variable, so management plans and policies for the species will need to consider that variation and potentially recognize management differences among D. reticularia subspecies.

Individual egg production of Hy-Line Brown hens during the early laying phase in response to dietary CP levels

The aim of this study was to investigate the effects of gradually increased dietary CP level on the dynamics of individual egg production of laying hens from 18 to 54 weeks of age. Forty Hy-Line Brown hens were divided into five treatments of eight replicates each and were fed diets formulated to have five different CP concentrations: 14, 15, 16, 17, and 18% CP with the same energy content. For each experimental diet, the contents of lysine, methionine + cysteine, threonine, and tryptophan were maintained at minimum requirement concentrations by supplying synthetic amino acids. Clutch characteristics were recorded (e.g., number, size, patterns, egg weight, etc.) and individual egg production curves were modeled according to Grossman and Koops (2001). Clutch size was defined as the unstopped length of individual egg production on a daily basis. BWs were also recorded every week to account for changes in BW during the experimental period. Three hens were excluded from the statistical analyses as their laying patterns were very inconsistent. Four clutch patterns with data weighted on a weekly basis were identified. Heavier hens tended to lay more regular clutch patterns when compared to their lighter counterparts within the same treatment. In contrast, irregular clutch patterns (too many pauses between clutches) were more common in hens fed low CP diets (≤16%). This could be explained by imbalances in amino acids supply according to their theoretical requirements and adverse effects caused by amino acids interactions. Low CP diets were able to maintain egg production and mean clutch size up to 54 weeks of age. The maximum clutch size and the modeled proportion of maximum production for the increasing phase (k1) displayed a linear response to the graded addition of CP content to the diet. No differences were detected among treatments for the age at the beginning of the maximum clutch (22.6 ± 2.82 weeks). Egg weight displayed a quadratic response that was maximized when hens were fed 17% CP in the diet. Our approach appears to be promising for ranking individual laying hens based on their clutch performance to evaluate both CP and amino acids adequacy of diets.

Reproductive Traits Demonstrate How Well the Mediterranean Stripe-Necked Turtle Mauremys leprosa Can Flourish under Highly Degraded-Polluted Conditions.

We measured and compared the reproductive traits of the Mediterranean stripe-necked turtles Mauremys leprosa living in highly degraded-polluted vs. intact natural habitats in Algeria. Data on reproduction were obtained by using X-ray examination of gravid females and examination of nests. The results were opposite to the negative trend confirmed in most freshwater turtles exposed to pollution and suggested the ability of this species to flourish instead in highly degraded-polluted habitats. An optimum development was recorded for several reproductive patterns of the studied freshwater turtle under conditions considered uninhabitable for other vertebrates. Females exhibited record body sizes among conspecifics, which allowed them to carry significantly larger clutches, exceeding by up to 3 eggs the previously largest reported clutch. The mean clutch size (8.79 ± 2.70 eggs) was also higher than findings from previous studies, except for in some other polluted habitats. Furthermore, large females even with large clutches carried large eggs. Egg measurements in the disturbed habitat revealed new records exceeding those previously noted; in egg length (by 3.0 mm), egg width (by 2.8 mm), egg mass (by 1.8 g), and clutch mass (by 18.6 g). In comparison, the usual reproductive performances were observed in the intact natural habitat; female body sizes were significantly smaller and carried fewer eggs of smaller size.

Breeding Biology of the Chilean Elaenia Elaenia chilensis, a Long-Distance Migratory Passerine in South America

Studies examining breeding biology provide information about reproductive parameters, which are useful in formulating life-history theories. Although these studies have notably increased in the Neotropics in recent years, some gaps remain; thus, more research is needed to better understand life-history strategies of New World birds. Furthermore, research into the breeding biology of migratory birds is crucial to advance our understanding of trade-offs between reproduction and migration in Neotropical austral migrant birds. Our aims were to describe in detail the breeding biology of the Chilean Elaenia Elaenia chilensis, a long-distance Neotropical austral migrant, and to discuss current life-history theories for New World passerines. We monitored 113 nests during four consecutive breeding seasons (2014/2015–2017/2018) in the Andean-Patagonian Forest. The breeding season lasted 77 days and the nesting period, from egg laying to fledging, had a mean duration of 29.9 days. Mean clutch size was 2.4 eggs (range: 1–3) and decreased throughout the breeding season. The incubation and nestling stages lasted c. 14 days each. Fledgling number also decreased as the season progressed. The mean ± SE daily nest survival rate was 0.960 ± 0.005, corresponding to an overall nest success of 29.5%. Predation was the main cause of nest loss (61.1%). Reproductive parameters of the Chilean Elaenia coincide with characteristics of high-survival species that invest little in reproduction. Despite being a long-distance migrant, its life-history strategy does not seem to be much faster than that of its tropical resident congeners. This might not support the result reported in the Northern Hemisphere that migratory birds have a faster pace of life than resident birds.

Compensating for Small Body Size: The Reproductive Ecology of Southern Spotted Turtle (Clemmys guttata) Populations

Gradients in environmental conditions across a species' geographic distribution can drive variability in a variety of life history traits. In North American freshwater turtles, both body and clutch size have commonly been shown to vary latitudinally, and these two traits are often directly related, with larger individuals producing larger clutches. We studied the reproductive ecology in two Georgia populations of Spotted Turtles (Clemmys guttata) from 2016–2020 by attaching radio transmitters to female turtles during the breeding season. We x-rayed turtles to determine clutch sizes and used thread bobbins to locate nesting locations, allowing us to determine nest fates. Across all Spotted Turtle clutches (n = 41), mean clutch size was 2.1 (range: 1–4) eggs per clutch. Approximately 92% of individuals that we monitored produced at least one clutch during the breeding season, and we identified 16 instances of individuals producing more than one clutch in a single year, including six turtles triple clutching during 2018. We located 24 Spotted Turtle nests during the study, nine (37.5%) of which either hatched or partially hatched. The other nests were either depredated (41.7%), did not hatch due to infertility or environmental reasons (8.3%), or had an undetermined fate (12.5%). Our results indicate that annual reproductive output in southern Spotted Turtle populations can exceed that of northern populations where individuals produce a single larger clutch per reproductive season. Finally, opportunistic observations in Florida from 2014–2021 indicated that the reproductive season can begin over a month earlier than in southern Georgia, highlighting the variability in reproductive ecology even across a relatively short latitudinal distance.

Female reproductive characteristics of the Balkan sand lizard Lacerta agilis bosnica (Schreiber, 1912)

The sand lizard (Lacerta agilis), which occupies a large part of temperate Eurasia and includes several morphologically and genetically distinct lineages, is a model species for life-history studies. Yet, for major parts of the species range, basic data on female reproductive traits are lacking. Here we present the first data on female reproductive traits of Lacerta agilis bosnica, a poorly studied lineage inhabiting montane areas of the Balkan Peninsula. Ten females caught in mid-June 2017 on Mt. Maljen (950 m a.s.l.) in western Serbia were monitored and examined in the lab, as well as their eggs and hatchlings. We additionally examined the state and number of oocytes in 31 females from scientific collections. Mean clutch size is quite high (8.0 ± 0.4 eggs) in relation to small mean snout-vent length of gravid females (74 ± 1 mm), mean relative clutch mass is relatively low (0.37 ± 0.02), and egg incubation period (51 ± 1 days at 24-26 °C) is rather long for L. agilis. While mean values of the above traits are within the variation range found across conspecific populations studied thus far, mean values for egg size (mass, 0.42 ± 0.02 g; length, 11.8 ± 0.2 mm; width, 7.7 ± 0.1 mm) and hatchling size (mass, 0.47 ± 0.03 g; SVL, 25.0 ± 0.5 mm; tail length, 30.4 ± 1.6 mm) are clearly smaller than in all previously studied populations of this species.