It’s a dog-eat-croc world: dingo predation on the nests of freshwater crocodiles in tropical Australia

Predation on eggs is an important source of mortality for many long-lived organisms, but causes of egg mortality from specific predators remain poorly known in most cases. Understanding the identity of predators, and the rates and determinants of their effects on a cohort of recruits, can provide a valuable background for attempts to exploit, control or conserve populations. We used remotely triggered cameras to study predation on the nests of freshwater crocodiles (Crocodylus johnstoni) inhabiting Lake Argyle, in tropical Australia. We also supplemented our work on natural crocodile nests with artificial nests. Overall, 80 of 111 natural nests were opened by predators, and predation occurred throughout the study period (7 weeks). Unlike in other parts of the species’ range, most nest-robbers were dingoes (Canis lupus dingo, responsible for 98% of all predator visits in the northern sites, and 54% in the Ord River site), with minimal additional predation by reptiles and birds. Contrary to expectation, rates of nest predation were not influenced by spatial clumping of nests: the probability of predation per nest did not change with total numbers of nests laid in an area, and artificially aggregated versus dispersed nests experienced similar levels of predation. Nest vulnerability was linked to abiotic features including slope of surrounding banks, compactness of nesting substrate, and distance from the nearest forest. Abundant aquatic food resources support a large crocodile population, but a lack of suitable nest-sites forces the crocodiles to concentrate nesting in small areas readily accessible to wide-ranging nest predators. Collectively, our results suggest that distinctive attributes of the lakeside landscape alter predator guilds and fashion unique predator–prey interactions.     

Determinants of habitat selection by hatchling Australian freshwater crocodiles

Animals almost always use habitats non-randomly, but the costs and benefits of using specific habitat types remain unknown for many types of organisms. In a large lake in northwestern Australia (Lake Argyle), most hatchling (<12-month-old) freshwater crocodiles (Crocodylus johnstoni) are found in floating vegetation mats or grassy banks rather than the more widely available open banks. Mean body sizes of young crocodiles did not differ among the three habitat types. We tested four potential explanations for non-random habitat selection: proximity to nesting sites, thermal conditions, food availability, and exposure to predation. The three alternative habitat types did not differ in proximity to nesting sites, or in thermal conditions. Habitats with higher food availability harboured more hatchlings, and feeding rates (obtained by stomach-flushing of recently-captured crocodiles) were highest in such areas. Predation risk may also differ among habitats: we were twice as likely to capture a crocodile after seeing it in open-bank sites than in the other two habitat types. Thus, habitat selection of hatchling crocodiles in this system may be driven both by prey availability and by predation risk.     

Do trade‐offs between predation pressures on females versus nests drive nest‐site choice in painted turtles?

Predation strongly influences reproductive behaviours because reproducing individuals must balance mortality risks to themselves and to their offspring. In many freshwater turtles, the nest predation risk decreases with nest distance from water, whereas the predation risk to females increases farther from water. To determine whether predation pressure influences the distance from water at which female turtles nest, we measured predation pressure on nesting females and on nests, as well as the distances of nests to water, in two populations of painted turtles. Using models, we found that female survival in both populations was high and did not vary with distance from water. Nest survival was also uncorrelated with nest distance to water, although it was significantly lower than adult survival in both populations and was only 1.2% in one population. Our results suggest that nest sites are not predictably safe from predators. Instead, turtles may hedge their bets by nesting over a wide range of distances from water because any distance is risky for nests and no distance is particularly risky for the nesting female. We suggest that other factors, such as suitable incubation conditions and/or post‐emergence hatchling survival, probably play a larger role than predation in driving nest‐site choice in painted turtles.     

Conditional female strategies influence hatching success in a communally nesting iguana

The decision of females to nest communally has important consequences for reproductive success. While often associated with reduced energetic expenditure, conspecific aggregations also expose females and offspring to conspecific aggression, exploitation, and infanticide. Intrasexual competition pressures are expected to favor the evolution of conditional strategies, which could be based on simple decision rules (i.e., availability of nesting sites and synchronicity with conspecifics) or on a focal individual's condition or status (i.e., body size). Oviparous reptiles that reproduce seasonally and provide limited to no postnatal care provide ideal systems for disentangling social factors that influence different female reproductive tactics from those present in offspring‐rearing environments. In this study, we investigated whether nesting strategies in a West Indian rock iguana, Cyclura nubila caymanensis, vary conditionally with reproductive timing or body size, and evaluated consequences for nesting success. Nesting surveys were conducted on Little Cayman, Cayman Islands, British West Indies for four consecutive years. Use of high‐density nesting sites was increasingly favored up to seasonal nesting activity peaks, after which nesting was generally restricted to low‐density nesting areas. Although larger females were not more likely than smaller females to nest in high‐density areas, larger females nested earlier and gained access to priority oviposition sites. Smaller females constructed nests later in the season, apparently foregoing investment in extended nest defense. Late‐season nests were also constructed at shallower depths and exhibited shorter incubation periods. While nest depth and incubation length had significant effects on reproductive outcomes, so did local nest densities. Higher densities were associated with significant declines in hatching success, with up to 20% of egg‐filled nests experiencing later intrusion by a conspecific. Despite these risks, nests in high‐density areas were significantly more successful than elsewhere due to the benefits of greater chamber depths and longer incubation times. These results imply that communal nest sites convey honest signals of habitat quality, but that gaining and defending priority oviposition sites requires competitive ability.     

Salt marsh elevation is a strong determinant of nest‐site selection by Clapper Rails in Georgia,USA

As sea levels rise, birds nesting in coastal marshes will be particularly vulnerable to increased tidal inundation. Understanding how marsh birds select their nesting habitat along the elevational gradient of these marshes will provide insight into how these species might be affected by rising sea levels. Clapper Rails (Rallus crepitans) are coastal marsh‐nesting birds whose nests are vulnerable to flooding, but it is not clear if they select for habitat along the elevational gradient or only use other habitat cues. Our objective was to determine if Clapper Rails select higher‐elevation nest sites, while also controlling for selection of other habitat variables at both landscape and territory levels, by comparing nest habitat to habitat in other areas of territories and at random points in the marsh landscape. At the landscape level, Clapper Rails did not exhibit selection for the elevational gradient, with nests and random points at similar elevations. At the territory level, however, nest‐site selection was most influenced by elevation and plant height, with Clapper Rails selecting nest sites with higher elevations and in areas with taller plants. However, the strength of the elevation effect was uncertain, suggesting the importance of precise elevation measurements in the field. Given this selection for higher‐elevation nest sites, Clapper Rails may be somewhat resilient to increased tidal inundation. However, the potential for increased intra‐ and interspecific competition for high‐elevation marshes should make conservation of these habitats a priority.     

Use of mistletoes by the Grey Go‐away‐bird (Corythaixoides concolor,Musophagidae) in a semi‐arid savannah,south‐west Zimbabwe

Mistletoes are preferred nesting sites for many bird species in a range of habitats. However, no studies have examined the use of mistletoes by nesting birds in the semi‐arid savannah. We studied nesting in mistletoe and its role in determining nesting success in the Grey Go‐away‐bird in south‐west Zimbabwe. We modelled the effects of mistletoe, mistletoe abundance, nest microclimate, concealment and nest height on daily survival rates (DSR) using program MARK. A constant survival model was best fitted for the Grey Go‐away‐bird suggesting a constant nest survival rate across the nesting period. Mistletoe nests had lower DSR than nests placed elsewhere in the canopy. Mistletoe abundance and nest height had a positive association with DSR whereas visibility distance, microclimate and concealment were negatively associated with DSR. Overall, survival for nests in mistletoe was 22.1% compared with 90.5% for nests in other substrates over the 50‐day nesting period. In conclusion, the low nest survival in mistletoe suggests either that the factors used to select mistletoe as nest sites by these birds are poor predictors of nest success or that nesting in mistletoe may be maladaptive.     

Nest site characteristics of four sympatric species of hornbills in Khao Yai National Park, Thailand

Characteristics of nest sites, nest trees and nest holes were documented for four sympatric species of hornbills in Khao Yai National Park: the Great Buceros bicornis. Wreathed Rhy-ticeros undulatus , Oriental Pied Anthracoceros albirostris and Brown Hornbills Ptilolaemus tickelli. Nearly all hornbills nested in cavities in the trunks of at least 13 different genera of living trees. Sixty percent of the 80 nests found were in two tree genera, Dipterocarpus (34%) and Eugenia (26%), which comprised only 7% and 3%, respectively, of all large trees in 302 sample plots. Hornbills tended to prefer holes high in large, emergent trees for nesting, except for the Brown Hornbills, which preferred nest holes within or below the main forest canopy (15–25 m high). Most nest sites were between 700 and 800 m a.s.l. (79% of the total of 80 nests). Brown Hornbill nests were located in areas with a significantly higher altitude than were those of the Oriental Pied Hornbill. Hornbills tended to select nest entrances according to their body size, and all four hornbill species used oval to elongated nest entrances, with the Great Hornbill preferring the most elongated entrances. Hornbills did not select a specific nest entrance orientation.     

Microhabitat nest‐site selection by ducks in the boreal forest

The boreal forest is one of the North America’s most important breeding areas for ducks, but information about the nesting ecology of ducks in the region is limited. We collected microhabitat data related to vegetation structure and composition at 157 duck nests and paired random locations in Alberta’s boreal forest region from 2016 to 2018. We identified fine‐scale vegetation features selected by ducks for all nests, between nesting guilds, and among five species using conditional logistic regression. Ducks in the boreal forest selected nest sites with greater overhead and graminoid cover, but less forb cover than random sites. Characteristics of the nest sites of upland‐ and overwater‐nesting guilds differed, with species nesting in upland habitat selecting nests that provided greater shrub cover and less lateral concealment and species nesting over water selecting nests with less shrub cover. We examined the characteristics of nest sites of American Wigeon (Mareca americana), Blue‐winged Teal (Spatula discors), Green‐winged Teal (Anas crecca), Mallards (Anas platyrhynchos), and Ring‐necked Ducks (Aythya collaris), and found differences among species that may facilitate species coexistence at a regional scale. Our results suggest that females of species nesting in upland habitat selected nest sites that optimized concealment from aerial predators while also allowing detection of and escape from terrestrial predators. Consequently, alteration in the composition and heterogeneity of vegetation and predator communities caused by climate change and industrial development in the boreal forest of Canada may affect the nest‐site selection strategies of boreal ducks.     

Nest‐site selection by Slender‐billed Parakeets in a Chilean agricultural‐forest mosaic

ABSTRACT Species in the family Psittacidae may be particularly vulnerable to anthropogenic habitat transformations that reduce availability of suitable breeding sites at different spatial scales. In southern Chile, loss of native forest cover due to agricultural conversion may impact populations of Slender‐billed Parakeets (Enicognathus leptorhynchus), endemic secondary cavity‐nesting psittacids. Our objective was to assess nest‐site selection by Slender‐billed Parakeets in an agricultural‐forest mosaic of southern Chile at two spatial scales: nest trees and the habitat surrounding those trees. During the 2008–2009 breeding seasons, we identified nest sites (N= 31) by observing parakeet behavior and using information provided by local residents. Most (29/31) nests were in mature Nothofagus obliqua trees. By comparing trees used for nesting with randomly selected, unused trees, we found that the probability of a tree being selected as a nest site was positively related to the number of cavity entrances, less dead crown, and more basal injuries (e.g., fire scars). At the nesting‐habitat scale, nest site selection was positively associated with the extent of basal injuries and number of cavity entrances in trees within 50 m of nest trees. These variables are likely important because they allow nesting parakeets to minimize cavity search times in potential nesting areas, thereby reducing energetic demands and potential exposure to predators. Slender‐billed Parakeets may thus use a hierarchical process to select nest sites; after a habitat patch is chosen, parakeets may then inspect individual trees in search of a suitable nest site. Effective strategies to ensure persistence of Slender‐billed Parakeets in agricultural‐forest mosaics should include preservation of both individual and groups of scattered mature trees.     

Influence of olfactory and visual cover on nest site selection and nest success for grassland‐nesting birds

Habitat selection by animals is influenced by and mitigates the effects of predation and environmental extremes. For birds, nest site selection is crucial to offspring production because nests are exposed to extreme weather and predation pressure. Predators that forage using olfaction often dominate nest predator communities; therefore, factors that influence olfactory detection (e.g., airflow and weather variables, including turbulence and moisture) should influence nest site selection and survival. However, few studies have assessed the importance of olfactory cover for habitat selection and survival. We assessed whether ground‐nesting birds select nest sites based on visual and/or olfactory cover. Additionally, we assessed the importance of visual cover and airflow and weather variables associated with olfactory cover in influencing nest survival. In managed grasslands in Oklahoma, USA, we monitored nests of Northern Bobwhite (Colinus virginianus), Eastern Meadowlark (Sturnella magna), and Grasshopper Sparrow (Ammodramus savannarum) during 2015 and 2016. To assess nest site selection, we compared cover variables between nests and random points. To assess factors influencing nest survival, we used visual cover and olfactory‐related measurements (i.e., airflow and weather variables) to model daily nest survival. For nest site selection, nest sites had greater overhead visual cover than random points, but no other significant differences were found. Weather variables hypothesized to influence olfactory detection, specifically precipitation and relative humidity, were the best predictors of and were positively related to daily nest survival. Selection for overhead cover likely contributed to mitigation of thermal extremes and possibly reduced detectability of nests. For daily nest survival, we hypothesize that major nest predators focused on prey other than the monitored species’ nests during high moisture conditions, thus increasing nest survival on these days. Our study highlights how mechanistic approaches to studying cover informs which dimensions are perceived and selected by animals and which dimensions confer fitness‐related benefits.     

Nest site selection by yellow-faced honeyeaters Lichenostomus chrysops

When choosing subsequent nest sites, species that produce multiple broods in a single breeding season have the option of dispersing from a site where they previously suffered depredation, i.e., a predator-avoidance tactic. In our study on yellow-faced honeyeaters Lichenostomus chrysops it was found that 89% of nest failures were attributed to nest depredation, the primary cause of reproductive failure. Pairs re-nested further from depredated nesting attempts than from successful nesting attempts and progressively higher above the ground as the breeding season progressed. Pairs nesting in dioecious Coprosma quadrifida plants only nested in non-fruiting male plants. Artificial nests were used to test the hypothesis that nest height and plant preferences were strategies to reduce the risk of depredation. There was no evidence that either higher nests or nests in non-fruiting C. quadrifida achieved reduced levels of depredation during 14 days of artificial nest exposure. Specific nest site characteristics were not found to be associated with nest outcome for either natural or artificial nests. Our study provides further evidence that species may choose a diverse range of nest sites in order to avoid predators from developing specific search images and then, following depredation, compensate by rapidly re-nesting away from the failed attempt.     

Spatiotemporal patterns of duck nest density and predation risk: a multi‐scale analysis of 18 years and more than 10 000 nests

Many avian species are behaviorally‐plastic in selecting nest sites, and may shift to new locations or habitats following an unsuccessful breeding attempt. If there is predictable spatial variation in predation risk, the process of many individuals using prior experience to adaptively change nest sites may scale up to create shifting patterns of nest density at a population level. We used 18 years of waterfowl nesting data to assess whether there were areas of consistently high or low predation risk, and whether low‐risk areas increased, and high‐risk areas decreased in nest density the following year. We created kernel density maps of successful and unsuccessful nests in consecutive years and found no correlation in predation risk and no evidence for adaptive shifts, although nest density was correlated between years. We also examined between‐year correlations in nest density and nest success at three smaller spatial scales: individual nesting fields (10–28 ha), 16‐ha grid cells and 4‐ha grid cells. Here, results were similar across all scales: we found no evidence for year‐to‐year correlation in nest success but found strong evidence that nest density was correlated between years, and areas of high nest success increased in nest density the following year. Prior research in this system has demonstrated that areas of high nest density have higher nest success, and taken together, our results suggest that ducks may adaptively select nest sites based on the local density of conspecifics, rather than the physical location of last year's nest. In unpredictable environments, current cues, such as the presence of active conspecific nests, may be especially useful in selecting nest sites. The cues birds use to select breeding locations and successfully avoid predators deserve continued attention, especially in systems of conservation concern.     

Social and Thermal Cues Influence Nest‐site Selection in a Nocturnal Gecko,Oedura lesueurii

In oviparous species lacking parental care, successful reproduction depends on females selecting nest sites that facilitate embryonic development. Such sites may be limited in the environment, which can lead to multiple females using the same nest site simultaneously. However, there are several alternative explanations for communal nesting, including natal homing, predator satiation, and adaptive benefits to offspring. We used laboratory experiments to evaluate three hypotheses about nest‐site selection in velvet geckos (Oedura lesueurii), which often nest communally. We investigated whether the trend to nest communally is influenced by the following: (1) evidence of previous nesting (hatched eggshells); (2) body size; and/or (3) thermal regimes. When given the choice, females laid their eggs in shelters containing hatched eggshells rather than in empty shelters, and this was not influenced by body size. Females selected nest sites that were cooler than their own mean selected body temperatures, suggesting that thermal requirements of their developing embryos could outweigh their own thermoregulatory preferences. Field observations of natal homing and high predation rates on gravid females suggest that imprinting on nest sites and/or predator swamping also play roles in communal nesting. Collectively, our results suggest that female velvet geckos use multiple cues to select appropriate nest sites, and hence that multiple mechanisms result in communal nesting behavior in this species.     

Determinants of reproductive success and offspring sex in a turtle with environmental sex determination

Despite the importance of maternal effects in evolution, and knowledge of links among nest site choice, timing of nesting, offspring sex, and reproductive success in animals with environmental sex determination, these attributes have not been rigorously studied in a combined and natural context. To address this need we studied the relationships between three maternal traits (nest site choice, lay date, and nest depth) and two fitness‐related attributes of offspring (hatchling sex and embryonic survival) in the riverine turtle Carettochelys insculpta, a species with temperature‐dependent sex determination, for four years. Predation and flooding were the major sources of embryonic mortality in 191 nests. Embryonic survival was influenced by both lay date and nest site choice: in one year when nesting began later than average, nests laid later and at lower elevations were destroyed by early wet season river rises. In other years early nesting precluded flood mortality. However, turtles did not nest at the highest available elevations, and a field experiment confirmed that turtles were constrained to nest at lower elevations where they could construct a nest chamber. The principal determinant of hatchling sex in 140 nests was lay date, which in turn was apparently related to the magnitude of the previous wet season(s). Clutches laid earlier in the season (a female's first clutch) produced mainly males, while later clutches (her second clutch) yielded mostly females, due to seasonal increases in air temperatures. Accordingly, later nesting produced female‐biased hatchling sex ratios in 1996, while earlier nesting resulted in sex ratios near unity in the other years. However, all‐female nests were more likely to be flooded than mixed‐sex or all‐male nests in years when nesting was late. In conclusion, we found evidence that the position of two maternal trait distributions (elevation of the nest site and lay date), associated with the reproductive strategy of C. insculpta, reflect a combination of natural selection, physical constraints, and phenotypic plasticity. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 1–16.     

Honey Buzzard Pernis apivorus nest‐site selection in relation to habitat and the distribution of Goshawks Accipiter gentilis

The selection of a suitable nest‐site is critical for successful reproduction. Species' preferences for nest‐sites have presumably evolved in relation to local habitat resources and/or interactions with other species. The importance of these two components in the nest‐site selection of the Eurasian Honey Buzzard Pernis apivorus was assessed in two study areas in eastern Austria. There was almost no difference in macro‐ and micro‐habitat features between nest‐sites and random plots, suggesting that Honey Buzzards did not base their choice of nest‐site on habitat characteristics. However, nests were placed significantly further from nests of Northern Goshawk Accipiter gentilis than would be expected if nest‐sites had been chosen at random. Furthermore, in one study area Honey Buzzards appeared to favour areas close to human settlements, perhaps indicating a mechanism to avoid Goshawks, which tend to avoid the proximity of humans. No habitat variable was significantly associated with the loss of Honey Buzzard young, but predation was higher in territories closer to breeding pairs of Goshawks at both study sites. Although Honey Buzzards are restricted to nesting in forests, their choice of nest‐site therefore appears to be largely dictated by the distribution of predators. Studies of habitat association may yield misleading results if the effects of predation risk on distribution are not considered.     

Genetic structure at three spatial scales is consistent with limited philopatry in Ricord's Rock Iguanas (Cyclura ricordii)

Cyclura ricordii is an endemic iguana from Hispaniola Island and is threatened on the IUCN Red List. The main threats are predation by introduced mammals, habitat destruction, and hunting pressure. The present study focused on two nesting sites from Pedernales Province in the Dominican Republic. The hypothesis that natal philopatry influences dispersal and nest‐site selection was tested. Monitoring and sampling took place in 2012 and 2013. Polymorphic markers were used to evaluate whether natal philopatry limits dispersal at multiple spatial scales. Ripley's K revealed that nests were significantly clustered at multiple scales, when both nesting sites were considered and within each nesting site. This suggests a patchy, nonrandom distribution of nests within nest sites. Hierarchical AMOVA revealed that nest‐site aggregations did not explain a significant portion of genetic variation within nesting sites. However, a small but positive correlation between geographic and genetic distance was detected using a Mantel's test. Hence, the relationship between geographic distance and genetic distance among hatchlings within nest sites, while detectable, was not strong enough to have a marked effect on fine‐scale genetic structure. Spatial and genetic data combined determined that the nesting sites included nesting females from multiple locations, and the hypothesis of “natal philopatry” was not supported because females nesting in the same cluster were no more closely related to each other than to other females from the same nesting site. These findings imply that nesting aggregations are more likely associated with cryptic habitat variables contributing to optimal nesting conditions.     

Nest site selection by a neotropical swarm-founding wasp: seasonal alternation of nest orientation

Nest orientation in social insects has been intensively studied in warmer and cooler climates, particularly in the northern hemisphere. Previous studies have consistently shown that species subjected to these climatic conditions prefer to select mostly southern locations where the nests can gain direct sunlight. However, very little is known on nest orientation in tropical and subtropical social insects. We studied nest orientations initiated by swarms throughout a year in a Brazilian swarm-founding wasp, Polybia paulista von Ihering (Hymenoptera: Polistinae). Swarms selected various orientations as nest sites, but there was a particular trend in that swarms in the winter period (May–August) preferred to build northward-facing nests. This preference is opposite from that of social wasps observed in the northern hemisphere. Colonies of this species can potentially last for many years with continuous nesting, but nesting activities of colonies during the winter are severely limited due to cool temperature and a shortened day length. Northward-facing nests are warmer through the gain of direct solar heat during the winter period; consequently, choosing northward-facing sites may be advantageous for swarms in terms of a shortened brood development and shortened time needed to increase metabolic rates during warm-up for flight.     

Nest site selection and patterns of nest re-use in the Hooded Crow Corvus cornix

Capsule: Hooded Crows Corvus cornix selected nesting trees based on species, height, grouping and distance from an occupied house. Nest re-use was common and pairs that re-used old nests produced more fledglings than those that built a new nest.

Aims: To determine the features of trees that influenced whether they were used by Hooded Crows as nest sites, to establish what factors influenced nest re-use between years and to explore potential costs or benefits of nest re-use.

Methods: In a large area of Orkney, Scotland, the features of trees that contained a Hooded Crow nest were compared to those of trees where nests were absent. Patterns of nest re-use between years were examined in relation to the availability of alternative sites, previous nesting success and the number of equivalent options to the tree used previously within 200?m of this site.

Results: Hooded Crows favoured spruce and pine trees as nest sites, above the most locally abundant tree species, elder and willow. Preference for trees increased with tree height, local tree density and distance from occupied houses. Over half of the crows studied re-used an old nest when one was available and crows that re-used an old nest fledged more offspring than those that built a new nest. The likelihood of a new nest being built increased as the number of potential locations to build increased. Territories where a nest survived the winter were more likely to be reoccupied the following year than those where nests fell, while territories with fewer trees around the old site were most likely to be abandoned, suggesting that those were territories of lower quality.

Conclusions: Hooded Crows displayed strong preferences for nest sites that might favour nesting success by offering concealment, shelter and protection from ground-based predators. Nest re-use was common, especially when alternative sites were scarce, and appeared to facilitate greater reproductive output.     

THE ECOLOGY OF THE NILE CROCODILE (CROCODYLUS NILOTICUS LAURENTI) ON CENTRAL ISLAND, LAKE RUDOLF

1. Lake Rudolf, nothern Kenya, has one of the largest undisturbed populations of the Nile Crocodile. In 1965 the Kenya Game Department initiated the Lake Rudolf Crocodile Research Project. Central Island, where the crocodiles live under undisturbed conditions, was chosen for studying breeding behaviour and ecology of the reptile. Eight months were spent on the island. 2. On the island most of the crocodile population was confined to a crater lake, Lake C, which supported up to 500 animate at the height of the 1965-66 breeding season. 3. The 1200 m shoreline of Lake C was shared out between about a dozen large males each guarding his territory by patrolling up and down the shore. The territorial shore lengths ranged from 60 to 230 m. The territories extended about 50 m into the water. 4. The crocodiles were first seen courting on 10.10.65 in Lake C. The territorial males exhibited a “courtship splash display”. Copulation ranged from 30 to 100 seconds; eleven copulations averaged 58 seconds. 5. The factors important in site selection for nesting are shade, suitable soil, proximity to water and the degree of slope of the shore. Because the shores of a second crater lake, Lake A, satisfied these conditions they had the largest number of nests. The fully exposed sites on Lake C, and the Lake Rudolf shores, had very few nests. 6. The females dig the nests with their forelimbs, using them in turn. The hind limbs and the belly are used to push away the soil collecting at the mouth of the burrow. The female guards the nest constantly throughout the incubation period of three months against monitor luzards. Laying began in the third week of November, 1965 reaching its peak during the second week of December. The crocodile egg is oblong, measuring 55.5 to 89.0 mm in length and 43.0 to 54.0 mm in width. Mean weights of the eggs from 15 clutches ranged from 83.7 to 126.6 g. Clutch sizes on Central Island varied from 14 to 46 eggs, giving a mean of 33 eggs per clutch. When the young are about to hatch, the mother releases them by digging up the nest. The young when they hatch are about 31.0 cm long and weigh about 76.8 g. They are guarded by the mother for at least six weeks. Infant mortality is probably very considerable.     

Nest site characteristics and nesting success of the five‐spotted wrasse Symphodus roissali in the north‐western Mediterranean Sea

The effects of site characteristics on the distribution of nests and nesting success were examined in the five‐spotted wrasse Symphodus roissali in the north‐western Mediterranean Sea. Nesting males selected nest sites mainly on flat substrata and close to a margin in the rocky littoral strip; however, substratum slope and degree of shelter from wave action were the determinants for a greater success.