Clutch Predation Research Articles

Seasonal Fecundity of Sagebrush Brewer's Sparrow (Spizella Breweri Breweri) at The Northern Edge of its Breeding Range

AbstractWe examined the effects of environmental and ecological factors associated with seasonal fecundity on spatial and temporal patterns of productivity in Sagebrush Brewer's Sparrow (Spizella breweri breweri) in British Columbia, the northwestern edge of its breeding range. This study is the first examination of seasonal fecundity in this species. Seasonal fecundity of females varied from 1998 to 2000. It was highest in 2000, when nest predation was lowest and number of clutches per female was intermediate, and lowest in 1998, when nest predation and number of clutches per female were the highest and warm El Niño conditions led to early breeding. Potential fecundity gains from early breeding were diminished by the interaction of shifting predation rates and variable effects of weather at different elevations. Early breeding in 1998 proved an advantage only at the low-elevation site, because an early spring storm destroyed 43% and 20% of first nests at two high-elevation sites. High seasonal fecundity varied between the sites, such that the best site in 1998 became the least productive in 1999 and vice versa. The overriding factor driving spatiotemporal variation was shifting rates of nest predation, though the elevation-related storm effects and variation in number of clutches were partly responsible. To maintain high productivity for Sagebrush Brewer's Sparrow at the northern edge of its range, where conditions are unpredictable and where there is no consistently best or worst site in terms of productivity, managers must protect sites from habitat loss or alteration across a range of elevations and conditions.Fécondité Saisonnière de Spizella Breweri Breweri à la Limite Nord de Son Aire de Reproduction

Effects of clutch sizes and incubation stage on nest desertion in the female Common Eider Somateria mollissima nesting in the high Arctic

In bird species, one of the trade-offs between reproduction and survival appears in the parental decision to desert the nest. Nest desertion is modulated by several factors including clutch size. However, the incubation stage at which predation occurs is also an important factor. In this study, we examined whether nest desertion was linked to initial clutch size, partial clutch predation (final clutch size) and the incubation stage at which it happened in a capital breeder: the female common eider (Somateria mollissima) nesting in the high Arctic. The study was performed in Kongsfjorden in 2002 on the western coast of the Svalbard Archipelago (78°55′N, 20°07′E). We observed that nest desertion was higher when the initial clutch size was small. Also, females deserted their nests more during the first third of incubation than later. Thus, as incubation proceeded, nest desertion was less likely to occur even after egg reduction. Our results pointed out that this parental decision in female eiders seemed to depend on initial clutch size and on the date into incubation of clutch reduction.

Hatching success in Avocet Recurvirostra avosetta and Black-winged Stilt Himantopus himantopus

Capsule Daily survival rate of nests was influenced by laying date and nesting period (laying versus incubation) in both species and by colony size in Black-winged Stilts. Aims To investigate the effect of clutch size, colony size, reproductive phenology and nesting period on hatching success of Avocets and Black-winged Stilts. Methods The study was undertaken at two localities in southwestern Spain (Doñana and Odiel Natural Parks) during 1990 and 1991 breeding seasons. The Mayfield method was used to estimate hatching success. Results Both species bred colonially and some colonies included nests of both species. Neither year, locality, species or clutch size had a significant effect on hatching success. Daily survival rate was lower for late nests than for early and intermediate, and lower during egg-laying than during incubation in both species. Hatching success of Black-winged Stilt nests was lower in large colonies (>50 nests) than in medium-sized ones (11–50 nests). Conclusion Late clutches within a colony (clutches with the least hatching success) might be replacements or belong to late breeders, but adults were not individually marked, precluding clarification. The results suggest a high probability of clutch predation and/or desertion in early stages of the nesting period, especially shortly after laying the first egg. The fact that hatching success in large colonies was lower than in medium-sized ones, but only for Black-winged Stilts (not for Avocets), might help to explain the difference in coloniality of the two species.

Shorebird Breeding Biology in Wetlands of the Playa Lakes, Texas, USA

Wetlands in the Playa Lakes Region of Texas are important habitats for North American wintering waterfowl and migrant shorebirds. However, shorebird breeding biology has been overlooked in characterizing the region’s ecological importance. In 1998 and 1999, American Avocet (Recurvirostra americana), Black-necked Stilt (Himantopus mexicanus), Killdeer (Charadrius vociferous), and Snowy Plover (C. alexandrinus) breeding ecology were studied in playas, saline lakes, and riparian wetlands in the Playa Lakes Region of Texas. Chronology of nest initiation, clutch sizes, and hatching success for 298 Snowy Plover, 111 American Avocet, 43 Killdeer, and 26 Black-necked Stilt clutches were measured. All four species nested in saline lakes, American Avocet and Killdeer also nested in playas, and Snowy Plover nested on riparian wetlands. American Avocet had higher hatching success in 1999 (52%) than 1998 (8%), because of more suitable hydrological conditions and lower predation. Hatching success was higher in 1998 than 1999 for Killdeer (1998, 63%; 1999, 21%) and Snowy Plover (1998, 47%; 1999, 33%) due to failures caused by flooding and hail in 1999. In other regions, clutch predation limits shorebird productivity, but hatching success in the Playa Lakes Region appears to be limited by unpredictable precipitation patterns and wetland hydroperiod. As such, breeding shorebird conservation and management should focus upon maintaining wetland hydrological integrity.

Appearance and vulnerability of artificial duck nests to avian predators

Use of artificial nests in studies of nest success in birds has become increasingly popular, but this practice has been criticised because the appearance and success of artificial nests may differ from natural nests. Typically, artificial nests are presented with few visible eggs throughout the entire exposure period while natural nests during their life have different appearances, possibly producing stage‐dependent predation rates. In ducks, nests may appear with openly visible eggs, eggs covered with nest material and covered by an incubating female. To test how nest appearance may affect nest survival, I simulated such duck nest appearances, and used direct observations to record responses of marsh harriers Circus aeruginosus, the dominant duck nest predator at the Lake Engure, Latvia, during the breeding seasons 2000–2002. I recorded 274 harrier flights over all types of artificial nests, 74 nest discoveries and 54 predation events. Logistic regression analyses showed that nest appearance was a significant predictor of the fate of the nest: nests with openly visible eggs were discovered more often than nests covered with nest material. Nests with dummy females had discovery rates similar to the average of all artificial nest types suggesting that they best reflect the predation risk of artificial nests and could be used in future studies. After discovering nests covered with dummy females, harriers never attacked but tried to scare them off to get access to the eggs. In 52% of cases of nest discovery, harriers gave up before touching the dummy. This shows that duck passive nest defence may prevent clutch predation.

Is clutch size limited by incubation ability in northern lapwings?

Summary The incubation‐limitation hypothesis states that clutch size in shorebirds is constrained by the ability to incubate more than four eggs successfully. In order to test predictions from this hypothesis, clutches of northern lapwings (Vanellus vanellus) were here experimentally increased and reduced by one egg at the onset of incubation. Parental behaviour, incubation time, hatching synchrony, egg viability, hatching success and body condition of hatchlings was compared with unmanipulated clutches. Nest desertion and egg breakage was not observed in any of the experimental nests, showing that clutch enlargement did not alter the parental behaviour adversely. There were no differences among the experimental groups in male and female attentiveness, but the total nest attentiveness was lower in reduced clutches than in the other clutch sizes; nor did the parents’ frequency of nest visits differ between clutch sizes. Enlarged clutches were incubated longer than controls and reduced clutches. There were, however, no significant differences among clutch sizes in partial or total clutch predation rates. Hatchability of the eggs (proportion of eggs hatching of those present in nests at the end of incubation) was marginally lower in the enlarged clutches (92·5% vs. 100% in the two other groups). Contrary to predicted, hatching success was highest in enlarged clutches. The numbers of hatched eggs calculated from Mayfield estimates of daily nest and egg survival rates were 0·93, 2·10 and 3·14 in three‐, four‐ and five‐egg clutches, respectively. When controlling for egg volume, mean body mass of newly hatched chicks was lower in clutches with five eggs than in other nests. We suggest that the lowered body condition of chicks could outweigh the benefits of laying five instead of four eggs in northern lapwings. Future studies of the selective mechanisms of clutch size in shorebirds should not only focus on the number of young that hatch, but also their quality.

The evolution of egg size in socially polyandrous shorebirds

In classical and multi‐clutch polyandry, females lay multiple clutches during a breeding season for more than one mate. The production of multiple clutches may be energetically demanding. We used comparative analyses to investigate three possible ways of reducing such egg‐laying costs in polyandrous shorebirds: (1) reduction in egg size, (2) reduction in clutch size, and (3) evolutionary increase in female size. Paired comparisons of polyandrous and non‐polyandrous taxa showed that females of polyandrous shorebirds lay smaller eggs than females of closely related monogamous and polygynous species. Directional analyses corroborated this result by indicating a significant decrease in egg size after phylogenetically independent origins of polyandry. The comparative analyses uniformly rejected the two alternatives, i.e. neither clutch size nor female size is related to social mating pattern. We also tested and rejected three alternative explanations for reduced egg size in polyandrous taxa. First, we found no evidence that polyandrous females have evolved smaller egg sizes in response to selection to match smaller size of males, which provide the parental care in these species. Second, reduction in egg size was not related to longer breeding seasons (and hence more opportunity for re‐nesting). Third, reduced egg sizes were also not related to rates of clutch predation (another potential correlate of multiple clutch production). Our results are thus consistent with the hypothesis that selection for reducing laying costs explains small egg size in socially polyandrous shorebirds.

Seasonal Reproduction of a Neotropical Frog, the Cave Coquí (Eleutherodactylus cooki)

The aim of this study was to evaluate factors contributing to seasonal reproductive variation in a Neotropical frog, the Puerto Rican cave coquí (Eleutherodactylus cooki). There was a relatively small seasonal variation in ambient temperature and relative humidity in the caves occupied by E. cooki. Nonetheless, the reproduction of E. cooki was strongly seasonal, with clutches produced from March to November, and no additional clutches deposited from December to February. This seasonal reproductive pattern may reflect a response to small changes in the thermal environment, because the frequency of clutch production and number of clutches deposited per nest site increased when air temperature was warmest (during the middle of the breeding season). Clutches occurred singly (71% of all clutches) or in groups of two (23%), three (6%), or four (< 1%). The median clutch size was 15 (range = 1–29). Significant egg mortality occurred, despite male attendance of nest sites. The average rate of egg mortality was 16% per week. Extrapolating to a hatching period of 3.5 weeks, 44% of produced eggs survived to hatching. It appears that combined effects of weak environmental variation, clutch predation, and male parental care substantially influence the reproductive output of E. cooki.

Nest‐site selection, egg pigmentation and clutch predation in the ground‐nesting Namaqua Sandgrouse Pterocles namaqua

Nest survival can, among a variety of factors, depend on nest-site complexity and concealment, and clutch crypsis. Nest-site selection by Namaqua Sandgrouse Pterocles namaqua was strongly non-random. Nests were sited within a local concentration of objects, most of them less than 15 cm high and concentrated within 30 cm of the nest centre. Nest-to-object orientation was random, indicating that the nest was sited close to objects neither for shade nor shelter from prevailing winds. A stepwise logistic regression analysis, using nine different object type, height and distance category totals as variables of nest-site complexity and concealment, found no effect of these variables on nest fate (survival vs mammal predation). A random-walk model simulating the foraging movements of a small mammal predator raised the possibility that the high level of nest predation suffered by Namaqua Sandgrouse was largely incidental (i.e. random). Namaqua Sandgrouse eggs were highly variable in appearance, but intra-clutch variability was less than that between clutches of different individuals. Intra-clutch diversity in pigment cover the number of wreathed eggs, the dominant pigment pattern, and the overall shade of the clutch (light/dark) did not affect clutch survival. However, clutches exhibiting diversity in background colout, pigment pattern or pigment intensity between eggs survived significantly better than clutches whose eggs were uniform for these variables suggesting there is some selection for clutch crypsis through visual diversity.

Pairing status of male willow ptarmigan: is polygyny costly to males?

Polygyny appears to be beneficial for males, yet comprises less than 20% of all pair bonds formed by male willow ptarmigan,Lagopus lagopus.This study tested whether polygyny was costly to males. Polygynous males defended larger territories than monogamous and unpaired males and were more likely to be adults than males of other pairing status. Pairing status changed throughout the life of some males. Naturally polygynous males were in better body condition in the early part of the breeding season than other male types, and unpaired territorial males had the lowest condition. Naturally polygynous males had a tendency to lose the least amount of body mass over the season. Naturally polygynous and monogamous males had larger combs than males of other pairing status. Polygynous males had higher reproductive success, similar survival and similar future reproductive success compared with monogamous and unpaired territorial males. Even in years of high clutch predation, and accounting for higher levels of extra-pair paternity in the clutches of polygynous males, naturally polygynous males were more successful than other male types. A group of experimentally polygynous males (i.e. they became polygynous because of a male removal experiment) had similar reproductive success to naturally polygynous males, but lower overwinter survival than other male types. These results suggest that naturally polygynous males were older and ‘better’ than other males and this allowed them to defend larger territories and attract more than one female. Males that became polygynous only as a result of our experiment, however, appeared to suffer costs from this increased breeding effort.

Effects of Research Activities on Nest Predation in Arctic-Nesting Geese

I examined the effects of nest visits and markers on nest predation in black brant (Branta bernicla nigricans) and lesser snow geese (Chen caerulescens caerulescens) at Anderson River, Northwest Territories, Canada. In 1993, clutch size at the end of incubation was 0.6 egg less (P = 0.020) at brant nests and 0.4 egg greater (P = 0.032) at snow goose nests, visited repeatedly, than at nests visited only once. I found no effect of nest visits on clutch size of brant (P = 0.500) in 1991. There was weak evidence that nest markers increased nest failure (P = 0.052) among snow geese in 1991 but markers did not influence the frequency of complete (P = 0.700) or partial (P = 0.232) clutch predation in brant in 1991 or in either species in 1993 (P > 0.117 in all cases). Nest markers did not affect clutch size or nest fate in these species, and were useful for identifying nests from a distance.

Effects of clutch size manipulations on reproductive behaviour and nesting success in the cooperatively breeding Bell Miner (Manorina melanophrys)

An experimental manipulation of clutch size was carried out on a wild population of the cooperatively breeding Bell Miner (Manorina melanophrys, Meliphagidae) to assess which factor(s) limit clutch size in this species. Results provide some support for the ‘trade-off hypothesis’ since there is a cost of reproduction for the breeding female in terms of loss of body mass. The breeding female performs most of the nestling care. Clutches of three eggs are also laid during the mid-breeding season which is the period most favourable for breeding (i.e. nestlings grow faster). This evidence also supports the ‘intrabrood competition hypothesis’. Clutches that have lost an egg were more likely to be deserted; this may be an antipredator strategy since partial clutch predation has been recorded in the field. Nest predation was high in this study (64.9%), suggesting that many small clutches may be a strategy to decrease the effect of nest predation on reproductive success over the whole breeding season (‘nest predation hypothesis’). Both the ‘trade-off hypothesis’ and the ‘nest predation hypothesis’ may apply in this case since they are not mutually exclusive. The size of the attending group did not greatly affect reproductive success in the short term, although if both age structure and size of the group are taken into account, reproductive success can be better predicted.

Clutch Predation, Cover, and the Overdispersion of Nests of the Willow Ptarmigan

Clutch predation is generally considered a selective force in nest site selection by gound—nesting birds. We examined characteristics of vegetation and cover around nest sites and inter—nest spacing for Willow Ptarmigan (Lagopus lagopus) to determine whether choice of nest location influenced probability of predation. Types of vegetation around successful and depredated nests and random points were similar. However, hens chose sites that had more lateral and overhead cover than that found at random points. Amount of cover was similar for successful and depredated nests. We Suggest that hens choose cover to deter predation on themselves or to reduce energy costs of incubation. Inter—nest distances were larger and nests were located closer to the centroid of the territory than if nest sites had been selected at random. Hens that renested placed their nests farther from their first nests but not farther from neigboring nests than expected if they had located them at random. Probability of a clutch being preyed upon was not related to its distance from a clutch that had previously been depredated. We conclude that, for the breeding densities that we encountered, nests were spaced far enough apart to deter area—restricted search by predators. Predation may have been a factor causing over—dispersion of nests in the past, but current selection may be masked by other factors such as the hen's behavior or stochasticity.

The adaptive significance of spawning synchronization in the Caribbean damselfish Stegastes dorsopunicans (Poey)

In the dusky damselfish Stegastes dorsopunicans (Poey) two levels of population reproductive synchrony exist. At one level, there is a broad peak in spawning activity every month between full moon and new moon. Within these lunar peaks of spawning activity, spawning is concentrated on specific days, often flanked by days with no spawning, resulting in spawning peaks within the broader monthly peak. On days of higher spawning activity, more females spawn in a nest that receives eggs, and the average number of eggs a male receives is higher. Larger clutches suffer lower mortality from both complete and partial clutch predation by the father (filial cannibalism). Males are more likely to eat complete clutches when the clutches are small. Fathers also appear to eat a subset of their clutches, but the number of eggs eaten is independent of clutch size, so larger clutches have a lower percentage mortality from partial clutch loss. A separate source of clutch mortality, complete clutch loss to nocturnal predators, affects all clutches equally and does not select for large clutch size and spawning synchrony. The differences in rates of clutch cannibalism between synchronized and nonsynchronized days provides an adaptive explanation for spawning synchrony in this noncolonial fish; female synchrony may have evolved in response to differential egg mortality.

The Roles of Predation, Food and Agricultural Practice in Determining the Breeding Success of the Lapwing (Vanellus vanellus) on Upland Grasslands

SUMMARY (1) Lapwing breeding densities decreased by 74% on pastures and 56% on meadows following agricultural improvement of upland grasslands. Fledgling production was 63% lower on improved relative to unimproved areas. Three possible hypotheses to account for these decreases have been examined: (i) increased predation of clutches; (ii) a reduction in invertebrate food and/or its availability; (iii) a greater destruction of clutches by agricultural machinery and/or trampling by livestock. (2) Overall, 76% of clutches on improved pastures were taken by predators compared to only 47% on unimproved pastures. Increased predation largely accounted for the reduced breeding success on improved pastures relative to unimproved pastures. (3) Although land improvement resulted in decreases in several of the invertebrate groups upon which lapwings feed, reduced food availability had only minor effects on breeding success. (4) Clutch destruction during agricultural activities was almost four times higher on

Clutch Size Variation and Patterns of Attrition in Fecundity of Willow Ptarmigan

Using a compartmental life history model we comapred clutch sizes and patterns of attrition in fecundity from egg to reproductively mature offspring for both first nests and replacement clutches in two populations of Willow Ptarmigan (Lagopus lagopus) at La Perouse Bay (LPB) and Chilkat Pass (CP) in northern Canada. From her initial clutch of 10.8 eggs, a female at LPB fledged on average 2.9 offspring, a reproductive efficiency of 27%. Of hens losing first clutches, 83% renested and these subsequent clutches contributed 23% to annual fecundity. A female at CP laid an average of 8.1 eggs in the first clutch and fledged 3.0 (37%) offspring. About 67% of females renested if they lost first nests, and renests contributed 14% to net annual fecundity at CP. Over 4 yr at LPB, clutch size, patterns of attrition in fecundity, and return rates of females did not vary, but at CP all measures of fecundity, total nest failure, and female return varied dramatically over 7 yr. Despite the larger clutch size of LPB hens, the overall mean values of net annual fecundity and the rate of return (a measure of survival) of females between years did not differ between the two popualtions. However, patterns of attrition in fecundity differed greatly between sites. Differences in clutch size and renesting ability between LPB and CP may be caused by differences in resource availability or differences in predictability of clutch predation. Clutch size and renesting rate may be higher at LPB to cope with high and predictable egg loss. Clutch loss at CP was variable and unpredictable, and the lower clutch size and renesting rate there may have developed because of lower food availability. We suggest ways to test these hypotheses.

Intra-seasonal decline of clutch size in Lesser Snow Geese.

Different mechanisms proposed to explain the intra-seasonal decline in clutch size of Lesser Snow Geese (Anser caerulescens caerulescens) were tested at the La Perouse Bay colony, Manitoba, Canada. Ovary examination of females collected after laying revealed that the actual number of eggs produced per female decreased over the laying period. This finding eliminates nest-parasitism, partial clutch predation and renesting attempts as sufficient explanations for seasonal clutch size decline. Follicular atresia induced by reserve depletion was also rejected since its occurrence was similar among early and late nesters. The decline in clutch size was observed within age-classes, and therefore age effects on clutch size and laying date per se do not account for the observed relationship. Clutch size and laying date were respectively positively and negatively correlated with the amount of nutrient reserves in females at the onset of laying, and also covaried within individuals observed breeding in several seasons. Laying date repeatability was estimated at 0.22. It is postulated that the seasonal decline in clutch size results mainly from a positive feed-back of female's nutrient reserves on the hormones controlling ovary development. Hatching synchrony or shortness of the breeding season may be the ultimate factors responsible for the intra-seasonal clutch size decline in Lesser Snow Geese.

Nest Site Selection and Clutch Predation in the Snowy Plover

Nest Site Selection and Clutch Predation in the Snowy Plover

Saqueo y depredación de nidadas de tortugas marinas, durante las temporadas 2003 a 2012, en seis playas del Golfo de Paria, Venezuela

Poaching and predation of sea turtle clutches, during the 2003 and 2012 seasons, on six beaches of the Paria Gulf in Venezuela. Looting and predation of nests are among the major threats to marine turtles. Six beaches of Paria Gulf, northeastern Venezuela, have been protected and had a reduction of clutch poaching and predation on leatherback (Dermochelys coriacea), green (Chelonia mydas), and hawksbill (Eretmochelys imbricata) turtles. During ten years (2003-2012) of nesting seasons (March through October) the six beaches were observed for nesting, poaching and predation. The most frequent losses are caused by poaching, followed by the common fox (Cerdocyon thous), opossum (Didelphis marsupialis) and tamandua (Tamandua tetradactila). The most poached beach is Silvano, followed by Los Garzos (main nesting beach at the site) and Cerezo, which is more distant from the conservation team activity.