Predation on wader nests in Europe

The population declines of waders in Europe are widely considered to have resulted from habitat loss and degradation due to agricultural changes. However, recent empirical evidence suggests that levels of predation on wader nests are unsustainably high in many cases, even in some situations where breeding habitat is otherwise favourable. We review the published and 'grey' literature on nest predation on waders in Europe and quantify the relative importance of the major predators. Nest cameras offer the least biased method of identifying and quantifying nest predators. A small number of camera studies, in combination with others utilizing nest temperature loggers, indicate that nocturnal/mammalian predators make the largest contribution to wader nest predation. More than half of site-years or studies reviewed reported clutch failure rates of over 50% attributable to predation alone, a rate that is likely to be associated with declining populations, although parameters such as chick and adult survival will also affect population trends. Correlates of wader nest predation are documented, with time of season, field type and management, distance to habitat/field edge, wader nest density, and abundance of mammalian predators being most consistently identified. Future directions of research into wader productivity are discussed, and we suggest that studies quantify additional life-history parameters such as chick survival, as well as examining the predator community, wherever possible.     

Nest predation of Common Pheasants Phasianus colchicus

The Common Pheasant Phasianus colchicus is currently the most abundant, widespread and economically important gamebird in Europe. The Game and Wildlife Conservation Trust has undertaken several recent studies of Pheasant breeding ecology to improve the management of this species. Although predation is often the most important cause of nest failure in declining ground-nesting birds in agricultural landscapes, the causes of predation and the identity of predators are often unknown. In this paper, we analyse data from approximately 450 nests of radiotagged hen Pheasants collected from six sites between 1990 and 2003 and present results on the fate and survival rates of Pheasant nests in relation to habitat, predation control and other covariates. Survival rates during the laying stage and incubation stage were 28 and 37%, respectively, and overall nest survival was 10%. Nest predation rates were significantly lower on two sites where intensive predation control was undertaken than on four sites with only low levels of predation control. Red Foxes Vulpes vulpes and corvids were the most important nest predators, accounting for at least half of all predation events. We assess these results in the context of other ground-nesting farmland birds.     

Breeding biology and breeding success of the Lesser Grey Shrike Lanius minor in a stable and dense population

The Lesser Grey Shrike Lanius minor is highly endangered throughout Europe, having declined markedly in abundance and range. Long-term changes in climate and agricultural practices have been identified as the main reasons for its decline. To determine which factors influence short-term changes in breeding success, we examined several aspects of its breeding biology. Our investigation revealed that our study area bears a large and stable population of this species. In 1996 and 1997, we recorded 84 and 77 breeding pairs in an area of 20 km², with an average of 4.20 and 3.85 pairs/km² respectively. Data on breeding density, clutch size and fledging success from 1989 to 1997 (excluding 1992) indicate a stable breeding population with a constant high breeding success. Reproductive success declined through the season, mainly through seasonal variation in clutch size rather than chick mortality. However, breeding success was generally high (69% and 79% of the nests produced chicks], with low hatching failure and few nest losses. The main cause of breeding failure was nest predation (at least 50% of nest losses), mainly by magpies (at least 66% of depredated nests). Although in this population the Lesser Grey Shrike tends to aggregate in clusters, breeding density had no obvious effect on breeding success and nest predation.     

The reproductive biology of the White-necked Picathartes Picathartes gymnocephalus

The reproductive biology of the White-necked Picathartes Picathartes gymnocephalus , a threatened species endemic to the Upper Guinea rainforest of West Africa, was studied in Sierra Leone from 1990 to 1996. The modal clutch size was two (mean 1.92) eggs. Incubation averaged 20 days and the nestling period 25 days. Nesting success (probability of eggs laid surviving to fledge) was 22.9%. Only 0.44 chicks fledged per nesting pair. The main known causes of nest mortality were predation and infanticide. Nestlings fledged when almost 30% smaller than adult size. A life-table indicates that populations in Sierra Leone could be declining slowly. Alternatively, White-necked Picathartes could be very long-lived (annual adult survival could be greater than 90%), in which case populations would be self-sustaining.     

Changes in stream benthic organic matter following watershed disturbance

Benthic organic matter was collected quarterly from streams draining a 9-yr-old clearcut, an 18-yr-old "old-field", a 25-yr-old successional forest, and two reference watersheds at Coweeta Hydrologic Laboratory in the Appalachian Mountains of North Carolina. USA. Samples were separated into large benthic organic matter (LBOM >1 mm) and fine benthic organic matter (FBOM <1 mm). An additional survey of large (>5 em diam.) and small (1–5 cm diam.) wood was conducted. Standing stocks of LBOM ranged from 124 to 235 g AFDM m⁻² (ash tree dry mass) and were significantly higher in streams draining reference watersheds and the successional forest than in either the recent clearcut or old-field. Reference sites exhibited LBOM peaks in late autumn and spring. No seasonal patterns were observed in disturbed streams. Standing stocks of FBOM averaged 113 to 387 g AFDM m⁻², and the stream draining the successional forest had significantly higher FBOM levels than the other sites. In reference streams, FBOM abundance peaked in spring. In disturbed streams, FBOM standing stocks were highest in summer or late autumn. Standing stocks of large wood ranged from 0 to 3956 g AFDM m⁻² and were significantly higher in the reference streams than in streams draining the old-field or successional forest. Small wood averaged 11 to 342 g AFDM m⁻² and was significantly lower in the stream draining the old-field than at the other sites. Comparisons of organic matter inputs with standing stocks indicated that disturbed streams at Coweeta receive less material and process it faster than reference streams. Disturbed streams also appear to be less retentive than reference streams and exhibit a gradual decline in FBOM during the winter when large, long-duration storms combined with low particle generation rates deplete accumulated FBOM.     

An estimate of the sustainable rate of shell extraction from the Dutch Wadden Sea

1. Shell production by cockles Cerastoderma edule was studied to examine whether or not the present licensed rate of shell extraction in the Dutch Wadden Sea exceeds the current rate of shell addition to the exploitable stocks.
2. Long-term data on numbers of cockles and weights of their shells were used to estimate their annual production on Balgzand, a 50-km² tidal flat area in the western-most part of the Wadden Sea. During the 1969–97 period, it amounted to an average of 125 g m^–2, including 107 g m^–2 of shells large enough to be exploitable for shell-lime fishery.
3. The very irregular annual recruitment of cockles was the main cause of the wide 95% confidence limits (74 and 140 g m^–2 year^–1) of this 28-year estimate. Moreover, high mortality rates in severe winters substantially reduced production per recruit in some year classes.
4. About one-third of the estimated production does not reach exploitable stocks, because it is fragmented by birds (particularly eider ducks), permanently buried in the sediment, or removed by the fishery for live cockles.
5. During the last few decades, the estimated mean amount added annually to the exploitable stocks was 88 million kg or 132 000 m³ of large cockle shells. This amount compares favourably with the current annual level of removal of 134 000 m³ of shells, three-quarters of which are cockles.
6. Even at temporarily lower production rates, the exploitation of shell stocks at its present rate is not expected to lead to a rapid exhaustion of the existing stocks in the tidal inlets of the Dutch Wadden Sea, as these stocks will be in the order of a few million m³.     

The prevalence of non-breeders in raptor populations: evidence from rings, radio-tags and transect surveys

Age-specific survival and breeding (ASSAB) models were developed with data from 146 common buzzards ( Buteo buteo ) radio-tagged in southern Britain during 1990–1998, in a 120-km2 study area that had on average 25 egg-laying pairs. Survival checks were aided by philopatric behaviour and a maximum annual tag failure rate of 7%: minimum survival rates, that were estimated by assuming death of buzzards with lost tags, were close to maximum rates that were estimated using only the recorded deaths. First-year survival rate estimates for 35 buzzards fitted in 1990–1991 with 25–30-g backpack radios were 69–74% (minimum-maximum), close to the 61–71% for 16 buzzards with 12-g tail-mount radios; the backpacks transmitted for 2–4 yr. Overall survival rates were 66–73% in the first year, 91–97% in the second and 88–91% thereafter. Survival estimates from 288 recent British ring recoveries were lower in the first and second years, at 55% and 75%, but similar (88%) thereafter. Most deaths were from natural causes (40%) or interaction with artefacts (36%). ASSAB models, from radio-tracking and the observed 1.71 young clutch−1, predicted breeding by 16–21% of all the buzzards present in spring, or up to 25% with the minimum likely productivity of 1.4 young clutch−1 or 12% net emigration. Ringing data predicted breeding rates of 33–38%. The models were tested with density data from nest surveys and new radio-corrected-transect and truncation-mark-resighting estimates of buzzard numbers. Surveys in autumn and late winter estimated breeding rates of 21–25%. The high non-breeder density in spring, of three other buzzards for each paired bird with eggs, has important implications for understanding evolutionary fitness, predation and population ecology.     

Demographic parameters of reintroduced grey partridges in central Italy and the effect of weather

Grey partridge populations declined in Europe from mid-1950s onwards mostly due to modifications of agricultural cropping. In Italy, the decline was even more dramatic because of over-hunting and restocking with allochthonous birds. We carried out a research on a re-introduced population in Central Italy from 1995 to 2005, with the aim of evaluating the reintroduction success and separating the intrinsic and external factors influencing year-to-year changes in partridge density with particular respect to the weather. Average spring density was 4.5 pairs per square kilometre (SD?=?1.52); our population reached a peak few years after the reintroduction and then declined. Brood production rate was close to that of declining European populations (average 33.9%; SD?=?10.21), and chick survival rate (average 40%; SD?=?17.61) determined the change of breeding abundance from year t to year t?+?1. Our population seemed to be mainly affected by brood production and chick survival rates and by the weather; in particular, higher early winter and spring temperatures increased breeding density whilst higher early summer temperatures decreased brood production rate.     

Grey-faced petrel (Pterodroma gouldi) productivity unaffected by kiore (Pacific rats,Rattus exulans) on a New Zealand offshore island

Burrow-nesting seabird populations are vulnerable to predation by introduced rats, because of their nesting habits and slow life histories. We investigated whether control of kiore (Pacific rats, Rattus exulans) by removal trapping, and during an unsuccessful community-led island-wide eradication attempt, had any effects on nest survival of grey-faced petrels (Pterodroma gouldi) on Ririwha (Stephenson Island), northeastern New Zealand. We compared nest survival between two plots at which rats were trapped and six un-trapped plots in 2010, as well as at all plots during and after the poisoning programme in 2011–2012. Neither mean rates of breeding burrow occupancy nor nest survival differed between trapped and un-trapped plots in 2010. We found no significant differences between years or between plots throughout the poisoning programme. Extrapolation of daily nest survival rates to the full 172-day combined egg and chick period gave an estimate of mean annual productivity for all plots combined of 0.285 (95% confidence interval 0.252–0.318), which is higher than on comparable predator-free islands. Although the absence of a detectable effect of kiore on breeding grey-faced petrels on Ririwha is reassuring, we can be less sure that smaller burrow-nesting seabirds on the island are secure.     

Hatch Success and Recruitment Patterns of the Bog Turtle

Researchers suggest that several bog turtle (Glyptemys muhlenbergii) populations in North Carolina, USA, are in decline and have few remaining individuals and low annual survival probability. Most populations are dominated by older adults with few juveniles encountered; however, the proportion of juveniles encountered in 2 populations is higher. It is unknown why the juvenile:adult ratio varies among populations. We conducted a nest monitoring study in 2016 and 2017 to test the hypothesis that sites with fewer juvenile encounters would be where nest predation was highest. We documented the fate of 272 eggs from 83 nests encountered across 7 sites in North Carolina. On average 28% of eggs hatched across all sites over both years, but we observed large variation in hatch success among sites. Predation by mesopredators and small mammals was the primary cause of nest failure. The probability of nest predation decreased with greater emergent vegetation density and increased with greater distance to the edge of the wetland. Cooler temperatures, which prolonged incubation and thus increased predation risk, may also hinder recruitment at higher elevation sites. Our observations are consistent with the hypothesis that nest predation would be highest at sites with fewer juvenile encounters. Managers concerned about low bog turtle recruitment rates should consider the role of nest predation and the potential benefits of management that increases hatch rates. © 2020 The Wildlife Society.     

Factors that influence vital rates of Seaside and Saltmarsh sparrows in coastal New Jersey,USA

As saltmarsh habitat continues to disappear, understanding the factors that influence the population dynamics of saltmarsh breeding birds is an important step in the conservation of these declining species. Using 5 yrs (2011–2015) of demographic data, we evaluated and compared apparent adult survival and nest survival of Seaside (Ammodramus maritimus) and Saltmarsh (A. caudacutus) sparrows at the Edwin B. Forsythe National Wildlife Refuge in New Jersey, USA. We determined the effect of site management history (unditched vs. ditched marshes) on adult and nest survival to aid in prioritizing future management or restoration actions. Apparent adult survival (61.6%, 95% CI: 52.5–70.0%) of Seaside Sparrows averaged > 1.5 times greater than that of Saltmarsh Sparrows (39.9%, 95% CI: 34.0–46.2%). Nest survival and predation and flooding rates did not differ between species, and predation was the primary cause of nest failure for both species. Apparent adult survival and nest survival did not differ between unditched and ditched marshes for either species, indicating that marsh ditching history may not affect the quality of breeding habitat for these species. Because predation was the primary cause of nest failure for both species in New Jersey, we suggest that future studies should focus on identifying predator communities in salt marshes and the potential for implementing predator‐control programs to limit population declines.     

Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.     

Population ecology of Trituras cristatus and T. vulgaris (Urodela) in SW Sweden

The population ecology of newts was investigated between 1969 and 1974 in two localities near Gothenburg, SW Sweden: the Gunnebo park pond (about 300 m²) where Triturus cristatus Laurenti and T. vulgaris L. are sympatric, and a rock-pool (6 m²) in Billdal with only T. vulgaris. At Gunnebo, a population of about 350 breeding T. cristatus was found with about as many males as females but males being more aquatic than females. An annual survival of 0.7–0.8 was estimated for the adults. The T. vulgaris population at the same locality was estimated to about 250–300 breeding adults with a sex ratio possibly in favour of males. The survival of adults was found to be extremely low and a very small percent of the adults seems to breed more than once. The Billdal T. vulgaris population was estimated to contain nearly 70 breeding adults with a sex ratio very near to 1:1. The annual survival of adults was found to be 0.5. The different survival of the two T. vulgaris populations are discussed with particular reference to predation. The age at which newts breed for the first time seems to vary; for T. vulgaris five years may well be the normal age. Factors that may limit the sizes of the populations, possible reasons for differences in frequency of occurrence in water, and possible predators are discussed.     

Survival rates, causes of failure and productivity of Skylark Alauda arvensis nests on lowland farmland

This paper analyses data from 995 Skylark Alauda arvensis nests found on lowland farms in southern England from 1996 to 1998. The majority of recorded nest failures were caused by predation except in agricultural grass, where trampling and agricultural operations were equally important. Nest survival rates varied between crop types, nests in cereals being around twice as likely to succeed as nests in grass or set-aside. In cereals, nest survival rates increased with increasing distance from the nearest tramline and declined over the course of the breeding season. Predator control also had a significant independent effect on nest survival rates. On one farm where many other factors were held constant, a highly significant increase in nest survival rates from 12.3% to 40.7% coincided with the introduction of intensive predator control, which also appeared to bring forward mean laying dates. Most environmental factors explaining significant variation in nest survival rates did so only at the chick stage. The mean number of chicks produced per nesting attempt was 1.26 in cereals, 0.78 in set-aside and 0.63 in grass, the differences being due primarily to variation in nest survival rates. Low densities of Skylark territories in cereal crops are not therefore the consequence of low breeding success at the scale of the individual nest and probably reflect limitations on the number of attempts made in a season. Measures taken to improve the attractiveness of cereal crops as a nesting habitat for Skylarks, and beneficial changes in grassland management, are likely to increase overall productivity.     

The populations of fish in the River Tees system on the Moor House National Nature Reserve, Westmorland

The age, growth, population densities and annual production of an isolated population of brown trout ( Salmo trutta L.) and bullhead ( Coitus gobio L.) were investigated over a 5 year period in Trout Beck in the northern Pennines. Additional data were obtained from two other sites; Great Dodgen Pot Sike and the River Tees.
Trout growth rates were low, particularly in Dodgen Pot Sike, but ages up to VIII were recorded. Bullhead growth rates were similar to those in the Tees at Cow Green (Crisp et al. , 1974), though the Moor House bullheads had a higher survival rate. Population densities of trout ranged from 0.10–0.22/m², with a fry contribution of 0.80%. The bullhead population in Trout Beck was sparse, generally 0.1/m², though an 0 group value of 0.46/m^a was estimated in 1967. At Tees Bridge values ranged from 2.5–7/8/m². Most trout matured by age III, though in Great Dodgen Pot Sike only half of the females were mature at age IV.
Annual production was estimated from Allen graphs. Trout production ranged from 1.02–3.50 g/m²/year, the fry contributing up to 51.5% of the total. A value of 0.48 g/m²/year was obtained for bullheads in the Trout Beck system in a year of good recruitment, whilst bullhead production at Tees Bridge was 7.43 g/m²/year, with fry and I group contributing 48.7 and 37.5% respectively. The high survival rate, irregular recruitment, and poor growth of these high altitude populations is discussed. Growth and reproductive peculiarities of the Great Dodgen Pot Sike trout are also discussed.     

Interannual variation in the breeding biology of the Antarctic prion Pachyptila desolata at Bird Island, South Georgia

Interannual variation in aspects of the breeding biology of Antarctic prions was studied for three summers (1989–1992) at Bird island, South Georgia. Egg size, mass and incubation period remained constant. Laying, hatching and fledging were significantly delayed and less synchronous in 1991/92 (range of laying dates 51 days compared to 10–15 days in the two other seasons). This was due to an unusually cold and protracted winter, with ice blocking burrows into the spring, restricting availability of nest sites. Brooding lasted longer in 1991/92 but the overall fledging period was unchanged. Skeletal growth rates did not vary amongst years; growth in mass was slower in 1989/90 but fledging mass was similar in all three years. In 1989/90 and 1991/ 92 later hatched chicks grew (in mass) faster. The survival of chicks from hatching to fledging did not vary amongst years or with hatching date. Feeding frequency was similar between years, once allowance had been made for starlit nights. Thus late and asynchronous breeding in 1991/92 did not result in reduced breeding success either through predation or starvation.
Crustaceans formed 98–99% of the mass of the identifiable portion of regurgitated food samples. Significant annual variation was found within these crustaceans with the presence of krill (least in 1990/91) being inversely related to that of amphipods and copepods. There was no relationship between diet composition and chick growth or survival. Other seabird species, lacking the morphological specialization for feeding on copepods and amphipods, had very low breeding success in 1990/91, when krill was scarce.     

Population dynamics of Bythotrephes cederstroemii in south-east Lake Michigan 1995–1998

1. Population characteristics (density, size, reproductive patterns) of the predatory cladoceran Bythotrephes cederstroemii in south-east Lake Michigan were monitored at an offshore station (110 m) in 1995–98 and at a nearshore station (45 m) in 1997–98.
2. The mean density of B. cederstroemii at the offshore station was generally highest in July–September (145–914 m⁻²) and at the nearshore station in October–November (168–1625 m⁻²). In 1995 and 1998, density was also high at the offshore station in November (211–284 m⁻²). Fish predation may limit B. cederstroemii in nearshore regions in the summer. The maximum annual densities of B. cederstroemii for 1995–98 were generally similar to those reported from the late 1980s, when the species arrived in Lake Michigan.
3. Body size increased rapidly each year to a maximum in August. Thereafter, body size declined and converged for stage-2 and 3 individuals, suggesting food scarcity or size-selective fish predation was affecting large individuals.
4. Most reproduction occurred asexually (90%), and by stage 2 or 3 females (99%). Asexual brood size was highest when B. cederstroemii first appeared each year, and decreased in August, when larger neonates were produced. There appeared to be differences in reproductive mode for stage 2 and 3 females, with a higher percentage of stage 2 females reproducing sexually.     

Early survival and growth in populations of grayling with recent common ancestors—field experiments

Among eight populations of grayling Thymallus thymallus that shared common ancestors 8–28 generations earlier, mean egg mortality ranged between 1·2 and 59·8%; mortality during yolk sac absorption was low (0middot;0–8middot;0%) and mean survival to swim-up was high (90–97%), with two exceptions (20% and 50%). Survival probabilities differed significantly among populations, even after statistically adjusting for size at swim-up and water depth, water velocity, gravel size and temperature. Development time from fertilization to first observed swim-up was significantly different among populations, ranging between 27 to 40 days, or 264 to 280 degree-days. Mean specific growth rates during the first external feeding period varied between 1·2 and 2·0% day^-1 among populations. Population-specific growth rates were independent of temperature. Rates of divergence were of the same order as in other salmonid studies showing rapid evolution. The phenotypic differences may be due partly to genetic differentiation among the populations.     

Managing multiple vital rates to maximize greater sage-grouse population growth

Despite decades of field research on greater sage-grouse, range-wide demographic data have yet to be synthesized into a sensitivity analysis to guide management actions. We reviewed range-wide demographic rates for greater sage-grouse from 1938 to 2011 and used data from 50 studies to parameterize a 2-stage, female-based population matrix model. We conducted life-stage simulation analyses to determine the proportion of variation in population growth rate (λ) accounted for by each vital rate, and we calculated analytical sensitivity, elasticity, and variance-stabilized sensitivity to identify the contribution of each vital rate to λ. As expected for an upland game bird, greater sage-grouse showed marked annual and geographic variation in several vital rates. Three rates were demonstrably important for population growth: female survival, chick survival, and nest success. Female survival and chick survival, in that order, had the most influence on λ per unit change in vital rates. However, nest success explained more of the variation in λ than did the survival rates. In lieu of quantitative data on specific mortality factors driving local populations, we recommend that management efforts for greater sage-grouse first focus on increasing female survival by restoring large, intact sagebrush-steppe landscapes, reducing persistent sources of human-caused mortality, and eliminating anthropogenic habitat features that subsidize species that prey on juvenile, yearling, and adult females. Our analysis also supports efforts to increase chick survival and nest success by eliminating anthropogenic habitat features that subsidize chick and nest predators, and by managing shrub, forb, and grass cover, height, and composition to meet local brood-rearing and nesting habitat guidelines. We caution that habitat management to increase chick survival and nest success should not reduce the cover or height of sagebrush below that required for female survival in other seasons (e.g., fall, winter). The success or failure of management actions for sage-grouse should be assessed by measuring changes in vital rates over long time periods to avoid confounding with natural, annual variation. © 2011 The Wildlife Society.     

Densities and energetics of two streamliving larval populations of Sericostoma personatum (Trichoptera)

Two populations of Sericostoma personatum Spence were studied during one year in two first order woodland streams, varying in water flow and temperature regime. The life cycles look two and three years, respectively.
Numbers in drift varied with water flow, and daily elimination rates of about 1% due to catastrophic drift were found in one of the streams. Differences in elimination rates between the two populations are discussed in relation to predation, catastrophic drift, and quantity of food present during the year.
The production was about 0.9 g AFDW m^-2 yr^-1 in both streams, 20–22% of which was production of cases. P/B ratios were 2.4 and 3.8, and reflect differences in life cycle.
Total potential leaf consumption was estimated to about 50 g AFDW m^-2 yr^-1 in both streams, which makes up about 10% of yearly leaf input. The seasonal pattern of the consumption is discussed in relation to biomass, temperature and leaf input. There was little agreement between the patterns of leaf input and leaf consumption.