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1.
In Central Europe, massive losses in species richness of breeding birds have been documented in the last decades, but the
question arises whether species richness is currently still decreasing or again increasing due to conservation efforts. In
this study, we investigated regional and local species richness as well as mean number of breeding pairs and mean biomass
per tetrad over a period of some 20 years at Lake Constance. Three quantitative censuses of 303 tetrads (2 × 2 km2) repeated at 10-year intervals (1980–1981, 1990–1992, 2000–2002) revealed an increase in regional species richness (total
number of breeding species). At the same time, however, a strong decline in local species richness (number of breeding species
per tetrad), number of breeding pairs, and estimated biomass were observed. Changes of species richness differed markedly
between Nonpasserine and Passerine birds. Whereas species richness of Nonpasserines remained constant from 1980 to 1990, and
even increased between 1990 and 2000, that of Passerines decreased in both periods. This indicates that effects of conservation
efforts apparently eclipse more general effects of climate and habitat change in Nonpasserines. The massive abundance and
biomass losses observed in formerly common Passerine species are not compensated by gains in populations of Nonpasserine species.
The results of the three bird censuses at Lake Constance imply that ongoing habitat degradation and human impacts as well
as increasing effects of climate change are the main drivers of the observed population changes. 相似文献
2.
Kieran Lawton Graham Robertson Roger Kirkwood José Valencia Roberto Schlatter David Smith 《Polar Biology》2006,29(3):229-238
The Diego Ramirez Islands lie 60 nautical miles southwest of Cape Horn and are the breeding site for three species of burrowing
seabirds: blue petrels (Halobaena caerulea), common diving petrels (Pelecanoides urinatrix) and sooty shearwater (Puffinus griseus). Burrowing seabirds are highly vulnerable to predation by introduced vertebrate pests, and Diego Ramirez is an important
breeding site because it is one of a few remaining subantarctic island groups with no introduced predators. Diego Ramirez
is the only known breeding site for blue petrels in the southeast Pacific region, holding about 80% of the global population
of that species, and with a population ten times larger than any other population in the world. We estimated the population
size in 2002, using a novel application of the distance sampling technique to determine burrow density, and a burrow-scope
with excavations to determine occupying species. We found that density was correlated with slope angle and soil wetness. Burrow
densities in flatter terrain with drier soils were 2.03 burrows/m2 (95% confidence intervals: 1.82–2.27) and 1.11 burrows/m2 (0.84–1.48) in steeper terrain with wetter soils. The occupation rate of burrows were significantly different between habitat
types (t=2.74, d.f. 11, P<0.05); in flatter drier habitats the proportion of burrows that led to a nest was 0.85 (0.74–0.96), in steeper wetter habitats
this decreased to 0.64 (0.50–0.78). We used a digital elevation model to calculate true area rather than planar area for the
two habitat types on the main island of Bartolome, and charts to calculate planar area for the remainder of the archipelago.
There were 1.35 (1.15–1.54) million pairs of blue petrels and 99,000 (65,000–134,000) pairs of common diving petrels on the
archipelago. These are similar figures to those from the only previous estimate, made in 1980. We found breeding sooty shearwaters
for the first time, and estimated a population of several thousand pairs. We emphasise the facility of distance sampling as
an unbiased technique with practical advantages over commonly used area search methods for monitoring populations of burrowing
seabirds. These advantages include increased survey efficiency allowing a larger sample size for a given effort and a correspondingly
tighter estimation of density. 相似文献
3.
4.
Pascual López-López José Verdejo Emilio Barba 《European Journal of Wildlife Research》2009,55(2):125-132
In this paper, we describe and analyze the diet of peregrine falcons during a long-term period (1982–2002). A combination
of direct observations of prey brought to nests, prey remains, and regurgitated pellets were used to calculate diet diversity
and dietary overlap between peregrine pairs. We also examined diet diversity in relation to breeding performance. All peregrine
pairs fed mainly on birds, with pigeons the most common prey. An increase in pigeon availability has been associated with
both an increase in population size and an increase in breeding performance (measured as the average productivity of pairs
per year) of a small peregrine falcon population in eastern Spain. Average productivity was lower when dietary breadth was
higher. We speculate that our results were the synergistic effect of declining persecution and increased pigeon availability
through increased popularity of keeping racing pigeons. There is a conflict of interests between pigeon fanciers and peregrine
conservation. As a consequence, this could result to an increased risk of mortality by direct persecution. In accordance with
this, conservation measures aimed at preventing direct persecution are encouraged. 相似文献
5.
V. A. Korovin 《Biology Bulletin》2011,38(10):980-984
The Demoiselle crane population was studied in the southern Chelyabinsk region (52°12′N; 60°21′E) during 1988–2008. Counts
of nesting pairs were annually conducted over an area of 100–130 km2 in May. The number of breeding pairs varied from 6.5 to 9.5 per 100 km2; on average, there were 8 pairs per 100 km2 during 1989–1991. In 2000–2008, the population density increased from 7.5 to 12 pairs per 100 km2, on average, 9.3 pairs per 100 km2. Demoiselle crane nesting in steppe pastures and perennial grass fields has been rarely
observed for the last decade. Now the main nesting biotopes of the species are stubble fields accounting for up to 70% of
all nidification cases documented. The decline in agricultural production in recent decades has resulted in the appearance
of long-fallow lands, in which 17 to 35% crane pairs nest. 相似文献
6.
There is an urgent need to understand how climate change will impact on demographic parameters of vulnerable species. Migrants
are regarded as particularly vulnerable to climate change; phenological mismatch has resulted in the local decline of one
passerine, whilst variations in the survival of others have been related to African weather conditions. However, there have
been few demographic studies on trans-Saharan non-passerine migrants, despite these showing stronger declines across Europe
than passerines. We therefore analyse the effects of climate on the survival and productivity of common sandpipers Actitis hypoleucos, a declining non-passerine long-distant migrant using 28 years’ data from the Peak District, England. Adult survival rates
were significantly negatively correlated with winter North Atlantic Oscillation (NAO), being lower when winters were warm
and wet in western Europe and cool and dry in northwest Africa. Annual variation in the productivity of the population was
positively correlated with June temperature, but not with an index of phenological mismatch. The 59% population decline appears
largely to have been driven by reductions in adult survival, with local productivity poorly correlated with subsequent population
change, suggesting a low degree of natal philopatry. Winter NAO was not significantly correlated with adult survival rates
in a second, Scottish Borders population, studied for 12 years. Variation in climatic conditions alone does not therefore
appear to be responsible for common sandpiper declines. Unlike some passerine migrants, there was no evidence for climate-driven
reductions in productivity, although the apparent importance of immigration in determining local recruitment complicates the
assessment of productivity effects. We suggest that further studies to diagnose common sandpiper declines should focus on
changes in the condition of migratory stop-over or wintering locations. Where possible, these analyses should be repeated
for other declining migrants. 相似文献
7.
A. R. Martin S. Poncet C. Barbraud E. Foster P. Fretwell P. Rothery 《Polar Biology》2009,32(4):655-661
More white-chinned petrels (Procellaria aequinoctialis) are accidentally killed in fisheries than probably any other seabird in the world, but the population impact of this mortality
is poorly understood, partly because there have been no recent estimates of the species’ abundance. The breeding aggregation
on the sub-Antarctic island of South Georgia is believed to be larger than all others combined. We estimated the size of this
population by calculating the area of suitable habitat and the density of occupied burrows within it. Some 670,000 occupied
nests were estimated for the island at mid-incubation, representing 0.9 million pairs of breeding-age birds associated with
South Georgia in the survey seasons (2005/06 and 06/07). This is 40–45% of the previous estimate, but still represents well
over half of the global population. If the population is declining due to fishery bycatch, as is likely, the scale of annual
mortality in this population alone is at least in the high tens of thousands, and plausibly hundreds of thousands. 相似文献
8.
Griffon vulture (Gyps fulvus) population surveys were conducted during 1996–2002 in the island of Crete (Greece) to document population status and structure. Fieldwork was carried out during the breeding period when birds could be monitored in their colonies. Total population size was estimated at 379 individuals (range = 341–417) with adult birds comprising 63%. The breeding population was estimated at 141 pairs, which were distributed on an average in 23 colonies per year (range = 16–30) while the mean number of breeding pairs that laid eggs was 98 (range= 64–126). Crete thus supports the largest insular population of the species in the world and hosts 70–80% of the breeding population of the species in Greece. Population density was estimated at 6.9 individuals/100 km2, 2.6 breeding pairs/100 km2 and 1.8 nesting pairs/100 km2. The average home range of an occupied colony (i.e., breeding group) was estimated at ca. 204 km2 producing a theoretical foraging range of 8 km radius around the breeding cliff. No trends in the total number of individuals and breeding pairs appeared to exist, although significant differences in population size of individual colonies occurred between the years. The majority of the population was concentrated in small-sized colonies, which showed a low occupancy rate. The number of abandoned sites and the colonization of new ones could represent a shift of breeding pairs to alternative colonies provoked by local food abundance and conspesific attraction. 相似文献
9.
Rimgaudas Treinys Asko L?hmus Darius Stonius Saulis Skuja Eugenijus Drobelis Bronius ableviius Saulius Rumbutis Deivis Dementaviius Vladas Narueviius Antanas Petraka Danas Augutis 《Journal of Ornithology》2008,149(1):75-81
Recent trends in the European Black Stork Ciconia nigra population are geographically distinct: range expansion and adaptation to human activity dominate in western and central
Europe, while declines—probably induced by landscape change—are reported in the east. We studied the large Lithuanian Black
Stork population in the transition zone to explore whether, and how, the detrimental influences of recent Baltic landscape
changes are balanced by the West European tendency of behavioural adaptation to human activity. Based on monitoring in sample
plots, the current population was estimated at 650–950 pairs, indicating a significant decrease (possibly over 20%) during
the last two decades. In comparison to the Latvian and Estonian populations, however, this decline is smaller, and the reproductive
success remains at a high level [66% breeding success and 2.99 ± 0.97 (SD) fledglings per successful attempt, 2000–2006];
this north–south gradient suggests a climate-mediated impact of habitat degradation in the Baltic countries. The storks are
also nesting closer to forest edges and in younger stands than 15–30 years ago, which has probably reduced the nest-tree limitation,
as indicated by an increased use of large oaks. Thus, habitat degradation and adaptation seem to be taking place simultaneously
in the Lithuanian Black Stork population, as was expected from its geographical location. In general, our study supports the
view that, whenever possible, species conservation strategies and the use of indicator species should be geographically explicit. 相似文献
10.
In the fell-field habitat at 140–270 m altitude on the sub-Antarctic Ile de la Possession, Iles Crozet, the dimorphic beetle
Amblystogenium pacificum Putzeys (Coleoptera: Carabidae) was studied monthly throughout the southern year 1993–1994 by timed hand collections involving
turning stones on the rocky fell-field. There were many mating couples and females containing well-developed eggs in every
month and the species reproduced throughout the year, with no evidence of a winter cessation of egg production. However, the
frequency of mating couples was about twice as great in the summer half-year (October–March) as in the winter half (April–September).
Relatively small differences in monthly mean temperatures between the summer and winter at Iles Crozet render all-year reproduction
not unexpected when comparisons are made with the temperatures and phenology of Carabidae in cool habitats in other parts
of the world. Mating pairs were collected at unusually high frequencies for carabids. The frequency of such pairs, taken per
unit effort by hand collecting, was highest in October–December, lower from January to May and intermediate from June to September.
Comparison of beetles taken as solitary, non-mating individuals with those taken as mating couples showed that in summer,
females of the black morph of this dimorphic species were more frequently involved in mating than expected, but no differences
were detected in winter. Female beetles were divided into younger individuals (putative age 1–2 years) and older females (putative
age 3–5 years or more) by the amount of claw-wear on individuals of this species. This division indicated that about 40% of
the older females showed no egg development when captured, but only about 20% of the younger females were non-breeding. However,
of the reproducing beetles, young and old females matured similar numbers of eggs. An altitude transect showed that the proportion
of the black morph increased significantly with altitude. Studies at 140–270 m showed that a significantly smaller proportion
of the older females of the brown morph were breeding than in the younger brown individuals, and this effect was particularly
evident in the colder winter period. No such age differences existed amongst the black morph. 相似文献
11.
For a number of decades, the lesser white-fronted goose (Anser erythropus) has been almost-absent from the Fennoscandian fauna and has a current population size of only about 60 breeding pairs, with
fewer than 10 pairs in Sweden. During the period 1981–1991 more than 200 young have been reintroduced in northern Sweden.
However, the origin and possible relatedness of lesser white-fronted individuals were unknown when the breeding program started.
We have used DNA fingerprinting to assess the similarity of 18 individuals, i.e., the entire captive population used for breeding
in 1991 and about 60% of the captive population used in 1981–1991. Minisatellite probe 33.15 provided an index for an average
similarity of 0.39 between the mates of the 12 breeding pairs used for producing offspring for reintroduction. This is a higher
similarity than in natural populations of birds in general but lower than in populations that have passed through serious
population bottlenecks. Individuals originating from different breeders are more dissimilar than those from the same breeder.
However, the close relationships (similarity, 0.5–0.6) found in a group of five individuals from different breeders show that
selecting individuals from different breeding groups is not sufficient to prevent mating between closely related individuals. 相似文献
12.
Olivier Gilg David Boertmann Flemming Merkel Adrian Aebischer Brigitte Sabard 《Polar Biology》2009,32(9):1275-1286
The ivory gull, a rare high-Arctic species whose main habitat throughout the year is sea ice, is currently listed in Greenland
as ‘Vulnerable’, and as ‘Endangered’ in Canada, where the population declined by 80% in 20 years. Despite this great concern,
the status of the species in Greenland has been largely unknown as it breeds in remote areas and in colonies for which population
data has rarely, if at all, been collected. Combining bibliographical research, land surveys, aerial surveys and satellite
tracking, we were able to identify 35 breeding sites, including 20 new ones, in North and East Greenland. Most colonies are
found in North Greenland and the largest are located on islands and lowlands. The current best estimate for the size of the
Greenland population is approx. 1,800 breeding birds, but the real figure is probably >4,000 adult birds (i.e. >2,000 pairs)
since all colonies have not yet been discovered and since only 50% or less of the breeding birds are usually present in the
colonies at the time the censuses take place. Although this estimate is four to eight times higher than that previously arrived
at, the species seems to be declining in the south of its Greenland breeding range, while in North Greenland the trends are
unclear and unpredictable, calling for increased monitoring efforts. 相似文献
13.
Assessing the importance of artificial nest‐sites in the population dynamics of endangered Northern Aplomado Falcons Falco femoralis septentrionalis in South Texas using stochastic simulation models 下载免费PDF全文
Habitat availability might be the most important determinant of success for a species reintroduction programme, making investigation of the quality and quantity of habitat needed to produce self‐sustaining populations a research priority for reintroduction ecologists. We used a stochastic model of population dynamics to predict whether attempts to improve existing breeding territories using artificial nest platforms improved the population growth rate and persistence of a reintroduced population of Northern Aplomado Falcons Falco femoralis septentrionalis in South Texas. We further assessed whether the creation of new territories, i.e. conversion of entire areas to suitable habitat and not simply the erection of nest platforms, would lead to a subsequent increase in the nesting population. Our model was able to reproduce several characteristics of the wild population and predicted the number of breeding pairs per year strikingly well (R2 = 0.97). Simulations revealed that the addition of nest platforms improved productivity such that the population would decline to extinction without them but is stable since their installation. Moreover, the model predicted that the increase in productivity due to nest platforms would cause the population to saturate available breeding territories, at which point the population would contain a moderate proportion of non‐territorial birds that could occupy territories if new ones become available. Population size would therefore be proportional to the increase in available territories. Our study demonstrates that artificial nest‐sites can be an effective tool for the management of reintroduced species. 相似文献
14.
The Wild rabbit (Oryctolagus cuniculus) is an endemic species of the Iberian Peninsula and is essential for the conservation of endangered predators. Rabbits are
also of high importance as a hunting species. From 1988, rabbits suffered the severe effects of rabbit hemorrhagic disease,
which caused large declines in most populations. Despite this fact, the National Red Data Lists continued to classify rabbits
as a “Least Concern” species. We used available hunting bag data from 1973 to 2002 to model national trends of rabbit abundance
and to evaluate the conservation status according to the criteria of the National Red Data List and the World Conservation
Union (IUCN). Generalized Additive Models were used as the statistical framework. The rabbit population of Spain suffered
a large decline of about 71% between 1973 and 1993. This decline was 49% in the period 1980–1990. Based on both Spanish and
World Conservation Union criteria, rabbits should be listed as ‘Vulnerable’, which demands a Conservation Plan Program. We
suggest that the lack of concordance between the best available evidence and the conservation status of the species is a consequence
of sociological constraints in conservation decisions. Rabbit conservation could face strong opposition from important socio-economic
lobby groups (hunters and farmers). As such, governments and researchers may prefer to exclude rabbits from any status category
requiring conservation action, despite the evidence of decline. We call for the urgent development of a nation-wide conservation
program for rabbits which includes both socioeconomic constraints and the available biological data on population trends. 相似文献
15.
Peter Sunde Kasper Thorup Lars B. Jacobsen Miriam H. Holseg?rd-Rasmussen Nina Ottessen Susanne Svenné Carsten Rahbek 《Journal of Ornithology》2009,150(3):537-548
Knowledge of a species’ spatial behaviour is essential for understanding its behavioural ecology, as well as a prerequisite
to planning of conservation strategies. The Little Owl (Athene noctua) has shown a substantial decline in north-western Europe and is on the road of extinction in Denmark. To quantify relevant
aspects of spatial behaviour in the last remaining Danish population, we followed 27 radio-tagged owls representing 14 territories
during a period of 2 years. Mated owls were resident at nesting sites year-round with half of all nocturnal locations found
within 125 m. Mean nightly distance from roosts peaked in January at 249 m (95% CI = 195–319) and dipped in May to 89 m (66–121).
Distance from roosts varied non-linearly with temperature with the longest distances found at 6°C. Home range size varied
with more than a tenfold difference between pairs, with pairs with neighbours maintaining 2–3 times larger ranges than isolated
pairs independent of habitat composition. Mean home range size of 14 pairs was 41 (95% CI 27–64) and 2.6 ha (1.5–4.5) for
90 and 50% minimum convex polygons, respectively. Males and females behaved similarly, except in the breeding season where
females foraged closer to the nest. Mates overlapped completely in activity distributions and were located closer to each
other than expected by chance, suggesting a permanent pair-bond. Inter-mate distances were not shorter prior to egg laying
compared to the rest of the year, indicating little male investment in mate guarding. No mates left their partner, but widowed
birds left their territory within 6–12 months if unable to attract a new mate.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
Viability of meta-populations of wetland birds in a fragmented landscape: testing the key-patch approach 总被引:1,自引:0,他引:1
The key patch approach assumes that metapopulations in fragmented landscapes are likely to be viable with at least one “key”
sub-population that is sufficiently large to ensure re-colonization of surrounding minor habitat patches. It is based on a
minimum viable number of breeding pairs and within-breeding season dispersal distance, linked to size of the animal and longevity.
It was tested using census data of 15 wetland bird species (bearded tit, bluethroat, great reed warbler, sedge warbler, Savi’s
warbler, grasshopper warbler, spotted crake, water rail, common snipe, common teal, garganey, little bittern, night heron,
great bittern and marsh harrier) in 14 wetland complexes of variable size (3–55 km2) spread across the Netherlands (distances ranging 4–156 km). First, for each species it was assessed whether a wetland harbored
a key subpopulation, which was the case for the sedge warbler (7 key subpopulations), grass-hopper warbler (2), water rail
(2), bearded tit, bluethroat, Savi’s warbler, common teal, garganey, great bittern and marsh harrier (all one key subpopulation).Together
with the adjacent sub-populations present within breeding season dispersal distance, 10 out of the 15 studied species formed
viable meta-populations. This was compared with the trend in the census data of 13 species for 1990–2000 and was found to
correspond significantly (likelihood ratio test, P = 0.003): species without a viable meta-population had declined (2 out of 4) or remained stable (2 out of 4), whereas viable
meta-populations had increased (6 out of 9) or remained comparatively stable (2 out of 9). One wetland complex, the Oostvaardersplassen,
stood out in that it haboured key sub-populations for 9 out of the 15 species studied. Variation in quantity of specific habitat
(area or perimeter marshland, woodland or open water) in a wetland complex was of limited importance explaining abundance
patterns, since all covaried strongly with total area among the wetland complexes, with the exception of water perimeter.
Apparently, these wetlands on peat harbour largely similar landscapes. Indeed, population sizes of most birds covaried strongly
and in a PCA two distinct clusters of species were identified that shared high numbers of breeding pairs in the same, larger,
wetland complexes, the first (3 species) including the great reed warbler, and the second (9 species) the water rail. 相似文献
17.
Breeding season food limitation drives population decline of the Little Owl Athene noctua in Denmark
Many farmland bird species have declined markedly in Europe in recent decades because of changes in agricultural practice. The specific causes vary and are poorly known for many species. The Little Owl, which feeds extensively on large invertebrates and is strongly associated with the agricultural landscape, has declined over most of northwestern Europe, including Denmark. We investigated the likely reasons for the population decline in Denmark by identifying patterns of local extinction (scale, 5 × 5 km2) and estimating demographic parameters affecting local survival, focusing on changes over time and their relationship to habitat characteristics. The distribution of the Little Owl in Denmark contracted considerably between 1972–74 and 1993–96. The extent of contraction varied across the country, and the only habitat correlate was that local disappearance was associated with smaller amounts of agricultural land. Analyses of ring recovery data suggested a constant annual adult survival rate of 61% from 1920 to 2002, which is similar to estimates from countries with stable populations. First‐year annual survival rates were much lower than values previously reported. From the 1970s into the 21st century, the mean number of fledglings declined from around 3 to < 2 young per territory, but the decline in clutch size was considerably less. Reproductive parameters were higher closer to habitat types known to be important foraging habitats for Little Owls, and were also positively correlated with the amount of seasonally changing land cover (mostly farmland) within a 1‐km radius around nests as well as temperatures before and during the breeding season. Experimental food supplementation to breeding pairs increased the proportion of eggs that resulted in fledged young from 27 to 79%, supporting the hypothesis that the main proximate reason underlying the ongoing population decline is reduced productivity induced by energetic constraints after egg‐laying. Conservation efforts should target enhancement of food availability during the breeding season. Other farmland species dependent on large invertebrates are likely to share the problems that Little Owls face in modern agricultural landscapes. 相似文献
18.
Aboulghasem Roohi Ahmet E. Kideys Ameneh Sajjadi Abdolla Hashemian Reza Pourgholam Hasan Fazli Ali Ganjian Khanari Elif Eker-Develi 《Biological invasions》2010,12(7):2343-2361
Monitoring for 6 years (2001–2006) showed that the population explosion of the alien ctenophore Mnemiopsis leidyi in the southern Caspian Sea coincided with a decline in the abundance and species number of mesozooplankton. While this decline
appeared to have reduced the nourishment of sprat (also known as kilka), it seemed to have affected phytoplankton favorably
mainly due to the decrease in grazing pressure. During 2001–2002, when M. leidyi abundance and biomass were at their highest levels, abundance of dinoflagellates and cyanophytes exceeded that of diatoms.
Before the invasion (1996) and in some years after the invasion (2003, 2004 and 2006) diatom abundance was higher than the
abundance of other groups. In September 2005, an unprecedented bloom of the toxic cyanophyte Nodularia sp. was observed in the southern Caspian Sea. Disappearance of edible zooplankton such as Eurytemora spp. was among the first changes observed after the expansion of M. leidyi in the area. Some changes in the macrobenthic fauna were also conspicuous after the increase of this ctenophore. While the
biomass of some deposit feeders, such as the polychaete Nereis diversicolor and oligochaete species increased, benthic crustaceans decreased sharply in abundance during 2001–2003 and completely disappeared
during 2004–2006. Iranian catches of kilka, the most abundant and widespread zooplanktivorous fish, decreased significantly
in the southern Caspian Sea after 1999. Iranian landings of kilka dropped ~70% from 69,070 ± 20,270 t during 1995–2000 to
23,430 ± 12,240 t during 2001–2006, resulting in a loss of at least 125 million US dollars to the economy. There were also
changes in the total catches of large predators such as the kutum and mullet, which mainly feed on kilka, between 1991 and
2006. 相似文献
19.
PAOLO FASCE LAURA FASCE ALEXANDRE VILLERS FRANCO BERGESE VINCENT BRETAGNOLLE 《Ibis》2011,153(3):581-591
Few studies have quantified the dynamics of recovering populations of large raptors using long‐term, spatially explicit studies. Using data collected over 37 years in the western Italian Alps, we assessed the trends in distribution, abundance, fecundity and breeding population structure of Golden Eagles Aquila chrysaetos. Using the spatial distribution of territory centroids in 2007, we found that the spatial distribution of eagle territories was over‐dispersed up to 3 km. Although population size and total productivity increased from 1972 to 2008, the proportion of pairs that laid eggs showed a strong decline, falling to no more than 50% after 2003. On average, 15% of successful nests produced two fledglings, and productivity also declined over time. No significant relationship between population growth rate and total population size was detected, but the percentage of pairs that bred and breeding success showed evidence of density dependence, as they declined significantly with increasing density. Our results suggest that density dependence, operating across heterogeneous habitats, is currently regulating this population, while the carrying capacity may still be increasing. This may explain the apparent paradox of reduced breeding effort despite increasing total productivity. 相似文献
20.
The gentoo penguin (Pygoscelis papua) is one of the most widespread penguin species and has been proven to be highly plastic in many aspects of its ecology. However,
data from their sub-Antarctic range suggest an unexplained decline of their populations over the last 10–20 years, stressing
the need for additional knowledge on their breeding ecology and demography. The present study provides insights into the breeding
ecology of the gentoo penguin at a major breeding site, Kerguelen Archipelago, over three breeding seasons (1987, 2002 and
2003). Similarly to other northern populations, gentoo penguins breeding at Kerguelen exhibited winter laying, slow provisioning
rate, slow growth rate associated with an extended rearing period and relatively low breeding success compared to southern
populations. Our study also revealed interannual differences in the timing of laying and growth parameters as well as unusual
sex differences in parental investment. Despite their high plasticity, there are indications that gentoo penguins at the northern
edge of their range might work at the upper limit of their capacities. Sub-Antarctic populations would, therefore, be more
sensitive to environmental changes than more southerly ones and need to be closely monitored. 相似文献