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1.
Timothy J. E. Harrison Jennifer A. Smith Graham R. Martin Dan E. Chamberlain Stuart Bearhop Gillian N. Robb S. James Reynolds 《Oecologia》2010,164(2):311-320
Food availability influences multiple stages of the breeding cycle of birds, and supplementary feeding has helped in its understanding.
Most supplementation studies have reported advancements of laying, whilst others, albeit less numerous, have also demonstrated
fitness benefits such as larger clutches, shorter incubation periods, and greater hatching success. Relatively few studies,
however, have investigated the effects of supplementary feeding for protracted periods across multiple stages of the breeding
cycle. These effects are important to understand since long-term food supplementation of birds is recommended in urban habitats
and is used as a tool to increase reproductive output in endangered species. Here, we compare the breeding phenology and productivity
of blue tits Cyanistes caeruleus and great tits Parus major breeding in food-supplemented and non-supplemented blocks in a broadleaf woodland in central England over three seasons (2006–2008).
Supplementation was provided continuously from several weeks pre-laying until hatching, and had multiple significant effects.
Most notably, supplementation reduced brood size significantly in both species, by half a chick or more at hatching (after
controlling for year and hatching date). Reduced brood sizes in supplemented pairs were driven by significantly smaller clutches
in both species and, in blue tits, significantly lower hatching success. These are novel and concerning findings of food supplementation.
As expected, supplementary feeding advanced laying and shortened incubation periods significantly in both species. We discuss
the striking parallels between our findings and patterns in blue and great tit reproduction in urban habitats, and conclude
that supplementary feeding may not always enhance the breeding productivity of birds. 相似文献
2.
Virginie Rolland Jeffrey A. Hostetler Tommy C. Hines H. Franklin Percival Madan K. Oli 《European Journal of Wildlife Research》2011,57(4):717-727
Reproductive success is a critical component of individual fitness, and also an important determinant of growth rates of populations
characterized by early maturity and high fecundity. We used radiotelemetry data collected during 2003–2008 to estimate reproductive
parameters in a declining northern bobwhite (Colinus virginianus) population in South Florida, and to test hypotheses regarding factors influencing these parameters. The overall clutch size
was 12.10 ± 0.22, but females laid more eggs in their first clutch (12.43 ± 0.24) than in subsequent clutches (10.19 ± 0.53)
within a nesting season. Daily nest survival was higher for first (0.966 ± 0.003) than subsequent nests (0.936 ± 0.011). Hatchability
(proportion of laid eggs that hatched conditional upon nest survival to hatching) was 0.853 ± 0.008, but was higher for nests
incubated by females (0.873 ± 0.009) than those incubated by males (0.798 ± 0.018). The proportion of individuals attempting
a second nest was 0.112 ± 0.024 and 0.281 ± 0.040 when the first nest was successful and failed, respectively. Hatchability
was lower when the nesting habitat was burned the previous winter. We found no evidence that food strip density (a management
practice to provide supplemental food) influenced any of the reproductive parameters. Mean summer temperature affected hatchability,
nest survival, and proportion of nests incubated by males. Overall, the reproductive output in our study population was lower
than that reported for most other bobwhite populations, indicating that low reproductive performance may have contributed
to bobwhite population declines in our study site. These results suggest that current management practices, particularly those
related to habitat and harvest management, need careful evaluation. 相似文献
3.
Annual egg and chick production and breeding success at the Adélie penguin (Pygoscelis adeliae) colony Edmonson Point (74°21′S–165°10′E), Victoria Land, is presented for eight breeding seasons between 1995 and 2005.
During this period the colony consisted of 10–13 subcolonies and averaged 2098 ± 278 breeding pairs. A sample of over 100
nests (114–150), belonging to two subcolonies, was monitored each year. Some breeding parameters remained constant while others
showed substantial annual variation. Laying date showed little variation, and laying was highly synchronous: 82.5% of clutches
were initiated in a 10-day period, 9–18 November. In contrast, clutch size (1.77–1.97) and incubation period (34.4 ± 2.5)
varied significantly. Variation among years was also recorded in hatching success (from 58 to 86%) and breeding success. This
last parameter, measured as number of chicks reared to crèche per nest with eggs, varied between 0.34 and 0.97. 相似文献
4.
We studied the effect of breeding group size and nest position on breeding success in the chinstrap penguin (Pygoscelis antarctica). Large subcolonies sited at Vapour Col, Deception Island, had higher breeding success than small subcolonies, which suffered
a higher chick mortality than large subcolonies. Hatching date was earlier in large colonies. Relationships were not found
between mean hatching date per subcolony and mean chick survival. Chick mortality related to nest position showed no difference
between central and peripheral nests in large subcolonies. Central nests hatched earlier than peripheral nests. Nests in large
subcolonies, whatever their position, were more successful compared with nests in small subcolonies.
Received: 16 April 1997 / Accepted: 12 July 1997 相似文献
5.
Provision of supplementary food for wild birds may increase the risk of local nest predation
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In countries such as the UK, USA and Australia, approximately half of all households provide supplementary food for wild birds, making this the public's most common form of active engagement with nature. Year‐round supplementary feeding is currently encouraged by major conservation charities in the UK as it is thought to be of benefit to bird conservation. However, little is understood about how the provision of supplementary food affects the behaviour and ecology of target and non‐target species. Given the scale of supplementary feeding, any negative effects may have important implications for conservation. Potential nest predators are abundant in urban areas and some species frequently visit supplementary feeding stations. We assess whether providing supplementary food affects the likelihood of nest predation in the vicinity of the feeder, by acting as a point attractant for potential nest predators. We provided feeding stations (empty, peanut feeder, peanut feeder with guard to exclude potential nest predators) in an area of suburban parkland in the UK and monitored the predation rate of eggs placed in artificial nests located at distances that replicated the size of typical suburban gardens. Nest predators (Magpies Pica pica, Grey Squirrels Sciurus carolinensis) were frequent visitors to filled feeders, and predation caused by Magpies, European Jays Garrulus glandarius and Grey Squirrels was significantly higher when nests were adjacent to filled feeders. The presence of a feeder guard did not significantly reduce nest predation. As supplementary feeding is becoming increasingly common during the breeding season in suburban habitats, we suggest that providing point attractants to nest predators at this time may have previously unconsidered consequences for the breeding success of urban birds. 相似文献
6.
Sooty Falcon Falco concolor reproduction and population dynamics on the islands in the Sea of Oman
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Michael J. McGrady Waheed A. Al‐Fazari Mansoor H. Al‐Jahdhami Malcolm A. C. Nicoll Madan K. Oli 《Ibis》2017,159(4):828-840
Knowledge of demographic parameters affecting population dynamics is critical to the formulation of effective conservation strategies. Sooty Falcon Falco concolor is a little‐studied, Near‐threatened species; estimates of global population size and trend for this species are uncertain. They lay eggs during mid‐summer and sometimes nest in colonies. This unusual breeding ecology suggests that demographic parameters driving their population growth rate may differ from those of most other falcons. We studied Sooty Falcon reproduction at breeding aggregations on Fahal Island and the Daymaniyat islands in the Sea of Oman during 2007–2014, modelled population growth and identified important life history parameters using elasticity analysis. The mean (± se) clutch and brood size was 2.83 ± 0.06 and 2.11 ± 0.07, respectively. Overall, 11.7% of nests failed between the egg and nestling stages, and the failure rate differed significantly between Fahal and the Daymaniyats, and across years. The mean proportion of eggs that hatched annually was 0.66 ± 0.02, and broods were significantly smaller on the Daymaniyats than on Fahal. Falcons on Fahal Island had a higher rate of hatching, a higher rate of nests that produced at least one chick, and produced more chicks per nest than on the Daymaniyats. We suggest that Fahal's proximity to the mainland gives breeding Sooty Falcons access to a more plentiful and stable source of food, especially during the period between arrival from the wintering grounds and the onset of the autumn migration of prey birds, resulting in the better reproductive rates for falcons on Fahal Island, relative to those on the Daymaniyat Islands. The annual asymptotic population growth rate (λ) was 0.87 (95% confidence interval (CI) 0.75–0.99), suggesting a declining population, although Sooty Falcons enjoyed a slightly higher population growth rate on Fahal than on the Daymaniyats. Because our study population is on the edge of the breeding range and is isolated from other breeding areas, measures to improve reproductive success of Sooty Falcons breeding on the islands in the Sea of Oman could be important for conservation of Sooty Falcons in Oman. 相似文献
7.
Thea van de Mortel William Buttemer Peter Hoffman John Hays Andrew Blaustein 《Oecologia》1998,115(3):366-369
Ultraviolet-B (UV-B) irradiation of DNA generates mutagenic photoproducts such as cyclobutane pyrimidine dimers (CPDs) which
can affect the growth and development of amphibian embryos. Differential ability to repair UV-B-induced DNA damage may be␣responsible
for differences in population stability between␣some amphibian species. Photoreactivation via the enzyme photolyase is a major
mechanism used to remove CPDs from DNA. The aim of this study was to determine if photolyase activity differed in three sympatric
Australian amphibian species, one of which has suffered marked population declines (Litoria aurea) and two whose populations do not appear to be in decline (L. dentata and L. peronii). The specific activity of photolyase was measured in each species and compared to the hatching success of their eggs under
unfiltered summer sunlight. The mean specific activities of photolyase were 1.10 ± 0.18 × 1011, 5.76 ± 1.01 × 1011, and 2.66 ± 0.15 × 1011 CPDs repaired per hour per microgram of egg protein extract, for L. aurea, L. dentata and L. peronii, respectively. When intrinsic differences in hatching success between species were controlled for, the relative percentage
hatching success under unfiltered sunlight of L. aurea (77%) was lower than that of L.␣peronii (91%) and L. dentata (98%); however, these values did not differ significantly. L. aurea had the lowest photolyase activity of the three species and showed a non-significant trend of reduced hatching success under
UV-B exposure.
Received: 15 December 1997 / Accepted: 9 March 1998 相似文献
8.
Juan Moreno Alberto J. Redondo Alejandro Cantarero Rafael Ruiz-de-Castañeda Sonia González-Braojos 《Acta ethologica》2011,14(2):85-89
The female nutrition hypothesis posits that provisioning intensity of incubating females by their mates may depend on female
needs and ensure proper incubation and a corresponding high hatching and breeding success of breeding pairs. Here, we have
handicapped female pied flycatchers Ficedula hypoleuca at the beginning of incubation by clipping two primaries on each wing and filmed nests during incubation and later nestling
provisioning to estimate male involvement in incubation feeding at the nest and in offspring care. Incubation feeding was
more frequent at late nests. Correcting for this seasonal effect, incubation feeding was significantly affected by treatment
and twice as high at experimental as at control nests. There was no effect of the experiment on female incubation attendance.
The handicap did not result in any effect on hatching and breeding success, nestling growth and male or female provisioning
and mass at the end of the nestling period. Males adjust their incubation feeding activity at the nest to female energetic
requirements during incubation. 相似文献
9.
Population dynamics and reproduction of Northern Lapwings Vanellus vanellus in a meadow restoration area in central Sweden 总被引:1,自引:0,他引:1
To investigate the effectiveness of a meadow restoration programme, we studied the relationships between population changes and environmental changes, return rates and hatching success in a population of Northern Lapwings Vanellus vanellus. The study was performed on mixed farmland (59 km2 ) in central Sweden, an area that underwent extensive meadow restoration between 1985 and 1994. The study included more than 2600 nests, supplemented with observations of 127 individually colour-ringed Northern Lapwings. The breeding population varied (2.7–5.3 pairs/km2 ), but showed no significant trend with time. The population increased in years with high spring flooding levels. Population size was unrelated to demographic factors (e.g. hatching success the previous year (14–50%), and return rate). Lapwings moved considerably between years and their nest site fidelity was unrelated to previous hatching success or other factors, suggesting that changes in habitat quality and migration between populations were important in regulating population size. Recent extensive meadow restoration did not seem to aid the Northern Lapwing population; birds continued nesting on tillage even though most nests were destroyed by farming activities. A relatively high relaying frequency improved hatching success, which was still lowest in the most preferred habitats (spring sown crops, total hatching success c. 30%). The few Northern Lapwings breeding in the least preferred habitats (meadows and cultivated grassland) had a better hatching success (> 70% total hatching success), suggesting that habitat selection was not determined by hatching success. From these results, recommendations are made for the management of Northern Lapwing (and associated species) populations on farmland. 相似文献
10.
Decreased trophic position as a function of increasing body size of a benthic omnivorous fish from the largest freshwater lake in China 总被引:1,自引:0,他引:1
Potential body size-trophic position relationships of the Darkbarbel catfish Pelteobagrus vachelli (Richardson 1846) were examined using stable isotope analysis. Pelteobagrus vachelli is a benthic feeding fish from Lake Poyang, the largest freshwater lake in China. Two-source mixing model with mussel (Corbicula fluminea) and snail (Bellamya aeruginosa) as baseline primary consumers of planktonic and benthic food webs, respectively, was used to estimate contribution of carbon
derived from planktonic vs. benthic food web. Results showed that as an indicator of trophic position, δ15N was negatively correlated with the body length and weight of the fish; on the other hand, as an indicator of the end-member
food sources, δ13C was not correlated with fish size. The mixing model results showed that the averaged trophic position of our sampled 3.3–12.7 cm
Pelteobagrus vachelli was 3.1 ± 0.2 and derived 68 ± 27% of their food from the benthic food web, confirming that the feeding behavior of the catfish
favors benthic food sources. 相似文献
11.
The amount of time a bird allocates to incubation is likely to be limited by energetic constraints. If food is abundant, energetic constraints may be reduced and the time spent incubating (incubation attendance) may increase. Moreover, the onset of incubation in relation to clutch completion may be advanced, resulting in a higher degree of hatching asynchrony. We measured the effect of experimentally increased food availability on incubation attendance and an estimate of hatching asynchrony in the Australian reed warbler Acrocephalus australis . Supplementary food was provided every other day, from a few days before the start of egg laying until just prior to hatching. Incubation attendance was measured with temperature loggers at nests receiving supplementary food and control nests. Hatching asynchrony was inferred from mass and size differences between siblings shortly after hatching. We found that 1) food supplementation resulted in an increase in incubation attendance, when comparing both nests receiving supplementary food to control nests as well as feeding to non-feeding days in nests receiving supplementary food, and 2) food supplementation resulted in a greater hatching asynchrony, without affecting clutch size, average egg volume or the likelihood of eggs hatching. This suggests that food availability acts in a proximate way to modify the extent of incubation attendance and hatching asynchrony. We discuss the adaptive significance of increased incubation attendance and a shift in the degree of hatching asynchrony in relation to food availability. 相似文献
12.
Mass changes in female southern elephant seals, sampled sequentially at different points through their annual cycle, were
measured at King George Island, South Shetland Islands, during the 1995/1996 and 1996/1997 field seasons. Females weighed
after they had given birth showed an increase of 37 ± 36 kg (mean ± SD), which represented 6.2 ± 6.4% in relation to their
mass in the first breeding season. During the first aquatic phase, between the end of lactation and the beginning of moult,
females gained a mean of 128 ± 35 kg, (n = 18) (2.19 ± 0.65 kg day−1), which represented between 27 and 83% of the mass they had lost during lactation. Nine females followed during moulting
showed a mass loss rate of 5.0 ± 0.4 kg day−1, which was half the rate during lactation. Total mass loss during moulting (129 ± 22 kg) was not significantly different
from mass gain for the same females between lactation and moult (135 ± 37 kg). Furthermore, at the end of moulting, female
mass was not significantly different from the mass at the end of lactation. These masses represented 65 ± 5% and 64 ± 5%,
respectively, of their initial mass after parturition. During the second period at sea, from the end of the moult until females
hauled out to give birth in the following breeding season, the estimated mass gain was 1.45 ± 0.24 kg day−1 (n = 5), which was not significantly different to the rate of mass gain shown by the same females during the first period at
sea (2.26 ± 0.70 kg day−1). Total mass gain during the second aquatic phase (364 ± 63 kg) was not correlated with the mass at the end of moulting,
but it was positively related to the mass loss experienced by females from parturition until the end of the moulting period
in the first breeding season.
Accepted: 5 September 1998 相似文献
13.
Karel Weidinger 《Polar Biology》1997,17(5):469-472
Timing and duration of the breeding cycle of the Cape petrel Daption capense were studied during two breeding seasons (1990/1991 and 1991/1992) at Nelson Island, South Shetland Islands, Antarctica.
In 1991/1992 the copulatory period extended over 53 days, with median date and a peak about 28 and 19 days respectively, before
the median date of laying. Laying began 85 days after arrival, with mean (= median) date on 2 December (SD = 2.5 days). The
distributions of laying, hatching and fledging dates showed a similar degree of synchrony and did not differ between years.
Incubation and chick period were equally long (46 days), the former being less variable (coefficient of variation = 2.8% and
4.6%, respectively). Mean completed nesting cycle (92 days) was about 2 days shorter at Nelson Island than elsewhere and tended
to shorten as the breeding season progressed. Its mean length represented 86% of the whole nesting period (107 days), which
in turn represented 56% of the period of continuous colony attendance. Timing and duration of nesting stages did not differ
between colonies or sets of nests subjected to various levels of disturbance.
Received: 8 July 1996 / Accepted: 11 November 1996 相似文献
14.
Ivonne I. Vega‐Ruiz Jos Alfredo Castillo‐Guerrero Guillermo Fernndez 《Journal of Field Ornithology》2021,92(1):18-29
Understanding breeding phenology and success can elucidate population dynamics, which is especially important for species in need of conservation. We describe the factors affecting the breeding biology of American Oystercatchers (Haematopus palliatus frazari) at El Rancho Island, a critical site that contains ~ 7% of the total estimated population, on the coast of Sinaloa, Mexico. We monitored 192 nests over four years (2016–2019). The breeding season lasted from March to June and mean laying dates differed among years, with the mean laying date in 2019 an average of 20 days earlier than in 2016. Clutch sizes decreased as the breeding season progressed. Both breeding success and productivity differed among years, with the lowest values in 2016 (30% hatching success and 0.6 chicks/nest) and the highest in 2019 (66% hatching success and 1.2 chicks/nest). Hatching success was affected by year, laying date, type of habitat, and distance to the high tide line. American Oystercatchers that laid eggs earlier in the season, used mixed marsh and dune habitat, and with nests relatively close to the waterline (< 50 m) had greater breeding success. Overall, however, the breeding success of American Oystercatchers was low and influenced by a combination of several intrinsic and extrinsic factors. Management measures may be required to increase breeding success and ensure the conservation of this subspecies. 相似文献
15.
Simone Vincenzi Scott Hatch Thomas Merkling Alexander S. Kitaysky 《Proceedings. Biological sciences / The Royal Society》2015,282(1812)
Supplementation of food to wild animals is extensively applied as a conservation tool to increase local production of young. However, in long-lived migratory animals, the carry-over effects of food supplementation early in life on the subsequent recruitment of individuals into natal populations and their lifetime reproductive success are largely unknown. We examine how experimental food supplementation early in life affects: (i) recruitment as breeders of kittiwakes Rissa tridactyla born in a colony on Middleton Island (Alaska) between 1996 and 2006 (n = 1629) that bred in the same colony through 2013 (n = 235); and (ii) breeding success of individuals that have completed their life cycle at the colony (n = 56). Birds were raised in nests that were either supplemented with food (Fed) or unsupplemented (Unfed). Fledging success was higher in Fed compared with Unfed nests. After accounting for hatching rank, growth and oceanic conditions at fledging, Fed fledglings had a lower probability of recruiting as breeders in the Middleton colony than Unfed birds. The per-nest contribution of breeders was still significantly higher for Fed nests because of their higher productivity. Lifetime reproductive success of a subset of kittiwakes that thus far had completed their life cycle was not affected by the food supplementation during development. Our results cast light on the carry-over effects of early food conditions on the vital rates of long-lived animals and support food supplementation as an effective conservation strategy for long-lived seabirds. 相似文献
16.
The caterpillars of Eutachytptera psidii (Lepidoptera: Lasiocampidae) mark trails between their nest and distant feeding sites with a trail pheromone secreted from
the ventral surfaces of their last abdominal segments. The threshold sensitivity to artificial trails prepared from an hexane
extract of the pheromone was 0.75 × 10−3 caterpillar-equivalents per cm of trail. In tests of trail-specificity involving four other social species, the caterpillars
responded only to trails prepared from a pheromone extract of the closely related genus Gloveria. Tests were conducted to determine the efficiency with which colonies abandon exhausted feeding sites in favor of new food
finds. On their first forays after their food sources were experimentally moved from established feeding sites to new sites,
67.5 ± 3.6% of all the evening’s activity occurred on pathways leading to the previously established sites. During their next
two forays, 86.3 ± 3.7% and 92.1 ± 2.0% of all activity occurred on pathways leading to the new sites. Efficient abandonment
of exhausted feeding sites is attributed to the persistence of the trail pheromone, differential marking of new and old pathways
and to the caterpillar’s ability to discern trail strength and to choose stronger over weaker trails at choice points. 相似文献
17.
Feeding territoriality and the reproductive consequences in brown skuas<Emphasis Type="Italic">
Catharacta antarctica lonnbergi</Emphasis> 总被引:3,自引:3,他引:0
In the maritime Antarctic, brown skuas (Catharacta antarctica lonnbergi) show two foraging strategies: some pairs occupy feeding territories in penguin colonies, while others can only feed in unoccupied areas of a penguin colony without defending a feeding territory. One-third of the studied breeding skua population in the South Shetlands occupied territories of varying size (48 to >3,000 penguin nests) and monopolised 93% of all penguin nests in sub-colonies. Skuas without feeding territories foraged in only 7% of penguin sub-colonies and in part of the main colony. Females owning feeding territories were larger in body size than females without feeding territories; no differences in size were found in males. Territory holders permanently controlled their resources but defence power diminished towards the end of the reproductive season. Territory ownership guaranteed sufficient food supply and led to a 5.5 days earlier egg-laying and chick-hatching. Short distances between nest and foraging site allowed territorial pairs a higher nest-attendance rate such that their chicks survived better (71%) than chicks from skua pairs without feeding territories (45%). Due to lower hatching success in territorial pairs, no difference in breeding success of pairs with and without feeding territories was found in 3 years. We conclude that skuas owning feeding territories in penguin colonies benefit from the predictable and stable food resource by an earlier termination of the annual breeding cycle and higher offspring survivorship.Research licence: Umweltbundesamt Bonn 13.4-94003-1/5-7. 相似文献
18.
Test of a digestion optimization model: effect of variable-reward feeding schedules on digestive performance of a migratory bird 总被引:1,自引:0,他引:1
Birds on migration often alternate between feeding and nonfeeding periods, in part because food resources may be patchily
distributed and in part because birds on migration may adopt a risk-prone foraging strategy characterized by selection of
variable rather than constant food rewards. Optimal digestion models predict that increases in intermeal interval like those
encountered by some migratory birds should result in longer retention time of digesta and higher digestive efficiency if birds
are maximizing their rate of energy intake. We tested these predictions by comparing residence time of digesta and extraction
efficiency of lipid for captive yellow-rumped warblers (Dendroica coronata) feeding adlibitum and when we added intervals of time when the birds received no food. We increased the likelihood that the warblers were maximizing
their rate of energy intake by increasing light levels during spring to induce hyperphagia (treatment birds (16L:8D light:
dark cycle) ate 2.13 ± 0.14 g dry food day−1 (n = 8) while control birds (10L:14D) ate 1.25 ± 0.03 g dry food day−1 (n = 6)). Treatment birds offered food only every other 2–3 h ate 50% more during the 4-h test period than when they were always
feeding adlibitum. Despite these differences in food intake, extraction efficiency of glycerol trioleate remained high and constant (93%),
and mouth-to-anus total mean retention time (TMRT) did not change (overall mean: 54.8 ± 6.0 min). Residence time of lipid
in the stomach increased whereas residence time of lipid in the intestine decreased when birds fed only every other 2–3 h
compared to when birds always fed ad libitum. None of the results were consistent with the predictions of the optimal digestion model unless we assume that birds were
minimizing their feeding time rather than maximizing their rate of energy gain. Furthermore, the ability of yellow-rumped
warblers to maintain high extraction efficiency with no change in TMRT suggests some spare digestive capacity when food intake
increases by as much as 50%.
Received: 14 June 1997 / Accepted: 20 November 1997 相似文献
19.
Jordi Ruiz-Olmo Antoni Batet Francesc Mañas Ramon Martínez-Vidal 《European Journal of Wildlife Research》2011,57(4):827-842
Otters are elusive semi-aquatic mammals, occurring in low densities and difficult to count. A study was conducted in 15 stretches
(10–12 km) of four tributaries of the Ebro River, with the aims to understand spatial and temporal changes in otter abundance
and breeding success and the causes of such variations. Between 1990 and 2009, both otter parameters were assessed by means
of visual spring–early summer censuses, carried out by sets of observers located every 500 m. A total of 134 censuses were
carried out, involving 4,540 twilight watches (7,896.5 h) and 520 otter sightings were recorded. Also, 39 different habitat
characteristics (including prey species) were established for each stretch. Otter abundance was assessed by means of three
indexes related to the census effort and the length and surface units (in terms of otter habitat). Excluding the upper stretches,
we found on average 0.07–0.26 adult and subadults per kilometre (1.45–6.26/km2). Important interannual fluctuations in otter abundance and breeding success were found in some Pyrenean stretches located
downstream of a large reservoir. This was linked to the effect of autumn floods (in part due to the opening of dams) on the
fish stocks (mainly Barbels). Similar habitat conditions resulted in similar abundances between stretches, and different habitat
conditions generated different abundances in adjacent stretches of the same river. No significant differences were found for
litter size between small cubs (1.60 ± 0.70 cubs per litter) and large cubs (1.39 ± 0.50) as a whole, but differences between
stretches were found. On average we found between 0.009 and 0.130 large cubs per year per kilometre. Otters bred more successfully
in stretches with higher otter densities. Otter abundance and breeding success correlated negatively with altitude as a consequence
of the interaction of several habitat characteristics with altitude. The stepwise linear regression linked the number of adult
otters per kilometre with the ecosystem production (chlorophyll a concentration), while the number of large cubs per kilometre per year was linked with the food (fish + crayfish) abundance.
The findings bring about a consistent and congruent scenario of otter abundance and breeding success explained by the different
steps along the food chain. 相似文献
20.
Mass transfer from mother to pup during the lactation period, and mass recovery for the same females during the foraging
period were measured in the southern elephant seal at King George Island, Antarctica. During the 19.2 ± 0.9-day lactation
period measured (which represented 87% of the entire nursing), females lost a mean mass of 10.56 ± 1.76 kg/day (n = 27), while their pups gained a mean mass of 5.27 ± 1.1 kg/day. There was a correlation between daily body weight gain in
pups and daily weight loss by their mothers. Pup weaning mass was positively related to maternal post-partum mass. Serial
samples showed that weight losses by females and gains by their pups were not linear over lactation, but showed lower values
at the beginning and at the end of lactation. During the 60.5 ± 6.2-day foraging phase between the end of lactation and molt,
females gained 2.21 ± 0.65 kg/day (n = 12), or 54% of the mass lost during nursing. Growth rates reported here are higher than those reported in other breeding
sites. However, the ratio of body mass loss by females to gain by their pups was similar, suggesting that higher growth rates
and greater weaning mass at South Shetland are due to a higher mean weight of females on arrival at this breeding site. The
foraging period was shorter and the mass gained greater than those measured at South Georgia; this could be related to relatively
shorter distances to foraging areas.
Received: 20 September 1996 / Accepted: 28 April 1997 相似文献