摘要:

The breeding densities of birds could be limited by resources, such as food and nest sites, or they could be held at a lower level by natural enemies, such as predators and parasites. In this paper, I review the experimental evidence for each of these limiting factors affecting bird breeding densities. Of 18 experiments involving winter food provision (mostly on tits, Paridae). 11 led to increased breeding densities compared with control areas. Of four involving summer food depletion (all on forest insectivores), none led to decreased breeding densities. In experiments with Red GrouseLagopus 1. scoticus, fertilizing areas of heather moor led to increased densities during a period of population increase but did not prevent a later decline. Of 32 studies on tree‐cavity nesters, the provision of nestboxes led to increased breeding density in 30 (95%) studies, each involving one or more species of hole nesters. Of 15 experiments involving predator removal (mostly on ducks and gamebirds), at least 14 led to increased hatching success, four out of eight led to increased post‐breeding numbers, and six out of 11 led to increased breeding density. In one experiment, the removal of strongyle parasites from a Red Grouse population prevented a cyclic decline on five out of five occasions. Taken together, these experiments confirmed that all main potential external limiting factors have affected breeding density in one bird species or another. They also confirmed that the same species has been limited by one factor in certain areas or years and by another factor in different areas or ye

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01115.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The causes of collision and electrocution accidents involving birds and power lines, and measures to mitigate such accidents, are reviewed. It is convenient to group the causes according to (1) biological, (2) topographical, (3) meteorological and (4) technical aspects. As regards collisions with power lines, the important biological variables are connected with the morphology, aerodynamic capability, physiology, behaviour and life‐history strategies of birds. To understand the electrocution problem, the relationship between body size and electrocuting installations must be considered.Removing earth wires (and modifying earthing methods). modifying line, pole and tower design, installing underground cables and conspicuous marking of lines, poles and towers are important measures for tackling the problems. The route planning process should include careful mapping of (1) topographical features which are leading lines and flight lanes for migrating birds and/or are important for local movements of resident species, (2) topographical elements such as cliffs and rows of trees that force birds to fly over power lines, (3) primary ornithological functions or uses of the area to avoid key areas for birds and avoid separating these areas and (4) local climatic conditions (including seasonal variations) like fog frequency and prevailing wind direction. The outcome depends largely on a combination of these factors.Objective assessment of the effects of mitigating measures, in particular wire marking, is required. The mitigating efforts should be directed against species known to be potential collision victims, and their design should be the result of a careful analysis of the biology and ecology of the target species.Because of the cumulative effects of negative impacts on bird populations today and the alarming number of species with endangered or vulnerable status being killed in connection with utility structures, the problem deserves increased general awarenes

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01116.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The progeny of early‐nesting SparrowhawksAccipiter nisushave a higher survival rate than those of late nesters. To ascertain the reasons for greater survival in early‐season Sparrowhawk fledglings, I studied post‐fledging dispersal behaviour in this species by direct observations and radio‐tracking during 3 years in Rockingham Forest, Northamptonshire, U.K.Post‐fledging brood‐parasitism was found among early‐dispersed young of both sexes.Early‐dispersed young spent up to 6 days being fed by the parents of other fledged, but still dependent, broods, as far as 6 km from their own nests.Three broods were provided with supplementary food for 4 weeks, starting 1 week before expected dispersal. These young dispersed when significantly older than young from control broods. In both groups, males dispersed, on average, 3–4 days earlier than females. The ultimate dispersal age of young in control broods was negatively correlated with their rate of mass gain during the nestling period. Unlike the young of the control broods, fledglings in broods with augmented food were usually silent.These findings offer an explanation for why Sparrowhawk young that disperse early in the season survive better than those wh

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01117.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

On the basis of SparrowhawksAccipiter nisusfound dead in various parts of Britain during 1979–1991. wing‐length was found to provide the most reliable index of overall body‐size because it gave the best and most consistent correlations with five other measures of body‐size.A marked latitudinal trend in the body‐size of Sparrowhawks was found within Britain, with birds of each sex and age group increasing in size from south to north, in line with Bergmann's Rule. For each successive degree of latitude (approximately 110 km), wing‐length increased by an average of 0.86 mm in adult males and O.75 mm in adult females. No obvious west‐east trend in body‐size was found

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01118.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

This paper presents the first data on the diet of the RavenCorvus coraxin the Canary Islands, based on analysis of 2315 pellets collected from all of the islands and islets in the archipelago. The Ravens on three groups of island showed differences in diet, but in all cases the diet was clearly omnivorous, both in its qualitative and quantitative composition. It is evident that a broadening of the Raven's trophic niche has occurred in comparison with those living in continental areas. While the diet has a strong plant component on the wetter islands (frequency of occurrence>87%), an appreciable animal component in the diet (principally vertebrates) is more frequent on the drier islands of the archipelago (frequency of occurrence>96%). The composition of the plant component of the diet varied markedly from one island to another. Remains of refuse are more commonly found in the Raven's diet on the central and western islands. We concluded that while the animal diet is essential from the bioenergetic point of view, the vegetation diet is only a complementary food source. The Raven plays an important role in seed dispersal among the different habitats within each island.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01119.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The Stone‐curlewBurhinus oedicnemusis a short‐billed terrestrial wading bird (Burhinidae; Charadriiformes) which forages primarily for surface living invertebrates in open, sparsely vegetated habitats during twilight and nighttime. Visual field topography in restrained alert birds was investigated using an ophthalmoscopic reflex technique. The visual fields have the following features: (1) Eye movements of significant amplitude appear to be absent. (2) The retinal binocular field is relatively small, with the bill placed near its centre. It extends vertically through 80° in the median sagittal plane with a maximum width of 18° occurring 5° above the bill. (3) With the head in a typical posture (eye‐bill‐tip angle approximately 15° below the horizontal), the binocular field stretches from 60° below to 20° above the horizontal. (4) The blind area behind the head is relatively narrow (15° at the horizontal), giving the bird near panoramic vision in the horizontal plane, but the widest blind area (32°) occurs directly above the head. (5) Monocular retinal fields in the horizontal plane are 182° wide and are asymmetric about the optic axis. (6) There is a blind sector of 7–12° at the margin of the optical fields, indicating that binocular field widths are not maximized. Interspecific comparisons of these visual field features suggest that the foraging of Stone‐curlews is guided pri

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01120.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The mean weight of eggs in clutches of the Great TitParus majorvaries markedly between clutches. Eggs are lighter in years of high density of breeding pairs than in years of low density, but egg weight is also inversely correlated with the density of breeding Blue TitsParus caeruleus.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01121.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The incidence of extra‐pair paternity in a Great TitParus majorpopulation at Wytham Wood, Oxford, in 1985–1987 was determined using two polymorphic allozymes. In 831 nestlings from 94 broods, 27 genetic exclusions were detected in 25 (3%) nestlings from 16 broods. Seven (44%) of these broods contained offspring that excluded the putative male parent from being the genetic parent. The distribution of exclusion types indicated that excluded offspring were the result of fertilizations by extra‐pair males and not of egg‐dumping. The true frequency of extra‐pair paternity was estimated as 14% of offspring. These results suggest a mixed reproductive strategy for males in which they breed mo‐nogamously whilst simultaneously seeking extra‐pair matings with females o

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01122.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Adult and post‐natal breeding‐dispersal movements of RedshankTringa totanus, DunlinCalidris alpinaand Ringed PloverCharadrius hiaticulawere quantified in west Scotland. Data from 373 returning birds marked as breeding adults and 142 returning birds marked as chicks are presented. Unlike most previous studies, this study measured dispersal movements up to 40 km and attempted to overcome distance‐related biases. For each species, adult males were significantly more nest site‐faithful between years than were adult females. Likewise, first‐time breeding males bred significantly closer to their natal site than did females. The settlement intensity per unit area of habitat showed marked differences between species, age classes and sex in the relative attractiveness of potential areas at different distances to settling birds. Adult dispersal was negatively and significantly related to breeding success in the previous year and positively related to capture on the nest in the previous year. Dispersal movements of adult Ringed Plover breeding on unstable cultivated habitats were significantly related to habitat quality (measured in terms of nest survival) and were always to habitat of better or equa

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01123.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Breeding LapwingsVanellus vanelluswere studied in the Eden Valley (Cumbria) and in Teesdale (County Durham) between 1990 and 1992. A total of 300 adult Lapwings and 801 near‐fledged young were uniquely colour‐ringed. Breeding adults were highly site‐faithful, almost always nesting in the same or an adjacent field in successive years. Second‐year birds were less site‐faithful, with more birds nesting in adjacent and other fields and fewer in the same field in successive years. In Teesdale, 74% of colour‐ringed young Lapwings returned in their first or second year of life to within 5 km from where they hatched. In contrast, in the Eden Valley only 37% of young birds in their first or second year of life returned to within 5 km from where they hatched. From an analysis of British ringing recoveries in April and May, 61% of Lapwings were recovered within 10 km from where they were ringed as chicks. A further 11% were recovered more than 100 km from where they were ringed. Young Lapwings were highly philopatric, with 45% of males and 52% of females breeding in the same field or a field adjacent to where they hatched. The majority of Lapwings (67%) began breeding at 1 year old. Of the remaining birds, 27% bred for the first time when 2 years old and 6% for the first time in their third year of life. There was no difference between the sexes. Chicks hatching and subsequently fledging late in the season returned less frequently to the study areas in subsequent years than did chicks hatching earlier in

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1994.tb01124.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY