Ian Newton

UK Centre for Ecology & Hydrology | CEH · Wallingford, OXON

Irruptions by boreal seed‐eating and frugivorous birds are assumed to be driven by the production of seeds and fruits, crops of which are highly variable between years. Using data from Sweden, we tested whether irruptions of Common Crossbills Loxia curvirostra were correlated with low Norway Spruce Picea abies seed production in the same year as th...

Populations of some fish‐ and meat‐eating birds suffered dramatic declines globally following the introduction of organochlorine pesticides during the late 1940s and 1950s. It has been hypothesised that these population declines during the 1950s–1970s were largely driven by a combination of reproductive failure due to eggshell‐thinning, egg breakag...

Owing to the intensity of game management in Britain, managers of grouse moors have illegally killed raptors to increase the numbers of Red Grouse Lagopus l. scotica available for shooting. This paper summarizes evidence for the recent scale of illegal raptor killing on grouse moors and its effects on populations. It provides insights into how rapt...

With recent increases in the numbers of reintroduction projects, it has become crucial to know the main factors that allow colonization of new areas and prevent the extinction of small and reintroduced populations. Dispersal is one of the most important phenomena in population biology with consequences to the proportion of individuals that keep bre...

• The present biodiversity crisis has led to an increasing number of reintroduction programs, and this conservation method is likely to be increasingly used in the future, especially in the face of climate change. Many fundamental questions in population ecology are focused on the mechanisms through which populations escape extinction. • Population...

Population density around the natal site is often invoked as an explanation for variation in dispersal distance, with the expectation that competition for limiting resources, coupled with increased intra-specific aggression at high densities, should drive changes in dispersal distances. However, tests of the density-dependent dispersal hypothesis i...

Supplementary feeding is a common practice to raise reproductive output in raptors and other species; nevertheless, its application in conservation has only recently been discussed critically. Here, we analyse the effect of supplementary feeding in territorial raptors, taking advantage of two long‐term datasets for the Spanish imperial eagle ( Aqui...

This review examines the main developments that have occurred over the past 50 years in our understanding of three aspects of raptor biology: (1) natural factors that limit breeding densities; (2) influences of toxic chemicals; and (3) movements and migrations. Early evidence indicated that raptor breeding densities were limited naturally by the av...

Many threatened species in Europe have been expanding their distributions during recent decades owing to protection measures that overcome historical human activity that has limited their distributions. Range expansion has come about via two processes, natural expansion from existing range and reintroductions to new ranges. Reintroductions may prov...

Organochlorine pesticides disrupted reproduction and killed many raptorial birds, and contributed to population declines during the 1940s-1970s. We sought to discern whether and to what extent territory occupancy and breeding success changed from the pesticide era to recent years in a resident population of Peregrine Falcons Falco peregrinus in sou...

This paper reviews the literature on survival estimates for different species of raptors and owls, examines the methods used to obtain the estimates, and draws out some general patterns arising. Estimating survival usually involves the marking of birds so that they can be recognised as individuals on subsequent encounters This article is protected...

We report on an 11–year study of floater interference in a population of Spanish Imperial Eagles Aquila adalberti. We analyzed changes over the years in the productivity of 15 territories to test predictions of two hypotheses of density-dependent productivity in relation to the presence of floaters (birds without territories). According to the ‘int...

Factors influencing vital demographic rates and population dynamics can vary across phases of population growth. We studied factors influencing survival and fidelity of peregrine falcons in south Scotland-north England at two stages of population growth: when the population was recovering from pesticide-related declines and density was low, and whe...

Endangered species subjected to reintroduction programmes often occur as small and isolated populations with local high density and depressed fecundity. Variation in territory quality may lead to this low fecundity owing to increasing occupation of suboptimal territories as population density grows, known as the habitat heterogeneity hypothesis ( H...

Satellite tracking is an invaluable tool in the study of bird movements. However, the normally small sample size it involves makes it difficult to obtain data spanning the entire range of migratory behaviour found in particular populations. We recently reported that Spanish immature Short-toed Snake Eagles leave their winter quarters in sub-Saharan...

This is the second paper in a series to mark the research interests of former 8B editor Stanley Cramp, and looks at the impact of pesticides on birds over the past 50 years or so. Cramp's interest in this subject was related to the effects of organochlorine pesticides, and this paper summarises the way in which these pesticides affected both indivi...

The partial recovery of large birds of prey in lowland Britain has reignited conflicts with game managers and prompted a controversial U.K. government proposal to investigate ways of limiting losses to pheasant shooting operations. Yet best estimates are that buzzards are only a minor source of pheasant mortality–road traffic, for example, is far m...

We used analyses of stable hydrogen isotope (δ2H) measurements in Common Crossbill feathers (δ2Hf) to infer the region of origin of Crossbills collected from different irruptions into Britain, Iceland and the Faeroes, comparing these values with those from birds sampled in breeding areas in Britain and elsewhere in the western Palaearctic. No diffe...

Peregrine Falcons, Falco peregrinus tundrius, were historically unknown to Inuit and early explorers in the Pituffik (Thule) area, northwest Greenland (75.90– 77.60° N). Here we provide information collected from 1993–2005 on what we believe is a recently established and expanding population of High Arctic nesting Peregrines in the area associated...

The three main energy-demanding events in the yearly cycles of birds—breeding, moult and migration—tend to occur at different times of year from one another, with minimal overlap. The sequence in which these various events occur varies according to the ecological conditions (including those encountered during migration) in which particular populati...

This paper is concerned mainly with the differences between obligate and facultative migration in birds. Obligate migration is considered “hard-wired”, in that the bird seems pre-programmed to leave its breeding area at a certain time each year, and to return at another time. Timing, directions and distances are relatively constant from year to yea...

Little information exists on the movements of Gyrfalcons Falco rusticolus outside the breeding season, particularly amongst High Arctic populations, with almost all current knowledge based on Low Arctic populations. This study is the first to provide data on summer and winter ranges and migration distances. We highlight a behaviour previously unkno...

Birds use change in daylength during the year to time events during their annual cycles. Individual Eurasian siskins Carduelis spinus can breed and winter in widely separated areas in different years. Birds at different latitudes will experience different changes in photoperiod. So how does latitude affect photoperiodic control? Our aim in this stu...

Recent research has confirmed the efficacy of migration monitoring to estimate trends in the populations of raptors sampled at traditional watch-sites. We used autumn satellite tracks of 57 adult Ospreys (Pandion haliaetus) captured on the breeding range in North America between 1995 and 2000 to assess the extent to which migration monitoring sampl...

Each year over five years (1962–67), the ratio of first-year to adult Bullfinches netted in Wytham Woods, near Oxford, increased from July or August to October, then declined to a fairly constant level from January onwards. The first-year to adult ratio in October, used as a measure of annual productivity, varied from 2.8 to 5.5 in different years....

Counts of singing male songbirds on Bookham Common (southeast England), conducted almost every year from 1949 to 1979, covered the periods of Sparrowhawk decline and recovery. We examined these counts for evidence of an influence of Sparrowhawk predation on the breeding densities of their songbird prey. Of 13 species examined, no convincing evidenc...

This paper summarises the migration periods of birds at Dungeness Bird Observatory, Kent, southeast England, as calculated from daily counts conducted over an 18‐year period. Mean spring migration dates for different species ranged between 6 February (Greenfinch Carduelis chloris) and 26 May (Reed Warbler Acrocephalus scirpaceus), and mean late sum...

IntroductionSome general points about pesticidesDirect impacts on populationsIndirect effects on populations through food shortageAlteration of habitats by pollutantsGenetic aspectsUse of historical materialConclusion

Differences between species in breeding seasons are thought to be mediated through differences in their reproductive physiology. Little is known about how the timing and duration of gonadal maturation varies between raptor species, how the timing of moult relates to the gonadal cycle, whether the timing and degree of sexual maturation varies betwee...

Stochastic variation of sex ratio has long been appreciated as a potential factor driving small populations to extinction, but it is not the only source of sex-ratio bias in small populations. We examined whether some consequences of sex allocation could affect extinction risk in small populations of size-dimorphic birds such as eagles. We report v...

At three nests of Accipiter nisus the young were brooded almost continuously for the first seven or eight days, then steadily less until days 12–15, and thereafter chiefly during rain. The male provided almost all the food for the first seven or eight clays, after which his rate of prey delivery slackened off. This coincided with increased hunting...

Sexual DimorphismMating SystemsDispersionDensitiesLife History StrategiesFood ConsumptionEffects on Prey PopulationsEvolutionary Aspects

Gyrfalcons Falco rusticolus use the same nest-sites over long periods of time, and in the cold dry climate of Greenland, guano and other nest debris decay slowly. Nineteen guano samples and three feathers were collected from 13 Gyrfalcon nests with stratified faecal accumulation in central-west and northwest Greenland. Samples were 14C dated, with...

Capsule Adult European Goldfinches in east‐central England started moult on 30 July (estimated 95% range 13 July–16 August) and took 77 days (se = ± 4 days) to moult their primary wing feathers.

Capsule For 3748 bird carcasses found on 4.7 km of shoreline, the main cause of death was starvation. Three percent of deaths were attributed to wind turbines.Aims To assess the main mortality causes from bird bodies washed ashore near wind turbines built in 1993.Methods Weekly searches were made for bird carcasses to ascertain causes of death. Exp...

Among other things, this study confirms that Merlins nesting near afforested areas continue to rely on open country for their hunting.

This study of the breeding success of Sparrowhawks in an area of pesticide usage in southern Scotland shows that, although some recovery in the population is now evident, success remains low because of a number of factors—failure to lay, egg-breakage, embryonic deaths—which have been linked with high pesticide residues.

Though breeding on remote moorlands, the Merlin moves to lowland areas for the winter, and is there exposed to contamination by pesticides. An examination of the nest record cards reveals a similar pattern of breeding failure to that reported for the Peregrine and Sparrowhawk in recent years. Losses of part and even whole clutches after the start o...

Weights of birds in winter, by I. Newton & P. R. Evans

1. An account is given from sight observations of the foods eaten by the Bullfinch throughout the year. 2. The diet can be broadly divided according to season : buds in spring, insects in early summer, berries in autumn and seeds during late summer and winter. 3. It is suggested that during bud eating, the embryonic flower only is taken, which is w...

Capsule No obvious effects were detected, except for reduced Cormorant Phalacrocorax carbo presence after construction. Aim To check for differences in the numbers and behaviour of seabirds following construction of two turbines 1 km offshore. Methods Shore‐based two‐hour watches were conducted several times per month during 26 months before turbin...

Moult is one of the three main energy‐demanding events in the yearly cycles of birds, and in most species occurs at a different time from breeding and migration. The sequence in which these events occur varies according to the ecological circumstances in which particular populations live, and in general moult is more variable in timing than other e...

The numbers of Eurasian Sparrowhawks Accipiter nisus that breed in any landscape depend primarily on the amount of woodland, but within that woodland breeding densities vary with the prey supply. In continuous woodland, pairs space themselves regularly, but more widely in areas where prey are scarce. In particular areas, providing that the environm...

An estimated 19% of the world's 9,856 extant bird species are migratory, including some 1,600 species of land- and waterbirds. In 2008, 11% of migratory land- and waterbirds were classed by BirdLife International as threatened or near-threatened on the IUCN Red List. Red List indices show that these migrants have become more threatened since 1988,...

In a study area in south Scotland, Sparrowhawks did not occupy the available nesting places at random, but more often used those places where breeding success was highest (here called high-grade places). Most birds stayed on particular nesting places for only one year, but others stayed up to 8 years. Some birds moved from low- to high-grade places...

Long-term capture-recapture of female Sparrowhawks Accipiter nisus nesting in three different areas enabled age-related survival rates to be calculated, after correcting for age-related and annual variations in recapture frequency. The data provided strong evidence for an improvement in survival rates in the first 3 years of life and for a decline...

The method most commonly used to assess the timing and duration of moult in birds is based on the moult scores of individuals caught in moult, while non-moulting individuals caught at the same time are ignored. Underhill and Zucchini (1988) produced a statistical model of avian moult which incorporated data from non-moulting birds and which could b...

The distribution of feather tracts and their sequence of moult in the Bullfinch is described. The adult post‐nuptial moult, which is complete, lasted 10–12 weeks, and the post‐juvenile moult, which is partial, 7–9 weeks. Adult moult began with the shedding of the first (innermost) primary and ended with the replacement of the last. Variations in th...

Species may differ in the relationship between the numbers of breeding pairs present and woodland area, because the proportion of a wood that forms suitable habitat will vary with woodland size. In this paper, we examine the pattern of variation in abundance with woodland area for eight breeding bird species, and also show how this pattern varied b...

Over a 20-year period, the numbers of Eurasian Sparrowhawk Accipiter nisus nests found in a 200 km2 area in south Scotland remained relatively stable (mean 33.3 pairs, CV = 10.6%). Nest numbers fluctuated from year to year in a manner expected of a population subject to density-dependent regulation. The numbers of non-breeders (floaters) could not...

Annual counts of the five commonest bird species in an oak wood in southeastern England over 22 years showed evidence for density-dependent feedback in their year-to-year fluctuations. The counts also showed evidence for effects of winter weather in two species (Wren Troglodytes troglodytes and Robin Erithacus rubecula). Evidence for density-depend...

The timing and duration of primary moult were estimated for wild adult Starlings Sturnus vulgaris near Monks Wood in 1977-78, and for captive birds in 1999. The model of Underhill and Zucchini (1988) was modified to allow for a non-linear increase in the moult score, based on scores of captive birds. For wild birds, estimates of moult duration in 1...

On the basis of Sparrowhawks Accipiter nisus found 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 wit...

Using ring recoveries, the post-fledging survival of Sparrowhawks was examined in relation to the growth rates and fledging masses of young and in relation to the size and sex composition of broods, which contained up to six young. On most aspects, no significant relationships were found: light young survived as well as heavy ones, both in the popu...

Males hunted at shorter distances from the nest and less often in open country than did females. Possible explanations are 1) the smaller male is more manouevrable in thick cover and better able to catch prey there; 2) females, preferring larger prey, find such species more available in farmland; and 3) by keeping in cover, males decrease their cha...

The levels of various contaminants were measured in 550 addled and deserted Peregrine Falco peregrinus eggs obtained in Britain during 1963-86. In this period the population was recovering from a low level imposed by organochlorine pesticides. Over the whole period, HEOD levels declined in eggs from both inland and coastal regions, while DDE levels...

During the northern winter, Palaearctic migrant species are not evenly distributed within sub-Saharan Africa. Species numbers are greatest in a belt of savannah, lying south of the Sahara, and decline southwards. For any one latitude, species numbers are also greater in the east of Africa than in the west. Only about 3% of 187 species winter exclus...

The habitats and foods of ten species of finches studied near Oxford, England, are described in detail, and differences in feeding habits between them are related to differences in bill‐ and leg‐structure, body‐weight and behaviour. The Hawfinch, Siskin, Redpoll and Crossbill live primarily in woodland, the Greenfinch, Linnet and Goldfinch primaril...

In south Scotland, most Peregrines returned to the same territories to breed in successive years, though a few females changed territory from one year to the next. Annual mortality among breeding birds was at most 9% among females (or 11% in both sexes combined). There may have been considerable annual variation, however, and excluding one exceptio...

Twenty-nine Red Kites, that were tagged as nestlings in Wales, bred for the first time at 2–7 years old (mean 3–6). A minimum of 41% of tagged young had entered the breeding population by the 7th year. Individuals moved up to 22 km between birthplace and breeding place and, having bred, most stayed in the same locality from year to year. No differe...

In two recent papers, we found support for the hypothesis of an association between the occurrence of top predators and biodiversity. Such results were recently criticized. Cabeza, Arponen & Van Teeffelen (2008 ) claim that the proper way to test the investigated relationship was to conduct a regional‐level complementarity analysis that pools all p...

1. Beja & Palma (2008, Journal of Animal Ecology, 77, doi: 10.1111/j.1365-2656.2007.01312.x) attempt to provide a critical analysis of the effectiveness and limitations of a previously published method (Ferrer et al. 2006, Journal of Animal Ecology, 75, 111-117.) to discriminate between Habitat Heterogeneity Hypothesis and the Individual Adjustment...

California condors (Gymnogyps californianus) released into the wild in Arizona ranged widely in Arizona and Utah. Previous studies have shown that the blood lead concentrations of many of the birds rise because of ingestion of spent lead ammunition. Condors were routinely recaptured and treated to reduce their lead levels as necessary but, even so,...

(1) This paper examines removal and other experimental studies on the role of territorial behaviour in the limitation of bird densities. Experimental design is discussed, as are the types of conclusions that can be drawn. (2) Experiments have been conducted on more than 40 species from a wide range of taxonomic groups. Most provided evidence for de...

We used the stable isotope composition of body feathers to show the extraordinarily varying regional provenance of an irruptive conifer seed specialist, the common crossbill Loxia curvirostra. In the boreal region of the western Palearctic, this species specialises on the seeds of Norway spruce Picea abies. The patterns of deuterium in the feathers...

Records indicate that many bird species have changed some aspects of their migratory behavior during the last century or more, in response to changed conditions with earlier arrival in spring, earlier or later departure in the autumn, shortening or lengthening of migratory routes, directional changes, and reduced or enhanced migratoriness. Many of...

This chapter is concerned with the variations in annual cycles between bird species are regulated by both external and internal influences. Migration is timed so that birds can be present in their breeding areas at least for long enough to breed successfully, but are absent for the unfavorable season when their survival chances would be much lower...

This chapter deals with the types and amounts of fuel accumulated by birds, with the process of fueling and other changes in body composition, and with how these features vary with the types of journeys undertaken. The full cost of migration consists of the energy needed to fuel the flight plus the energy needed to maintain the bird over the whole...

This chapter illustrates different types of evidence indicating that events at stopover sites can influence the migratory bird populations. The chapter views the limitation of breeding populations through migration events mainly as a three-step process, involving food availability at stopover sites, carry-over effects of migration performance on su...

This chapter examines some of the more puzzling migration patterns of birds in order to understand how they might have evolved, and why they continue to persist. Some extraordinary journeys can be explained most plausibly in terms of past conditions which may have influenced their development. The five aspects considered in the chapter are —indirec...

This chapter focuses on some of the difficult journeys of birds, and the various adaptations that enable them to complete the migration successfully. While some birds migrate around mountain ranges, others cross even the highest ranges, including the Himalayas. The main problems are the climb to high altitudes and the extreme cold, low air densitie...

This chapter explains the possible factors causing the decline in population of migrants. Many European species that winter in Africa have declined in recent decades, raising questions about whether the causal factors lie in the breeding or wintering areas. The distributions, ecology, and movements of the migrants within Africa have therefore attra...

In many bird populations, sex and age groups differ in aspects of their migrations. Such differences include the proportions of each sex and age group undertaking migration, the timing of outward and return journeys, and the distances traveled. The sex and age differences occur in the proportions of individuals that migrate, in the timing of outwar...

This chapter focuses on the speed and duration of journey of birds. Depending on the distance traveled, a one-way migratory journey can last for several hours up to several months, including resting, fueling, and flight times. Some species that migrate long distances between northern and southern hemispheres spend around half of each year on migrat...

This chapter deals with vagrancy, which is a natural phenomenon resulting from several different types of causal factors. The term vagrant is applied to any exotic visitor of a species which does not normally breed, overwinter or pass through the region concerned. Vagrants are birds that appear from time to time far removed from their usual haunts,...

This chapter discusses migrating pattern within the species, and duration of distances during migration, etc., with apt examples. When spring approaches, migratory birds begin to move from lower to higher latitudes in order to re-occupy their breeding areas. The large-scale distributional changes during breeding enable birds to exploit the surge in...

This chapter is concerned with two other groups of irruptive birds, namely, those owls and other predators that specialize on voles and other cyclically fluctuating prey species, and waterfowl that depend on ephemeral wetlands. Again, the large-scale movements of these species can best be understood in light of their underlying ecology, which I the...

This chapter deals with the control of migration with the factors that stimulate migration at appropriate times of year and influence the preferred directions. It is concerned with the external factors to which birds respond, such as day length and food supply, and also with the internal regulating mechanisms. In obligate migration, all main aspect...

This chapter summarizes some major recorded mortality incidents attributed to inclement weather and other factors, including in-flight losses caused by storms and other adverse weather en route, usually over water; unseasonable cold weather soon after arrival in breeding areas; and unseasonable cold weather before departure from breeding areas. Mig...

The author divides bird movements into six main types, namely, everyday routine movements, dispersal movements, migration, dispersive migration, irruptions (or invasion migrations), and nomadism. The large-scale movements of birds can conveniently be divided into dispersal, dispersive-migration, migration, irruption, and nomadism, although these di...

This chapter describes the evolutionary aspects of migration. Autumn migration gives improved winter survival through providing access to greater food availability in winter quarters. Some bird populations are obligate migrants and others are obligate residents. Some studies on the relative merits of migratory versus resident behavior have involved...

Variants occur around the basic outward-return movement between fixed breeding and wintering ranges in a limited number of species, which can all be related to the particular ecological circumstances faced by the species concerned. All these aspects are described in this chapter. The birds from different parts of the breeding range inherit differen...

This chapter describes how birds behave in different weather conditions, with the altitudes at which they fly, with day–night patterns of migration, and with the influence of social factors, such as the sizes and formations of flocks. In all these aspects of migration, the interest is in seeing how birds of different kinds adjust their behavior to...