26 research outputs found
Genetic diversity, recombination and cross-species transmission of a waterbird gammacoronavirus in the wild
Viruses emerging from wildlife can cause outbreaks in humans and domesticated animals. Predicting the emergence of future pathogens and mitigating their impacts requires an understanding of what shapes virus diversity and dynamics in wildlife reservoirs. In order to better understand coronavirus ecology in wild species, we sampled birds within a coastal freshwater lagoon habitat across 5 years, focussing on a large population of mute swans (Cygnus olor) and the diverse species that they interact with. We discovered and characterised the full genome of a divergent gammacoronavirus belonging to the Goose coronavirus CB17 species. We investigated the genetic diversity and dynamics of this gammacoronavirus using untargeted metagenomic sequencing of 223 faecal samples from swans of known age and sex, and RT-PCR screening of 1632 additional bird samples. The virus circulated persistently within the bird community; virus prevalence in mute swans exhibited seasonal variations, but did not change with swan age-class or epidemiological year. One whole genome was fully characterised, and revealed that the virus originated from a recombination event involving an undescribed gammacoronavirus species. Multiple lineages of this gammacoronavirus co-circulated within our study population. Viruses from this species have recently been detected in aquatic birds from both the Anatidae and Rallidae families, implying that host species habitat sharing may be important in shaping virus host range. As the host range of the Goose coronavirus CB17 species is not limited to geese, we propose that this species name should be updated to ‘Waterbird gammacoronavirus 1’. Non-invasive sampling of bird coronaviruses may provide a tractable model system for understanding the evolutionary and cross-species dynamics of coronaviruses
Sampling strategies for species with high breeding-site fidelity: A case study in burrow-nesting seabirds
Sampling approaches used to census and monitor populations of flora and fauna are diverse, ranging from simple random sampling to complex hierarchal stratified designs. Usually the approach taken is determined by the spatial and temporal distribution of the study population, along with other characteristics of the focal species. Long-term monitoring programs used to assess seabird population trends are facilitated by their high site fidelity, but are often hampered by large and difficult to access colonies, with highly variable densities that require intensive survey. We aimed to determine the sampling effort required to (a) estimate population size with a high degree of confidence, and (b) detect different scenarios of population change in a regionally important species in the Atlantic, the Manx shearwater (Puffinus puffinus). Analyses were carried out using data collected from tape-playback surveys on four islands in the North Atlantic. To explore how sampling effort influenced confidence around abundance estimates, we used the heuristic approach of imagining the areas sampled represented the total population, and bootstrapped varying proportions of subsamples. This revealed that abundance estimates vary dramatically when less than half of all plots (n dependent on the size of the site) is randomly subsampled, leading to an unacceptable lack of confidence in population estimates. Confidence is substantially improved using a multi-stage stratified approach based on previous information on distribution in the colonies. In reality, this could lead to reducing the number of plots required by up to 80%. Furthermore, power analyses suggested that random selection of monitoring plots using a matched pairs approach generates little power to detect overall population changes of 10%, and density-dependent changes as large as 50%, because variation in density between plots is so high. Current monitoring programs have a high probability of failing to detect population-level changes due to inappropriate sampling efforts. Focusing sampling in areas of high density with low plot to plot variance dramatically increases the power to detect year to year population change, albeit at the risk of not detecting increases in low density areas, which may be an unavoidable strategy when resources are limited. We discuss how challenging populations with similar features to seabirds might be censused and monitored most effectively
Some aspects of bill morphology in relation to ecology in the great tit Parus major
The study concluded that bill size was highly adaptive in that it was
related to fitness (in the broad sense) or to some correlate of fitness. The
results are considered in terms of existing niche theory and especially of
"character displacement" and the "variable niche hypothesis"
Breeding biology and feeding ecology of Black guillemots
Since 1974 a population study of Black Guillemots has been
conducted on Flatey Island, NW Iceland. The main aspects
are summarized below.
Population numbers and distribution. The population has
been censused several years, also those of 20 islets near Flatey.
Information was collected on past status. Great changes have
occurred since turn of the century. Last major change began in
1967; the population started increasing of such a scale that
it can only have resulted from massive immigration. These
changes are thought to be due to rats and Mink.
Attendance and population structure. Data was gathered
on timing of spring return to nesting areas, status of attending
birds, sex ratio, area and nest-site fidelity, pair-bond
maintenance, and post-breeding departure. Special attention
has been given to the problem of censusing birds attending
nesting areas.
Breeding biology. Breeding biology variables were quantified
and studied on a seasonal basisj;timing of laying, clutch
size, interval between eggs, egg size, reproductive output,
lengths of incubation and nestling periods. Supernormal clutch
and brood experiments were conducted. I looked at length of
replacement time of lost clutches, factors influencing timing of
laying, its effect and that of clutch and egg size on breeding
performance. Egg and chick losses were analyzed. Many interesting
population phenomena seem to have been associated with the unusually
rapid population increase.
Feeding ecology. Analyses were made of prey taken,
feeding rhythm and areas, and factors influencing feeding
rate and prey selection. Some information was collected on
share of the sexes in feeding chicks, and kleptoparasitism.
Study was made of chick growth, fledging condition and postfledging
survival.
Population dynamics. About 3300 birds were ringed,
providing basis for determining age at maturity, adult survival,
and mortality. Pre-breeding survival was calculated
using data from ringing schemes. A population model was
constructed for the population, showing magnitude of immigration.
Ringing provided data on dispersal.</p
The breeding biology of the Manx shearwater
Chapter 1 is purely introductory and gives a brief account of the
taxonomic status of the subject of this thesis, the Manx Shearwater
Puffinus puffinus. The main study area, Skokholm Island, Pembrokeshire
is described and a general account of what is already known of the breeding
biology of the Manx Shearwater is provided as a background to the more
detailed studies described in the present work which was continued over
five breeding seasons, 1973-1977.
In Chapter 2 I demonstrate that male and female Manx Shearwaters
differed in the length of their bills and tarsi but not in wing length.
However most of the chapter is concerned with the weights and measurements
of shearwaters, most of which were of known age but unknown sex, caught
at the colony by night. In 1973 and 1974 the weight of all age groups was
highest in March and then declined to a minimum in June and July. Weight
increased slightly in August. It was generally true that the older a bird
was, the heavier it was in any particular month, and this effect appeared
to hold good until the birds were 8-10 years old. Unlike weight, bill
and wing length did not alter with age. The implications of these results
are discussed in the light of current hypotheses concerning the delayed
onset of breeding shown by many seabirds including the Manx Shearwater.
In the pre-laying period, covered by Chapter 3, both male and
female Manx Shearwaters lost weight up until about two weeks before
laying. Males lost weight more rapidly than females and this was related
to the fact that males visited the burrow more regularly. In the two
weeks prior to laying the male continued regularly to visit the burrow
at night but the female was virtually absent from the colony; it appears
that she may travel into the Bay of Biscay to feed during this period
of absence. In the pre-laying period the weight of breeding birds was
not different from the weight of birds which have bred formerly but
which were not known to be breeding during the current season. However,
breeding birds tended to be heavier than birds which started to breed
in a future year. To test the possibility that young birds may be
prevented from breeding by a shortage of burrows artificial burrows
were dug, and some were occupied by young birds, probably breeding
for the first time. A burrow-blocking experiment was also carried out.
The possibility that competition for burrows was greater in an area
of higher as opposed to lower burrow density was investigated by
comparing the pre-laying attendance pattern of breeders in the two
areas. No difference was found.
Chapter 4 shows that the breeding success of newly-formed pairs
was lower than that of established pairs, mostly because newly-formed
pairs were less successful at incubation. The lower success of
new pairs was not due to the new pairing per se but to the fact that
such new pairs tended to include birds without previous breeding
experience. Thus experienced birds may avoid the disadvantageous
consequences (to breeding success) of forming a new pair if they
mate with another experienced bird, and this they did. Divorce and
change of breeding burrow were both more likely after a breeding
failure than a success. Both the laying date and egg volume of
individual female Manx Shearwaters varied little from year to year,
once the first few years of breeding were passed. I am unable to
reconcile this finding with Perrins' (1970) suggestion that the
laying date of the female Manx Shearwater is determined by the difficulties
she may encounter early in the season in building up sufficient food
reserves to form the egg. Instead I propose that, although early laying
would be advantageous from the point of view of chick survival
(Perrins 1966), the shearwaters do not lay earlier because of the
difficulties that would be encountered in successfully incubating
an early egg. Evidence supporting this idea is presented.
In each of the four study years the fledging weight of chicks
declined as the season progressed, as described in Chapter 5. Various
lines of evidence, including an egg-swapping experiment, support the
view that this decline was mostly due to a deterioration of feeding
conditions late in the season, rather than to a tendency for parents
less proficient at rearing heavy young to breed later. It seems that
date of fledging and weight at fledging may both influence the
fledgling's chances of survival but I am unable to determine the
relative importance of these two factors. Different pairs of
shearwaters differed in their ability to feed chicks, but chick-feeding
performance was not related to age or breeding experience.
Chapter 6 evaluates the parameters necessary for the construction
of a life table. Of the chicks which fledge from Skokholm at least
25andnbsp;% survive to breed on Skokholm, whilst adult survival is about
90andnbsp;%. About 20andnbsp;% of those adults known to be alive and to have bred
previously do not breed in any one year- The age of first breeding,
currently about six, has increased over the past ten or fifteen years.
Among the birds which have been ringed as chicks on Skokholm and
which bred there during the study period there was a 2:1 ratio of
males to females. I suggest that about half the females fledging from
Skokholm settle to breed in other colonies. The body measurements
(used as an indicator of sex) and abundance of Skokholm-ringed birds
on nearby Skomer Island support this hypothesis. The Manx Shearwater
life table is therefore constructed to take account of immigration
to and emigration from the Skokholm colony. Recruitment to the
breeding population and loss by mortality are roughly equal.
Chapter 7 shows that the calls given by male and female Manx
Shearwaters were different. The response of other shearwaters to these
calls was investigated by means of playback experiments. Females
recognized the calls of their male mates but I am unable to show
a selective response of males to the calls of their female mates.
This difference is considered to be related to the different roles
of the two sexes and to be associated with the fact that most calls
heard from the ground were given by males whilst most calls uttered
in flight were probably given by females. There is no evidence that
nestlings can recognize the calls of their parents.
The value of colonial breeding is considered in the concluding
Chapter 8. It seems that Manx Shearwaters in the dense Main Colony
experienced a lower rate of predation, but they did not have greater
reproductive success than those breeding in areas of lower burrow
density elsewhere on the island. Although nesting habitat on Skokholm
is not fully utilised there may be a limited supply of breeding
burrows available. This would create competition for burrows which,
together with competition for food, is suggested as an important
influence on the breeding biology of the Manx Shearwater.
There are four appendices. The first shows that birds first
caught in the colony at two years old were caught earlier in the
year when three years old than those which were caught for the
first time at three. Similarly, birds which have been caught when
two or three years old were caught earlier in the year when four years
old than those birds which were caught for the first time at four.
These differences in time of return to the colony appear not to be
associated with sex. Appendix 2 discusses the relationship between
the body size of offspring and their parents. In the Manx Shearwater
it appears that about three-quarters of the phenotypic variance of
body size is due to genetic causes, and may therefore be inherited.
Appendix 3 describes a simple experiment designed to test the
possibility that vision may be one sense used by Manx Shearwaters
attempting to locate their breeding burrow. The result of the
experiment was positive but more extensive tests would be required
to assess the relative roles of vision and any other senses that may
be employed in burrow location. Appendix 4 describes an unsuccessful
visit to the Basque coast of northern Spain to assess the status of
the Manx Shearwater in the south-east corner of the Bay of Biscay
in the pre-laying period, late April. I tentatively suggest that it is
only in exceptional circumstances that many shearwaters feed south
of about 46° N.</p
Interspecific competition between Blue and Great tits
Great tits (Aves: Passeriformes; Parus major) and blue tits
(Parus caeruleus) nested in boxes in Wytham Woods near Oxford. The
breeding densities of both species were limited by the availability
of nest sites. The larger great tits were dominant in obtaining nest
boxes. This was most important where breeding sites were scarce. The
two species did not maintain interspecific territories or interfere
with interspecific nest site spacing beyond the immediate vicinity
of the nest. Blue and great tit numbers fluctuated in parallel where
nest sites were not limiting resources. Annual changes in breeding
numbers of great tits were negatively related to blue tit breeding
density but great tit density did not seem to affect changes in the
blue tit population.
Overlap in the feeding sites of blue and great tits was greatest
during the summer and interference competition was lowest at this time.
The nestling diets of the two species were very similar. Despite an
apparent abundance of food for nestlings, adults were pressed to feed
large broods. Food for nestlings was probably a limiting and
depletable resource.
The date of clutch initiation of great tits, but not blue tits,
was retarded at high densities of blue or great tits. The clutch
sizes of both species were probably negatively affected by high breeding
densities of congeners but the results were not clear cut.
Heavy great tit fledglings are most likely to survive to breed.
Great tit fledglings were heavier at low densities of blue tits. An
experiment in which blue tit young were removed from a section of the
Woods, showed that great tit nestlings were heavier and developed
faster, and that female condition was better, than in a control
section or section where blue tit broods were supplemented.
In terms of resource competition, blue tits were the better
scramble competitors and great tits the better interference
competitors.</p
Sparrowhawk (Accipiter nisus) predation on tits (Parus spp.)
The present research was conducted to assess the effect of
Sparrowhawk predation on the tit population of Wytham Woods, Oxford.
Chapter 1 describes the history of the Wytham hawk population
until this study began and the nesting biology of the hawks during
the study. Six to nine pairs of hawks settled in the wood each year,
but reproductive success was low due to pesticide contamination.
Chapter 2 shows that tit nesting success was reduced when they
nested near hawk nests. Circumstantial evidence is presented for
reduced tit nesting success throughout the wood since the return of
the hawks.
Chapter 3 examines rates of hawk predation during the nesting
period. Findings indicate that hunting rates and the percentage of
the diet formed by tits are regulated by prey availability or
vulnerability, with highest predation rates occurring at the time
that tits fledge.
In Chapter 4 the selection of tits by hawks is analysed.
Results indicate that on the basis of brood and physical
characteristics adult tits were selected on the basis of availability
and juvenile tits were selected primarily by date of fledging.
The ratio of adult to juveniles taken differed between years and was
thought to be related to the number of tits available per hawk each
year.
Chapter 5 presents estimates showing that 22-42% of each
segment of the tit population was killed by hawks each year.
The effects of these losses are discussed, concentrating on the
shift in the structure of the tit breeding population which has
occurred since the hawks returned to the wood.
In Chapter 6 the findings of the study are compared to the
findings of previous predator-prey research and the attributes of
Wytham as an area for studying predation discussed.</p
Factors affecting the status of the chough in Britain, with observations on its behaviour
This thesis aims to fill gaps unfilled by the recent upsurge in
Chough studies. These are: the classification and functional analysis
of aspects of their behaviour, examining feeding preferences in
relation to land management, finding how literary attitudes towards
them developed and obtaining quantitative insights into their past
distribution to apply to possible explanations for their status
changes.
Three pairs near Llangranog, Dyfed were observed and findings were
complemented with analysis of RSPB film offcuts.
All observed behaviours were defined and classified according to
social context and frequency of use. Of 45 behaviours seen, 21 had not
previously been recorded. Single-link cluster diagrams were presented
to illustrate observed postures and comparable corvid postures.
Three aspects of their social behaviour were further examined:
Food-begging by juveniles and females was related to time since
fledging and copulation date respectively. Begging success depended on
technique repertoire, which increased with time; increased foraging
group size decreased the individual's vigilance time spent, with an
earlier detection of potential tourist disturbance; wing-flicking did
not occur with short flights nor after flights due to disturbance. It
was frequent after landing while as frequent before take-off as during
foraging excepting tourist disturbed flights. Ritualised forms of
wing-flicking and bill-wiping formed the basis of Chough communication.
Flow diagrams and canal models describing the functional organisation
of these behaviours are presented.
Choughs feed on short, mainly grass swards maintained by grazing,
exposure and occasionally, cutting.
When given the Jackdaw's old name, Choughs acquired their thieving
reputation and were also regarded as fire-raisers until the 1830's.
Distribution and abundance from 1750 to 1982 were estimated at county
and national level. Their status was not significantly affected by
climate. Grazing artificially boosted their numbers, agricultural
changes and persecution from 1750 until 1940 caused their decline.</p