Bio: Dieter Wend is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.
TL;DR: The shapes of the tips of Corncrake Crex crex secondary remiges grown by chicks and adults were compared and the average shape of the tip of secondaries of one year old adults was different from that of older birds.
Abstract: The shapes of the tips of Corncrake Crex crex secondary remiges grown by chicks and adults were compared. Measurements of secondaries of birds of known age were obtained from wild Corncrakes in Britain and captive‐bred birds originating from Germany and Poland. The tips of secondaries grown in the hatching year were more pointed than those grown in subsequent years in both samples. Secondaries grown in the hatching year are retained until the autumn of the next calendar year. Consequently the average shape of the tips of secondaries of one year old adults was different from that of older birds. The sum of the angles measured at the tips of secondaries 3 to 6 inclusive (numbered ascendantly) was used to quantify this difference. The angle sum scores of known first‐years and older birds overlapped, but it is possible to estimate the proportions of the two age classes in a sample of adults of unknown age by assuming that the distribution of scores is the combination of two normal distributions with means and...
TL;DR: A new approach to the estimation of the adult survival rate of Corncrakes is described based on surveys of males calling during the breeding season and measurements on captured birds of a plumage characteristic that changes with age, which produces the first survival estimate for adult female CorncRAkes.
Abstract: The mean annual survival rate of adult Corncrakes Crex crex was estimated by three independent approaches: ring-recovery, ring-recapture and the shape of secondary remiges. The last method is new and uses measurements of the shape of the tips of the secondaries, which changes in the first post-juvenile wing moult to become less pointed. The estimates obtained by the three approaches were mutually compatible and indicated that annual survival is likely to be within the range 0.2‐0.3. This low survival rate is likely to make the growth rate of Corncrake populations particularly sensitive to the effects of agricultural and conservation management on breeding success and recruitment. The survival rate of adult female Corncrakes was estimated for the first time (0.259) and was found not to differ significantly from an estimate for adult males (0.298) made in the same study area by the same method. It is concluded that the method based upon population counts and measurements of the shape of remiges has potential value for studies of the demography of Corncrakes and other species. Estimates of the demographic rates of birds are important for studies of population dynamics and can provide insights relevant to conservation management (Green 2002), but practical problems often make reliable estimates difficult to obtain, in spite of considerable advances in analytical methods (White & Burnham 1999). This is especially true for the estimation of survival rates in the Corncrake Crex crex. Several workers have noted the low return rate of ringed Corncrakes to restricted study areas in subsequent years (Alnas 1974, Swann 1986, van den Berg 1991, Fox 1993). Estimates of dispersal distance and survival of male Corncrakes in Scotland and Ireland by Green (1999) indicated that there was much long-distance (> 10 km) natal dispersal, leading to low return rates of birds ringed as chicks, but that breeding dispersal was restricted and adult survival was low (< 0.2), even after allowing for emigration from the study areas. In these circumstances, it has not been practical to obtain sufficient recaptures for robust estimation of survival from conventional Cormack‐Jolly‐Seber analysis. The ringing of 900 Corncrakes and considerable efforts to recapture them in subsequent years resulted in only 40 recaptures, and, more importantly, the low survival rate led to only six of these recaptures being made more than 1 year after ringing and there were none at all more than 2 years after ringing (Green 1999). This lack of recaptures over periods of more than about 2 years has also been noted in studies in Sweden (Alnas 1974), The Netherlands (van den Berg 1991) and Ireland (Fox 1993). This makes the estimation of recapture and survival rates by Cormack‐Jolly‐Seber methods problematic. In this paper I describe a new approach to the estimation of the adult survival rate of Corncrakes based on surveys of males calling during the breeding season and measurements on captured birds of a plumage characteristic that changes with age. As well as yielding a new estimate for males, this method produces the first survival estimate for adult female Corncrakes. I also estimate adult survival from the few available ring recoveries and compare this with the estimate from the new method and the existing estimate from ring-recapture.
TL;DR: The proportion of adult corncrakes that are 1-year old was estimated from feather characteristics of birds collected before, during and after the population decline and showed a marked transitory reduction during the decline.
Abstract: Long-term studies of demographic rates provide clues about the external causes of animal population declines, but systematic monitoring is rarely in place until after the decline has occurred. This study evaluates alternative hypotheses about the demographic mechanisms underlying the historical collapse of corncrake (Crex crex) populations in Britain and Ireland in the late nineteenth and early twentieth centuries using characteristics of museum specimens. The proportion of adult corncrakes that are 1-year old was estimated from feather characteristics of birds collected before, during and after the population decline and showed a marked transitory reduction during the decline. This pattern would be expected if the decline was caused by a large reduction in the recruitment of young birds to the breeding population and is the opposite of what would be expected if a change in adult survival had caused the decline. These results are consistent with previous suggestions that the corncrake population decline was caused by adverse effects on breeding productivity caused by the mechanization of the harvesting of hay crops.
TL;DR: This paper describes a general statistical framework for estimating the true stage distribution of a sample when misclassification rates can be estimated and analyzes age-structured harvest records from black bears in Pennsylvania to illustrate how incorporating mis classification errors leads to changes in point estimates and provides a measure of precision.
Abstract: Ecologists often use samples from the age or stage structure of a population to make inferences about population-level processes and to parameterize matrix models. Typically, researchers make a simplifying assumption that age and stage classes are determined without error, when in fact some level of misclassification often can be expected. If unaccounted for, misclassification will lead to overly optimistic levels of precision and can cause biased estimates of age or stage structure. Although several studies have used information from known-age individuals to quantify errors in age or stage distribution, the problem of estimating the age or stage structure in face of such errors has received comparably little attention. In this paper, we describe a general statistical framework for estimating the true stage distribution of a sample when misclassification rates can be estimated. The estimation process requires auxiliary information on misclassification rates, such as data from individuals of known age. We analyze age-structured harvest records from black bears in Pennsylvania to illustrate how incorporating misclassification errors leads to changes in point estimates and provides a measure of precision.
TL;DR: The 65th annual report of the British Trust for Ornithology's Ringing Scheme covering work carried out and data received in 2001 as mentioned in this paper, shows that the survival rates of young birds was key in the population decline; reduction in survival rates also seemed to have driven the fall of Marsh Tits.
Abstract: This is the 65th annual report of the British Trust for Ornithology's Ringing Scheme covering work carried out and data received in 2001. As part of the BTO's production of the landmark Migration Atlas: movements of the birds of Britain & Ireland, which will review movements of birds using Britain & Ireland, novel approaches to the investigation of the movement patterns and distances were developed. These allow the objective comparison of whether different species are sedentary, short‐distance or long‐distance migrants and the investigation of differential migration between birds of different age and sex. The BTO continues to carry out a programme of work investigating the declines in bird populations. In 2001, an investigation of Song Thrush population dynamics showed that the survival rates of young birds was key in the population decline; reduction in survival rates also seemed to have driven the fall in numbers of Marsh Tits. Work on movements of waders between roosts on the Moray Basin showed little ...