Divorce in an Island Bird Population: Causes, Consequences, and Lack of Inheritance

SummaryA survey of Scottish Crossbills Loxia scotica was carried out in 3,506 km2 of conifer woodland in northern Scotland during January to April 2008 to provide the first estimate of the global population size for this endemic bird. Population estimates were also made for Common Crossbills L. curvirostra and Parrot Crossbills L. pytyopsittacus within this range. Crossbills were lured to systematically selected survey points for counting, sexing and recording their calls for later call-type (species) identification from sonograms. Crossbills were located at 451 of the 852 survey points, and adequate tape-recordings made at 387 of these. The Scottish Crossbill had a disjunct distribution, occurring largely within the eastern part of the study area, but also in the northwest. Common Crossbills had a mainly westerly distribution. The population size of post-juvenile Scottish Crossbills was estimated as 13,600 (95% C.I. 8,130–22,700), which will approximate to 6,800 (4,065–11,350) pairs. Common Crossbills were more abundant within this range (27,100, 95% C.I. 14,700–38,400) and Parrot Crossbills rare (about 100). The sex ratio was not significantly different from parity for Scottish Crossbills. The modal number at survey points was two but numbers were larger in January than later in the survey. The numbers and distribution of all crossbill species are likely to vary between years, depending upon the size of the cone crops of the different conifers: all were coning in 2008. Common Crossbill and Parrot Crossbill numbers will also be affected by irruptions from continental Europe. A monitoring scheme is required to detect any population trend, and further work on their habitat requirement (e.g. conifer selection at different seasons) is needed to inform habitat management of native and planted conifer forests to ensure a secure future for this endemic bird.

Download Full-text

On the importance of g(0) for estimating bird population densities with standard distance-sampling: implications from a telemetry study and a literature review

Ibis ◽

10.1111/j.1474-919x.2007.00689.x ◽

2007 ◽

Vol 149 (4) ◽

pp. 693-700 ◽

Cited By ~ 26

Author(s):

ERICH BÄCHLER ◽

FELIX LIECHTI

Keyword(s):

Literature Review ◽

Distance Sampling ◽

Population Densities ◽

Bird Population ◽

Standard Distance

Download Full-text

Assessment of invasive rodent impacts on island avifauna: methods, limitations and the way forward

Wildlife Research ◽

10.1071/wr15047 ◽

2015 ◽

Vol 42 (2) ◽

pp. 185 ◽

Cited By ~ 11

Author(s):

Lise Ruffino ◽

Diane Zarzoso-Lacoste ◽

Eric Vidal

Keyword(s):

Population Growth ◽

Population Level ◽

Bird Conservation ◽

Bird Population ◽

Breeding Parameters ◽

Population Growth Rates ◽

Bird Populations ◽

Field Evidence ◽

Bird Breeding

Bird conservation is nowadays a strong driving force for prioritising rodent eradications, but robust quantitative estimates of impacts are needed to ensure cost-effectiveness of management operations. Here, we review the published literature to investigate on what methodological basis rodent effects on island bird communities have been evaluated for the past six decades. We then discuss the advantages and limitations of each category of methods for the detection and quantification of impacts, and end with some recommendations on how to strengthen current approaches and extend our knowledge on the mechanisms of impacts. Impact studies (152 studies considered) emphasised seabirds (67%), black rats (63%) and the Pacific Ocean (57%). Among the most commonly used methods to study rodent impacts on birds were the observation of dead eggs or empty nests while monitoring bird breeding success, and the analyses of rodent diets, which can both lead to misleading conclusions if the data are not supported by direct field evidence of rodent predation. Direct observations of rodent–bird interactions (19% of studies) are still poorly considered despite their potential to reveal cryptic behaviours and shed light on the mechanisms of impacts. Rodent effects on birds were most often measured as a change or difference in bird breeding parameters (74% of studies), while estimates of bird population growth rates (4%) are lacking. Based on the outcomes of this literature review, we highlight the need for collecting unbiased population-level estimates of rodent impacts, which are essential prerequisites for predicting bird population growth scenarios and prioritising their conservation needs. This could be achieved by a more systematic integration of long-term monitoring of bird populations into rodent management operations and modelling bird population dynamics. We also strongly recommend including various complementary methods in impact assessment strategies to unravel complex interactions between rodents and birds and avoid faulty evidence. Finally, more research should be devoted to a better understanding of the cases of non-impacts (i.e. long-term coexistence) and those impacts mediated by mechanisms other than predation and ecosystem-level processes.

Download Full-text

The Analysis of Geographic Scale and Population Processes in Bird Population Monitoring Data

Ecological Indicators ◽

10.1007/978-1-4615-4661-0_10 ◽

1992 ◽

pp. 929-960 ◽

Cited By ~ 2

Author(s):

Raymond J. O’Connor

Keyword(s):

Population Monitoring ◽

Monitoring Data ◽

Geographic Scale ◽

Bird Population ◽

Population Processes

Download Full-text

Recovery of the bird population within pine forests after the catastrophic fires in 2010

Samara Journal of Science ◽

10.17816/snv201764113 ◽

2017 ◽

Vol 6 (4) ◽

pp. 66-71

Author(s):

Julia Alexandrovna Sorokina ◽

Elena Evgenievna Boryakova

Keyword(s):

Bird Communities ◽

Anthropogenic Pressure ◽

Ecological Groups ◽

Fire Dynamics ◽

Volga River ◽

Bird Population ◽

Central Russia ◽

History Of ◽

Population Restoration ◽

Reference Environment

Process of bird population restoration after fires was investigated in two protected areas in the Volga river basin in central Russia. Anthropogenic pressure in Kerzhensky and Mordovsky nature reserves is very low, it made possible to discover some characteristics of the process of bird population restoration in reference environment. The counts were carried out both in the affected areas of the reserves, and in unaffected parts. The studied area was in its five year after the fire. Dynamics of post fire bird population restoration and its dependence on both the age and history of the original ecosystems were investigated. The authors present the results of dominant species analysis and information about their distribution in the investigated natural reserves. The authors show peculiarities and proportions of ecological groups of birds in the studied territories as well as their proportion. The influence of hydrological parameters on bird communities composition was investigated, it turned out that post fire partial inundation leads to increase of waders of Gallinago and Tringa genera. Species diversity of bird communities in affected areas was considered. Using Pielous index it was found that species evenness remained relatively high, i.e. no significant increase of dominance was observed after the fires. The authors analyzed the composition of ornitocomplexes in terms of different faunistic groups.

Download Full-text