Reliable Population Estimates Research Articles

Making the Housing Unit Method Work: An Evaluation of 2010 Population Estimates in Florida

The housing unit (HU) method—in which population estimates are derived from estimates of occupied HUs—is the most commonly used method for making small-area population estimates in the United States. It is widely used because it is conceptually simple, can utilize a wide variety of data sources, can be applied at virtually any level of geography, and often produces reliable estimates. Yet the HU method is more nearly a general approach to population estimation than it is a specific methodology. In this paper, we describe and evaluate several data sources and estimation techniques that can be used in applying the HU method. Using a set of county and subcounty estimates produced by the Bureau of Economic and Business Research (BEBR) at the University of Florida for April 1, 2010, we analyze errors by population size and growth rate, calculate errors for each of the three components of the HU method, and investigate the accuracy of estimates based on several different data sources and estimation techniques. We compare the accuracy of the 2010 estimates with previous BEBR estimates and estimates produced by the U.S. Census Bureau. We conclude that although some data sources and estimation techniques work better than others, the HU method can be tailored to produce reliable population estimates for a wide variety of geographic areas.

Determining population trends and conservation status of the common quail (Coturnix coturnix) in Western Europe

In this paper we review the conservation status and population trends of the common quail (Coturnix coturnix) from 1900 to the present. Data are sometimes contradictory with regard to the status of this species as it has some features that make it difficult to produce reliable population estimates. Recent data clearly suggest, either at a local scale or at a trans–national scale, that the Atlantic common quail populations have remained stable in the last two decades, and that restocking practices with farm–reared quails (hybrids with the Japanese quail, Coturnix japonica) do not affect our estimates. The complex movement patterns showed by this species require special attention. Analysis of ring recoveries can give important information, especially about the nomadic movement of quails in search of suitable habitats after the destruction of winter cereal crops due to harvesting. Thus, when developing a breeding distribution model for this species, continuously updated information on seasonal habitat and weather must be included for optimal prediction. Including fortnightly data of vegetation indices in distribution models, for example, has shown good results. Obtaining reliable predictions about changes in species distribution and movements during the breeding period could provide useful knowledge about the conservation status and population trends and would help in the design of future management measures.

Transience in the humpback whale population of New Caledonia and implications for abundance estimation

AbstractA phenomenon of transience in the humpback whale population breeding in New Caledonia has been highlighted in recent analyses. We used these data to illustrate the risk of flawed inference when transience is not properly accounted for in abundance estimation of resident populations. Transients are commonly defined as individuals that pass through the sampling area once, i.e., have a null probability of being caught again, and therefore induce heterogeneity in the detection process. The presence of transients can lead to severe bias in the estimation of abundance and we demonstrate how to correct for this feature when estimating abundance of resident populations. In New Caledonia, very different conclusions about the number of resident whales in the southern lagoon between 1999 and 2005 are obtained when the abundance estimate accounts for the transient whales. Without correction, the estimates of the abundance were up to twice as high across all years compared to the estimates of the resident population when a correction for transients had been incorporated. Having reliable population estimates when assessing the status of endangered species is essential in documenting recovery and monitoring of population trends. Therefore, we encourage researchers to account for transients when reporting abundances of resident populations.

Application of the Capture-Recapture Method in Estimating the Size of the Active Homosexual Male Population in Hangzhou City of China

The homosexual population is particularly susceptible to sexually transmitted disease because of various high-risk sexual behaviors among them. The authors explored the application of capture-recapture methods in estimating the size of the sexually active homosexual male population in Hangzhou. Homosexual men at 9 activity sites were investigated in Hangzhou, Zhejiang. The total active homosexual male population of Hangzhou estimated by the capture-recapture method and multiplier method was 2014 (95% confidence interval [CI] = 1899-2129) and 2012.5 (95% CI 1925 to 2101), respectively. This study shows that the capture-recapture method can be used to enumerate and provide accurate and reliable estimates of the active homosexual population in any area, provided that certain conditions are controlled.

Estimating wild boar Sus scrofa population size using faecal DNA and capture‐recapture modelling

Increasing populations of wild boar and feral domestic pigs Sus scrofa have evoked growing concern due to their potential as disease reservoir and as an origin of agricultural damages. Reliable population estimates are needed for effective management measures of this species. As an alternative to traditional methods, non‐invasive genetic population estimation approaches based on hair or faeces sampling have yielded promising results for several species in terms of feasibility and precision. We developed and applied a non‐invasive population estimation approach based on wild boar faeces in a study area situated in the Palatinate Forest, southwestern Germany. We collected 515 faeces samples along transects in January 2008. We carried out genotyping using six microsatellite markers to discriminate between individuals. During the trial, we identified 149 individual wild boar. Using multimodel inference and model averaging, we obtained relatively consistent estimates. Population densities calculated using the estimated population sizes ranged from 4.5 (2.9‐7.8) to 5.0 (4.0‐7.0) wild boar/km2. In the future, to further improve the precision of population estimates based on wild boar faeces, the detection probability should be increased. However, even when comparing a conservative population estimate to the hunting bag, our results show that the present hunting regime in our study area is not effective in regulating the wild boar population. The method which we present here offers a tool to calibrate hunting or other management measures for wild boar.

Population Estimates: Towards Standardised Protocols as a Basis for Comparability

Summary. Population estimates are an essential demographic parameter for assessing the threat status of species and the international significance of national populations. Murgui (2011) provides the most up-to-date review of the bird population estimates produced in Spain over past decades and he describes their methodological limitations, particularly those derived from data availability, sampling bias and analytical shortcomings. Two of the main procedures associated with the generation of reliable population estimates, the calculation of densities and their extrapolation over whole-species ranges are discussed here with the aim of contributing to improving comparability between estimates. In this connection, we present some new approaches developed in the Catalan Winter Bird Atlas 2006–2009, such as the stratification of density estimates using habitat suitability indices derived from species distribution modelling, and the consideration of detectability not only for common species but also for scarcer...

Assessing predictors of pellet persistence in European rabbits Oryctolagus cuniculus: towards reliable population estimates from pellet counts

AbstractThe European rabbit Oryctolagus cuniculus is a key species in Mediterranean ecosystems of the Iberian Peninsula, and reliable methods for monitoring its abundance are urgently required. Although clearance plot pellet counts may be useful in monitoring rabbit populations, such counts are potentially affected by variation in the persistence of rabbit pellets. The aim of our study was to assess persistence of rabbit pellets in the Iberian Peninsula for reliable estimates of rabbit abundance from clearance plot counts. We carried out the experiment from July 2006 to November 2007 at seven localities in central southern Spain. Marked fresh pellets were monthly placed at experimental plots, and their persistence was monitored monthly. Persistence was estimated from the proportion of marked pellets remaining between consecutive counts. Independent variables in analysis included slope steepness, vegetation, rabbit and ungulate activity, meteorology and temporal variables. Persistence significantly varied among localities and seasons and with their interaction. The final model showed that pellet persistence was best explained by total rainfall between counts, and also included the time between visits and slope steepness and the interactions rainfall∗time between visits and rainfall∗slope. Our results suggest that estimating pellet persistence for each locality and season is necessary to make estimates obtained from different localities and months comparable. In the Mediterranean region, early summer at the start of the dry season would be the recommended time for yearly rabbit monitoring based on any pellet‐count index, since reduced rainfall favours pellet persistence. Sampling protocols must standardise the number of days between counts, and plots must be established in areas with gentle slope to maximise pellet persistence between counts.

Global population status of shy albatross and an assessment of colony-specific trends and drivers

Context Monitoring the status of albatross populations and identifying the factors driving observed trends remain international conservation and management priorities. The shy albatross is endemic to Australia and breeds only on three Tasmanian islands. Aims To provide a reliable total population estimate for shy albatross, including an assessment of demographic trends for each of the three populations where possible. We consider also key drivers of population trends for each population, particularly the potential role of fisheries by-catch, with an overall aim of determining the status of the species. Methods Aerial photography and ground surveys were used to estimate the number of annual breeding pairs and trends in adult and juvenile survival rates were calculated using mark–recapture methods. At-sea distribution data was used to identify population specific trends in the overlap of shy albatross and fisheries to evaluate the potential influence of fisheries by-catch on the populations. Key Results The Albatross Island population increased post-harvesting but has recently stabilised at around 5200 breeding pairs, less than half its estimated historic size. This trajectory change appears driven by a decrease in juvenile survival. The small (170 breeding pairs) Pedra Branca population has recently declined, probably due to reduced breeding success associated with the increasing population of Australasian gannets (Morus serrator) on the island. The largest population (on Mewstone) comprises at least 9500 breeding pairs. Trends for this population are unknown. However, this paper demonstrates that these birds have greater overlap with trawl and longline fishing effort and are consequently at higher risk of fishing-related mortality. Conclusions Given the extent of fisheries overlap, survival rates for Mewstone individuals are likely to be lower than the Albatross Island population. Combined with recent trends on Pedra Branca and Albatross Island, we suggest that the current status of the shy albatross is likely to be stable at best and quite possibly decreasing. Implications The concerns raised about the conservation status of shy albatross reinforce the importance of continued population monitoring focussed particularly on establishing the trend of Mewstone. A thorough assessment of interactions with trawl fishing operations also is a management priority for this species.

Assessing fine-spatial-resolution remote sensing for small-area population estimation

Small-area population estimation is an important task that has received considerable attention from the remote-sensing community in the past four decades. The wealth of related studies reveals that the notion of living space had been considered a key linkage between population and remote-sensing measurements. Unfortunately, a formal definition for this important variable has proved difficult, due, in part, to the relatively coarse spatial resolution of the remote-sensing data used for population estimation. The advent of airborne Light Detection And Ranging (LiDAR) sensors for measuring elevation at fine spatial resolutions has provided new opportunities for considering the three-dimensional nature of living space in urban environments and for improving small-area population estimations. In this study, we assess the potential of fine-spatial-resolution LiDAR measurements (1 m) coupled with automated techniques for building extraction and land-use classification. The study seeks to provide an answer to the question: what level of information extracted from fine-spatial-resolution LiDAR and aerial photographs can be realistically translated into improved small-area population estimation? This question is addressed through a comparative study of up to seven linear models with building count, building area and/or building volume as explanatory variables at one of two land-use levels: single-family dwelling, multi-family dwelling and other types, versus residential and other types. Results show that, while building volume fits more naturally the population figures, it also represents the most challenging variable to measure by automated means. Because of this, a simple model expressed in terms of residential-building counts results in more reliable population estimates.

An Estimate of Leopard Population Density in a Private Reserve in KwaZulu-Natal, South Africa, using Camera—Traps and Capture-Recapture Models

Camera-trap surveys, when combined with capture-recapture models, are an accurate and cost-effective method for estimating the abundance of individually identifiable carnivore species such as leopards, Panthera pardus. Reliable population estimates for leopards are particularly useful as they enable informed conservation and management decisions for a species that, although widespread, is heavily persecuted. Here we present the results of a camera-trap survey that estimated the population density of leopards in Zululand Rhino Reserve (ZRR) in northern KwaZulu-Natal, South Africa. We divided our study area in half and subsampled each section for 40 days using 34 paired camera-trap stations. The combined data yielded captures of six individual leopards (3 male, 3 female) photographed on 19 occasions. Using the program CAPTURE, population abundance was estimated according to two models; one that assumes homogeneous capture probabilities among individual leopards (Mo) and one that allows for heterogeneity in ...

The status of the harbour seal (<i>Phoca vitulina</i>) in Ireland

The status of Ireland’s harbour seal population and its relationship with that of Britain and Western Europe are poorly understood. Prior to 2003, limited research efforts and poor co-ordination of survey methods fell short at providing an accurate assessment of overall distribution and population size on a regional or national scale. However, in August 2003, the Republic of Ireland’s harbour seal population was assessed by means of a geographically extensive survey conducted during the annual moult, providing an up-to-date minimum population estimate and a reliable baseline for future surveys. Trends on a national scale could not be assessed due to absence of a reliable historic population estimate; however there is some evidence of local decreases and increases in harbour seal numbers in Northern Ireland and southwest Ireland respectively. Research effort to date on aspects of the ecology of the harbour seal in the Republic of Ireland is reviewed and current research and management priorities highlighted.

The influence of survey frequency on population estimates of moorland breeding birds

Capsule A minimum of four constant‐effort‐search survey visits are required to generate reliable population estimates of breeding birds on moorland that are not subject to biases associated with varying levels of detectability through the season. Aims To investigate the influence of the number and the combination of survey visits on the population estimates of breeding birds on moorland. Methods Four constant‐effort‐search surveys (80–100 minutes per km2 per visit) of moorland in southwest Scotland were undertaken in each of six years, 2003–2008. Using standard protocols, the numbers of apparent territories that would have been identified for each possible combination of survey visits were determined.glms were used to assess the influence of the frequency of survey visits, and different combination scenarios on the derived population estimates for Red Grouse, European Golden Plover, Common Snipe, Eurasian Curlew, Sky Lark, Winter Wren and Stonechat. Independent assessments of population density were made by transect sampling for Red Grouse and Sky Lark. Results Robust population estimates were possible from three survey visits for European Golden Plover, Eurasian Curlew and Stonechat. However, there were differences between species in the seasonal variation of their detectability. Four survey visits would underestimate the populations of Red Grouse (probably by 67–91%), Sky Lark (probably by 31–61%) and Winter Wren (by an undetermined proportion). Common Snipe were also likely to be underestimated after four survey visits, but the value of the derived estimate as an index of population density deserves further investigation. Conclusions If there is a need to carry out a multi‐species survey on moorland, we suggest that a minimum of four survey visits is required to ensure the derivation of reliable population estimates for a suite of the most readily detectable species. Population estimates derived from three or fewer survey visits risk biases through uneven sampling in periods of differing detectability. With evidence for changes in the breeding phenology of birds associated with changing climate or weather patterns, it arguably becomes more important to ensure that surveys sample an adequately broad period of the breeding season.

Application of Cohort Analysis to Large Terrestrial Mammal Harvest Data

Cohort analysis (also known as virtual population analysis) is a method of population reconstruction from age-specific harvest data. Because cohort analysis requires data over a whole life span to reconstruct a population for a single year, this method is impracticable for longer-lived animals. Three models are routinely combined by fisheries scientists to make cohort analysis more cost effective and to provide real-time estimates of population size; these models may be applied to large terrestrial mammal harvest data. Each model has unique assumptions about hunting mortality rates or age distributions, and the reliability of estimates depends on meeting these assumptions. In this study, we first tested previously used assumptions for these models through an analysis of long-term moose (Alces alces) harvest data, followed by an examination of the robustness of estimates for each moose age class. We developed practical ways to achieve more realistic assumptions for two of three models and showed that meeting these assumptions was more important in estimations of large terrestrial mammal population parameters than for fish population parameters. Therefore, we recommend compliance with assumptions of the three models for more reliable population estimates of large terrestrial mammals.

From both sides: Dire demographic consequences of carnivorous mice and longlining for the Critically Endangered Tristan albatrosses on Gough Island

The IUCN recently uplisted the Tristan albatross ( Diomedea dabbenena) to Critically Endangered. Here we present new data indicating negative population trends on Gough Island arising from low adult survival (∼91%, ascribed to accidental mortality on fishing gear) and low breeding success (averaging 32%, due to mouse predation). Fledgling production from 1979 to 2007 and numbers of incubating adults from 1956 to 2007 have both decreased by ∼1% p.a. Consecutive annual counts of incubating adults and a population model permit the first reliable estimates of the Tristan albatross population, presently 5400 breeding adults and 11,300 birds in all age- and stage-classes. Population models explore scenarios of likely demographic trends using combinations of hypothetical best-case estimates vs. observed estimates for two key parameters: adult survival and breeding success. These scenarios highlight the relative benefits to the species of eradicating mice or mitigating bycatch. The model scenario using observed estimates predicts annual growth rate at −2.85%. Adult survival rates have probably decreased in recent years, concomitant with increased longline fishing effort, which might explain the discrepancy between counts and modelled trends. Negative trends cannot be reversed by improving breeding success alone, and adult survival must exceed an improbable 97% to balance the current chick production. A worst-case scenario including a fixed number of adult deaths annually predicted a catastrophic 4.2% p.a. decrease and extinction in ∼30 years. Population growth was most sensitive to adult survival, but even using an adult survival estimate without fishery mortality, current breeding success is insufficient to maintain the population. These findings do not support the ‘compensatory mitigation of bycatch’ model (offsetting bycatch impacts by eradicating invasive species), and the impacts of both fishery mortality and mouse predation must be addressed to improve the conservation status of the Critically Endangered Tristan albatross.

Estimating Denominators

There is a need for alternative approaches to obtain population denominators when census information is unavailable, unreliable, or not available at the appropriate spatial resolution. The aim of this study is to develop an exportable population model, based on a single satellite-derived indicator, for estimating fine-scale population data and characterizing high-incidence areas in an urbanized area. A Landsat 7 enhanced thematic mapper plus image was processed to generate population density indices at the block and block-group levels, using both an unsupervised pixel-based and a supervised classification. Spatial disaggregation was used to calculate population estimates, distributing the total population of the city of Besanon (France) into census areas by means of their respective population density indices. Accuracy assessment was performed through comparisons with census counts. At the block-group level, the simplest model produced relatively accurate and reliable population estimates within the range of observed counts. A strong agreement was found between observed and estimated incidence rates for non-Hodgkin lymphoma (intraclass correlation coefficient [ICC] = 0.73), but not for female breast cancer (ICC = 0.40). Withdrawing the sprawled block groups improved the agreements considerably (ICC = 0.84 and 0.71, respectively). This apportioning procedure offers a way to obtain estimated population sizes (or at least densities) for areas with no accurate census, but does not substitute for censuses where good census data exist. Because it is rapid, relatively cheap, and computationally easy, it should be of special interest to epidemiologists, environmental scientists, and public health decision makers.

Estimating regional population size and annual harvest intensity of the sooty shearwater in New Zealand

Recent comprehensive survey data from multiple New Zealand offshore islands were combined with demographic population models to produce the first formal estimate of the total population of sooty shearwaters within New Zealand territory. We estimated the total population over 1994–2005 to be 21.3 (19.0–23.6) million individual birds in the New Zealand region. This population consisted of 12.8 (12.0–13.6) million adults, 2.8 (2.5–3.1) million chicks, and 4.4 (4.2–4.7) million breeding pairs. Breeding sooty shearwaters were concentrated primarily around the southern islands of New Zealand, with 53% breeding in the Titi Islands surrounding Rakiura (Stewart Island). Rakiura Maori muttonbirders were estimated to harvest 360 000 (320 000–400 000) sooty shearwaters per year, equivalent to 18% of the chicks produced in the harvested areas and 13% of chicks in the New Zealand region. Overall, 11% of the chicks within the Titi Islands live on unharvested ground. Systematic and widespread surveys of breeding colonies in South America are needed before a reliable global sooty shearwater population estimate can be calculated.

Estimation of Bottom Trawl Catch Efficiency for Two Demersal Fishes, the Atlantic Croaker and White Perch, in Chesapeake Bay

AbstractThe use of fisheries‐independent trawl survey data to estimate fish abundance in shallow coastal systems can present challenges for producing reliable population estimates. We used hydroacoustic and trawl data to estimate the catch efficiency of a demersal trawl that is presently used in surveys to support stock assessments in Chesapeake Bay, USA. Specifically, we determined the efficiency of catching Atlantic croakers Micropogonias undulatus and white perch Morone americana, two of the most common species captured in the trawl survey. Monotypic hauls (>90% by abundance) from 2003 to 2004 were used to estimate catch efficiency, defined as the ratio of the observed catch to the number of fish encountered by the trawl, which we estimated by deploying a scientific echosounder directly in front of the trawl net. The catch efficiency estimates ranged from 0.18 to 1.26 for Atlantic croakers (n = 29 tows) and from 0.11 to 0.60 for white perch (n = 7 tows). For Atlantic croakers, Spearman's rank correlation between the total and predicted catch was 0.53. A post hoc analysis of the Atlantic croaker efficiency estimates based on general linear modeling suggests that trawl efficiency is a function of fish behavior, gear geometry, and habitat. Efficiency declined with increasing fish density and increasing trawl width; to lesser extent, an increasing proportion of fines in the sea bed and decreasing depth were also associated with declines in efficiency. We conclude that because catch efficiency is variable, the trawl should be integrated with hydroacoustics to obtain improved population data.

Returning to New Orleans after Hurricane Katrina

Hurricane Katrina displaced approximately 650,000 people and destroyed or severely damaged 217,000 homes along the Gulf Coast. Damage was especially severe in New Orleans, and the return of displaced residents to this city has been slow. The fraction of households receiving mail (which, in the absence of reliable population estimates, is a good indicator for returns) was 49.5 percent in August 2006, and 66.0 percent in June 2007 (Greater New Orleans Community Data Center, 2007). Low-income minority families appear to have been slower than others to return (William H. Frey and Audrey Singer, 2006). In this paper, we examine the determinants of returning to New Orleans in the 18 months after the hurricane. The data come from a study of low-income parents, mainly African American women, who were enrolled in a community college intervention prior to the hurricane. Although the sample is not representative of the pre-Katrina population of the city, it nonetheless is of great interest. The relatively slow return of low income, primarily African American, residents is a politically charged issue. One (extreme) view is that the redevelopment plans are designed to discourage low-income minority residents from returning. A quite different view is that members of this group have found better opportunities outside of New Orleans, and do not want to return. Because few data sets trace individuals from before to after the hurricane, this debate has taken place largely without the benefit of evidence.

SpitzerConstraints on the Stellar Populations of Lyα‐Emitting Galaxies atz= 3.1

We investigate the stellar populations of a sample of 162 Lyman-alpha emitting galaxies (LAEs) at z = 3.1 in the Extended Chandra Deep Field South, using deep Spitzer IRAC data available from the GOODS and SIMPLE surveys to derive reliable stellar population estimates. We divide the LAEs according to their rest-frame near-IR luminosities into IRAC-detected and IRAC-undetected samples. About 70% of the LAEs are undetected in 3.6 micron down to [3.6] = 25.2 AB. Stacking analysis reveals that the average stellar population of the IRAC-undetected sample has an age of ~ 200 Myr and a mass of ~ 3x10^8 solar masses, consistent with the expectation that LAEs are mostly young and low-mass galaxies. On the other hand, the IRAC-detected LAEs are on average significantly older and more massive, with an average age > 1 Gyr and mass ~ 10^10 solar masses. Comparing the IRAC colors and magnitudes of the LAEs to z ~ 3 Lyman break galaxies (LBGs) shows that the IRAC-detected LAEs lie at the faint blue end of the LBG color-magnitude distribution, suggesting that IRAC-detected LAEs may be the low mass extension of the LBG population. We also present tentative evidence for a small fraction (~ 5%) of obscured AGN within the LAE sample. Our results suggest that LAEs posses a wide range of ages and masses. Additionally, the presence of evolved stellar populations inside LAEs suggests that the Lyman-alpha luminous phase of galaxies may either be a long-lasting or recurring phenomenon.

Status of Marco Polo sheep Ovis ammon polii in China and adjacent countries: conservation of a Vulnerable subspecies

To determine the status and distribution of the Vulnerable Marco Polo sheep or argali Ovis ammon polii surveys were made in the Pamir Mountains, where the Hindu Kush, Karakoram, and Kunlun ranges meet. In China a total of 851 Marco Polo sheep were observed within the Taxkorgan Nature Reserve and 1,448 north of the Reserve. No reliable population estimate is avail- able for Tajikistan but in five census blocks totalling 1,977 km 2 densities ranged from negligible to 1.4 km 2 . A total of 624 sheep were counted in Afghanistan, and total numbers may approach 1,000. Fewer than 150 individuals are said to visit Pakistan seasonally. Hunting for meat has decimated the Marco Polo sheep popula- tions in all four countries but with better protection they appear to be on the increase in China. Transboundary cooperation is essential if the species is to be adequately protected and managed as argali readily cross inter- national borders, and a four-country Pamir Peace Park has been proposed and is under discussion.