@article{alldredge_pacifici_simons_pollock_2008, title={A novel field evaluation of the effectiveness of distance and independent observer sampling to estimate aural avian detection probabilities}, volume={45}, ISSN={0021-8901 1365-2664}, url={http://dx.doi.org/10.1111/j.1365-2664.2008.01517.x}, DOI={10.1111/j.1365-2664.2008.01517.x}, abstractNote={Summary 1. The validation of field sampling techniques is a concern for applied ecologists due to the strong model assumptions implicit in all methods. Computer simulations make replication easy, but they do not give insights into how much bias occurs in real populations. Testing sampling methods on populations of known size can establish directly how well estimators perform, but such populations are very hard to find, and replicate, and they may have unusual attributes. 2. We present a field validation of distance and double-observer methods of estimating detection probabilities on aural avian point counts. Our research is relevant to conservation agencies worldwide who design thousands of avian monitoring programmes based primarily on auditory point counts. The programmes are a critical component in the management of many avian species. 3. Our validation used a simulation system which mimics birds calling in a field environment. The system allowed us to vary singing rate, species, distance, the complexity of points, and other factors. 4. Distance methods performed poorly, primarily due to large localization errors, and estimates did not improve for simplified points. 5. For the double-observer method, two pairs of observers tended to underestimate true population size, while the third pair tended to double-count birds which overestimated the population. Detection probabilities were always higher and population estimates lower when observers subjectively matched birds compared to an objective rule and showed a slight negative bias and good precision. A simplified 45-degree matching rule did not improve the performance of double-observer estimates which had a slight positive bias and much lower precision. Double-observer estimates did improve on the simplified points. 6. Synthesis and applications . We encourage ecologists working with sampling methods to develop similar methods of working with simulated populations through use of technology. Our simulated field evaluation has demonstrated the difficulty of accurately estimating population size when limited to aural detections. Problems are related to limitations in the ability of observers to localize sound, estimate distance, and accurately identify birds during a count. Other sources of error identified are the effects of observers, singing rate, singing orientation and background noise.}, number={5}, journal={Journal of Applied Ecology}, publisher={Wiley}, author={Alldredge, Mathew W. and Pacifici, Krishna and Simons, Theodore R. and Pollock, Kenneth H.}, year={2008}, month={Oct}, pages={1349–1356} }
 @article{alldredge_simons_pollock_2007, title={A field evaluation of distance measurement error in auditory avian point count surveys}, volume={71}, ISSN={["1937-2817"]}, DOI={10.2193/2006-161}, abstractNote={ABSTRACT Detection distance is an important and common auxiliary variable measured during avian point count surveys. Distance data are used to determine the area sampled and to model the detection process using distance sampling theory. In densely forested habitats, visual detections of birds are rare, and most estimates of detection distance are based on auditory cues. Distance sampling theory assumes detection distances are measured accurately, but empirical validation of this assumption for auditory detections is lacking. We used a song playback system to simulate avian point counts with known distances in a forested habitat to determine the error structure of distance estimates based on auditory detections. We conducted field evaluations with 6 experienced observers both before and after distance estimation training. We conducted additional studies to determine the effect of height and speaker orientation (toward or away from observers) on distance estimation error. Distance estimation errors for all evaluations were substantial, although training reduced errors and bias in distance estimates by approximately 15%. Measurement errors showed a nonlinear relationship to distance. Our results suggest observers were not able to differentiate distances beyond 65 m. The height from which we played songs had no effect on distance estimation errors in this habitat. The orientation of the song source did have a large effect on distance estimation errors; observers generally doubled their distance estimates for songs played away from them compared with distance estimates for songs played directly toward them. These findings, which we based on realistic field conditions, suggest measures of uncertainty in distance estimates to auditory detections are substantially higher than assumed by most researchers. This means aural point count estimates of avian abundance based on distance methods deserve careful scrutiny because they are likely biased.}, number={8}, journal={JOURNAL OF WILDLIFE MANAGEMENT}, author={Alldredge, Mathew W. and Simons, Theodore R. and Pollock, Kenneth H.}, year={2007}, month={Nov}, pages={2759–2766} }
 @article{simons_alldredge_pollock_wettroth_2007, title={Experimental analysis of the auditory detection process on avian point counts}, volume={124}, ISSN={["1938-4254"]}, DOI={10.1642/0004-8038(2007)124[986:EAOTAD]2.0.CO;2}, abstractNote={Abstract We have developed a system for simulating the conditions of avian surveys in which birds are identified by sound. The system uses a laptop computer to control a set of amplified MP3 players placed at known locations around a survey point. The system can realistically simulate a known population of songbirds under a range of factors that affect detection probabilities. The goals of our research are to describe the sources and range of variability affecting point-count estimates and to find applications of sampling theory and methodologies that produce practical improvements in the quality of bird-census data. Initial experiments in an open field showed that, on average, observers tend to undercount birds on unlimited-radius counts, though the proportion of birds counted by individual observers ranged from 81% to 132% of the actual total. In contrast to the unlimited-radius counts, when data were truncated at a 50-m radius around the point, observers overestimated the total population by 17% to 122%. Results also illustrate how detection distances decline and identification errors increase with increasing levels of ambient noise. Overall, the proportion of birds heard by observers decreased by 28 ± 4.7% under breezy conditions, 41 ± 5.2% with the presence of additional background birds, and 42 ± 3.4% with the addition of 10 dB of white noise. These findings illustrate some of the inherent difficulties in interpreting avian abundance estimates based on auditory detections, and why estimates that do not account for variations in detection probability will not withstand critical scrutiny. Análisis Experimentales del Proceso de Detección Auditiva en Puntos de Conteo de Aves}, number={3}, journal={AUK}, author={Simons, Theodore R. and Alldredge, Mathew W. and Pollock, Kenneth H. and Wettroth, John M.}, year={2007}, month={Jul}, pages={986–999} }
 @article{alldredge_simons_pollock_2007, title={Factors affecting aural detections of songbirds}, volume={17}, ISSN={["1939-5582"]}, DOI={10.1890/06-0685}, abstractNote={Many factors affect the number of birds detected on point count surveys of breeding songbirds. The magnitude and importance of these factors are not well understood. We used a bird song simulation system to quantify the effects of detection distance, singing rate, species differences, and observer differences on detection probabilities of birds detected by ear. We simulated 40 point counts consisting of 10 birds per count for five primary species (Black-and-white Warbler Mniotilta varia, Black-throated Blue Warbler Dendroica caerulescens, Black-throated Green Warbler Dendroica virens, Hooded Warbler Wilsonia citrina, and Ovenbird Seiurus aurocapillus) over a range of 15 distances (34-143 m). Songs were played at low (two songs per count) and high (13-21 songs per count) singing rates. Detection probabilities averaged across observers ranged from 0.60 (Black-and-white Warbler) to 0.83 (Hooded Warbler) at the high singing rate and 0.41 (Black-and-white Warbler) to 0.67 (Hooded Warbler) at the low singing rate. Logistic regression analyses indicated that species, singing rate, distance, and observer were all significant factors affecting detection probabilities. Singing rate x species and singing rate X distance interactions were also significant. Simulations of expected counts, based on the best logistic model, indicated that observers detected between 19% (for the worst observer, lowest singing rate, and least detectable species) and 65% (for the best observer, highest singing rate, and most detectable species) of the true population. Detection probabilities on actual point count surveys are likely to vary even more because many sources of variability were controlled in our experiments. These findings strongly support the importance of adjusting measures of avian diversity or abundance from auditory point counts with direct estimates of detection probability.}, number={3}, journal={ECOLOGICAL APPLICATIONS}, author={Alldredge, Mathew W. and Simons, Theodore R. and Pollock, Kenneth H.}, year={2007}, month={Apr}, pages={948–955} }
 @article{rice_collazo_alldredge_harrington_lewis_2007, title={Local annual survival and seasonal residency rates of semipalmated sandpipers (Calidris pusilla) in Puerto Rico}, volume={124}, ISSN={["0004-8038"]}, DOI={10.1642/0004-8038(2007)124[1397:LASASR]2.0.CO;2}, abstractNote={Abstract We report seasonal residency and local annual survival rates of migratory Semipalmated Sandpipers (Calidris pusilla) at the Cabo Rojo salt flats, Puerto Rico. Residency rate (daily probability of remaining on the flats) was 0.991 ± 0.001 (x̄ ± SE), yielding a mean length of stay of 110 days. This finding supports the inclusion of the Caribbean as part of the species' winter range. Average estimated percentage of fat was low but increased throughout the season, which suggests that birds replenish some spent fat reserves and strive for energetic maintenance. Local annual survival rate was 0.62 ± 0.04, within the range of values reported for breeding populations at Manitoba and Alaska (0.53–0.76). The similarity was not unexpected because estimates were obtained annually but at opposite sites of their annual migratory movements. Birds captured at the salt flats appeared to be a mix of birds from various parts of the breeding range, judging from morphology (culmen's coefficient of variation = 9.1, n = 106). This suggested that origin (breeding area) of birds and their proportion in the data should be ascertained and accounted for in analyses to glean the full conservation implications of winter-based annual survival estimates. Those data are needed to unravel the possibility that individuals of distinct populations are affected by differential mortality factors across different migratory routes. Mean length of stay strongly suggested that habitat quality at the salt flats was high. Rainfall and tidal flow combine to increase food availability during fall. The salt flats dry up gradually toward late January, at the onset of the dry season. Semipalmated Sandpipers may move west to other Greater Antilles or south to sites such as coastal Surinam until the onset of spring migration. They are not an oversummering species at the salt flats. Conservation efforts in the Caribbean region require understanding the dynamics of this species throughout winter to protect essential habitat. Tasas de Supervivencia Anual Local y de Residencia Estacional de Calidris pusilla en Puerto Rico}, number={4}, journal={AUK}, author={Rice, Susan M. and Collazo, Jaime A. and Alldredge, Mathew W. and Harrington, Brian A. and Lewis, Allen R.}, year={2007}, month={Oct}, pages={1397–1406} }
 @article{alldredge_pollock_simons_shriner_2007, title={Multiple-species analysis of point count data: a more parsimonious modelling framework}, volume={44}, ISSN={["1365-2664"]}, DOI={10.1111/j.1365-2664.2006.01271.x}, abstractNote={Summary}, number={2}, journal={JOURNAL OF APPLIED ECOLOGY}, author={Alldredge, Mathew W. and Pollock, Kenneth H. and Simons, Theodore R. and Shriner, Susan A.}, year={2007}, month={Apr}, pages={281–290} }
 @article{alldredge_pollock_simons_2006, title={Estimating detection probabilities from multiple-observer point counts}, volume={123}, ISSN={["1938-4254"]}, DOI={10.1642/0004-8038(2006)123[1172:EDPFMP]2.0.CO;2}, abstractNote={Abstract Point counts are commonly used to obtain indices of bird population abundance. We present an independent-observer point-count method, a generalization of the dependent-observer approach, based on closed-population capture- recapture methods. The approach can incorporate individual covariates, such as detection distance, to account for individual differences in detection probabilities associated with measurable sources of variation. We demonstrate a negative bias in two-observer estimates by comparing abundance estimates from two- and four- observer point counts. Models incorporating data from four independent observers were capable of accounting for this bias. Modeling individual bird differences in detection probabilities produced abundance estimates 15–21% higher than models that did not account for individual differences, in four out of five data sets analyzed. Although independent-observer methods are expensive and impractical for large- scale applications, we believe they can provide important insights into the sources and degree of perception bias (i.e., probability of detecting an individual, given that it is available for detection) in avian point-count estimates. Therefore, they may be useful in a two-stage sampling framework to calibrate larger surveys based on single-observer estimates. Estimación de Probabilidades de Detección a Partir de Conteos en Puntos Hechos por Varios Observadores}, number={4}, journal={AUK}, author={Alldredge, Mathew W. and Pollock, Kenneth H. and Simons, Theodore R.}, year={2006}, month={Oct}, pages={1172–1182} }
 @article{marsh_lawler_kwan_delean_pollock_alldredge_2004, title={Aerial surveys and the potential biological removal technique indicate that the Torres Strait dugong fishery is unsustainable}, volume={7}, ISSN={["1469-1795"]}, DOI={10.1017/S1367943004001635}, abstractNote={Abstract}, journal={ANIMAL CONSERVATION}, author={Marsh, H and Lawler, IR and Kwan, D and Delean, S and Pollock, K and Alldredge, M}, year={2004}, month={Nov}, pages={435–443} }
 @article{alldredge_peek_wall_2002, title={Nutritional quality of forages used by elk in northern Idaho}, volume={55}, ISSN={["0022-409X"]}, DOI={10.2307/4003131}, abstractNote={The nutritional quality (digestible energy, crude protein, and minerals) of 7 known elk (Cervus elaphus Linnaeus) forages was assessed at 4 different time periods from May to November. Species evaluated were elk sedge (Carex geyeri Boott), Kentucky bluegrass (Poa pratensis Linnaeus), western goldthread (Coptis occidentalis Nuttall), clover (Trifolium repens Linnaeus), service-berry (Amelanchier alnifolia Nuttall), redstem ceanothus (Ceanothus sanguineus Pursh), and Scouler willow (Salix scouleriana Barratt). Mineral concentrations generally met estimated requirements for elk in all seasons, except sodium remained below requirements in all seasons. Crude protein in most plant species sampled was adequate for adult gravid or lactating cows throughout the year, although concentrations in graminoids fell below requirements during August. Forage provided adequate digestible energy for gravid or lactating cows only during May, indicating potential deficiencies in summer and autumn. Elk must be selective of plant parts, plant taxa, and foraging habitat to gain adequate nutrition. In this area, summer and fall forage quality may be critical to lactating cow elk. DOI:10.2458/azu_jrm_v55i3_alldredge}, number={3}, journal={JOURNAL OF RANGE MANAGEMENT}, author={Alldredge, MW and Peek, JM and Wall, WA}, year={2002}, month={May}, pages={253–259} }
 @article{alldredge_peek_wall_2001, title={Alterations of shrub communities in relation to herbivory in northern Idaho}, volume={75}, number={2}, journal={Northwest Science}, author={Alldredge, M. W. and Peek, J. M. and Wall, W. A.}, year={2001}, pages={137–144} }
 @article{alldredge_peek_wall_2001, title={Shrub community development and annual productivity trends over a 100-year period on an industrial forest of Northern Idaho}, volume={152}, ISSN={["0378-1127"]}, DOI={10.1016/S0378-1127(00)00608-3}, abstractNote={Understory community structure of conifer plantations and naturally regenerated stands on north and south aspects is assessed in stands up to 100 years following initial overstory removal on an industrial forest of northern Idaho. Industrial forests differ from other forests as they are managed for timber production, yet these forests maintain substantial wildlife populations and provide recreational opportunities. Species occurrence, stem density, twig density and height were compared between north and south aspects and between plantation and natural regeneration stands. Differences were detected relative to aspect and stand type but variation among sites was also significant. Annual shrub productivity, biomass of current year’s twigs, was estimated for all shrub species in 77 different stands. Productivity curves were developed for plantation and natural regeneration type stands on both north and south aspects which predict total stand annual productivity from time of initial cutting to over 100 years after overstory removal (R2>0.90). Maximum annual shrub productivity occurred between 7 and 14 years after overstory removal and broadcast burning. The findings of the study indicate that early successional stages across the landscape can, by forest management, be maintained to produce forage and influence animal distribution.}, number={1-3}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Alldredge, MW and Peek, JM and Wall, WA}, year={2001}, month={Oct}, pages={259–273} }