Daytime Counts Research Articles

Are increasing roosting waterbird numbers responsible for eutrophication of shallow lakes? Examples from a Danish Ramsar site

AbstractThe Water Framework Directive (WFD) requires actions from European Union Member States to reduce external nutrient loading in lakes of moderate/poor/bad ecological status and restore their good ecological status. Several poor-quality Danish lakes have been exempted from WFD criteria (and more proposed), due to suspected major imported nutrient contributions from waterbirds, without supporting evidence. Here, we estimated relative nutrient contributions from increasing numbers of roosting waterbirds compared to total nutrient loadings in four brackish lakes (43–491 ha) at an internationally important Ramsar site/EU Birds Directive Special Protection Area. Combining night- and daytime counts of roosting numbers of the most numerous species with intake and faecal output models, we estimated roosting birds (mostly geese) contributed 0.2–0.4% of all N inputs (0.3–1.2 kg N/ha/year) and 0.6–2.0% of all P inputs (0.04–0.12 kg P/ha/year) in three lakes (one of which has been proposed exempted from WFD criteria), but potentially as high as 14% and 76%, respectively, at a fourth clearwater lake without direct inflow or outlets. These results confirm the need for case-by-case assessments of avian nutrient import relative to total nutrient balance before exempting lakes from WFD conditions due to supposed natural loading from waterbirds.

Design modifications affect bat box temperatures and suitability as maternity habitat

Abstract Artificial roosting structures (e.g. bat boxes) are widely used as conservation tools for many animals, including bats. Although it is relatively easy to monitor bat box temperatures, we know little about the effect of design on temperatures within a box. Box microclimate affects energy budgets and physiological processes and, thus, suitability as a roost. Optimal temperature varies during the period when reproductive females aggregate to rear pups; warm roosts enhance pup development during gestation and lactation, while cool roosts facilitate energy savings by torpor, which is often important during post‐lactation. To better understand the relation of design to internal temperature, we simultaneously compared 20 box designs (19 variations of a rocket box and one three‐chamber flat box) in an open site, May to September 2018. We measured temperatures at the top, middle and bottom of each box and tallied counts of daytime and nighttime cool (≤30°C; TCOOL), permissive (30.1–39.9°C; TPERM) and stressful (≥40°C; TSTRS) temperature observations. We also measured temperature, solar radiation and wind speed at the site. We used generalized linear models with negative binomial distributions to test the effects of design, environmental variables and their interactions. Adding an external jacket or decreasing ventilation increased daytime and nighttime counts of TPERM. Increasing box volume (i.e. lengthening box by 50%) also positively affected daytime counts of TPERM, whereas decreasing box volume (by 50%) had the opposite effect. Adding an external water jacket was the only modification we tested that decreased counts of TCOOL at night. Counts of TSTRS were elevated by warmer, sunnier and less windy conditions outside, but these effects were lessened by increasing roof shading or reflectivity, adding ventilation or external jackets, or decreasing box volume. These results inform the development and implementation of novel bat box designs as conservation and management tools for maternal colonies of bats, with consideration for the effects of weather on internal temperatures.

Tundra Bean Geese Anser fabalis rossicus in central and southern Sweden autumn 2009–spring 2012

Daytime counts at 35 staging/wintering sites in 2009–2012 revealed that total numbers of Tundra Bean Geese Anser fabalis rossicus present in central and southern Sweden often reached 5000–10000. In mild winters, many of these birds stay in Sweden, mainly in the Hammarsjon area, in NE Scania. These findings show that the current population size of the Taiga Bean Goose A. f. fabalis is seriously over-estimated.

Smallholder Farms as Stepping Stone Corridors for Crop-Raiding Elephant in Northern Tanzania: Integration of Bayesian Expert System and Network Simulator

Crop-raiding elephants affect local livelihoods, undermining conservation efforts. Yet, crop-raiding patterns are poorly understood, making prediction and protection difficult. We hypothesized that raiding elephants use corridors between daytime refuges and farmland. Elephant counts, crop-raiding records, household surveys, Bayesian expert system, and least-cost path simulation were used to predict four alternative categories of daily corridors: (1) footpaths, (2) dry river beds, (3) stepping stones along scattered small farms, and (4) trajectories of shortest distance to refuges. The corridor alignments were compared in terms of their minimum cumulative resistance to elephant movement and related to crop-raiding zones quantified by a kernel density function. The "stepping stone" corridors predicted the crop-raiding patterns. Elephant presence was confirmed along these corridors, demonstrating that small farms located between refuges and contiguous farmland increase habitat connectivity for elephant. Our analysis successfully predicted elephant occurrence in farmland where daytime counts failed to detect nocturnal presence. These results have conservation management implications.

Use of Night Video to Enumerate Adult Pacific Lamprey Passage at Hydroelectric Dams: Challenges and Opportunities to Improve Escapement Estimates

AbstractReliable estimates of adult Pacific lamprey Entosphenus tridentatus escapement are critically needed to improve management of this declining and ecologically important species. The longest time series of Pacific lamprey counts are from count stations at Columbia River basin dams designed to enumerate adult salmonids during the day, but many Pacific lamprey pass at night. To estimate their total escapement, we used video to monitor nighttime lamprey passage in combination with daytime counts at two count stations at Bonneville Dam and two at The Dalles Dam in 2007–2008. We examined relationships among day and night counts and evaluated the potential for using expansion factors to estimate total escapement from past and future daytime count data. As expected, daytime counts systematically underestimated total lamprey passage, and day and night counts were positively correlated in most comparisons. Unexpectedly, ratios of night: day counts varied widely among sites and years because patterns of upstream and downstream movements past count stations varied. We highlight challenges associated with enumerating cryptic and nocturnal species, such as Pacific lamprey, the potential impact of species‐specific behaviors on enumeration efforts, and the importance of appropriate count station location and structure for video monitoring of fish passage.Received August 9, 2011; accepted April 27, 2012

Effect of vegetation type and environmental factors on European wild rabbitOryctolagus cuniculus counts in a southern Portuguese montado

This study assesses the effect of vegetation and variables related to weather and light conditions on the efficacy of rabbitOryctolagus cuniculus (Linnaeus, 1758) counts carried out in the south of Portugal. Counts were carried out in two years using driven line transects, and correlated with vegetation type and the variables using generalised linear models. The offset was a surveyed area estimated using Distance Sampling Theory as a means of correcting for detectability bias. More rabbits were observed in dense vegetation during day-time counts and in crops during night-time counts. In 1998, day-time counts were higher with higher average daily temperatures, whilst the night-time counts were higher with higher minimum daily temperatures. In 1999, day-time counts decreased with the amount of rainfall in the previous month, and the night-time counts decreased with the accumulated rainfall in the previous two months and with the higher wind speeds. In order to increase efficacy, counts should be carried out either at dawn or at dusk during the post-breeding season, and with greater intensity in dense scrub or open vegetation with high tree cover. During the breeding season and winter, counts should be carried out after dusk and with greater intensity in arable crops.

Evidence of concealment behavior by adult rainbow trout and brook trout in winter

Abstract – There has been little investigation of the winter ecology of adult trout during winter, especially in regard to concealment behavior. We compared day vs night underwater counts of adult rainbow trout and brook trout from four streams. At water temperatures between 1°C and 9°C, daytime counts accounted for 44% and 16% of nighttime snorkeling counts for rainbow trout and brook trout adults, respectively. As winter progressed, nighttime counts declined more so for brook trout than rainbow trout, but the decline was not significant for either species. Nocturnalism of both species was higher in streams with colder water temperatures. We observed few fish within concealment structure; however, by electrofishing concealment habitat during the day, we captured 10 times more adult trout than we counted immediately beforehand by snorkeling. Adult trout were concealed in cobble-boulder substrate and woody debris during the day.Note

The role of the Ghana coast in the annual cycle of migratory terns

Ntiamoa-Baidu, Y. & Nuoh, A. A. 2000. The role of the Ghana coast in the annual cycle of migratory terns. Ostrich 71 (1 & 2): 183. Data are presented on counts of migratory terns on the Ghana coast over a ten-year period, 1986–1996. Fourteen species of terns were recorded during the period. Influx of terns begins in late August, peaking in September/October, with the highest likelihood of tern occurrence on the Ghana coast recorded in August-November and April-May. Terns fed mostly offshore and used the coastal lagoons as roosting sites, although a few species e.g. Black Tern Chlidonias niger and Little Tern Sterna albifrons, foraged also on the lagoons. Two sites, Songor Lagoon and Densu Delta, regularly held over 50 % of the total count recorded for all sites. A comparison of the day-time counts with dusk roost counts indicate that the day time counts under-represent the total numbers of terns using the Ghana coast. Trends in the populations of the four most abundant tern species: Black Tern, Common Tern Sterna hirundo, Sandwich Tern S. sandvicensis and Royal Tern S. maxima, are analysed; and the implications for conservation of the species are discussed.

Habitat utilization and diel behavior of juvenile bull trout (Salvelinus confluentus) at the onset of winter

Abstract— Underwater observations were used to describe habitat use and diel behavior of juvenile bull trout (Salvelinus confluentus) at the onset of winter (0.8°C) in a second‐order central Idaho stream. All fish observed during daytime counts were concealed beneath “home stones” (mean dimensions 32.3 by 21.9 cm) in primarily pool and run habitats. Focal point depths and velocities averaged 57.2 cm and 4.7 cm/s (home stone removed). Fish maintained stations over substrate with low percentages of fine (< 2 mm, mean= 5.2%) sediment. Concealed bull trout were not evenly distributed across the stream channel. Significantly more home stones were distributed near the midline of the channel, compared to the channel margins. Fish size was positively correlated with home stone size. At night, bull trout exhibited a diel behavioral shift, some fish moved out of daytime concealment cover into the water column. At night, bull trout were observed feeding and resting, primarily in pool and run habitats. During both day and night, bull trout used riffles significantly less frequently than those habitats were available.

Variations in Numbers of Nonbreeding Great Skuas Attending a Colony

Diurnal and seasonal variations in numbers of nonbreeding Great Skuas Catharacta skua on Foula, Shetland, were monitored during the 1975, 1976, 1988 and 1989 breeding seasons. The accuracy and use of daytime and night-time counts are compared. All nonbreeders spend the night at clubs and most go to sea to feed in early morning. Hence, night-time counts represent total numbers of nonbreeders attending the colony, whilst daytime counts are more variable, although consistently timed afternoon counts can provide useful diurnal and seasonal comparisons. The mean number of nonbreeders attending the colony between May and August was significantly less in 1988 (732 individuals) and 1989 (662 individuals) than in 1975 (approximately 1949 individuals). This decline in numbers of nonbreeders since the mid-1970's coincided with a decline in the breeding population over the same period, although nonbreeding numbers decreased much more (breeders by 8% from 1975 to 1989, nonbreeders by 57%). Numbers of nonbreeders at the colony correlated with seasonal changes in diet that appeared to indicate changes in food availability. A reduced afternoon attendance by nonbreeders in 1989 (40%), compared with 1976 (67%), reflected unusually poor Great Skua breeding seasons on Foula in 1988 and 1989. Numbers of nonbreeders attending a colony appear to be good indicators of environmental changes that could usefully be added to current seabird monitoring programmes.