Trap Stations Research Articles

Planktic foraminifera, particle flux and oceanic productivity off Pakistan, NE Arabian Sea: modern analogues and application to the palaeoclimatic record

Abstract We use the flux of bulk sediment (CaCO 3 , biogenic opal, organic carbon, lithogenic material), and of planktic foraminifera (PF) and other shell-bearing plankton from sediment trap EPT-2 off Pakistan to (1) constrain the seasonal pattern of regional productivity and (2) search for indications of the NE monsoon winter situation that may serve as a modern analogue to better reveal the seasonal climatic signals preserved in the sedimentary record of the Arabian Sea. Our trap data show a clear seasonality of fluxes that can also be traced in the composition of non-bioturbated (varved) summer and winter sediment laminae preserved within the oxygen minimum zone. In EPT-2, the flux of PF is low during summer, but during winter and late spring it is higher, as at trap station WAST, in the upwelling area of the western Arabian Sea. Globigerina bulloides , a PF species linked to summer upwelling and high productivity, is of minor importance off Pakistan. In contrast, Globigerina falconensis dominates in flux and relative abundance, and is indicative of winter mixing, when NE monsoonal winds cool the highly saline surface waters and break up stratification. An enhanced horizontal flux of suspended sediments stirred up on the shelf and upper slope is clearly shown by the peak in occurrence of small benthic foraminifera during winter. Altogether, our data suggest that the particle flux in the northeastern Arabian Sea is determined by local sediment resuspension and winter productivity rather than by summer monsoonal upwelling, representing a ‘non-upwelling’ environment, in contrast to the ‘summer upwelling’ regime off Oman, Somalia and southern India. We used this evidence to reconstruct the seasonal intensity of both monsoons for the past 25 ka: the SW and NE monsoon both were weak during the last glacial period. The NE monsoon peaked during the cool phases of the glacial to interglacial climatic transition (i.e. during the Younger Dryas (YD) and Heinrich Event H1). The SW monsoon was reinforced after the YD. Both monsoons were enhanced during early Holocene time, when summer insolation and hence atmospheric forcing was at a maximum.

The reduction of heavy metals in a stormwater wetland

Sedimentation has long been recognised as the principal process in the removal of heavy metals from stormwater in natural or constructed wetlands. However, there are a range of other processes including filtration, adsorption, biological assimilation, decomposition, chemical transformation and volatilisation that may also play an important role. To date there have been few attempts to quantify the importance of the various processes. In the current study five sediment trap stations were set up in a long and narrow stormwater wetland and an analysis of total sediment and heavy metal concentration of key elements (Zn, Cu, Pb, Cr and As) was carried out. From the results it has been possible to assign an areal decay rate to the sedimentation process (1300 m per year) and a separate decay rate to the sum of the other processes (biological and chemical) that were acting to reduce heavy metal concentration. It was found that Zn, Pb and Cu concentrations on sediment decreased 57, 71 and 48%, respectively, through the wetland, the concentration of Cr remained relatively constant and that of As actually increased by 150%. It is suggested that the behaviour of the different metals can be explained in terms of their chemical behaviour and the role of organic matter in the wetland.

STATUS AND HABITAT RELATIONSHIPS OF NORTHERN FLYING SQUIRRELS ON MOUNT DESERT ISLAND, MAINE

Abstract Northern (Glaucomys sabrinus) and southern (G. volans) flying squirrels occur in Maine, but there is uncertainty about range overlap in southcentral Maine where the southern flying squirrel reaches its geographic range limit. We surveyed flying squirrels on Mount Desert Island (MDI), located along the central Maine coast, to update the current status and distribution of these species. We captured only northern flying squirrels, and populations (≥ 2 individuals) were located in two conifer stands and one mixed conifer-hardwood stand. All three stands were located in relatively older forests, outside a large area burned in a 1947 fire. Tree diameters were similar between trap stations with and without captures, understory density was low overall, and there was a trend of higher seedling density at capture locations. Low understory density may allow squirrels more effective gliding movements between trees, which may enhance predator avoidance. Although the southern flying squirrel was reported from ...

Use of habitat by the black rat (Rattus rattus) at North Head, New South Wales: an observational and experimental study

AbstractThis study investigated the habitats used by an introduced species of rodent, the black rat Rattus rattus (Linnaeus), at North Head in New South Wales, Australia. At a coarse scale, combined live‐trapping and radio‐tracking indicated that animals used forest proportionately more than open, heath or scrub macrohabitats that were available. To identify the components contributing to this pattern, microhabitat use was assessed by scoring vegetative and structural features around trap stations, and by using spool‐and‐line tracking. The results indicated that rats preferred microhabitats providing a deep cover of leaf litter and dense understorey with numerous vertical stems. As statistical analysis did not distinguish which of these components was more important in determining habitat use, we designed an experiment to test the importance of a single component: leaf litter. Cover of litter was enhanced experimentally at 75 trap stations and reduced at 75 others, and the response of rats monitored by live‐trapping on two occasions. Although no clear response was found in the first run of the experiment, due to low numbers, rats strongly selected trap stations with enhanced leaf litter in the second run. These results indicate that litter cover affects use of habitat by the black rat. Access to food resources and avoidance of predators may contribute to the observed local patterns of abundance.

Alkenone fluxes and anomalous U37K′ values during 1989–1990 in the Northeast Atlantic (48°N 21°W)

We report and discuss new data on alkenone fluxes from the North East Atlantic (48°N 21°W), in a site investigated by the Joint Global Ocean Flux Study and the North Atlantic Bloom Experiment from April 1989–March 1990. The investigated sediment trap station is situated within the North Atlantic Transition Zone in a region influenced by upwelling events induced by mesoscale eddy activity, for which branches of the North Atlantic Current act as major sources. The flux of alkenones in the NE Atlantic was consistent with the monthly evolution of particulate fluxes, rapidly increasing from April 1989 to June 1989 (peak bloom), and gradually declining until August 1989. The timing of the only bloom observed is not equivalent to the timing of alkenone flux maxima recorded elsewhere in the world's oceans. Hence, we further confirm that there is not a world-wide regular season of alkenone blooms. The annual alkenone flux profile in our trap resembled that of the coccospheres, but not so much that of coccoliths. This discrepancy may indicate that alkenones were mainly transported downwards to the sea-floor by coccospheres, as part of the intact structure of the dead coccolithophorid. The sedimentary concentration of alkenones, which is related to productivity and efficiency of preservation, may then be also partly dependent on the rate of disaggregation of coccospheres in the water column, and the factors that control them. Comparison of the ratios of amounts of alkenones per coccosphere and coccoliths, with those of amounts of alkenones per cell numbers from culture and field data, suggests that there could have been a contribution of alkenones to the traps by Coccolithus pelagicus, despite this species considered devoid of alkenones. We suggest, hence, that further laboratory tests of this species are carried out. U37K′ in the sediment trap material showed a poor correlation with sea surface temperature during spring 1989. We propose that the anomalously low U37K′ values reflects an input of alkenones from elsewhere to the trap, not from the overlying surface waters, associated to the presence of several eddies and phytoplanktonic material trapped within. The origin of the eddy-bound alkenones may be found in subpolar waters, as indicated by the presence of C. pelagicus tests in the trap, and also by the low U37K′ values which are similar to the values found in surface sediments near the polar front. Our data, thus, further illustrates the challenge of using short-term studies of annual water-column alkenone fluxes to understand average sedimentation patterns of alkenones to the deep ocean.

Coccolithophore (–CaCO3) flux in the Sea of Okhotsk: seasonality, settling and alteration processes

Coccolithophore fluxes were determined in the Sea of Okhotsk using samples from a 1year experiment (12 August 1990 to 12 August 1991) with sediment traps at 258 and 1061m depth. A special study was made on Coccolithus pelagicus, using fragmentation and the degree of etching, as indicators of transport mechanisms. A Corrosion Index for C. pelagicus is developed. The coccolithophore flux pattern at 258m depth was characterised by a strong seasonality, with flux peaks during autumn 1990 (late November to early December) and spring 1991 (March). The assemblage consisted almost entirely of the two species C. pelagicus and Emiliania huxleyi. During autumn, coccolithophore transportation to 258m depth mainly occurred within cylindrical fecal pellets and marine snow aggregates of silicoflagellates, and through agglutination on tintinnids. Grazing caused severe fragmentation of coccoliths and disintegration of coccospheres. Marine snow aggregates contained many intact coccospheres of C. pelagicus. During spring, coccolithophores were probably removed from the euphotic zone by the ballast effect of sinking diatoms. The coccolithophore flux peak in spring occurred immediately after the ice had retreated from the trap station, and the trapped assemblage included coccoliths of subtropical species. These features indicate drifting from an ice-free location to the south or east.The coccolith and coccosphere flux at 1061m was respectively 7 and 12 times lower than at 258m depth, and maximum fluxes were recorded 2months later. Increasing carbonate dissolution from 258 to 1061m depth is expressed in the coccolithophore–CaCO3 flux reduction of 82%, and in the increasing percentage of etched coccoliths of Coccolithus pelagicus from 32 to >90%.

MICROHABITAT USE BY A TROPICAL FOREST RODENT,PROECHIMYS SEMISPINOSUS,IN CENTRAL PANAMA

We studied microhabitat use by Proechimys semispinosus (Central American spiny rat) by livetrapping along transects in 5 forested sites in central Panama. Microhabitat was quantified by measuring 14 variables at each sampling station. Relative abundance of P. semispinosus was 1.86 individuals/100 station-nights, which was typical of abundances of this species and other members of the genus. Spiny rats were distributed throughout sampled microhabitat space defined by factor analysis of 14 variables. We used logistic regression analysis to relate presence–absence at trap stations to microhabitat structure. Variables describing disturbed and younger forest were strong predictors of presence at trap stations. Associations of P. semispinosus with younger forest (smaller trees and lianas and lower canopies) and treefall gaps within older forest may have implications for regeneration of local forest patches through the activities of these rodents as seed predators and dispersers of seeds and arbuscular mycorrhizal fungi spores.

MAMMALS OF THE RIO JURUÁ AND THE EVOLUTIONARY AND ECOLOGICAL DIVERSIFICATION OF AMAZONIA

We describe the nonvolant mammal fauna of the Rio Juruá of the western Amazon of Brazil, based on collections made during a year-long survey of the river. We, along with our colleagues Drs. Claude Gascon and Carlos Peres, designed the field project to examine the effects of the river on the differentiation among terrestrial vertebrates (mammals, birds, and amphibians and reptiles) at both the community and population levels. This monograph examines only the patterns of geographic variation and community structure of the small-bodied mammals. Species inventories were made at 16 primary trapping localities divided into eight pairs of cross-river sites, with two pairs in each of four regions from near the mouth to the headwaters of the Rio Juruá. A total of 81 species of nonvolant mammals were obtained, including nine new to science. Four of these are described herein; the others have been described elsewhere. We used a standardized trapping protocol to assess community structure at each of the 16 localities that included terrestrial and canopy trap stations in floodplain (várzea) and upland (terra firme) forest formations. Supplemental trapping was done in secondary habitats at all sites. We describe these sites, the trap effort expended, and the placement of trap stations relative to local habitats. We also describe each species of marsupial, sciurid rodent, murid rodent, and echimyid rodent encountered; comment on their systematics; and summarize aspects of habitat use, life history, geographic distribution, and geographic differentiation based on morphological and molecular traits. We examine patterns of differentiation in the mitochondrial cytochrome-b gene for samples of 41 of the 45 species of marsupials and rodents obtained within the Rio Juruá Basin, and discuss these patterns from the perspective of the entire Amazon and, in some cases, the Mata Atlântica of coastal Brazil. We also examine patterns of community organization within the Rio Juruá basin and throughout Amazonia, drawing attention to the geographic distribution of what appear to be major faunal units that are independent of habitat differences. Finally, we use principles of phylogeography to analyze patterns of geographic differentiation among the nonvolant mammals with regard to the Riverine Barrier Hypothesis. We show that, while there are few examples of taxa for which the Rio Juruá is apparently a barrier, most taxa either are largely undifferentiated throughout the basin or are sharply divided into reciprocally monophyletic mtDNA haplotype clades separable into upriver and downriver units. We argue that the concordance in the geographic placement of clade boundaries suggests a common history; moreover, both the age of these clades and their geographic position in relation to underlying geological features suggest that landform evolution has been an important, but underappreciated component of diversification within western Amazonia.

Evaluation of the efficiency of three types of traps for capturing pocket gophers

Trapping is an integral tool in research and control of damage caused by pocket gophers (Thomomys spp.). We evaluated three types of traps (Macabee®, Cinch, Blackhole® Rodent) in a California field trial by comparing the number of captures to activity at the sets (capture efficiency) and separately, the duration of time from first to last capture (time efficiency). On each of six study plots established on irrigated agriculture fields, 60 trap stations were established at locations of gopher mounds. One trap type was used per station and traplines were run continuously for about four days. We captured a total of 256 gophers. Overall, the Cinch trap had the highest capture efficiency (41.7%), followed by the Macabee® trap (27.7%) and the Blackhole® trap (18.3%). The Cinch trap had a significantly greater (P=0.003) capture efficiency than either of the other two trap types, which did not differ (P>0.05). From a time efficiency standpoint, the Cinch trap also ranked first (0.046), the Macabee® trap second at 0.036 and the Blackhole® trap last (0.032), though the differences were not significant (P=0.693). We conclude that the Cinch trap was the most efficient of the three trap types for capturing gophers in this study. Its chief drawback is that the large baseplate makes it more time-consuming to set. The Blackhole® Rodent trap was the least efficient for capturing gophers, and very time-consuming to set and check. Furthermore, the floor of the trap (solid plastic) may have induced trap shyness, even when covered by soil. The Macabee® ranked intermediate in both capture efficiency and time efficiency. Due to its small size and ease to set and check, it will probably remain a popular alternative for capturing pocket gophers. An integrated pest management approach is recommended for the most effective control of pocket gophers.

Funnel traps capture a higher proportion of juvenile great tits parus major than automatic traps

We compared capture rates of Great Tits at funnel traps, where several birds can be captured at once so that some decoy effect may appear, to those obtained at automatic traps, where only one bird can be trapped at a time, at trapping stations in northeastern Spain. Juvenile birds were mainly captured at funnel traps (79% of juvenile captures), whereas adult plumaged birds were captured at both types of traps (51% of captures were at the funnel traps) (test between ages, P<0.001). Juvenile Great Tits had lower body condition as measured by ptilochronology (P<0.01). These birds are more easily trapped in funnel traps, which may be acting as decoy traps, and thus are vulnerable to the same kinds of biases (eg age or body condition) that have been previously documented for decoy traps.

Small Mammals in Central Kansas Windbreaks in Winter

Field windbreaks consist of trees, shrubs, or a combination of both planted adjacent to fields or farmsteads to reduce the force of wind. Kansas has about 4,900 ha of farmstead windbreaks and 118,000 ha of field windbreaks (Soil Conservation Service, 1994). Johnson and Beck (1988) reviewed the literature and identified references to 28 species of mammals using windbreaks with seven species classified as high dependence/high use. The purpose of this study was to determine which small mammal species use field windbreaks in central Kansas during winter. Twenty field windbreaks of variable size (0.28 ha-11.66 ha) were studied in Stafford and Pawnee counties, Kansas. The number of rows in the windbreaks ranged from 1 to 17, with a mean of 6.7 rows. The most frequently occurring tree species in the windbreaks were eastern cottonwood (Populus deltoides) occurring in 100% of the windbreaks, eastern redcedar (Juniperus virginiana) (85%), Siberian elm (Ulmus pumila) (55%), honey locust, (Gleditsia triacanthos) (50%) and Osage orange (Maclura pomifera) (50%). Small mammal trapping was conducted during mid-February. Twenty-five trapping stations were set at 5-meter intervals along a transect that bisected each windbreak. Each station had one Sherman live trap (3 in x 3.5 in x 12 in) and one museum special snap trap (2.75 in x 5.5 in), baited with a mixture of peanut butter and oats. Trapping was conducted for three consecutive nights in each windbreak, resulting in 150 trap-nights per windbreak and a total of 3,000 trap-nights during the course of the sampling period. One hundred and forty-nine captures of six small mammal species were made in the 20 windbreaks. The species captured were white-footed mouse (Peromyscus leucopus), deer mouse (P. maniculatus), cotton rat (Sigmodon hispidus), western harvest mouse (Reithrodontomys megalotis), Elliot's short-tailed shrew (Blarina hylophaga), and house mouse (Mus musculus). Eighteen of the 20 windbreaks (90%) contained at least one species of small mammal, and one windbreak contained five of the six species, lacking only the Elliot's short-tailed shrew. The average number of small mammal species per windbreak was 1.75. The white-footed mouse was the species most often captured (51.7% of total captures), followed by deer mouse (40.2%), western

Population Ecology of Proechimys guairae (Rodentia: Echimyidae)

An ecological study of Proechimys guairae in Venezuela was made based on marking and recapturing of individuals at 225 trapping stations distributed over 9 ha. The trappability of individuals was >50% in most sampling events; there was no difference in capture rate between marked or unmarked individuals, or males and females. Adult individuals were present throughout the sampling period, but juveniles appeared at the beginning of the rainy season and disappeared in the dry season. Pregnant or lactating females were observed during most sampling periods. Most reproductive activity was concentrated from the middle of the dry season through the wet period. Estimated density was 1–3.5 individuals/ha; that variation appeared to be related to weather fluctuation and resource availability. Estimated effective population size (Ne) was 3–20 individuals/ha. Estimated home ranges value were significantly different for females and males. Adult females had no overlap of their home range, suggesting female territoriality. Home range of males did overlap. Data were compared with those of other species. Some ecological conditions that might have favored speciation guided by chromosomal mutations characterize P. guairae .

A new study method of microhabitat structure of small mammals

The variables in habitat studies are usually transformed in such a way that they become abstractions and intuition is lost. We tested a new method for the analysis of habitat using data collected in a grid laid at the "restinga de Maricá", in Rio de Janeiro State, Brazil. Thirty-seven microhabitat variables were measured at each trap station. We assume that these variables characterize the microhabitat structure at the moment when measurements were taken. The data are transformed in 3 ways: (1) the averages of the measured variables were calculated, as usual in habitat studies; (2) the data are transformed in densities per area in square meters without reduction in the number of variables; and (3) we calculated the natural logarithms of the data thus transformed. The 3 sets were analised through discriminant analysis. The logarithms of densities were the most efficient kind of transformation. This transformation resulted in a significance of p = 0.0001 with 39.72% of variance in the 1st discriminant function and of p = 0.0426 with 31.45% of variance in the 2nd function, and 84.62% of groups correctly classified. We obtained better classification results than previous similar works and we kept the intuition through the data analysis.

Habitat Selection by Female Rattus lutreolus Drives Asymmetric Competition and Coexistence with Pseudomys higginsi

Two native Australian rodents, the velvet-furred swamp rat ( Rattus lutreolus velutinus ) and the long-tailed mouse ( Pseudomys higginsi ), are sympatric in wet sclerophyll forests on Mount Wellington, Tasmania, Australia. Their relatively large macrohabitat overlap implies that these species partition one or more resources to coexist. We used census data to examine the role of microhabitat structure in resource partitioning. At trap stations where only one species or the other was trapped, significant differences in microhabitat structure existed. R. lutreolus was trapped in areas of densest vegetation ≤1 min height. Male and female R. lutreolus exhibited macrohabitat separation during the non-breeding season (winter). At that time, adult and subadult female rats occupied areas of thickest ground cover; males occupied surrounding, more open areas of forest at lower densities. After the onset of breeding, male rats visited areas occupied by female rats. P. higginsi was never trapped in areas where most female R. lutreolus were captured but was most often trapped in the same macrohabitat as male R. lutreolus . After the onset of breeding, relative rate of capture of P. higginsi increased in these areas as male R. lutreolus shifted their trap-revealed ranges to incorporate areas where females were resident. We propose that the seasonal intersexual habitat separation exhibited by R. lutreolus , and particularly the habitat use by females, may be an essential component in structuring the rodent community in wet sclerophyll forests.

RESPONSES OF A SMALL MAMMAL COMMUNITY TO HETEROGENEITY ALONG FOREST-OLD-FIELD EDGES

Despite the importance of edges effects in ecological systems, the causes and consequences of animal responses to habitat edges are largely unknown. We used three years of live-trapping and measures of the plant community around trap stations to explore the responses of white-footed mice (Peromyscus leucopus), meadow voles (Microtus pennsylvanicus), and short-tailed shrews (Blarina brevicauda) to forest-field edges in upstate New York. We found that capture probabilities of voles were highest in grass- and forb-dominated micro-habitats and in old-field zones distant from the forest edge. In contrast, capture probabilities of white-footed mice were highest in shrub-dominated microhabitats and in zones near the forest edge. Short-tailed shrews did not show strong micro- or macrohabitat associations. The responses by voles, the competitive dominant in our system, to variation along forest-field edges were more consistent across years than were those of the competitively inferior, white-footed mouse. Mice were less likely to use the old-field interiors when vole density was high than when it was low, suggesting competitive displacement of mice by voles. Finally, we found good agreement between the spatial activity patterns of mice and voles in old-fields and their impacts on patterns of survival of tree seeds and seedlings in concurrent studies. These results suggest that a dynamic interaction exists between the plant and animal communities along forest edges.

Responses of Australian Bush Rats, Rattus fuscipes, to the Odor of Introduced Vulpes vulpes

Predator-avoidance behavior of native bush rats (Rattus fuscipes) to an introduced predator (Vulpes vulpes) was investigated by measuring their responses to predator odor. Trapping success of wild bush rats was compared between clean traps and traps scented with fox odor, set along creeks in Namadgi National Park in southeastern Australia. Two experimental designs were used; the first measured trapping success of clean and scented traps alternating along a trapline through bush rat habitat in winter, spring and summer. The second design offered a choice of clean and scented traps at each trap station and was repeated in spring and summer. Relative trapping successes were analyzed to determine if rats avoided fox odor. Multiple t-tests showed no avoidance responses with similar numbers of captures in clean and fox-scented traps. Consequences of the apparent naivete of bush rats to the odor of an introduced predator are discussed.

Radio-tracking Revealed Home Ranges of Black-breasted Button-quail Turnix melanogaster in Remnant Vine Scrub between Hoop Pine Plantation and Agriculture

SummaryFifteen Black-breasted Button Quail Turnix melanogaster were trapped and banded at three of ten trap stations in remnant vine forest between a young Hoop Pine Araucaria cunninghamii plantation and agricultural land. Eleven individuals were tagged with radio-transmitters. Four individuals yielded sufficient data for home range analysis. Home range estimates ranged from 2.2 to 6.1 ha. Home ranges overlapped considerably (both within and between sexes). One male was found on a nest incubating three eggs, located at the junction of two overlapping female territories. Another nest containing two eggs appeared to have been abandoned. Observed roosts were found among the buttress roots of larger trees in the vine forest; roosting positions changed across nights. Radio-tracked birds were found solely within Microphyll Vine Forest and sometimes within lantana thickets within the vine forest. No use was made of surrounding agricultural land or young hoop pine plantation, although elsewhere in the region birds have been observed in older hoop pine plantations and a closed eucalypt forest with a well developed understorey.

Influence of Pocket Gophers on Meadow Voles in a Tallgrass Prairie

Creation of mounds by plains pocket gophers ( Geomys bursarius ) may affect the distribution of meadow voles ( Microtus pennsylvanicus ) and subsequent patterns of herbivory. An association between abundance of meadow voles and density of neighborhood mounds might be expected if voles use mounds as feeding sites (positive association), or if vole avoid mounds due to lack of cover (negative association). Mounds also may indirectly affect vegetative patterns, if mounds affect the distribution of herbivores. During two consecutive summers, we livetrapped voles and mapped mounds on three 80 m × 80 m plots. Regressions of vole captures at each trap station against the number of mounds within a range of radii of each trap were consistently negative across most spatial scales, but strongest correlation was found to be at 10 m. In all cases, bivariate scattergrams revealed a “factor-ceiling” distribution, with data points widely scattered below an upper limit. We also conducted an experiment to determine if seedlings had a greater or lesser mortality due to small-mammal herbivory when growing on mounds versus off mounds. A two-tailed paired t -test on the proportion of seedlings eaten after 13 days failed to show differences between on-mound and off-mound rates of herbivory ( P = 0.066); however, prior analyses showing voles avoiding areas with high rates of disturbance give weight to the hypothesis that seedlings growing off mounds experience higher rates of herbivory. Thus, through a second-order indirect effect, the presence of gopher mounds could lead to distinct changes in the plant community.

Development and Evaluation of Habitat Models for Herpetofauna and Small Mammals

Abstract We evaluated the ability of discriminant analysis (DA), logistic regression (LR), and multiple regression (MR) to describe habitat use by amphibians, reptiles, and small mammals found in California oak woodlands. We also compared models derived from pitfall and live trapping data for several species. Habitat relations modeled by DA and LR produced similar results, averaging about 70% classification success of the trapping stations to the correct group (capture or noncapture habitat). Although more variables were included in DA (4-5) than in LR (2-3), those included in LR were typically a subset of those in DA. On average, MR habitat models accounted for 56% of the variation in the index of relative species' abundance. The variables included in the MR models were seldom the same as those for DA and LR. Most differences between MR and the other two methods were related to differences in spatial scale: MR modeled habitat among grids, whereas DA and LR modeled habitat within grids. Habitat models for the same species differed between the trapping methods used. Live traps are most useful for describing general habitat relations of some small mammal species across large geographic areas, whereas pitfall traps are useful for intensive sampling of a larger portion of the vertebrate community within smaller geographic areas. Thus, the choice of trapping methods must be based on the study goals, biology of the species, and the spatial scale of study. For. Sci. 44(3):430-437.

25-Year Study of the Population Development of Central European Songbirds: A General Decline, Most Evident in Long-Distance Migrants

During the past century a decline hasbeen noted in European bird popula-tions, both in large species [1] andpossibly also in songbirds [2]. Todaythe “Red List” (of endangered spe-cies) includes about 50% of the avi-fauna in most Central Europeancountries; about 30% of species aredeclining to an extent that threatenstheir continued existence in CentralEurope. These include songbirds,mainly open-country species that areeasy to monitor. Trends in the num-bers of many unobtrusive songbirdspecies, however, have remainedlargely unclear [3]. To assess theirpopulation changes our institute be-gan a census program in 1972 with thehelp of hundreds of amateur ornitho-logists [4]. A trapping station in thisproject in southern Germany has pro-vided data on 35 species over 25 years– the first dataset based on strictlystandardized methods over such along period. During this entire periodthe number of trapped birds has fall-en slowly but continuously, by an av-erage of about 1% per year. The de-crease is greatest for long-distancemigrants, and it heralds profoundchanges in the Central European avi-fauna.Populations of large birds such as ea-gles and storks can be determined ac-curately, and most of the Europeanbreeding pairs are monitored. Forspecies that are more common or areharder to observe, such as crows andowls, only rough estimates are possi-ble [3]. Serious problems are encoun-tered in songbirds. Abundant, widelydistributed, and unobtrusive speciescannot be counted completely or di-rectly; regional estimates must bebased on indirect procedures such asrecording territorial song. Such esti-mates are often biased by varying,nonquantifiable “observer quality”[5]. Therefore only a few countrieshave established sufficiently reliableprograms for monitoring songbirdsduring the breeding period [6, 7].In 1968 we began testing standardizedtrapping procedures for monitoringsongbird populations in order to re-duce differences among observers bya more objective method. The resultswere positive [8], and in 1972 wetherefore initiated the “Mettnau-Reit-Illmitz” program (based onthree stations, Mettnau in southernGermany, Reit in northern Germany,and Illmitz in Austria. This programwas later extended, and temporarilygrew into an ESF network encom-passing Europe and Africa [9]). TheMettnau station has operated sincethe outset, and we report here on theresults of a full quarter of a century ofsongbird population monitoring.The samples are obtained by trappingpassage migrants during the autumnmigration while staging at rest sites.A suitable study area must (a) becharacterized by largely unchangingvegetation, (b) include different habi-tats so that birds with different eco-logical requirements can rest there,and (c) be a protected area of guaran-teed long-term existence. The Mett-nau peninsula, with a 50-year-old birdsanctuary, is ideal for the purpose[10]. The 35 songbird species selectedfor monitoring include regularly stag-ing long-, intermediate-, and short-distance migrants (Table 1).The birds are trapped in nylon netsnormally used to catch birds for ring-ing; 2 m high and 7 m long, they areset up between wooden bars on poles.A wall is formed by 52 nets extendingthrough 8 different habitats (from abrush zone through forested and wetregions). The annual trapping periodis June 30–November 6 and includesthe entire autumn migratory periodof songbirds in Central Europe. Thenets are checked hourly from dawnuntil soon after dusk; trapped birdsare ringed (to prevent double count-ing), subjected to biometric tests andthen released. The monitoring condi-tions (annual setting up of the nets,collecting the birds, data collection,etc.) are standardized as far as possi-ble [10]. Most of the investigatedbirds come from Central Europe, al-though some have traveled fromnorthern, eastern, and western Eu-rope, and a small proportion are localbreeding birds. These origins areknown from recoveries of ringed indi-viduals [11] and from biometric dataon population differentiation [10].Test studies have confirmed thatstandardized trapping procedures ef-fectively give reliable estimates ofsongbird populations. Safriel andLavee (1991) showed that the numberof palaearctic songbird migrants trap-ped in Sinai is correlated positivelywith estimates of their European pre-migratory population sizes [12]. Dunnet al. (1997) demonstrated that trendsin the annual capture indices of song-birds trapped during autumn migra-tion in Michigan are correlated posi-tively with trends in breeding birdsurvey data from their breedinggrounds and conclude that “intensivestandardized netting can be a usefulpopulation monitoring tool” [13]. Wehave consistently found that trends intrapping data reliably reflect thosefrom other sources such as single-spe-cies population studies and country-wide population estimates for RedLists, etc. [4]. Thus data from 147,661individuals that were caught at Mett-nau between 1972 and 1996 reflectthe population development of 35Central European songbird species,as follows.