Capturing American White Ibises in urban South Florida using two novel techniques

As many wildlife species, including wading birds, adapt to anthropogenic landscapes and, in some cases, exhibit altered behaviors, studies that involve capturing birds may require new methods better suited for use in urban areas and to accommodate altered animal behavior. We developed two novel techniques, a leg lasso and flip net, for capturing American White Ibises (Eudocimus albus) in urban environments in southern Florida, and also used a traditional technique (mist‐nets) in non‐urban wetland habitats. The flip net and leg lasso were developed to capture White Ibises habituated to the presence of humans. Ibises were captured in urban and wetland environments from October 2015 to August 2017 in Palm Beach, Broward, and Lee counties, Florida. We captured 6.0 ± 13.5 ibis/h with the flip net, 1.6 ± 0.8 ibis/h with the leg lasso, and 0.5 ± 2.6 ibis/h with mist‐nets. We captured larger (higher mass to tarsus length ratio) birds using the flip net and leg lasso than using mist‐nets, and captured more males with leg lassos than with other two techniques. The novel techniques we used are efficient, cost effective, easy to use, and also potentially useful for capturing other species of birds. Leg lassos and flip nets are also safe to use in populated areas for both birds and humans.     

Crossbow‐netting: a new method for capturing shorebirds

Capturing shorebirds during the non‐breeding season can be challenging because they are usually scattered over wide‐open intertidal areas while foraging and are sensitive to human disturbance at roosts where they gather during high tide in large vigilant flocks. Several techniques are available for capturing shorebirds, but, for a study of stopover ecology, we needed a method that would allow us to capture Dunlins (Calidris alpina) on a regular basis at high‐tide roosts during the day (ruling out mist‐nets), did not require the use of gun‐powder (ruling out cannon‐nets), and that would deploy a net faster than clap nets, whoosh nets, and wilsternets. Therefore, we developed a new method to capture shorebirds where a crossbow is used to pull a mist‐net over flocks of roosting birds. We tested this technique in four habitats (saltpans, salt marshes, beaches, and mudflats) in the Tagus estuary, Portugal, and captured over 380 birds representing eight different species. Advantages of this technique compared to other methods (e.g., mist‐nets, clap‐ and whoosh nets, and cannon‐nets) include (1) portability, (2) ease of set up, (3) minimal disturbance of birds near the capture area, and (4) no explosive materials are needed. Our results suggest that crossbow‐netting is a safe and useful capture technique, especially for studies requiring the capture of small numbers of birds on a regular basis.     

Capturing Common Loons during prenesting and nesting periods

ABSTRACT Several techniques have been used to capture Common Loons (Gavia immer), but effectiveness is limited during periods of the breeding season when loons do not have chicks. From 2005 to 2008, we studied loons in northern Wisconsin and used night lighting to capture loons on nests and also designed a lift net for capturing loons prior to nesting. At night, incubating loons were approached by boat and, when within about 30–60 m, we focused a spotlight on the loon and, once at the nest, captured loons using a landing net. Using this technique, we captured 23 loons in 29 attempts (79%). In addition, taped calls and loon decoys were used to entice prenesting, territorial loons into a shoreline‐based, lift‐net trap at a capture efficiency of 67% (10 captures in 15 attempts) during the second year of use. Our diurnal lift‐net trap and night‐light nest‐capture techniques allowed us to capture adult Common Loons during periods of the breeding season when previous investigators have found loons difficult to catch. These techniques may also be useful for capturing other species of territorial waterbirds, especially other species of loons.     

A pressure-operated drop net for capturing Greater Sage-Grouse

ABSTRACT.   A pressure-operated drop net was developed to capture endangered Greater Sage-Grouse ( Centrocercus urophasianus ) in Alberta, Canada. A drop net was developed because other capture methods, such as night lighting and walk-in traps, have largely been unsuccessful in Alberta, and rocket netting was too dangerous to be used with an endangered population. Nets (one black and one gray) were used to capture 13 birds (12 males and 1 female) in six attempts. Nets dropped quickly (about 1 s) and quietly and captured all birds under the net. More birds ( N = 12) were captured using a gray net than a black net, probably because it was less conspicuous. The presence of a drop net on the lek did not alter the behavior of the birds at the lek or influence lek attendance. The cost of a net, including all supplies, tools, and equipment needed, was $790 US ($900 CAN). This pressure-operated drop net system should prove effective for capturing other lekking species and other ground-dwelling birds that will respond to baiting.     

Floating mist nets: a technique for capturing birds in flooded habitat

ABSTRACT.   Banding birds is essential for detailed demographic studies of avian populations. Mist nets are a widely used, effective method of capturing birds for banding, but are difficult to use under certain conditions. While conducting a demographic study of Southwestern Willow Flycatchers ( Empidonax traillii extimus ), rising reservoir levels flooded large tracts of flycatcher breeding habitat and made traditional mist-netting techniques impossible to use. In response, we devised a technique for capturing birds over deep water using mist nets suspended between poles kept afloat on compact buoys. In 2005, we used this technique to safely capture 17 Willow Flycatchers that could not have been captured by any other means, and over 40 additional passerines were incidentally captured with no injuries occurring. This versatile apparatus was simple to build and employ, and capture success was similar to that over dry land.     

An improved, simple nest-box trap

ABSTRACT.   The success of ornithological studies often hinges on a researcher's ability to capture individuals quickly and efficiently. Sometimes it is necessary to capture the same individual multiple times, as is the case in many metabolic, ecotoxicological, and immunocompetence studies. Several methods of capturing cavity-nesting birds at their nest boxes have been described. However, these methods proved inefficient when attempting to catch wary individuals that had already been captured previously. Here we describe a simple and inexpensive method for capturing cavity-nesting birds using a square plate of sheet metal (5.8 × 5.8 × 0.2 cm), a drinking straw, a piece of duct tape, and a monofilament line. This method has the advantages of allowing selective capture of one, but not both members of a pair and being nearly invisible to trap-shy birds.     

A portable,remote‐controlled nest‐box trap

Many researchers catch adult birds at nest boxes using a vertical prop that supports a horizontal flap that drops down when an adult enters to feed nestlings. Because the prop is visible, some birds may be too wary to enter nest boxes, or they may dislodge the prop when they lean in; either way, they are not captured. We describe a remote‐controlled nest‐box trap that has the advantages of portability and being invisible to adults delivering food to nestlings. A receiver is installed on the ceiling of a nest box, the receiver is connected to a spring‐loaded flap that is triggered remotely with a transmitter from > 30 m away, and the flap drops down to cover the box entrance. In 2017 and 2018, our remote‐controlled traps did not increase the likelihood of capturing female Tree Swallows (Tachycineta bicolor), but did improve the likelihood of capturing males. We captured 16 male Tree Swallows in 30 attempts (53.3%) using our remote‐controlled trap compared to only 41 captures of males in 139 attempts (29.5%) with prop traps. In addition, whereas prop traps required an average of ~ 50 min to capture adults in successful attempts, our trap required only ~ 25 min. These results suggest that the savings in time for field researchers using our remote‐controlled trap can be substantial, with the added ethical benefit of reducing the amount of time that nestlings are not being fed. Our remote‐controlled trap is also economical to construct, requiring ~ $60 USD for parts and < 3 h to build.     

Design and effectiveness of a novel trap for capturing nesting songbirds

ABSTRACT Capturing songbirds at their nests can be challenging and time consuming. Although traps designed for capturing songbirds at their nests have been described in the literature, few are effective for capturing species with open‐cup nests. We describe a cylindrical trap designed to capture songbirds at nests up to 2 m above ground in grasses, forbs, shrubs, and small saplings. The nest trap is constructed using a rigid hoop, two pieces of mist net, three stakes, and twist ties. We used this trap to capture female Dickcissels (Spiza americana) and female Indigo Buntings (Passerina cyanea) at their nests, with success rates of 85% (N= 196) and 60–73% (N= 16), respectively. Trapping success was comparable to that using other passerine nest trap designs. Nest abandonment after trapping attempts was rare and similar to that reported in previous studies. Our nest trap is lightweight, easy to make, versatile enough to use in a variety of grassland and shrub habitats, and easily carried and deployed in the field.     

A radio-controlled live trap.

A live trap, designed to drop a net by radio control, was constructed to capture small wild mammals and birds. Advantages of the radio-controlled trap included capabilities to select and trap only the species desired, collect animals immediately after capture, eliminate injuries during capture and operate from a protected area a distance from the trap.     

Assessing the Helicopter and Net Gun as a Capture Technique for White-Tailed Deer

Abstract The helicopter and net gun is a technique used to capture white-tailed deer (Odocoileus virginianus) and is useful in a variety of habitat types and at various population densities with the ability to be highly selective. During capture, deer may sustain injuries or even die as a result of capture and handling, and may also be prone to capture myopathy. Therefore, our objectives were to determine 1) type and frequency of injuries sustained during the helicopter and net-gun capture, and 2) the effects of capture on survival of radiocollared deer. We captured 3,350 white-tailed deer from 1998 to 2005 using a net gun fired from a helicopter on 5 southern Texas, USA, ranches. Additionally, we captured 51 yearling males and 49 mature (≥4 yr of age) males and fitted them with radiocollars to monitor their survival. We recorded injuries and mortalities during capture and ranked the seriousness of injuries on a scale from 0 to 4. We recorded 281 injuries (8.4%) and as a result of capture, at least 206 deer had broken antlers (6.1%), 55 were injured (1.6%), and 20 were direct mortalities (0.6%). The most common antler injury was broken antler tines and the most common body injury was broken legs. Postcapture mortality rates were low (1%) for this capture method. Based on capture-related injuries, mortalities, and postcapture survival, we found the helicopter and net gun to be a safe capture technique compared to other capture techniques, particularly when conditions are favorable.     

Effects of capture and video‐recording on the behavior and breeding success of Great Tits in urban and forest habitats

Behavioral research often involves capturing and video‐recording birds, but these procedures may have undesired effects on the behavior of birds that have rarely been quantified. In addition, birds in urban and more natural areas may differ in their sensitivity to disturbance. We examined the possible effects of both capturing, weighing and measuring, and taking a blood sample, and the presence of video‐cameras on the behavior of male and female Great Tits (Parus major) breeding in urban and forest habitats. Using a 2 × 2 block design, we compared the behavior and breeding success of parents that either were or were not captured on their nests a few days before behavioral observations, and of parents that either were or were not habituated to the presence of a concealed video‐recorder mounted on nest boxes. We found no significant effects of habituation to the camera on bird behavior, but males captured in their nest boxes were more vigilant and hesitated longer before entering nest boxes, and also had slightly lower provisioning rates than males that had not been captured. Captured females also tended to be more vigilant than females that had not been captured, but their provisioning rates were not affected. Capturing males also influenced the behavior of their non‐captured mates, but capturing females had no effect on the behavior of their non‐captured mates. We found no difference in the effects of capture on Great Tits in urban and forest habitats, and our treatments also had no effect on the mass, size, and survival of nestlings until fledging. Our results suggest that, for Great Tits, being captured results in sex‐dependent behavioral effects that can last for at least several days. As such, we suggest that the possibility of similar effects in other species of birds should be considered in behavioral studies where birds must be captured, and recommend either that behavioral data be collected before capturing birds or that all birds in a study should be captured and handled in a standardized way.     

Coyote capture vulnerability relative to space use and trap density

Coyotes (Canis latrans) are reported to be less vulnerable to capture in familiar areas of territories, however, most studies do not control for trap density across the territory. We determined if accounting for trap density provided a better explanation of observed capture rates. Based on a sample of 24 captured coyotes (6 inside core areas and 18 on peripheries of occupied areas) the best fitting model describing capture location only accounted for trap density and not relative time spent in each region. Our results suggest that coyote capture rates are a function of trap density in an area and not novelty avoidance. Placing traps in core areas of territories can increase the probability of capturing individuals from specific territories to increase the effectiveness of management or research activities. © 2011 The Wildlife Society.     

Netguns: a technique for capturing Black‐backed Woodpeckers

ABSTRACT Effective capture techniques are essential for studying bird populations, but commonly used techniques have proven ineffective for capturing Black‐backed Woodpeckers (Picoides arcticus) during the nonbreeding period. As a result, little is known about the winter ecology of Black‐backed Woodpeckers. We used two netguns, one powered with a 0.308 cartridge and another with CO₂ propellant, to capture 101 Black‐backed Woodpeckers (N= 75 initial captures and 26 recaptures) in the Black Hills of South Dakota from 2008 to 2011. Captures with the 0.308 netgun resulted in an impact mortality probability of 0.061 ± 0.034 (SE), whereas no impact mortalities were associated with the CO₂ netgun. We also tracked birds for 72 h post‐release, and determined a capture‐related mortality rate of 0.102 ± 0.04 with the 0.308 netgun and 0.038 ± 0.027 with the CO₂ netgun. With the CO₂ netgun, we captured woodpeckers in 31 of 43 net deployments (72%), with an average of 7.2 ± 0.4 h of capture effort for each bird. Many unsuccessful attempts were caused by tree branches that prevented net deployment. Netguns powered by CO₂ provide an effective capture technique that we recommend for studies of Black‐backed Woodpeckers and possibly other species of birds that forage low on trees.     

Density estimation in live-trapping studies

Unbiased estimation of population density is a major and unsolved problem in animal trapping studies. This paper describes a new and general method for estimating density from closed-population capture–recapture data. Many estimators exist for the size (N) and mean capture probability ( p ) of a closed population. These statistics suffer from an unknown bias due to edge effect that varies with trap layout and home range size. The mean distance between successive captures of an individual (     ) provides information on the scale of individual movements, but is itself a function of trap spacing and grid size. Our aim is to define and estimate parameters that do not depend on the trap layout. In the new method, simulation and inverse prediction are used to estimate jointly the population density (D) and two parameters of individual capture probability, magnitude (g₀) and spatial scale (σ), from the information in     , p and     . The method uses any configuration of traps (e.g. grid, web or line) and any choice of closed-population estimator. It is assumed that home ranges have a stationary distribution in two dimensions, and that capture events may be simulated as the outcome of competing Poisson processes in time. The method is applied to simulated and field data. The estimator appears unusually robust and free from bias.     

Foraging behavior and energetics of Great Egrets and Snowy Egrets at interior rivers and weirs

ABSTRACT.   Wading birds may use different foraging methods and prey capture techniques in particular habitats or under specific conditions. We measured foraging behavior and its energetic costs for Great Egrets ( Ardea alba ) and Snowy Egrets ( Egretta thula ) at two weirs (small overflow dams that raise water levels in a stream or river) and in two naturally flowing rivers in Kansas in May and June 2000 and 2005. We observed 99 randomly selected birds (38 Great Egrets and 61 Snowy Egrets) for 1513 min, and noted strike rate, prey capture rate, capture efficiency, prey size, and social interactions. In addition, 30 of these birds were observed for 504 min to estimate ambulation velocities and foraging energetics. Both species had higher strike rates and prey capture rates in rivers, but caught larger fish at weirs. Capture efficiency was higher for Snowy Egrets at weirs, but did not differ between microhabitats for Great Egrets. Snowy Egrets had higher rates of conspecific aggression at weirs than in rivers, but little aggression was documented for Great Egrets. Established algorithms suggest that, while foraging in rivers, Snowy Egrets had similar costs for changes in velocity. Changes in ambulation velocity for Great Egrets were greater at weirs than rivers. For both species, the percentage of time spent standing was twice as high at weirs as in rivers. Both species also used low-cost foraging strategies at weirs that yielded larger fish, so net energetic gains at weirs were higher than in rivers. Weirs appear to be more important to Snowy Egrets than to Great Egrets. Estimates of energy gains and expenses provide valuable predictive power for understanding egret behavior.     

Facilitation between herons and smallmouth bass foraging on common prey

Understanding how multiple predators affect one another and their shared prey is an increasingly important goal for ecologists examining predator–prey dynamics and food-web structure. In a field experiment, we examined the outcome of interactions between terrestrial and freshwater predators foraging for the same prey in two temperate North American streams. We used a factorial design to examine the combined foraging effects of herons and smallmouth bass on striped shiners and central stonerollers. We found that there was facilitation between the two predators, resulting in risk-enhancement for the prey species, with particularly pronounced effects on the smallest (<70 mm) size classes. Facilitation is the least well-documented predator–predator interaction and has not been quantitatively demonstrated for freshwater and terrestrial predators. Our results indicate that bass may gain a net benefit from the presence of wading birds such as herons and egrets, and that concerns about the negative effects of birds on fish stocks through competition may be unwarranted.     

What are we missing with only ground‐level mist nets? Using elevated nets at a migration stopover site

ABSTRACT Mist nets deployed in a standard ground‐level fashion capture birds approximately 0.5–2.6 m above the ground. In habitats where the vegetation extends above this height, standard mist net deployment may inadequately sample the targeted avian community and age‐ and sex‐classes within species. Such sampling biases may raise questions regarding studies based on data from mist‐net captures. To determine if birds were equally likely to be captured by mist nets at different heights, we constructed a series of paired ground‐level and elevated mist nets (hereafter “net rigs”) at a research station in western New York State. Net rigs were operated during 14 migration seasons from 2000 to 2006 (spring and fall each year), and 19,735 birds of 118 species were captured. Capture rates were significantly higher in ground‐level nets, but 12 species were only captured in elevated nets. Of 44 species with at least 50 captures, 25 species were more likely to be captured in the ground‐level nets and two species in the elevated nets. For four of 18 species, more birds were captured in the elevated nets during fall migration than during spring migration. We conclude that standard ground‐level net placement was more efficient in capturing birds in the secondary growth habitats that we sampled. However, ground‐level nets may not adequately sample the entire targeted community or all age‐ or sex‐classes within species.     

Methods to Reduce Avian Bycatch in Small Mammal Studies Using Snap Traps

ABSTRACT Avian bycatch, a common and undesired occurrence in small mammal studies, should be minimized by researchers. We examined effects of trap covering, treadle color (copper or yellow plastic), trap size (mouse or rat), and trap weathering (traps <1 yr or ≥ 1 yr old) on avian bycatch during 3 years. We found that covered traps caught 81% fewer birds and 70% fewer small mammals than did uncovered traps, that mouse traps caught 30% more birds and 38% more small mammals than did rat traps, and no capture differences for treadle color or trap weathering. Covered traps effectively reduced avian bycatch and should be used when reduced small-mammal capture rates are acceptable.     

Emergence trap developed to capture adult large pine weevil Hylobius abietis (Coleoptera: Curculionidae) and its parasite Bracon hylobii (Hymenoptera: Braconidae)

A novel type of emergence trap capable of capturing and separating 'live' insect catches is described. The trap was shown to be 96% efficient at capturing newly emergent adult Hylobius abietis Linnaeus on bare ground and at least 82% efficient over stumps on a weedy Sitka spruce clearfell. The trap was more than 80% efficient at capturing Bracon hylobii Ratzeburg, the most commonly found parasite of H. abietis. It was also shown to be effective at capturing adult H. abietis of unknown age (98%), indicating that it could also be used to trap out H. abietis from known areas to estimate on-site overwintering densities. Fifty-four percent of newly emergent weevils were captured within 12 h of release on bare mineral soils. Forty-two percent of unknown age weevils and 52% of parasites were captured within 1 h of their release within the trap. The rapid rates of capture mean that when traps are checked frequently they can be used to reflect accurately temporal patterns of emergence. Its potential for use in control programmes and ecological studies is discussed.     

Can ecosystem services be integrated with conservation? A case study of breeding waders on grassland

We review published studies to show that changes in soil moisture levels have significant impacts on a range of wading bird species that use UK lowland grassland, including wet grassland, and obtain their food predominantly by probing the soil. We examine both the hydrological and the ecological literature and assess how management options could alter (1) ecosystem services (via water quality and flooding) and (2) habitat quality for wading birds. The combination of biodiversity goals with broader ecosystem services has been widely advocated and we suggest that appropriate management at multiple scales (e.g. small‐scale: ponds; large‐scale: integrated washlands) could potentially provide both ecosystem services and habitat for wading grassland birds. However, there is only a limited base of evidence on which to assess the potential linkage between these two areas, particularly for non‐wading bird species. Future work should be directed at identifying (1) how crop yield, ecosystem services and biodiversity relate to each other, (2) the extent of land needed to be managed to benefit these multiple purposes and bring about measurable gain (e.g. one or two ponds may make significant inroads in reducing run‐off and pollution but make little difference to wading birds) and (3) solutions to the challenges of setting up management options at large spatial scales (e.g. catchments).