Estimating mortality rates among passerines caught for ringing with mist nets using data from previously ringed birds

Mist netting is the most commonly used method for catching birds for scientific ringing, but despite decades of use, there have been few attempts to quantify the associated potential risks to the individuals caught. Any incidence of mortality through capture and handling, however low, is of potential ethical concern and may also introduce biases into the data. We estimate the mortality rate associated with capture of previously ringed (recaptured) passerines from the British and Irish Ringing Scheme (c. 1.5 million records) caught using mist nets. The importance of species, age, mass, month, time, previous captures, and an index of predator occurrence was tested using generalized linear mixed‐effects models. The average mortality rate was 0.0011, most of which was reported to occur before the individuals had been extracted from the nets (c. 70% of incidents). Juveniles appeared to be at higher risk and the incidence of predation from mist nets was seasonal, with increased risk during the winter. Species differed in their reported mortality rates with the apparent risk being greatest for Chiffchaff Phylloscopus collybita (0.0029) and Bullfinch Pyrrhula pyrrhula (0.0027). To improve our understanding (and hence minimize risk in future), we recommend collecting more complete data on incidences of mortality, and also injuries; exercising increased care when the species we have identified as being at greater risk are likely to be captured, and ensuring there are robust procedures for the checking of nets (as most reported incidents of mortality occur before handling). We also recommend that all Ringing Schemes should collate and make available data on capture‐related mortality. Overall rates of mortality associated with capture, although, were low and support the use of mist netting as a safe capture technique, without undue bias from mortality, when used by appropriately trained individuals.     

Opportunistic predation on birds trapped in mist nets in two areas in the Atlantic Forest of southeastern Brazil

Mist netting is the most popular method for capturing birds, but it can increase the predation rates of individuals trapped in the nets. From 2008 to 2017, we recorded eight instances of opportunistic bird predation from mist nets (MNs) in a matrix mixing restored forest and fragments of semideciduous seasonal forest in southeastern Brazil, three times (37.5%) by exotic primates and five times (62.5%) by birds of prey. Overall predation rates (1.17–1.20%) at these two sites were considered high but were lower than in other Brazilian studies. Placing MNs near the edges of forest fragments may have allowed attacks by either forest predators or marmosets, which are exotic edge species. Some previously described precautions may decrease the predation rates of birds in MNs, such as shorter observation intervals, greater attention to given site selection and maintaining a safe distance between the MNs and the ground.     

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.     

Vertical stratification of an avian community in New Guinean tropical rainforest

Vertical stratification of avian communities has been studied in both temperate and tropical forests; however, the majority of studies used ground-based methods. In this study we used ground-to-canopy mist nets to collect detailed data on vertical bird distribution in primary rain forest in Wanang Conservation Area in Papua New Guinea (Madang Province). In total 850 birds from 86 species were caught. Bird abundance was highest in the canopy followed by the understory and lowest in the midstory. Overall bird diversity increased towards the canopy zone. Insectivorous birds represented the most abundant and species-rich trophic guild and their abundances decreased from the ground to canopy. The highest diversity of frugivorous and omnivorous birds was confined to higher vertical strata. Insectivorous birds did not show any pattern of diversity along the vertical gradient. Further, insectivores preferred strata with thick vegetation, while abundance and diversity of frugivores increased with decreasing foliage density. Our ground-to-canopy (0–27 m) mist netting, when compared to standard ground mist netting (0–3 m), greatly improved bird diversity assessment and revealed interesting patterns of avian community stratification along vertical forest strata.     

Avifauna of two upland evergreen forest reserves,the Atewa range and Tano Offin,in Ghana

Ntiamoa-Baidu, Y., Asamoah, S.A., Owusu, E.H. & Owusu-Boateng, K. 2000. Avifauna of two upland evergreen forest reserves, the Atewa Range and Tan0 Offin, in Ghana. Ostrich 71 (1 & 2): 277–281.

Data are presented on the avifauna of two Upland Evergreen forest reserves in Ghana: Atewa Range Forest Reserve and the Tano Offin Forest Reserve. The data obtained for the two reserves using three survey techniques: transect counts, timed species counts and mist-netting are compared. A total of 105 species were recorded for the Atewa Range Forest Reserve while the Tano-Offin Forest Reserve yielded 110 species. Mean species encounter rate in the transect counts at Atewa was 24.2 per km while individual bird encounter rate was 52.6 per km; encounter rates at Tano Offin were 31.2 per km. and 98.2 per km for species and individual birds respectively. The most common species encountered in Atewa was the Yellow-whiskered Greenbul Andropadus latimstris (7.1% of observations in transect counts and 6.7% in spot counts), while the Green-crested Touraco (6.6% of transect counts) and Green Hylia (5.7% of spot counts) were the most abundant at Tan0 Offin. The records for Atewa included four globally threatened species while Tano yielded three threatened species. Two species of birds, the Equatorial Akalat Sheppardia aequatorialis and the yellow-bellied Greenbul Phyllastrepus flavostn'atus were recorded for the first time in Ghana from the two reserves. The bird community at Tan0 Ofin was significantly more diverse than that at Atewa. In both reserves, spot counts yielded more species (67.6% and 74.5% of total recorded at Atewa and Tan0 respectively), than transect counts and mist nets. 31 species recorded in both spot counts and transect counts at Atewa were not captured in mist nets, while nine species caught in mist nets were not recorded by the two methods. The figures for the Tano Offin reserve were 43 and six respectively. We conclude that of the three survey techniques, the timed species counts offer the most comprehensive results for rapid assessment of forest avifauna, but a combination of all three methods is necessary for complete coverage. The need for management of the two reserves to maintain their unique biodiversity in the face-of threats from mining and logging is discussed.     

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.     

4. A FIELD NATURALIST'S PEREGRINATIONS

Simmons, Robert. 1984. Pre-independence behaviour, morphometrics and trapping of Redbreasted Sparrowhawks. Ostrich 55:158-162.

During an intensive study of breeding Redbreasted Sparrowhawks Accipiter rufiventris, I developed a new technique of catching flying young by exploiting their innate curiosity about moving objects. Pine cones modified to resemble partially plucked birds were thrown past a perched sparrowhawk which dived at the cone and “kneaded” it on the ground. While still grounded, fledglings were covered with a raptor mist net, and later weighed and measured. Birds were caught up to the time the last one became independent (76 days). Both fledglings could dive competently at cones soon after they could fly and by day 55 they were taking prey transfers on the wing. Independence was reached when both birds became food-stressed (57th and 76th days). Since the second fledgling had achieved 99% feather growth at independence, I suggest that the adults may assess their young's flight skills to determine when prey provisioning can cease.     

Opportunistic predation of a Common Scale-backed Antbird (Willisornis poecilinotus) by a Goliath bird-eating spider (Theraphosa blondi) in the Eastern Brazilian Amazon

We report the opportunistic predation of a female Common Scale-backed Antbird (Willisornis poecilinotus) entangled in a mist-net by a Goliath bird-eating spider (Theraphosa blondi) in the Brazilian Amazon. We suggest that the predation event occurred for the following combination of reasons: the spider is common in the study area; the bird became entangled at dusk, when the spider begins its activity; and the lowest mist-net shelf was suspended close to the ground. To reduce opportunistic predation events we recommend that it is critical to keep intervals between mist-net checks to a maximum of 15 min in Amazon forests. We also emphasize that attention is required when installing mist-nets to avoid nets touching the ground when animals become trapped in them.     

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.     

Energy,predators and the behavior of feeding hummingbirds

Summary Current evidence suggests that many animals trade off energy gain against the risk of predation while feeding. In contrast, energetic considerations alone have proven successful in explaining and predicting the behaviour of feeding hummingbirds. This success may reflect the relative lack of natural predation on hummingbirds, but this study suggests that it may additionally reflect the lack of studies taking a predation perspective. In particular, when Anna's hummingbirds (Calypte anna) are faced with an obstructed view of their surroundings, they engage in behaviour suggestive of anti-predatory vigilance. In doing so, they voluntarily reduce their rate of energy intake. These birds also forgo better feeding opportunities that occur close to the ground, where observations suggest they are wary of opportunistic predators such as roadrunners (Geococcys californianus). While energy-based concepts will remain useful in the study of hummingbird feeding behaviour, the lack of predation on these birds should not be equated with an insensitivity to the risk of predation. This realization may lead to further insights into hummingbird-plant interactions, and hummingbird biology in general.     

Spatial distribution of understory fruit-eating birds and fruiting plants in a neotropical lowland wet forest

Spatial distribution of fruit-eating birds and fruiting shrubs of the Melastomataceae and Rubiaceae were examined on a 10 ha plot in tropical lowland wet forest of Costa Rica. Many plant species and most birds exhibited considerable spatial variation in their occurrence on the plot, as indicated by the distribution patterns of shrubs with ripe fruits and captures in mist nets, respectively. In many cases, captures of fruit-eating birds were correlated with abundance of fruiting plants, particularly for species that rely heavily on fruits. In general, fruit-eating birds concentrated their use of the plot to areas rich in fruiting shrubs. This differential use of certain areas likely results in differential visitation to fruiting plants located in these areas and in a heterogeneous dissemination of seeds into the habitat.     

Recapture Heterogeneity in Cliff Swallows: Increased Exposure to Mist Nets Leads to Net Avoidance

Ecologists often use mark-recapture to estimate demographic variables such as abundance, growth rate, or survival for samples of wild animal populations. A common assumption underlying mark-recapture is that all animals have an equal probability of detection, and failure to meet or correct for this assumption–as when certain members of the population are either easier or more difficult to capture than other animals–can lead to biased and inaccurate demographic estimates. We built within-year and among-years Cormack-Jolly-Seber recaptures-only models to identify causes of capture heterogeneity for a population of colonially nesting cliff swallows (Petrochelidon pyrrhonota) caught using mist-netting as a part of a 20-year mark-recapture study in southwestern Nebraska, U.S.A. Daily detection of cliff swallows caught in stationary mist nets at their colony sites declined as the birds got older and as the frequency of netting at a site within a season increased. Experienced birds’ avoidance of the net could be countered by sudden disturbances that startled them into a net, such as when we dropped a net over the side of a bridge or flushed nesting cliff swallows into a stationary net positioned at a colony entrance. Our results support the widely held, but seldom tested, belief that birds learn to avoid stationary mist nets over time, but also show that modifications of traditional field methods can reduce this source of recapture heterogeneity.     

The behavior of wild spectral tarsiers

Field data are presented from a 15-month study of spectral tarsiers in North Sulawesi, Indonesia, based on over 300 sightings of animals in the wild and supplemented by observations from other parts of the island. Animals in study area were caught in mist nets and marked with colored plastic bird rings so that tarsiers followed at night could be individually recognized. Ecological data presented cover the locomotion, use of forest strata, and diet of tarsiers. Although clearly specialized for vertical clinging and leaping, the spectral tarsier is less specialized than the western tarsier, occupying a wider range of habitats and using a wider range of vegetation strata and locomotor patterns. Diet is mostly insects collected both on the ground and in trees. Spectral tarsiers were found to be monogamous and territorial. Families regularly slept at the same sites each day and gave loud duet songs as they congregated at sleeping sites each dawn. Sometimes similar songs were given in the night during territorial conflicts. Family home ranges were plotted and average about 1 ha. Observations are included on mating, the development of young tarsiers, and the dispersion of juveniles. Tarsier young are very precocious and may travel independently as little as 23 days after birth. Tarsiers regularly scent marked their ranges by rubbing branches with urine and special epigastric glands. In addition, they have a varied repertoire of calls and the main vocalizations are described.     

Improving our understanding of demographic monitoring: avian breeding productivity in a tropical dry forest

The ratio of juvenile to adult birds in mist‐net samples is used to monitor avian productivity, but whether it is a “true” estimate of per capita productivity or an index proportional to productivity depends on whether capture probability is not age‐dependent (true estimate) or age difference in capture probability is consistent among years (index). Better understanding of the processes affecting age‐ and year‐specific capture probabilities is needed to advance the application of constant‐effort mist‐netting for monitoring and conservation, particularly in many tropical settings where capture rates are often low. We ranked members of the avian community by capture frequencies, determined if temporary emigration influenced the availability of birds to be captured, and assessed the distribution of birds relative to mist‐nets and the parity between capture‐based productivity estimates and number of fledglings in nest plots in a tropical dry forest in Puerto Rico in 2009 and 2010. Few captures characterized the community of 25 resident species and, when estimable, capture probabilities were low, particularly for juveniles (typically < 0.1). Negative trends in capture probability, temporary emigration, and the distribution of birds suggest that avoidance of mist‐nets influenced capture rates in our study. Increasing mist‐net coverage or moving mist‐nets between sampling periods could increase capture rates. The number of fledglings observed in nest plots (25 ha/plot) did not correlate well with capture‐derived estimates (20 ha/net stations), suggesting the presence of immigrants or failure to find all nests. Our results suggest that indices of breeding productivity from mist‐netting data may track temporal changes in productivity, but such data likely do not reflect “true” productivity in most cases unless age‐specific differences in capture probability are incorporated into estimates. Pilot studies should be conducted to evaluate capture rates and the spatial extent sampled by mist‐nets to improve sampling design and inferences before informing decisions.     

Tick infestation on birds in an urban Atlantic Forest fragment in north-eastern Brazil

Birds are important hosts for various tick species, playing a significant role in their biological life cycle and dispersion. In this study, we investigated tick infestations on birds trapped in an urban remnant of Atlantic Forest in Pernambuco state, Brazil. From February 2015 to March 2017, 541 birds belonging to 52 species were trapped with mist nets and examined for ectoparasites. Birds trapped in the late successional forest were significantly more infested than birds trapped in the early successional forest. In the same way, ectoparasite infestation varied significantly according to bird weight and collection plot. Overall, 198 birds (36.6%) belonging to 27 species were parasitized by ectoparasites (i.e., ticks, lice and/or mites). Ectoparasites were effectively collected from 111 birds, of which 99 belonging to 20 species were infested by ticks (n?=?261), namely, Amblyomma longirostre (13 nymphs), Amblyomma nodosum (21 nymphs), Amblyomma varium (one nymph), and Amblyomma spp. (five nymphs and 221 larvae). Most of the ticks (>?90%) were collected from Passeriformes. This study provides the second record of A. varium in Pernambuco state and confirms that birds, especially Passeriformes, are important hosts for larvae and nymphs of Amblyomma spp. in the Atlantic Forest biome of Pernambuco.

     

Compounding effects of habitat fragmentation and predation on bird nests

Habitat fragmentation and invasive species are two of the greatest threats to species diversity worldwide. This is particularly relevant for oceanic islands with vulnerable endemics. Here, we examine how habitat fragmentation influences nest predation by Rattus spp. on cup‐nesting birds in Samoan forests. We determined models for predicting predation rates by Rattus on artificial nests at two scales: (i) the position of the bird's nest within the landscape (e.g. proximity to mixed crop plantations, distance to forest edge); and (ii) the microhabitat in the immediate vicinity of the nest (e.g. nest height, ground cover, slope). Nest cameras showed only one mammal predator, the black rat (Rattus rattus), predating artificial nests. The optimal model predicting nest predation rates by black rats included a landscape variable, proximity to plantations and a local nest site variable, the percentage of low (<15 cm) ground cover surrounding the nest tree. Predation rates were 22 ± 13% higher for nests in forest edges near mixed crop plantations than in edges without plantations. In contrast, predation rates did not vary significantly between edge habitat where the matrix did not contain plantations, and interior forest sites (>1 km from the edge). As ground cover reduced, nest predation rates increased. Waxtags containing either coconut or peanut butter were used as a second method for assessing nest predation. The rates at which these were chewed followed patterns similar to the predation of the artificial nests. Rural development in Samoa will increase the proportion of forest edge near plantations. Our results suggest that this will increase the proportion of forest birds that experience nest predation from black rats. Further research is required to determine if rat control is needed to maintain even interior forest sites populations of predator‐sensitive bird species on South Pacific islands.     

A new method for catching cavity‐nesting birds during egg laying and incubation

ABSTRACT The physiological condition of female birds during the egg‐laying and incubation periods is of considerable interest and yet is relatively understudied in wild birds, primarily due to the difficulty of catching birds during this period without causing nest desertion. We therefore developed a box‐net to capture cavity‐nesting birds using sections of a mist‐net placed around a metal cubic frame. We captured female Great Tits (Parus major) as they left nest boxes during the egg‐laying and incubation periods and measured desertion rates. Using box‐nets, we captured 108 of 119 (90%) females during egg laying and 10 of 12 (83%) during incubation. Our recapture rate over two consecutive days during incubation was 50% (5 of 10). Females not captured left nest boxes before we attempted to capture them, escaped through a hole in the mist‐net, or remained in nest boxes for more than 2 h, after which we ended capture attempts. Overall, 22% of egg‐laying females deserted, with desertion rates highest early in the egg‐laying period. Desertion rates of females captured using box‐nets did not differ from those of undisturbed females. One of 10 females captured in a box‐net deserted during the incubation period. Box‐nets are portable, can be set up and taken down quickly and easily, and could potentially be used with nest boxes or natural cavities at any height. Box‐nets are easy to construct and adaptable for use with an array of cavity‐nesting birds, and can be an important tool for studying female physiology during egg laying and incubation.     

雾网在森林鸟类群落研究中的应用

雾网应用于森林鸟类群落生态学研究已有20多年的历史,用雾网研究森林中行动隐蔽、少鸣唱、没有领域的鸟类,特别是森林林下鸟类十分有效．该方法不受研究者经验的影响,可以对不同地区、不同群落进行比较研究．国外学者认为雾网是研究森林鸟类群落必不可少的研究工具．文中着重介绍了雾网的优缺点及其在森林鸟类群落研究中的应用,以期推动我国相关学科的研究．     

Traditional capture of Red-billed Quelea Quelea quelea in the Lake Chad Basin and its possible role in reducing damage levels in cereals

Mullié, W.C. 2000. Traditional capture of Red-billed Quelea Quelea quelea in the Lake Chad Basin and its possible role in reducing damage levels in cereals. Ostrich 71 (1 & 2): 15–20.

Three traditional methods of capturing Red-billed Quelea Quelea quelea practised by different ethnic groups, were studied in the Lake Chad Basin in Chad and Cameroon: capture of birds by triangular hand-held nets by Hadjeraï piégeurs (trappers); with standing fishing nets of the “mist net” type by Gambai; and by cast nets (épervier) by Massa and Mousgoum fishermen.

The Hadjeraï net was found to be both selective for queleas and highly efficient. As many as 1.2 million birds were captured from 13 June to 21 August 1994 around N'Djamena, Chad, alone, until activities ceased due to heavy rains. Birds were trapped in tree roosts during moonless periods of the night. They were plucked and fried the following morning, subsequently dried in the sun, and eventually transported to the market in N'Djamena to be sold. The piégeurs operated in teams of about 6 men and each team could process about 20 000 birds per day. Once this number had been captured, they withdrew from further trapping. The catches were almost entirely composed of queleas, with sometimes a small percentage (<1%) of Golden Sparrow Passer luteus. It was estimated that annually at least 5–10 million queleas were trapped, with a market value of about 19–38 million FCFA (USA37 500–75 000).

The impact of trapping on the population of queleas in the Lake Chad Basin, estimated at about 200 million individuals in 1976/77, was insignificant. Since activities of piégeurs are aimed at maximising revenues, and not at minimising damage levels, there is no causal relationship between crop damage and number of birds trapped. However, compared to crop losses in pearl millet due to quelea damage, revenues from selling quelea are up to 40% of capitalized crop losses due to quelea in the same area.     

Are mist nets a menace for threatened insects? A first attempt to gather quantitative data

We attempt to identify the threat to flying beetles imposed by mist nets deployed for bird studies in an area of Mediterranean mosaic of evergreen scrub and deciduous forest in Italy. The present paper is the first attempt to identify the non-target species which die in these artificial traps. A large number of large scarab beetles was entangled in mist nets during a complete ringing session. The seasonal trend of beetle populations and their daily flight activity were also recorded. The results lead us to suggest that the populations of some threatened dung beetles can be impoverished at local level and represent a bycatch of mist net techniques, especially in early spring and at sunrise, when their swarming and reproductive activity is high. When summed with other factors affecting these beetles, such as habitat loss and fragmentation, this tool may represent a threat for vulnerable insect populations. Trapping effects may also represent a depletion of food resource for some insectivorous birds. For these reasons we recommend cooperative research between ornithologists and entomologists to fully study the bycatch effects of mist netting on flying insects and their effects on food availability for insectivorous birds.