Nest spacing in relation to settlement time in colonial cliff swallows

How colonial animals space their nests in relation to conspecifics may provide clues as to whether coloniality provides net benefits or occurs only because breeding sites are limited. We examined how nearest-neighbour distance varied in relation to settlement time in the highly colonial cliff swallow, Petrochelidon pyrrhonota, comparing observed nearest-neighbour distances to those expected if birds spread out to maximize nest spacing. Cliff swallows generally settled closer to each other than required by the available substrate, and clustered their nests closer in large colonies than in small ones. The first settlers at a colony site spaced themselves further apart than later arrivals but did not maximize nearest-neighbour distances. The first arrivals maintained greater nest spacing throughout the season than did birds that arrived later. Colony size and amount of nesting substrate had no effect on initial settlement distances of the first arrivals, but eventual nearest-neighbour distances declined with colony size. First arrivals may gain less from nesting with conspecifics and thus are less likely to cluster their nests than later arrivals, which may often be young or na?ve birds that gain more from the social benefits of colonial nesting. The results are consistent with the presumed social advantages cliff swallows receive from coloniality and do not support the hypothesis that colonies result from nesting site limitation. Copyright 2000 The Association for the Study of Animal Behaviour.     

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.     

Predation of birds in mist nets by callitrichids (primates): how to prevent similar events

We report predation of four birds while caught in mist nets and recommend some means of prevention. Two birds were attacked by Callitrhix jacchus and one by Saguinus midas. The predator in the fourth case was unidentified. These cases were relatively rare, affecting 0.4–4.4% of the captured birds. Two of the predated birds were caught more than 1 m above the ground and may have been accessed from branches. The other two were caught close to the ground. Reducing time intervals between net checks and cutting off branches close to nets may reduce bird predation in mist nets.     

An enzootic vector-borne virus is amplified at epizootic levels by an invasive avian host

Determining the effect of an invasive species on enzootic pathogen dynamics is critical for understanding both human epidemics and wildlife epizootics. Theoretical models suggest that when a naive species enters an established host–parasite system, the new host may either reduce (‘dilute’) or increase (‘spillback’) pathogen transmission to native hosts. There are few empirical data to evaluate these possibilities, especially for animal pathogens. Buggy Creek virus (BCRV) is an arthropod-borne alphavirus that is enzootically transmitted by the swallow bug (Oeciacus vicarius) to colonially nesting cliff swallows (Petrochelidon pyrrhonota). In western Nebraska, introduced house sparrows (Passer domesticus) invaded cliff swallow colonies approximately 40 years ago and were exposed to BCRV. We evaluated how the addition of house sparrows to this host–parasite system affected the prevalence and amplification of a bird-associated BCRV lineage. The infection prevalence in house sparrows was eight times that of cliff swallows. Nestling house sparrows in mixed-species colonies were significantly less likely to be infected than sparrows in single-species colonies. Infected house sparrows circulated BCRV at higher viraemia titres than cliff swallows. BCRV detected in bug vectors at a site was positively associated with virus prevalence in house sparrows but not with virus prevalence in cliff swallows. The addition of a highly susceptible invasive host species has led to perennial BCRV epizootics at cliff swallow colony sites. The native cliff swallow host confers a dilution advantage to invasive sparrow hosts in mixed colonies, while at the same sites house sparrows may increase the likelihood that swallows become infected.     

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.     

Heritable choice of colony size in cliff swallows: does experience trump genetics in older birds?

The variation in breeding-colony size seen in populations of most colonial birds may reflect heritable choices made by individuals who are phenotypically specialized for particular social environments. Although a few studies have reported evidence for genetically based choice of group sizes in birds, we know relatively little about the extent to which animals potentially rely on experience versus innate preferences in deciding with how many conspecifics to settle at different times of their lives. We conducted a cross-fostering experiment in 1997-1998 on cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, USA, in which some individuals were reared in colonies different in size from those in which they were born. Breeding-colony sizes chosen by this cohort of birds were monitored by mark-recapture throughout their lives. A multistate mark-recapture analysis revealed that birds in their first breeding year chose colony sizes similar to those of their birth, regardless of their rearing environment, confirming a previous analysis. Beyond the first breeding year, however, cliff swallows' colony choice was less dependent on where they were born. Birds born in small colonies and reared in large colonies showed evidence of a delayed rearing effect, with these birds overwhelmingly choosing large colonies in later years. Heritabilities suggested strong genetic effects on first-year colony choice but not in later years. Cliff swallows' genetically based colony-size preferences their first year could be a way to ensure matching of their phenotype to an appropriate social environment as yearlings. In later years, familiarity with particular colony sites and available information on site quality may override innate group-size preferences when birds choose colonies.     

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.     

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.     

Barn swallows prefer to nest at sites hidden from neighboring nests within a loose colony

Some loosely colonial species scatter their nests within a colony. Most studies on mechanisms that generate such scattered nests within a colony have primarily focused on the measurement of distance related to the intensity of interactions among conspecific neighbors. However, these interactions can change not only with distance between nests but also with other factors. In particular, whether the nest is hidden from neighbors can strongly affect the intensity of interaction for birds that usually use sight for communication. To show the possible benefit of nesting at sites hidden from neighboring nests, we studied the nest arrangements and settlement patterns within a barn swallow colony. We tested whether the swallows prefer nesting at sites hidden from neighboring nests in cattle barns that are often used as colony sites by the swallows in Japan. We found that the sides of ceiling beams hidden from neighbors were preferred as nesting sites. A randomization test suggested that the rectangular sections occupied by swallows were not spaced out within a colony. The results suggested that the swallows preferred nesting sites hidden from their neighbors and did not space out their nests within a colony. This paper also refutes intraspecific brood parasitism as a plausible function of this behavior.     

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.     

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.     

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．     

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.     

Testosterone and group size in cliff swallows: testing the "challenge hypothesis" in a colonial bird

The "challenge hypothesis" states that increases in testosterone levels of male animals during the breeding season are directly related to the extent of intrasexual competition for resources or mates that they experience. Although often tested in territorial species, the challenge hypothesis has not been evaluated for colonial animals that live in groups of different sizes and that thus experience different intensities of intrasexual competition. We measured circulating testosterone levels of male and female cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, where these birds nest in colonies of widely different sizes. Males had significantly higher testosterone levels than females, as expected. For males especially, there was a seasonal rise in testosterone levels early in the nesting cycle, corresponding to the period when birds were establishing nest ownership and egg laying, and then a fall as they switched to parental duties. Testosterone levels varied significantly with colony size; for both sexes, birds in larger colonies had higher levels of testosterone than those in smaller colonies when controlling for date. Age and body mass were not related to testosterone levels. Higher levels of testosterone for birds of both sexes in larger colonies probably reflect greater competition for matings, often extra pair, in the more social nesting situations. The results support the predictions of the challenge hypothesis.     

Host and vector movement affects genetic diversity and spatial structure of Buggy Creek virus (Togaviridae)

Determining the degree of genetic variability and spatial structure of arthropod-borne viruses (arboviruses) may help in identifying where strains that potentially cause epidemics or epizootics occur. Genetic diversity in arboviruses is assumed to reflect relative mobility of their vertebrate hosts (and invertebrate vectors), with highly mobile hosts such as birds leading to genetic similarity of viruses over large areas. There are no empirical studies that have directly related host or vector movement to virus genetic diversity and spatial structure. Using the entire E2 glycoprotein-coding region of 377 Buggy Creek virus isolates taken from cimicid swallow bugs (Oeciacus vicarius), the principal invertebrate vector for this virus, we show that genetic diversity between sampling sites could be predicted by the extent of movement by transient cliff swallows (Petrochelidon pyrrhonota) between nesting colonies where the virus and vectors occur. Pairwise F(ST) values between colony sites declined significantly with increasing likelihood of a swallow moving between those sites per 2-day interval during the summer nesting season. Sites with more bird movement between them had virus more similar genetically than did pairs of sites with limited or no bird movement. For one virus lineage, Buggy Creek virus showed greater haplotype and nucleotide diversity at sites that had high probabilities of birds moving into or through them during the summer; these sites likely accumulated haplotypes by virtue of frequent virus introductions by birds. Cliff swallows probably move Buggy Creek virus by transporting infected bugs on their feet. The results provide the first empirical demonstration that genetic structure of an arbovirus is strongly associated with host/vector movement, and suggest caution in assuming that bird-dispersed arboviruses always have low genetic differentiation across different sites.     

The incidence of American swallow bugs (Oeciacus vicarius) in barn swallow (Hirundo rustica) colonies in northeast Texas

The American swallow bug (Oeciacus vicarius) is an important ectoparasite of cliff swallows (Petrochelidon pyrrhonota) and is known to harbor several types of arbovirus. A recent study in northeast Texas suggested that O. vicarius might occur in barn swallows (Hirundo rustica) at rates much higher than previously thought. The purpose of this study was to determine the extent to which barn swallows in northeast Texas are parasitized by O. vicarius and how well this parasite is adapting to this novel host. A sample of 498 nests at 54 colonies was inspected for O. vicarius. Forty colonies (74.1%) were infected, while 310 nests (62.2%) were infected. Large colonies were more likely to be infected than small colonies. Colonies that also contained cliff swallows were more likely to be infected than colonies without cliff swallows. Infection levels in barn swallow nests were comparable to those reported for cliff swallows, though age and sex class ratios differed. Demographic changes among swallow species, including range expansions, increased colony sizes, and more frequent interspecific nesting associations have likely facilitated the movement of O. vicarius from the cliff swallow into a novel host, the barn swallow.     

Group size and nest spacing affect Buggy Creek virus (Togaviridae: Alphavirus) infection in nestling house sparrows

The transmission of parasites and pathogens among vertebrates often depends on host population size, host species diversity, and the extent of crowding among potential hosts, but little is known about how these variables apply to most vector-borne pathogens such as the arboviruses (arthropod-borne viruses). Buggy Creek virus (BCRV; Togaviridae: Alphavirus) is an RNA arbovirus transmitted by the swallow bug (Oeciacus vicarius) to the cliff swallow (Petrochelidon pyrrhonota) and the introduced house sparrow (Passer domesticus) that has recently invaded swallow nesting colonies. The virus has little impact on cliff swallows, but house sparrows are seriously affected by BCRV. For house sparrows occupying swallow nesting colonies in western Nebraska, USA, the prevalence of BCRV in nestling sparrows increased with sparrow colony size at a site but decreased with the number of cliff swallows present. If one nestling in a nest was infected with the virus, there was a greater likelihood that one or more of its nest-mates would also be infected than nestlings chosen at random. The closer a nest was to another nest containing infected nestlings, the greater the likelihood that some of the nestlings in the focal nest would be BCRV-positive. These results illustrate that BCRV represents a cost of coloniality for a vertebrate host (the house sparrow), perhaps the first such demonstration for an arbovirus, and that virus infection is spatially clustered within nests and within colonies. The decreased incidence of BCRV in sparrows as cliff swallows at a site increased reflects the "dilution effect," in which virus transmission is reduced when a vector switches to feeding on a less competent vertebrate host.     

A Novel Tool to Mitigate By-Catch Mortality of Baltic Seals in Coastal Fyke Net Fishery

Developing methods to reduce the incidental catch of non-target species is important, as by-catch mortality poses threats especially to large aquatic predators. We examined the effectiveness of a novel device, a “seal sock”, in mitigating the by-catch mortality of seals in coastal fyke net fisheries in the Baltic Sea. The seal sock developed and tested in this study was a cylindrical net attached to the fyke net, allowing the seals access to the surface to breathe while trapped inside fishing gear. The number of dead and live seals caught in fyke nets without a seal sock (years 2008–2010) and with a sock (years 2011–2013) was recorded. The seals caught in fyke nets were mainly juveniles. Of ringed seals (Phoca hispida botnica) both sexes were equally represented, while of grey seals (Halichoerus grypus) the ratio was biased (71%) towards males. All the by-caught seals were dead in the fyke nets without a seal sock, whereas 70% of ringed seals and 11% of grey seals survived when the seal sock was used. The seal sock proved to be effective in reducing the by-catch mortality of ringed seals, but did not perform as well with grey seals.     

Immune Responses of a Native and an Invasive Bird to Buggy Creek Virus (Togaviridae: Alphavirus) and Its Arthropod Vector,the Swallow Bug (Oeciacus vicarius)

Invasive species often display different patterns of parasite burden and virulence compared to their native counterparts. These differences may be the result of variability in host-parasite co-evolutionary relationships, the occurrence of novel host-parasite encounters, or possibly innate differences in physiological responses to infection between invasive and native hosts. Here we examine the adaptive, humoral immune responses of a resistant, native bird and a susceptible, invasive bird to an arbovirus (Buggy Creek virus; Togaviridae: Alphavirus) and its ectoparasitic arthropod vector (the swallow bug; Oeciacus vicarius). Swallow bugs parasitize the native, colonially nesting cliff swallow (Petrochelidon pyrrhonota) and the introduced house sparrow (Passer domesticus) that occupies nests in cliff swallow colonies. We measured levels of BCRV-specific and swallow bug-specific IgY levels before nesting (prior to swallow bug exposure) and after nesting (after swallow bug exposure) in house sparrows and cliff swallows in western Nebraska. Levels of BCRV-specific IgY increased significantly following nesting in the house sparrow but not in the cliff swallow. Additionally, house sparrows displayed consistently higher levels of swallow bug-specific antibodies both before and after nesting compared to cliff swallows. The higher levels of BCRV and swallow bug specific antibodies detected in house sparrows may be reflective of significant differences in both antiviral and anti-ectoparasite immune responses that exist between these two avian species. To our knowledge, this is the first study to compare the macro- and microparasite-specific immune responses of an invasive and a native avian host exposed to the same parasites.     

THE ANNUAL RE-OCCUPATION OF BREEDING SITES BY THE FULMAR

The Fulmar has a long period at the breeding colony prior to egg-laying. The pattern of annual occupation and build-up in numbers has been examined in detail at Marsden, Co. Durham, at a colony in which over 100 eggs are laid annually (Order 3 of Fisher's classification). The re-occupation of the cliff starts in early November with an occasional visit by one or two birds. The main period of activity at the cliff is during the morning and, as the numbers build up, the diurnal period of occupation increases. By mid-December the first birds to arrive in the colony do so before dawn and the last to leave remain well after dark until near midnight. Almost throughout the pre-egg stage, the colony is deserted each night and re-occupied the next day and birds only stay regularly overnight just before egg-laying. A similar pattern of occupation occurs after breeding but in the reverse order. The numbers of birds at the colony in January and February exceed the breeding population and include many non-breeders. The non-breeders progressively decline in numbers until May when only the breeding birds remain with a few non-breeding birds. The daily variation in the numbers of birds at the cliff is influenced by the wind speed. In general, the birds leave the colony under freshening conditions and the number present at the colony can be interpreted in terms of the wind conditions over the last three days. It is suggested that the synchronised departures are primarily feeding trips, the birds using the strong winds to reach feeding areas, except that the departure just before egg-laying is linked to egg development and synchronised laying in the colony. Competition between Fulmars and Kittiwakes for nesting sites usually results in the Kittiwakes gaining the site. This is achieved by the Kittiwakes taking over the Fulmar sites during one of the latter's departures.