Chordeiles Minor Research Articles

Sound level measurements from audio recordings provide objective distance estimates for distance sampling wildlife populations

AbstractDistance sampling is widely used to estimate animal population densities by accounting for imperfect detection of individuals with increasing distance from an observer. Distance sampling assumes that distances are measured without error; however, it is often applied to human estimated distances, which are known to be inconsistent, inaccurate, and biased. We present an objective technique for estimating distance to vocalizing individuals that relies on the relative sound level (RSL) of the vocalization extracted from autonomous recording unit (ARU) recordings and show the error is less than human estimated error extracted from a literature case study.RSLpredicted distances can be obtained by manual measurement in sound viewing software, or automatically with automated signal recognition software. We built calibration datasets of Ovenbirds (Seiurus aurocapilla) and Common Nighthawks (Chordeiles minor) recorded at known distances and used regression ofRSLfrom those recordings to predict distance. There was no error bias ofRSLpredicted distances when compared to known distances for Common Nighthawk, minimal error bias for Ovenbird, and error from allRSLpredicted distances was less than human estimated error extracted from the literature. We then simulatedARUpoint count surveys with a known density and estimated that density with distance sampling to test whetherRSLdistance prediction does not violate the assumption that distances are measured without error. There was no difference in density estimates from known distance and density estimates obtained fromRSLpredicted distance, while density estimates contaminated with human estimated error were significantly lower than density estimates from known distance. We found that a calibration dataset of approximately 300 vocalizations was suitable to minimize error for both species, and so conclude thatRSLdistance prediction is an accessible method of improving distance estimates relative to human estimation. We provide general recommendations on how to collect calibration recordings for the application ofRSLdistance prediction to other species and areas.

Common Nighthawks (Chordeiles Minor) in Agricultural Landscapes: Genetic Structure of Populations Restricted to Urban Rooftop Nesting

Agricultural development may produce highly fragmented landscapes, which can influence population genetic structure for organisms restricted to insularized breeding habitats. Common Nighthawks (Chordeiles minor) in agriculturally dominated landscapes nest on urban gravel rooftop and might be subject to reduced gene flow among isolated urban sites. We conducted an analysis of the genetic variability and population genetic structure of Common Nighthawks nesting on rooftops in four towns in southeastern South Dakota, an area that has experienced extreme conversion of native prairie to agriculture. Using sequence data from a 725 bp region of the cytochrome b (cytb) mitochondrial gene sampled from 37 individuals representing a total of 30 different nests collected in summers 2014–2016, we found evidence of a recent population bottleneck and reduced mtDNA variability. The spatial dispersion of the 14 detected haplotypes and the presence of nine haplotypes unique to one of the four sampled towns further suggested a lack of panmixia among these nighthawks. These data are consistent with a hypothesis of habitat fragmentation due to agricultural expansion resulting in population isolation within this species of conservation concern.

Common Nighthawks (Chordeiles minor) in the Western Corn Belt: Habitat Associations and Population Effects of Grassland and Rooftop Nesting Habitat Conversion

Grassland habitat in the Northern Prairie region of North America has been greatly reduced since historical times, and conversion to agricultural row-crop production has recently intensified this decline. Common Nighthawk (Chordeiles minor) nesting habitat includes grasslands and flat, gravel rooftops, but relative occurrence of nighthawks in these habitats in the Northern Prairie region has not been previously quantified. We conducted point counts at 396 sites within two study areas in South Dakota, Nebraska, and Iowa; an eastern region dominated by row-crop agriculture and a western region with more grassland within the landscape. We compared land cover at points where nighthawks were present between the two regions and found higher incidences of cropland and grassland in the western region and higher developed land cover in the eastern region. We also compared land cover surrounding points where birds were present vs. absent for both regions combined and found greater cropland around points without birds and greater developed land cover around points with birds. We used Generalized Linear Models (GLMs) with binomial distributions to examine nighthawk presence relative to landscape variables, and ranked models with AICc. In the eastern study region, developed land cover was positively associated with nighthawk presence and cropland showed a weak negative trend with nighthawk presence. Nighthawks in the western region showed a positive association with cropland; suggesting that cropland has a positive effect on nighthawk occurrence, presumably by providing foraging opportunities, if grassland is present within the landscape at sufficient levels. If 2006-2015 regional conversion rates of grasslands and gravel rooftops continue, Markov models project suitable breeding habitat will decrease to levels where nighthawks might be extirpated as breeding birds from urban regions of the Western Corn Belt by 2026 and with substantial population reductions over the entire Northern Prairie region by 2106.

New species of parasitic nasal mites infesting birds in Manitoba, Canada (Mesostigmata, Rhinonyssidae).

Mites (Acari, Acariformes, Parasitiformes) are one of the most diverse and abundant groups of arthropods associated with birds. Several families of mites have colonised the respiratory tract of birds, the Rhinonyssidae (Mesostigmata) being the most diverse. There are 66 species of rhinonyssids (59 named, seven undescribed species) reported from Canadian birds. Two new species of rhinonyssids were discovered while surveying nasal mites from birds in Manitoba, Canada, and are herein described as Sternostomagallowayisp. n. from the horned lark (Eremophilaalpestris), and Vitznyssusericisp. n. from the common nighthawk (Chordeilesminor).

Classification threshold and training data affect the quality and utility of focal species data processed with automated audio-recognition software

ABSTRACTAutomated recognition is increasingly used to extract information about species vocalizations from audio recordings. During processing, recognizers calculate the probability of correct classification (“score”) for each acoustic signal assessed. Our goal was to investigate the implications of recognizer score for ecological research and monitoring. We trained four recognizers with clips of Common Nighthawk (Chordeiles minor) calls recorded at different distances: near, midrange, far, and mixed distances. We found distance explained 49% and 41% of the variation in score for the near and mixed-distance recognizers, but only 3% and 6% of the variation for the midrange and far recognizers. We calculated detection functions for each of the recognizers at various score thresholds and found that the detection function for the near and mixed-distance recognizers satisfied the assumptions of density estimation for most score thresholds, while the detection function for the midrange and far recognizers did not. The detection functions also showed that score threshold choice is a decision about sampling area, not just about the balance between recall and precision. Overall, we showed that training recognizers with ‘high-quality’ clips that were recorded at close range will improve the utility of the data without affecting how many true positives the recognizer detects.

First full annual cycle tracking of a declining aerial insectivorous bird, the Common Nighthawk (Chordeiles minor), identifies migration routes, nonbreeding habitat, and breeding site fidelity

Over one third of North American bird species are in decline, and for many species, we still lack fundamental biogeographic information such as migration routes and nonbreeding areas. Identifying causes of declines is limited because tracking many species throughout their annual cycle with high precision and accuracy is challenging. Common Nighthawks (Chordeiles minor (J.R. Forster, 1771)) have declined throughout much of their range and have yet to have their migratory and nonbreeding areas identified and characterized. We tracked Common Nighthawks by deploying a new 3.5 g Pinpoint GPS-Argos tag on adult males. Seven of 10 (70%) tags uploaded locations, providing the first data on migration, nonbreeding habitat, and annual site fidelity to breeding areas. Birds used similar loop migration routes and overwintered in Brazil’s Cerrado and Amazon regions. Nonbreeding season roosting home ranges were 148.22 ± 121 ha (mean ± SE) and included forest, grassland, and cropland. Breeding home-range fidelity was high; all tracked birds returned to within 1.27 ± 0.27 km of original capture locations. Our study is the first tracking of Common Nighthawks throughout their full annual cycle. Continued miniaturization of tracking technology, like the GPS-Argos transmitters used, is critical for identifying the causes of population declines of previously enigmatic migratory species.

“An inordinate fondness for beetles”: first description of Common Nighthawk (Chordeiles minor) diet in the boreal biome

ABSTRACT We present the first description of Common Nighthawk (Chordeiles minor) diet from the boreal biome. Knowledge of diet is important for this crepuscular aerial insectivore, whose population declines may be related to insect food sources. We collected 4 nestling diet samples as food boluses from 1 adult female and 3 adult males on the breeding grounds in northern Alberta, Canada. Coleopterans comprised the majority of samples, and the composition of the sample from the female differed from those collected from males. Further research is needed across the boreal forest to characterize foraging strategies and assess the potential role of food availability in population declines.

Elevated temperatures are associated with stress in rooftop-nesting Common Nighthawk (Chordeiles minor) chicks.

Grasslands and riparian forests in southeastern South Dakota have been greatly reduced since historical times, primarily due to conversion to row-crop agriculture. Common Nighthawk (Chordeiles minor) nesting habitat includes grasslands, open woodlands and urban rooftops, but nesting sites in southeastern South Dakota are confined to rooftops, as natural nesting habitat is limited. Nighthawks nesting on exposed rooftop habitats may encounter thermal conditions that increase operative temperatures relative to vegetated land cover types. Mean humidity has increased and mean wind speed and cloud cover have decreased during the nighthawk breeding season from 1948 to 2016 in southeastern South Dakota. These changes might contribute to increasing operative temperatures at exposed rooftop nest sites and this could influence chick condition. We studied nest micro-climate and the plasma stress response for 24 rooftop-nesting nighthawk chicks from 17 nests during 2015 and 2016. High humidity prior to blood collection reduced both baseline and stress-induced plasma corticosterone (CORT). In contrast, high maximum temperatures during the day before sampling increased stress-induced CORT. The magnitude of the chick stress response was significantly negatively related to maximum wind speed for the week prior to CORT measurement. Other weather and micro-climate variables were not significant effectors of CORT metrics. Most chicks had low baseline CORT and were able to mount a stress response, but a subset of chicks (n = 4) showed elevated baseline CORT and a negative association between the magnitude of stress response and ambient temperature. For this subset, mean ambient temperature for the day before sampling was significantly higher (2.3°C) than for chicks with typical baseline CORT levels. These data suggest that regional climate change trends could affect the ability of nighthawk chicks to mount a stress response, which, in turn, might influence the susceptibility of nighthawk chicks to climate change in the Northern Prairie region.

Common Nighthawks (<i>Chordeiles minor</i>) Can Take Off from Water

Common Nighthawks (Chordeiles minor) are aerial insectivores that often forage over water, at high speeds, and sometimes at high densities. Foraging nighthawks have regularly been observed flying < 1 m from the surface of water. under these circumstances, navigation errors or mid-air collisions could result in birds falling into the water, with the risk of drowning. We report two observations of Common Nighthawks that fell into a river and were able to take off from the surface of the water easily without any noticeable detrimental effects.

Observation of Common Nighthawks (Chordeiles minor) and Bats (Chiroptera) Feeding Concurrently

Abstract Records of bats and birds concurrently exploiting the same food source are rare in the literature. We observed an instance of bats and Chordeiles minor (Common Nighthawk) foraging in artificial light around the Washington Monument. Our observation corroborates earlier evidence that bats and Common Nighthawks both exploit the foraging opportunity created by artificial lights. Because the monument provided spatial perspective, we were also able to observe that bats and Common Nighthawks foraged at different heights, suggesting that they partitioned the available foraging space vertically.

Assessing the relative use of clearcuts, burned stands, and wetlands as breeding habitat for two declining aerial insectivores in the boreal forest

Fires are an ecological process essential for species dependent on early successional habitat in forested landscapes. In a wildlife context, clearcut forestry practices can mimic forest fires through the creation of early successional forest clearings, however, evidence that clearcuts provide the same ecological value as fire is mixed. In temperate deciduous/hardwood forests, many species that depend on early successional habitat are known to use clearcuts, including Eastern Whip-poor-wills (Antrostomus vociferous) and Common Nighthawks (Chordeiles minor), two threatened aerial insectivorous birds. However, the relative importance of recent clearcuts as breeding habitat relative to other more naturally open habitat types in the boreal forest is unknown. In May-July 2015 we studied occupancy and detectability of these two species in the boreal forest of northwestern Ontario. We first determined whether occupancy differed among three open habitats: burned stands, recent clearcuts, and open wetlands, and whether it differed in relation to the size of clearcut patches. We also examined how detectability of each species varied with time of day, season and weather conditions. Site occupancy for the Eastern Whip-poor-will and Common Nighthawk averaged 0.413 and 0.437, respectively. We found no significant difference in occupancy of either species in relation to burned stands, recent clearcuts, or open wetlands, although Eastern Whip-poor-will occupancy tended to be higher in burned stands. Occupancy did not show a linear relationship with patch size but neither species was found in the smallest open patches (<3ha), perhaps indicating a minimum size threshold, although further study is needed. The detection of each species was positively correlated with the occurrence of the other species, suggesting that they were both selecting similar site characteristics. Detectability for Eastern Whip-poor-will was highest after sunset and increased over the course of the breeding season, while for Common Nighthawk, detectability was similar during and after sunset and decreased over the season. Our results suggest that Eastern Whip-poor-will and Common Nighthawk show similar preference for natural and managed open sites and that recent clearcuts may provide early successional habitat in the absence of burned stands. Our results also extend the known breeding range of Eastern Whip-poor-will, which further emphasizes the need for future research on these poorly studied species in the boreal forest.

Do Urban American Crows (Corvus brachyrhynchos) Contribute to Population Declines of the Common Nighthawk (Chordeiles minor)?

ABSTRACT Ground-nesting Common Nighthawks (Chordeiles minor), adapted to living and reproducing in North American cities, nest on flat-topped gravel roofs. But populations of Common Nighthawks have declined in recent years throughout their range. One hypothesis to explain these declines is that American Crows (Corvus brachyrhynchos), which have increased dramatically in numbers in urban areas in recent years, may be depredating nighthawk nests. If urban crows are a factor in nighthawk declines, we predicted there would be higher rates of predation on nests in urban areas than in rural areas. We tested this hypothesis by placing and monitoring artificial nests containing Coturnix quail eggs in both urban and rural settings. Depredation of experimental clutches was significantly lower in rural, natural habitats than in the urban environment. The type of substrate on urban roofs may also be important in influencing rates of depredation, as egg-loss was more common at experimental nests on roofs with a small ...

Abundance and stability of populations of a chewing louse,Mulcticola macrocephalus(Phthiraptera: Philopteridae), on common nighthawks,Chordeiles minor(Caprimulgiformes: Caprimulgidae) in Manitoba, Canada

AbstractPopulations of the chewing louse,Mulcticola macrocephalus(Kellogg) (Phthiraptera: Philopteridae), were investigated on its host the common nighthawk,Chordeiles minor(Forster) (Aves: Caprimulgiformes: Caprimulgidae), from 1992 to 2013 in southern Manitoba, Canada. The louse was present in all but one year with an annual prevalence of 0.52, mean intensity of 16 lice per infested bird, a ratio of 0.81 males and 1.89 nymphs to female (n=178). Intensity was the same in the first 11 and last nine years of the study, but prevalence dropped from 0.59 to 0.34 between the two decades. Population variability for annual abundance, measured as PV, was 0.49. In August, adults and newly fledged nighthawks had a prevalence of infestation similar to the adults that immigrated in the spring, but mean intensity did not reach spring levels until September–October. Samples of hosts were small in some years, reducing the precision of parameter estimates, particularly those based on ratios. The population parameters forM. macrocephaluson a native migrant host were intermediate in the ranges of parameters for four species of lice on non-migratory, introduced feral pigeons,Columba liviaGmelin (Aves: Columbiformes: Columbidae), but the distributions ofM.macrocephalusamong nighthawks was less severely aggregated than those from pigeons.

Unusual Congregation of Savanna Nightjar &lt;I&gt;Caprimulgus affinis&lt;/I&gt; in a Wheat Field

On February 15, 2012, we were at Partala (22° 49′ 4.56′′ N; 80° 18′ 33.83′′ E), initiating People’s Biodiversity Register. Partala is situated in Narayanganj tehsil of Mandla district in Madhya Pradesh. The village is surrounded by forested hills on three sides, and a small river flows amidst them. The river banks are surrounded by agricultural fields with scattered trees. The main crops are paddy, wheat, maize, and various pulses. The dominant vegetation in this region is Tectona grandis, Terminalia arjuna, Aegle marmelos, Soymida febrifuga, Madhuca indica, Ficus religiosa, and Butea monosperma. At 18:15 hrs we reached a huge Peepal tree Ficus religiosa, which is one of the roosting sites of the Yellowfooted Green-pigeon Treron phoenicoptera. On reaching, we heard a cacophony of nightjar calls from an adjacent field. It was getting dark and we could only see silhouettes of the nightjars flying erratically, crisscrossing each other above the wheat field. There were around 30–35 birds, continuously calling and sallying on swarms of insects (moths). We identified them as Savanna Nightjar Caprimulgus affinis based on their distinct cweetzz, cweetzz, cweetzz calls. Along with nightjars, small insectivorous bats were also observed feasting on the moths. Two more species of nightjars, namely Indian Jungle Nightjar Caprimulgus indicus and Indian Little Nightjar Caprimulgus asiaticus, are found in this region. However, we could not hear the calls of these species to ascertain their presence in the congregation. The nightjars were scattered across the wheat field, and since visibility was extremely poor, we could not take photographs. We observed this congregation for almost half an hour, after which we could not follow their movements due to nightfall. Ali and Ripley (1983) indicate that the Savanna Nightjar forms loose flocks of 7 or 8 while undertaking local movements. Similarly, Rasmussen and Anderton (2005) also state that Savanna Nightjars ‘often fly in groups’. These anecdotes suggest the gregarious tendency of Savanna Nightjars. However, large congregations of Savanna Nightjars, as recorded by us, have not been published. A similar observation was made by P. Jeganathan (pers. comm.) in Sri Lankamalleshwara Sanctuary, Andhra Pradesh, on June 16, 2001. He observed 15 individuals, probably of Indian Little Nightjar Caprimulgus asiaticus, near an agricultural field foraging on insects. The European Nightjar Caprimulgus europaeus is known to form loose parties or flocks of 6 to 20 individuals on their passage to autumn migration (Ali and Ripley 1983). The only known gregarious species of nightjar is the Sand-colored Nighthawk Chordeiles rupestris of South America, with flocks of up to 50 individuals observed (del Hoyo et al. 1999). Del Hoyo et al. (1999) also mention that during migration and in the non-breeding season, more than one species of nightjar join to form groups of more than 20 birds, gathering at good food resources, such as grazing animals, animal corrals, lights or fires, or at insect swarms or termite emergence. Some species of nighthawk, such as Common Nighthawk Chordeiles minor and Lesser Nighthawk Chordeiles acutipennis, often forage in large flocks of several hundred birds. On February 16, 2012, we collected some moths which were identified as Helicoverpa sp., a common pest on wheat. King (1994) mentions that “Adult moths emerge from just after dark to midnight and crawl onto a plant or vertical substrate where their wings dry”. Williams et al. (2011) mentions that “Night birds such as the Tawny Frogmouth and nightjars feed on Helicoverpa moths as they are also active at night.” These probably explain the reason for the large congregation of Savanna Nightjars sighted by us at Partala. It is very likely that such assemblages are common in this region. However, this needs further investigation.

An Observation of Ground Feeding and Coprophagy by a Common Nighthawk in NW Manitoba

An Observation of Ground Feeding and Coprophagy by a Common Nighthawk in NW Manitoba

Nest Survival, Phenology, and Nest-Site Characteristics of Common Nighthawks In A New Jersey Pine Barrens Grassland

Abstract We monitored Common Nighthawk (Chordeiles minor) nests in a managed grassland in the New Jersey Pine Barrens in 2009 and 2010, and assessed habitat selection by comparing vegetation characteristics at nests with random locations. We found relatively high nest survival with an estimated 79% chance of survival through incubation (daily survival rate = 0.987, n = 16 nests); predation was the most common cause of failure (n = 2). Movements of young (up to 45 m from the original nest site) were frequent, which introduced uncertainty that prevented us from estimating survival through fledging. Nest sites had significantly more open ground cover (e.g., sand, lichen) than random sites, as well as less shrub and grass cover, shallower litter, and lower mean vegetation height.

Growth Rate and Relocation Movements of Common Nighthawk (Chordeiles minor) Nestlings in Relation to Age

Relocation by dependent young is a survival strategy that occurs among a wide range of taxa. The Common Nighthawk (Chordeiles minor) lays its eggs on bare substrate and, once hatched, nestlings may relocate to new sites daily. We located and monitored eight Common Nighthawk nests in Grand Teton National Park, Wyoming, quantified inter-use-site distances in relation to nestling age, and calculated a nestling growth rate curve. Common Nighthawk nestlings grow in a nearly linear fashion. Nestlings moved up to 48 m in a single day and larger, older nestlings tended to move greater distances between daily use-sites.

Mobbing of Common Nighthawks as Cases of Mistaken Identity

We report five instances of small birds mobbing Common Nighthawks (Chordeiles minor). In each case, the nighthawk was roosting in a tree during daytime and was mobbed by a group of birds in a manner typical of that directed toward an avian predator. We found only four previously published accounts of perched caprimulgiforms being mobbed. Mobbing birds probably mistake caprimulgiforms for owls because of convergence in plumage coloration and pattern between these two groups of crepuscular-nocturnal birds.

Late-Summer Feeding and Migration Behaviour and Numerical Trends of Common Nighthawks, &lt;em&gt;Chordeiles minor&lt;/em&gt;, near Pinawa, Manitoba, 1976-2009

Feeding concentrations of Common Nighthawks, Chordeiles minor, during the evening in late summer were observed and counted near the Pinawa, Manitoba, sewage lagoons during 28 of the 34 years from 1976 to 2009. Counts were frequent but non-systematic in 1976-1981, infrequent in 1982-1991, and both frequent and systematic in most years during the period 1992-2009. Results of 226 counts are analysed and interpreted as showing a major decline in the local breeding population during the 1980s but more stable numbers of transient birds, assumed to originate farther north. The timing and other characteristics of feeding and migratory behaviour are discussed. The limitations of interpreting data from a single location are acknowledged and some systematic survey methods are recommended, emphasizing the importance of all-round, long-range visibility to help distinguish between migration and foraging.

Extraction and analysis of colourful eggshell pigments using HPLC and HPLC/electrospray ionization tandem mass spectrometry

The literature on the pigments of avian eggshells is critically reviewed. Methods using methanolic sulfuric acid or hydrochloric acid to extract eggshell pigments are unsuitable to detect the occurrence of zinc protoporphyrin or zinc biliverdin because they demetallate these compounds. Extraction methods are described here using EDTA and acetonitrile-acetic acid or acetonitrile-dimethyl sulfoxide, which do not demetallate zinc protoporphyrin. Such extracts were prepared from eggshell of the common nighthawk, Chordeiles minor, and from another six bird species. Protoporphyrin and biliverdin were identified and fully characterized by HPLC/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) in all samples, but none contained zinc protoporphyrin. The zinc complex of biliverdin, claimed to be an additional pigment responsible for eggshell background colours, was labile to EDTA and acid pH and if occurring naturally could not be extracted intact by the published or the modified protocols. An explanation is advanced for the exceptional report that all porphyrins from uroporphyrin to protoporphyrin were found in eggshells of the fowl Gallus domesticus.