Poor-Will Research Articles

Behaviour and landscape contexts determine the effects of artificial light on two crepuscular bird species

ContextArtificial light at night (ALAN) is increasing worldwide, with many ecological effects. Aerial insectivores may benefit from foraging on insects congregating at light sources. However, ALAN could negatively impact them by increasing nest visibility and predation risk, especially for ground-nesting species like nightjars (Caprimulgidae).ObjectivesWe tested predictions based on these two alternative hypotheses, potential foraging benefits vs potential predation costs of ALAN, for two nightjar species in British Columbia: Common Nighthawks (Chordeiles minor) and Common Poorwills (Phalaenoptilus nuttallii).MethodsWe modeled the relationship between ALAN and relative abundance using count data from the Canadian Nightjar Survey. We distinguished territorial from extra-territorial Common Nighthawks based on their wingboom behaviour.ResultsWe found limited support for the foraging benefit hypothesis: there was an increase in relative abundance of extra-territorial Common Nighthawks in areas with higher ALAN but only in areas with little to no urban land cover. Common Nighthawks’ association with ALAN became negative in areas with 18% or more urban land cover. We found support for the nest predation hypothesis: the were strong negative associations with ALAN for both Common Poorwills and territorial Common Nighthawks.ConclusionsThe positive effects of ALAN on foraging nightjars may be limited to species that can forage outside their nesting territory and to non-urban areas, while the negative effects of ALAN on nesting nightjars may persist across species and landscape contexts. Reducing light pollution in breeding habitat may be important for nightjars and other bird species that nest on the ground.

Influence of localized artificial light on calling activity of Common Poorwill ( Phalaenoptilus nuttallii )

Influence of localized artificial light on calling activity of Common Poorwill ( Phalaenoptilus nuttallii )

The avian "hibernation" enigma: thermoregulatory patterns and roost choice of the common poorwill.

Compared to mammals, there are relatively few studies examining heterothermy in birds. In 13 bird families known to contain heterothermic species, the common poorwill (Phalaenoptilus nuttallii) is the only species that ostensibly hibernates. We used temperature-sensitive radio-transmitters to collect roost and skin temperature (Tskin) data, and winter roost preferences for free-ranging poorwills in southern Arizona. Further, to determine the effect of passive rewarming on torpor bout duration and active rewarming (i.e., the use of metabolic heat to increase Tskin), we experimentally shaded seven birds during winter to prevent them from passively rewarming via solar radiation. Poorwills selected winter roosts that were open to the south or southwest, facilitating passive solar warming in the late afternoon. Shaded birds actively rewarmed following at least 3days of continuous torpor. Average torpor bout duration by shaded birds was 122h and ranged from 91 to 164h. Active rewarming by shaded birds occurred on significantly warmer days than those when poorwills remained torpid. One shaded bird remained inactive for 45days, during which it spontaneously rewarmed actively on eight occasions. Our findings show that during winter poorwills exhibit physiological patterns and active rewarming similar to hibernating mammals.

Avian thermoregulation in the heat: evaporative cooling capacity of arid-zone Caprimulgiformes from two continents.

Birds in the order Caprimulgiformes (nightjars and allies) have a remarkable capacity for thermoregulation over a wide range of environmental temperatures, exhibiting pronounced heterothermy in cool conditions and extreme heat tolerance at high environmental temperatures. We measured thermoregulatory responses to acute heat stress in three species of Caprimulgiformes that nest in areas of extreme heat and aridity, the common poorwill (Phalaenoptilus nuttallii: Caprimulgidae) and lesser nighthawk (Chordeiles acutipennis: Caprimulgidae) in the Sonoran Desert of Arizona, and the Australian owlet-nightjar (Aegotheles cristatus: Aegothelidae) in the mallee woodlands of South Australia. We exposed wild-caught birds to progressively increasing air temperatures (Ta) and measured resting metabolic rate (RMR), evaporative water loss (EWL), body temperature (Tb) and heat tolerance limit (HTL; the maximum Ta reached). Comparatively low RMR values were observed in all species (0.35, 0.36 and 0.40 W for the poorwill, nighthawk and owlet-nightjar, respectively), with Tb approximating Ta at 40°C and mild hyperthermia occurring as Ta reached the HTL. Nighthawks and poorwills reached HTLs of 60 and 62°C, respectively, whereas the owlet-nightjar had a HTL of 52°C. RMR increased gradually above minima at Ta of 42, 42 and 35°C, and reached 1.7, 1.9 and 2.0 times minimum resting values at HTLs in the poorwill, nighthawk and owlet-nightjar, respectively. EWL increased rapidly and linearly as Ta exceeded Tb and resulted in maximum rates of evaporative heat dissipation equivalent to 237-424% of metabolic heat production. Bouts of gular flutter resulted in large transient increases in evaporative heat loss (50-123%) accompanied by only small increments in RMR (<5%). The cavity-nesting/roosting owlet-nightjar had a lower HTL and less efficient evaporative cooling compared with the species that nest and/or roost on open desert surfaces. The high efficiency of gular flutter for evaporative cooling, combined with mild hyperthermia, provides the physiological basis for defending Tb well below Ta in extreme heat and is comparable to the efficient cooling observed in arid-zone columbids in which cutaneous EWL is the predominant cooling pathway.

Species Richness, Relative Abundance, and Habitat Associations of Nocturnal Birds Along the Rio Grande in Southern Texas

Abstract The segment of the Rio Grande between International Falcon Reservoir and Del Rio, Texas (distance ca. 350 km), remains largely unexplored ornithologically. We surveyed nocturnal birds monthly during February–June 1998 at 19 stations along the Rio Grande (n = 6) and at upland stock ponds (n = 13) in Webb County, Texas. We conducted 10-min point counts (n = 89) after sunset and before moonset. Four species of owls and five species of nightjars were detected. Nightjars, as a group, were nearly five times more abundant (mean number/count = 2.63) than owls (mean number = 0.55). The most common owl, the great horned owl (Bubo virginianus), had a mean number of 0.25/point count. The mean for elf owls (Micrathene whitneyi) was 0.16/point count. The most common nightjars were the common poorwill (Phalaenoptilus nuttallii; 1.21/point count) and lesser nighthawk (Chordeiles acutipennis; 1.16/point count). Survey sites on the river supported more species (mean = 2.2) than did upland stock ponds (...

Common Poorwill activity and calling behavior in relation to moonlight and predation

We investigated the influence of lunar and environmental factors on behavior of Common Poorwills (Phalaenoptilus nuttallii) in southern Arizona under a diverse set of natural and artificial conditions. Radio-marked poorwills were most active shortly after sunset during the new moon. Movements declined as evening progressed. Activity remained high for several hours after sunset when the moon was full. Poorwills were heard calling from March through October, but most calling occurred between early May and September. Only ambient light was correlated with number of poorwills heard calling. More poorwills responded to playbacks of conspecifics when the moon was full than when it was new. Poorwills did not change their response to conspecifics during full moon when playback of poorwill calls followed playback of Great Horned Owl (Bubo virginianus) calls but, during the new moon, fewer birds responded following the owl call. Poorwill behavior is strongly influenced by lunar conditions; their ability to detect and evade predators is important when calling advertises their location.

A molecular phylogeny of the nightjars (Aves: Caprimulgidae) suggests extensive conservation of primitive morphological traits across multiple lineages

We report a molecular re-assessment of the classification of the nightjars which draws conclusions that are strongly at odds with the traditional, morphology-based classifications. We used maximum likelihood and Bayesian methods to compare the cytochrome b gene for 14 species from seven of the 15 genera of the Caprimulgidae and partial cytochrome b sequence data was available for a further seven species including three further genera. We found that within the Caprimulgidae there were four geographically isolated clades with bootstrap support greater than 70%. One of these clades contained just Chordeiles species, the remaining three clades each contained a mixture of genera including Caprimulgus sp. A clade of exclusively South American nightjars included the genera Caprimulgus, Uropsalis, Eleopthreptus and Hydropsalis. A clade of African and Eurasian birds included Caprimulgus and Macrodipteryx. Phalaenoptilus nuttallii and Caprimulgus vociferous formed a clade of North American birds. Two ecological factors appear to make morphological classification potentially misleading: first, the apparent retention of primitive anti-predator and foraging-related traits across genetically divergent groups; second, rapid divergence in other traits, especially those related to mating, which generate high levels of morphological divergence between species that are genetically very similar. The cytochrome b data suggests that the genus Caprimulgus is not monophyletic and is restricted to Africa and Eurasia and that Caprimulgus species from outside this area have been misclassified as a consequence of retention of primitive adaptations for crepuscular/nocturnal living. Some other genera also appear to have little support from the cytochrome b data.

Distribution and abundance of the common poorwill in southwestern saskatchewan

Distribution and abundance of the common poorwill in southwestern saskatchewan

Seasonal use of torpor by free-ranging Australian owlet-nightjars (Aegotheles cristatus).

With the exception of some data for common poorwills (Phalaenoptilus nuttallii) and anecdotal reports for a few other species, knowledge about the use of torpor by free-ranging birds is limited. Our study was designed to assess the use of torpor by free-ranging Australian owlet-nightjars (Aegotheles cristatus). We selected this species for study because of their relatively small body size (50 g), arthropod diet, nocturnal sedentary nature, taxonomic affiliation with other birds for whom the use of torpor is well documented, use of cavity roosts, and because of the cold winter (mean July minimum ambient temperature [T(a)] of approximately 0 degrees C) in the study area. We tracked 12 owlet-nightjars carrying temperature-sensitive transmitters for a total of 906 bird-days (range of 15-115 d per individual). Five different individuals entered torpor on 96 d in total. Torpor bouts occurred only between May 8 and September 8, the coldest period of the year. The lowest skin temperature (T(skin)) recorded for any bird was 19.6 degrees C, and the lowest core temperature was 22.4 degrees C. Surprisingly, torpor was rarely used at night because birds usually foraged then. Instead, torpor typically began near dawn, even on cold nights. Torpor bouts beginning at dawn lasted approximately 4 h. On 36% of days when torpor was used at dawn, birds reentered torpor later in the day. Torpor was not used during the breeding season, but this period also corresponds to the warm part of the year. There were no distinct daily minimum, maximum, or mean T(a) thresholds that could be used to reliably distinguish days when dawn torpor was used from those when it was not, although torpor was commonly employed when daily minimum T(a) fell below 3.9 degrees C. Our results show that even though Australia is typically thought of as a warm continent, at least some of the avifauna use torpor as a regular means of saving energy. We hypothesise that the reasons for this species' use of torpor include its ability to remain active all night foraging, either for terrestrial arthropods while walking or for flying insects taken on the wing, and/or its habit of roosting in cavities, which allows them to remain hidden in the daytime.

Roost-site characteristics of Common Poorwills, Phalaenoptilus nuttallii, in Saskatchewan

Roost-site characteristics of Common Poorwills, Phalaenoptilus nuttallii, in Saskatchewan

Field metabolic rates and body mass changes in common poorwills (Phalaenoptilus nuttallii: Caprimulgidae)

Abstract:We studied field metabolic rate (FMR) and mass changes in nesting common poorwills (Phalaenoptilus nuttallii; Caprimulgidae) using the doubly labelled water method. In June when poorwills ...

Evidence That Free-Ranging Common Nighthawks May Enter Torpor

Low ambient temperatures or food shortages are known to induce some normally endothermic mammals and birds (principally hummingbirds and goatsuckers) to enter torpor, a strategy that allows animals to reduce metabolism and hence body temperature as a means of saving energy. The goatsuckers (Caprimulgidae) are of special interest in this respect because several species are known to use torpor (Reinertsen 1983) and one, the common poorwill (Phalaenoptilus nuttallii), can allegedly hibernate (Jaeger 1948; 1949), the only avian species thought to do so. Recent studies of free-ranging poorwills indicate that torpor is used regularly outside the breeding season (Brigham 1992; Csada and Brigham 1994) and on occasion by incubating or brooding birds (Kissner and Brigham 1993). In laboratory studies, Lasiewski and Dawson (1964), induced captive common nighthawks (Chordeiles minor) to enter torpor by starving them. However, only one of four birds that entered torpor survived a drop in body temperature below 25° C. Firman et al. (1993) found no evidence for the use of torpor by free-ranging nighthawks during a summer with exceptionally cold wet weather, when torpor is most likely to occur. While acknowledging that a lack of evidence does not prove these birds cannot use torpor, Firman et al. (1993) concluded that it was highly unlikely they did so under natural conditions. Here we report two observations of free-ranging nighthawks that appear to have entered torpor. During an early morning (between 0600 and 0700 PST) bird survey in the last half of June, 1985, KHM encountered what he first thought was a dead nighthawk at about 1000 m asl, approximately 16 km southwest of Merritt, British Columbia (120°55' W, 50°01' N). The site had been selectively logged, producing a relatively open canopy. The air temperature was approximately 4° C. An upright head position indicated that the bird (a female) was alive. The bird did not move when touched and although the nighthawk was not picked up, its dorsal surface was cold to the touch. On a return visit to the site several hours later, the bird was not present. In August 1986 at about 1600 MST, PCJ found a nighthawk on the ground within 3 m of the edge of a small unnamed lake about 2 km from Bragg Creek, Alberta (114°34' W, 50°55' N; 1300 m asl). The day was unseasonably cold with an ambient temperature of approximately 5° C and a strong wind from the north. The bird (sex unknown) was cold to the touch. It was definitely alive but made no attempt to escape when picked up. It was quickly returned to the roosting spot and was gone the next morning. Although both birds apparently moved following the initial observations, we cannot rule out the possibility that they were taken by predators as opposed to rewarming and flying away. There was no physical evidence (e.g., feathers) to suggest predation even though the plumage of this species is easily removed (R.M. Brigham unpub. data). Therefore we conclude that the likely intances of torpor observed were of a facultative nature (spontaneously reversible) and not pathological. We must therefore reconsider the conclusion that free-ranging nighthawks do not use torpor (Firman et al. 1993). Although the use of this energy-saving strategy by these birds is likely rare, as suggested from laboratory data by Lasiewski and Dawson (1964), we think it likely that at least under some conditions, nighthawks can allow their body temperatures to fall below normal levels. Apparently they can rewarm either passively in sunshine or by active metabolism to normal body temperature. As a result of this, Hickey's (1993) conclusion that whippoor-wills (Caprimulgus vociferus) do not use torpor, may also have to be revisited.

Prey selection and foraging constraints in common poorwills (Phalaenoptilus nuttallii: Aves: Caprimulgidae)

Predators that hunt by sight should be constrained by light levels. This problem should be especially acute in aerial predators such as common poorwills (Phalaenoptilus nuttallii: Caprimulgidae), which capture small insects at night. The purpose of our study was to test the hypothesis that poorwills are constrained to catching larger insect taxa due to limitations of visual orientation under low light. We assessed diet by analysing poorwill faecal samples collected at nest and roost sites in the Cypress Hills of Saskatchewan where prey density is relatively low. Coleopterans (44% and 39% in 1991 and 1992, respectively) and lepidopterans (46% and 55%) dominated the diet, yet these two insect orders were rare in light‐suction trap (22% lepidopterans and 1% coleopterans) and sticky trap samples (11% lepidopterans and 2% coleopterans). Based on measurements of femur length, all consumed coleopterans were &gt; 5 mm long, even though 57% of those available were &lt; 5 mm. Our results suggest that poorwills are constrained to taking prey above a certain size, but above this threshold, particular prey types and larger sizes may be selected. Selection for coleopterans may reflect the need to acquire polyunsaturated fat to facilitate the use of torpor.

Reproduction constrains the use of daily torpor by free‐ranging common poorwills (Phalaenoptilus nuttallii) (Aves: Caprimulgidae)

The purpose of this study was to determine if common poorwills (Phalaenoptilus nuttallii) resist entering torpor during the breeding season. During the summers of 1991 and 1992, we studied poorwills in the Cypress Hills, Saskatchewan, Canada, near the northern limit of their distribution. Since poorwills are monogamous and share incubating and brooding responsibilities, we predicted that the non‐incubating or non‐brooding bird would enter torpor when stressed energetically (e.g. on cold and/or wet nights). Individuals carrying temperature‐sensitive radio transmitters entered torpor significantly less often during the breeding season (two of 195 bird nights) than the non‐breeding season (27 of 44 bird nights). During the breeding season we found no birds involved in an active nesting attempt in torpor. We conclude that reproduction constrains the use of torpor by adult birds, but why non‐incubating and non‐breeding birds did not enter remains unclear.

Brown Fat in Birds? A Test for the Mammalian BAT-Specific Mitochondrial Uncoupling Protein in Common Poorwills

Brown Fat in Birds? A Test for the Mammalian BAT-Specific Mitochondrial Uncoupling Protein in Common Poorwills

Evidence for the Use of Torpor by Incubating and Brooding Common Poorwills Phalaenoptilus nuttallii

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Prey selection in relation to insect availability by the common poorwill (Phalaenoptilus nuttallii)

We determined the diet of common poorwills (Phalaenoptilus nuttallii) by analysing fecal samples collected from roost and nest sites in the Okanagan Valley of British Columbia. The two major insect orders present in the diet in 1989 were Coleoptera (47% by volume) and Lepidoptera (49%), which comprised only 15 and 3%, respectively, of the insects sampled using sticky traps in 1989. Based on the femur length of coleopterans consumed, all coleopterans eaten were longer than 6.7 mm (excluding the head), whereas 76% of the coleopterans caught on sticky traps were less than 6.7 mm long. We found no evidence to support the prediction, based on optimal foraging theory, that poorwills would broaden their diet to include other insect taxa or size classes during 1990, when wet conditions likely depressed prey availability and foraging opportunities. There was no difference in the proportions of various taxa consumed or the size of coleopterans eaten between 1989 and 1990. Acknowledging the bias of our insect sampling regime, we conclude that the apparent prey selection by poorwills results passively from the constraints imposed by detecting prey under conditions of low light.

Lunar Influence on Foraging and Nesting Activity of Common Poorwills (Phalaenoptilus nuttallii)

-Whip-poor-wills (Caprimulgus vociferus) forage by from a perch, are active during periods of the night with moonlight, and synchronize hatching with the lunar cycle. In contrast, Common Nighthawks (Chordeiles minor) forage during continuous flight and do not increase activity during moonlit periods or synchronize their breeding activities with the lunar cycle. We used data on the foraging activity and nest timing of the Common Poorwill (Phalaenoptilus nuttallii) to test the hypothesis that moonlight influences the activity patterns and nest timing of this caprimulgid. If foraging strategy alone influences the response to the lunar cycle, activity by Common Poorwills should be correlated with lunar light levels and hatching should be synchronized with the lunar cycle. Our results support the general prediction that lunar light allows poorwills to forage during periods of the night. However, contrary to expectations, increased foraging activity was correlated only with increasing moon height and not the percent of the moon face illuminated. Furthermore, the nesting cycle was not synchronized with the lunar cycle. We conclude that knowledge of foraging style alone is not sufficient to predict the nature of lunarphilia by goatsuckers. We suggest that habitat choice, duration of twilight, the number of breeding attempts, and the physiological ability to enter torpor also may be important factors mediating lunar influence on foraging activity. Received 19 April 1991, accepted 13 January 1992. MOONLIGHT depresses nocturnal activity in many animals including crustaceans (e.g. Wolcott and Wolcott 1982), insects (e.g. Williams and Singh 1951), small mammals (e.g. Clarke 1983), bats (e.g. Fenton et al. 1977, Morrison 1978, Reith 1982), and birds (e.g. Watanuki 1986, Nelson 1989). An increased risk of predation often is cited as the reason for this response (Lockard and Owings 1974, Fenton et al. 1977, Morrison 1978, Watanuki 1986, Nelson 1989). In contrast, some birds increase activity during the bright phase of the lunar cycle (e.g. nocturnal singing by both nocturnal and diurnal birds; Cooper 1980, Elliot 1983, Barclay et al. 1985). To date, however, the general influence of moonlight on the behavior of visually orienting nocturnal predators is poorly understood. Intuitively, we would expect an increased level of activity with increased lunar light levels. The Whip-poor-will (Caprimulgus vociferus) is a nocturnal insectivore that exhibits increased locomotory, vocal, and nest-visiting activity during periods of bright moonlight (Mills 1 Present address: Department of Biology, University of Regina, Regina, Saskatchewan S4S OA2, Canada. 1986). Mills (1986) found that the nesting cycles of Caprimulgus species are synchronized with the lunar cycle, such that the first two weeks of the nestling period coincide with the period with the most moonlight. Observations of Caprimulgus species in North America, Africa, and Europe also indicate that moonlight positively influences singing behavior (Wynne-Edwards 1930, Brauner 1952, Cooper 1980, Jackson 1985), leading Mills (1986) to suggest that caprimulgids are lunarphilic, meaning that they are limited to foraging crepuscularly (dusk and dawn; Martin 1990) and during periods of the night with moonlight. In contrast to the lunarphilic response of Caprimulgus species, Common Nighthawks (Chordeiles minor) only forage crepuscularly, and not during the night, regardless of moonlight levels (Aldridge and Brigham 1991, Brigham and Fenton 1991). Furthermore, there is no evidence for synchrony of hatching dates in C. minor or C. acutipennis nests with the lunar cycle (Mills 1986). The different foraging styles of Chordeiles and Caprimulgus could explain the differences in nesting synchrony and activity periods. Whippoor-wills attack flying insects in upward-directed sallies of short duration from a perch or the ground (a sit-and-wait or sallying strategy; Mills 1986). Anecdotal evidence suggests

Daily Torpor in a Free-ranging Goatsucker, the Common Poorwill (Phalaenoptilus nuttallii)

Numerous laboratory studies show that common poorwills (Caprimulgidae: Phalaenoptilus nuttallii) are capable of entering daily torpor when deprived of food. Using temperature-sensitive radio transmitters, I measured the skin temperature of free-ranging birds under natural conditions to test three hypotheses about the use of torpor by poorwills. I predicted that (1) poorwills would enter torpor only in "energy emergencies" (defined as birds with low body mass), (2) only the nonincubating or brooding member of a pair would use torpor during the breeding season, and (3) poorwills would be less likely to enter torpor on moonlit nights when longer periods of activity can be sustained. My results show that adult poorwills of both sexes enter torpor regularly in April, May, and September, but not during the breeding season. I found no evidence that torpor was used only in energy emergencies or that the lunar cycle influenced the use of torpor. Skin temperatures regularly dropped below 10°C and in one instance fell below 3 C. On one occasion an individual bird remained torpid for at least 36 h. I found limited evidence suggesting that the temperature at twilight, but not insect abundance, can be used to predict whether birds will remain active or enter torpor.

The Status and Distribution of the Common Poorwill in the Cypress Hills, Saskatchewan

The Status and Distribution of the Common Poorwill in the Cypress Hills, Saskatchewan