In April 1984, in Kruger National Park, we used radio tracking to study th roosting and foraging ... more In April 1984, in Kruger National Park, we used radio tracking to study th roosting and foraging behavior of Epomophorus wahlbergi and Scotophilus viridis, two b known to roost in trees. Most E. wahlbergi roosted in foliage in riverine forest, although so roosted in a shelter cave; the S. viridis invariably roosted in hollow mopane trees along the st sides or tops of ridges. Neither species showed any strong evidence of changing the day roo they used to minimize commuting distance to foraging areas, although both species regularl switched locations of day roosts within localized areas. Switching day roosts may reduce predation We identified the E. wahlbergi by their single post-dental palatal ridge, a feature diagnostic of this species in this part of Africa (Hayman and Hill, 1971). The Scotophilus we studied would key out as Scotophilus
We review recent studies of torpor use by free-ranging caprimulgiform birds in North America and ... more We review recent studies of torpor use by free-ranging caprimulgiform birds in North America and Australia: common poorwill (45 g), whip-poor-will (55 g), common nighthawk (80 g), Australian owlet-nightjar (50 g), and Tawny Frogmouth (500 g). Reproductive activity, ambient temperature, body size, and prey abundance influence the energy status of endotherms and may be correlated with torpor use under natural conditions; our review suggests that no one factor is most important. To date, most studies have been correlational in the wild, and experimental studies at multiple locales are now needed to resolve uncertainties concerning the evolutionary and ecological significance of torpor.
Bats are among the most heterothermic mammals, with nearly all species investigated under free-ra... more Bats are among the most heterothermic mammals, with nearly all species investigated under free-ranging conditions to date exhibiting some degree of daily torpor and/or hibernation. We investigated thermoregulation during late winter by seven Nycteris thebaica in a warm, semi-arid habitat in northern South Africa, using temperaturesensitive transmitters to measure skin temperature (T skin ). Unexpectedly, we found no evidence for any expression of daily torpor or hibernation based on a total of 86 days of data from 7 bats (one male and six females), despite air temperatures as low as ~ 10 ºC. Instead, daytime T skin was distributed unimodally with most values in the 33 -
Proceedings of The Royal Society B: Biological Sciences, Jun 17, 2008
Group fission is an important dispersal mechanism for philopatric adults. In Cypress Hills Interp... more Group fission is an important dispersal mechanism for philopatric adults. In Cypress Hills Interprovincial Park, Saskatchewan, tree-roosting big brown bats (Eptesicus fuscus) exhibit fission-fusion roosting behaviour. During 2004-2007, the majority of females previously resident to roosting area 1 (RA1) moved to a new roosting area (RA4). We examined how genetic relationships, inferred from data for microsatellite loci and mitochondrial DNA, influenced new roost area (RA) selection during 2006 when colony members were split between the RAs. We found that females who moved to RA4 had higher average relatedness than those that remained in RA1. We found that nearly all females belonging to matrilines with high average relatedness moved to RA4 while females from matrilines with low average relatedness were split between the two RAs. These results suggest that closely related maternal kin preferentially move to new RAs. However, daily roosting preferences within a RA are not based on genetic relationships probably because daily roosting associations between kin and non-kin are used to ensure adequate roost group size. Studying the effects of kinship on the fission and movements of groups not only enhances our understanding of social behaviour and population genetics but also informs conservation decisions.
Roost availability may limit some bat populations, implying that there may be a selective advanta... more Roost availability may limit some bat populations, implying that there may be a selective advantage associated with the ability to reuse sites on an annual basis. We monitored aspen tree use by Eptesicus fuscus during multi-year studies (spanning up to 10 years) at the same site in Saskatchewan, Canada. We found that reuse of live trees over the medium-term (three years) was common and that, in some instances, reuse over the long-term (nine and 10 years) can occur. Our data also suggest that, over the medium-term, aspen roosts are reused by groups of bats more often than by solitary individuals. Our findings support the hypothesis that cavity roosting bats exhibit between year loyalty, not just to patches of forest but also to specific trees.
When bats emerge from their roosts in the evening to forage and drink, it appears as though their... more When bats emerge from their roosts in the evening to forage and drink, it appears as though their departure involves brief periods when many individuals emerge interspersed with periods during which few individuals emerge. Clustering is seen in many species of animals and probably has an anti-predator or information-transfer function. Regardless of its function, clustering in the emergence of bats may intensify as a result of large numbers of individuals trying to pass through a small exit hole in a short period of time. A total of 31 observations of emergence were made from May to Aug. 1992 and 1993 at a maternity colony of little brown bats (Myotis lucifugus), in Cypress Hills, Saskatchewan, Canada. To determine the effects of a predator on clustering in the emergence, a plastic great horned owl (Bubo virginianus) was used as a predator model and mounted close to roost exits on 8 nights. Recorded calls of a great horned owl were played back towards the roost. The predator model and associated calls did not affect the number of bats that emerged, the median time of emergence, or the degree of clustering in the emergence. There was a significant positive relationship between the extent of clustering in the emergence and the number of bats that emerged. Emergences of more than 25 bats were clustered. Thus, we found no evidence to support clustering during emergence as being an anti-predator response. However, clustering may be intensified with increased numbers of individuals trying to pass through a narrow space in a short period of time.
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, Nov 3, 2016
Nightjars represent a model taxon for investigating physiological limits of heat tolerance becaus... more Nightjars represent a model taxon for investigating physiological limits of heat tolerance because of their habit of roosting and nesting in sunlit sites during the heat of the day. We investigated the physiological responses of Rufous-cheeked Nightjars (Caprimulgus rufigena) and Freckled Nightjars (Caprimulgus tristigma) to high air temperatures (T a ) by measuring T b , resting metabolic rate (RMR) and total evaporative water loss (TEWL) at T a ranging from 10 -56 °C. Both species became hyperthermic at T a > T b . Lower critical limits of thermoneutrality occurred at T a between 35 and 37 °C, whereas we detected no clear upper critical limits of thermoneutrality. Between T a ≈ 37.0 and 39.9 °C, rates of TEWL increased rapidly with T a . At T a ≥ 40 °C, fractional increases in mass-specific TEWL rates were 78 to 106% of allometric predictions. Increasing evaporative heat dissipation incurred only small metabolic costs, with the RMR of neither species ever increasing by more than 20% above thermoneutral values. Consequently, both species displayed extremely efficient evaporative cooling; maximum evaporative heat dissipation was equivalent to 515% of metabolic heat production (MHP) at T a ≈ 56 °C in C. rufigena and 452% of MHP at T a ≈ 52 °C in C. tristigma. Our data reiterate that caprimulgids have evolved an efficient mechanism of evaporative cooling via gular fluttering, which minimizes metabolic heat production at high T a and reduces total heat loads. This likely aids in reducing TEWL rates and helps nightjars cope with some of the most thermally challenging conditions experienced by any bird.
Many studies have shown that endotherms become more heterothermic when the costs of thermoregulat... more Many studies have shown that endotherms become more heterothermic when the costs of thermoregulation are high and/or when limited energy availability constrains thermoregulatory capacity. However, the roles of many ecological variables, including constraints on foraging opportunities and/or success, remain largely unknown. To test the prediction that thermoregulatory patterns should be related to foraging opportunities in a heterothermic endotherm we examined the relationship between the lunar cycle and heterothermy in Freckled Nightjars (Caprimulgus tristigma), which are visually orienting, nocturnal insectivores that are dependent on ambient light to forage. This model system provides an opportunity to assess whether variation in foraging opportunities influences the expression of heterothermy. The nightjars were active and foraged for insects when moonlight was available, but became inactive and heterothermic in the absence of moonlight. Lunar illumination was a much stronger predictor of the magnitude of heterothermic response than was air temperature (T a ). Our data suggest that heterothermy was strongly related to variation in foraging opportunities associated with the lunar cycle, even though food abundance appeared to remain relatively high throughout the study period. Patterns of thermoregulation in this population of Freckled Nightjars provide novel insights into the environmental and ecological determinants of heterothermy, with the lunar cycle, and not T a , being the strongest predictor of torpor use.
Nocturnally active birds roosting in exposed diurnal microsites with intense solar radiation can ... more Nocturnally active birds roosting in exposed diurnal microsites with intense solar radiation can experience operative temperatures (Te) that markedly differ from air temperature (Ta). Quantifying Te thus becomes important for accurately modeling energy and water balance. We measured Te at roost and nest sites used by Rufous-cheeked Nightjars (Caprimulgus rufigena) with three-dimensionally printed biophysical models covered with the integument and plumage of a bird. Additionally, we estimated site-specific diurnal water requirements for evaporative cooling by integrating Te and Ta profiles with evaporative water loss (EWL) data for Rufouscheeked Nightjars. Between 12:00 and 15:00 hrs, average Te at roost sites varied from 33.1 to 49.9 °C, whereas at the single nest site Te averaged 51.4 °C. Average diurnal EWL, estimated using Te, was as high as 10.5 and 11.3 g at roost and nest sites, respectively, estimates 3.8-and 4.0-fold greater, respectively, than when calculated with Ta profiles. These data illustrate that under current climatic conditions, Rufous-cheeked Nightjars can experience EWL potentially approaching their limits of dehydration tolerance. In the absence of microsite changes, climate change during the 21 st century could perhaps create thermal conditions under which Rufouscheeked Nightjars exceed dehydration tolerance limits before the onset of their nocturnal active phase.
Although the amount of solar radiation received at roost sites used by bats has been speculated t... more Although the amount of solar radiation received at roost sites used by bats has been speculated to be a factor driving roost-site selection and roost switching behavior, few studies have scientifically quantified and recorded it over time. We demonstrated through a field test how silicon-cell pyranometers, which are commonly connected to dataloggers and used in atmospheric studies to measure solar irradiance on a planar surface, can also be used to measure and record relative solar radiation levels at roost trees used by bats and other wildlife. Using commercially available pyranometers might not be feasible for many wildlife studies because they are expensive; we demonstrate how they can be built relatively simply and inexpensively, and calibrated with a commercial silicon-cell pyranometer.
was 120.8 h and winter torpor bout duration correlated negatively with mean T a . Torpor bout dur... more was 120.8 h and winter torpor bout duration correlated negatively with mean T a . Torpor bout duration did not differ between sexes, although female minimum T sk was significantly lower than males. The summer Heterothermy Index varied, and was also significantly affected by T a . Mean arousal time was correlated with sunset time and arousals occurred most frequently on significantly warmer evenings, which are likely associated with an increased probability of foraging success. We provide the first evidence that torpor is used flexibly throughout the year by M. tuberculata, demonstrating that roost choice and season impact torpor patterns. Our results add to the growing knowledge that even small changes in seasonal climate can have large effects on the energy balance of small mammals.
We used radio tracking and direct observation to determine the effect of roost closure on the roo... more We used radio tracking and direct observation to determine the effect of roost closure on the roosting and foraging behaviour of big brown bats {Eptesicus fuscus) in maternity colonies near Ottawa. Individuals were site loyal, but after eviction they moved short distances to new roosts where they tended to produce fewer offspring. The time spent on the first foraging flight, the maximum distance travelled, and the use of feeding areas did not change with exclusion. The results suggest that bats roost to take advantage of site-specific factors that may increase reproductive success.
In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoi... more In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoid interferences with reproduction. In forest-roosting bats, deep tree cavities buffer roost microclimate from abrupt temperature oscillations and facilitate thermoregulation. Forest bats also switch roosts frequently, so thermally suitable cavities may be limiting. We tested how barbastelle bats (Barbastella barbastellus), often roosting beneath flaking bark in snags, may thermoregulate successfully despite the unstable microclimate of their preferred cavities. We assessed thermoregulation patterns of bats roosting in trees in a beech forest of central Italy. Although all bats used torpor, females were more often normothermic. Cavities were poorly insulated, but social thermoregulation probably overcomes this problem. A model incorporating the presence of roost mates and group size explained thermoregulation patterns better than others based, respectively, on the location and structural ...
Migratory connectivity is the degree to which populations are linked in space and time across the... more Migratory connectivity is the degree to which populations are linked in space and time across the annual cycle. Low connectivity indicates mixing of populations while high connectivity indicates population separation in space or time. High migratory connectivity makes individual populations susceptible to local environmental conditions; therefore, evaluating migratory connectivity continuously across a species range is important for understanding differential population trends and revealing places and times contributing to these differences. The common nighthawk Chordeiles minor is a widespread, declining, long‐distance migratory bird. Variable population trends across the nighthawk breeding range suggest that knowledge of migratory connectivity is needed to direct conservation. We used GPS tags to track 52 individuals from 12 breeding populations. We estimated migratory connectivity as 0.29 (Mantel coefficient: 0 = no connectivity, 1 = full connectivity) between the breeding and wi...
In April 1984, in Kruger National Park, we used radio tracking to study th roosting and foraging ... more In April 1984, in Kruger National Park, we used radio tracking to study th roosting and foraging behavior of Epomophorus wahlbergi and Scotophilus viridis, two b known to roost in trees. Most E. wahlbergi roosted in foliage in riverine forest, although so roosted in a shelter cave; the S. viridis invariably roosted in hollow mopane trees along the st sides or tops of ridges. Neither species showed any strong evidence of changing the day roo they used to minimize commuting distance to foraging areas, although both species regularl switched locations of day roosts within localized areas. Switching day roosts may reduce predation We identified the E. wahlbergi by their single post-dental palatal ridge, a feature diagnostic of this species in this part of Africa (Hayman and Hill, 1971). The Scotophilus we studied would key out as Scotophilus
We review recent studies of torpor use by free-ranging caprimulgiform birds in North America and ... more We review recent studies of torpor use by free-ranging caprimulgiform birds in North America and Australia: common poorwill (45 g), whip-poor-will (55 g), common nighthawk (80 g), Australian owlet-nightjar (50 g), and Tawny Frogmouth (500 g). Reproductive activity, ambient temperature, body size, and prey abundance influence the energy status of endotherms and may be correlated with torpor use under natural conditions; our review suggests that no one factor is most important. To date, most studies have been correlational in the wild, and experimental studies at multiple locales are now needed to resolve uncertainties concerning the evolutionary and ecological significance of torpor.
Bats are among the most heterothermic mammals, with nearly all species investigated under free-ra... more Bats are among the most heterothermic mammals, with nearly all species investigated under free-ranging conditions to date exhibiting some degree of daily torpor and/or hibernation. We investigated thermoregulation during late winter by seven Nycteris thebaica in a warm, semi-arid habitat in northern South Africa, using temperaturesensitive transmitters to measure skin temperature (T skin ). Unexpectedly, we found no evidence for any expression of daily torpor or hibernation based on a total of 86 days of data from 7 bats (one male and six females), despite air temperatures as low as ~ 10 ºC. Instead, daytime T skin was distributed unimodally with most values in the 33 -
Proceedings of The Royal Society B: Biological Sciences, Jun 17, 2008
Group fission is an important dispersal mechanism for philopatric adults. In Cypress Hills Interp... more Group fission is an important dispersal mechanism for philopatric adults. In Cypress Hills Interprovincial Park, Saskatchewan, tree-roosting big brown bats (Eptesicus fuscus) exhibit fission-fusion roosting behaviour. During 2004-2007, the majority of females previously resident to roosting area 1 (RA1) moved to a new roosting area (RA4). We examined how genetic relationships, inferred from data for microsatellite loci and mitochondrial DNA, influenced new roost area (RA) selection during 2006 when colony members were split between the RAs. We found that females who moved to RA4 had higher average relatedness than those that remained in RA1. We found that nearly all females belonging to matrilines with high average relatedness moved to RA4 while females from matrilines with low average relatedness were split between the two RAs. These results suggest that closely related maternal kin preferentially move to new RAs. However, daily roosting preferences within a RA are not based on genetic relationships probably because daily roosting associations between kin and non-kin are used to ensure adequate roost group size. Studying the effects of kinship on the fission and movements of groups not only enhances our understanding of social behaviour and population genetics but also informs conservation decisions.
Roost availability may limit some bat populations, implying that there may be a selective advanta... more Roost availability may limit some bat populations, implying that there may be a selective advantage associated with the ability to reuse sites on an annual basis. We monitored aspen tree use by Eptesicus fuscus during multi-year studies (spanning up to 10 years) at the same site in Saskatchewan, Canada. We found that reuse of live trees over the medium-term (three years) was common and that, in some instances, reuse over the long-term (nine and 10 years) can occur. Our data also suggest that, over the medium-term, aspen roosts are reused by groups of bats more often than by solitary individuals. Our findings support the hypothesis that cavity roosting bats exhibit between year loyalty, not just to patches of forest but also to specific trees.
When bats emerge from their roosts in the evening to forage and drink, it appears as though their... more When bats emerge from their roosts in the evening to forage and drink, it appears as though their departure involves brief periods when many individuals emerge interspersed with periods during which few individuals emerge. Clustering is seen in many species of animals and probably has an anti-predator or information-transfer function. Regardless of its function, clustering in the emergence of bats may intensify as a result of large numbers of individuals trying to pass through a small exit hole in a short period of time. A total of 31 observations of emergence were made from May to Aug. 1992 and 1993 at a maternity colony of little brown bats (Myotis lucifugus), in Cypress Hills, Saskatchewan, Canada. To determine the effects of a predator on clustering in the emergence, a plastic great horned owl (Bubo virginianus) was used as a predator model and mounted close to roost exits on 8 nights. Recorded calls of a great horned owl were played back towards the roost. The predator model and associated calls did not affect the number of bats that emerged, the median time of emergence, or the degree of clustering in the emergence. There was a significant positive relationship between the extent of clustering in the emergence and the number of bats that emerged. Emergences of more than 25 bats were clustered. Thus, we found no evidence to support clustering during emergence as being an anti-predator response. However, clustering may be intensified with increased numbers of individuals trying to pass through a narrow space in a short period of time.
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, Nov 3, 2016
Nightjars represent a model taxon for investigating physiological limits of heat tolerance becaus... more Nightjars represent a model taxon for investigating physiological limits of heat tolerance because of their habit of roosting and nesting in sunlit sites during the heat of the day. We investigated the physiological responses of Rufous-cheeked Nightjars (Caprimulgus rufigena) and Freckled Nightjars (Caprimulgus tristigma) to high air temperatures (T a ) by measuring T b , resting metabolic rate (RMR) and total evaporative water loss (TEWL) at T a ranging from 10 -56 °C. Both species became hyperthermic at T a > T b . Lower critical limits of thermoneutrality occurred at T a between 35 and 37 °C, whereas we detected no clear upper critical limits of thermoneutrality. Between T a ≈ 37.0 and 39.9 °C, rates of TEWL increased rapidly with T a . At T a ≥ 40 °C, fractional increases in mass-specific TEWL rates were 78 to 106% of allometric predictions. Increasing evaporative heat dissipation incurred only small metabolic costs, with the RMR of neither species ever increasing by more than 20% above thermoneutral values. Consequently, both species displayed extremely efficient evaporative cooling; maximum evaporative heat dissipation was equivalent to 515% of metabolic heat production (MHP) at T a ≈ 56 °C in C. rufigena and 452% of MHP at T a ≈ 52 °C in C. tristigma. Our data reiterate that caprimulgids have evolved an efficient mechanism of evaporative cooling via gular fluttering, which minimizes metabolic heat production at high T a and reduces total heat loads. This likely aids in reducing TEWL rates and helps nightjars cope with some of the most thermally challenging conditions experienced by any bird.
Many studies have shown that endotherms become more heterothermic when the costs of thermoregulat... more Many studies have shown that endotherms become more heterothermic when the costs of thermoregulation are high and/or when limited energy availability constrains thermoregulatory capacity. However, the roles of many ecological variables, including constraints on foraging opportunities and/or success, remain largely unknown. To test the prediction that thermoregulatory patterns should be related to foraging opportunities in a heterothermic endotherm we examined the relationship between the lunar cycle and heterothermy in Freckled Nightjars (Caprimulgus tristigma), which are visually orienting, nocturnal insectivores that are dependent on ambient light to forage. This model system provides an opportunity to assess whether variation in foraging opportunities influences the expression of heterothermy. The nightjars were active and foraged for insects when moonlight was available, but became inactive and heterothermic in the absence of moonlight. Lunar illumination was a much stronger predictor of the magnitude of heterothermic response than was air temperature (T a ). Our data suggest that heterothermy was strongly related to variation in foraging opportunities associated with the lunar cycle, even though food abundance appeared to remain relatively high throughout the study period. Patterns of thermoregulation in this population of Freckled Nightjars provide novel insights into the environmental and ecological determinants of heterothermy, with the lunar cycle, and not T a , being the strongest predictor of torpor use.
Nocturnally active birds roosting in exposed diurnal microsites with intense solar radiation can ... more Nocturnally active birds roosting in exposed diurnal microsites with intense solar radiation can experience operative temperatures (Te) that markedly differ from air temperature (Ta). Quantifying Te thus becomes important for accurately modeling energy and water balance. We measured Te at roost and nest sites used by Rufous-cheeked Nightjars (Caprimulgus rufigena) with three-dimensionally printed biophysical models covered with the integument and plumage of a bird. Additionally, we estimated site-specific diurnal water requirements for evaporative cooling by integrating Te and Ta profiles with evaporative water loss (EWL) data for Rufouscheeked Nightjars. Between 12:00 and 15:00 hrs, average Te at roost sites varied from 33.1 to 49.9 °C, whereas at the single nest site Te averaged 51.4 °C. Average diurnal EWL, estimated using Te, was as high as 10.5 and 11.3 g at roost and nest sites, respectively, estimates 3.8-and 4.0-fold greater, respectively, than when calculated with Ta profiles. These data illustrate that under current climatic conditions, Rufous-cheeked Nightjars can experience EWL potentially approaching their limits of dehydration tolerance. In the absence of microsite changes, climate change during the 21 st century could perhaps create thermal conditions under which Rufouscheeked Nightjars exceed dehydration tolerance limits before the onset of their nocturnal active phase.
Although the amount of solar radiation received at roost sites used by bats has been speculated t... more Although the amount of solar radiation received at roost sites used by bats has been speculated to be a factor driving roost-site selection and roost switching behavior, few studies have scientifically quantified and recorded it over time. We demonstrated through a field test how silicon-cell pyranometers, which are commonly connected to dataloggers and used in atmospheric studies to measure solar irradiance on a planar surface, can also be used to measure and record relative solar radiation levels at roost trees used by bats and other wildlife. Using commercially available pyranometers might not be feasible for many wildlife studies because they are expensive; we demonstrate how they can be built relatively simply and inexpensively, and calibrated with a commercial silicon-cell pyranometer.
was 120.8 h and winter torpor bout duration correlated negatively with mean T a . Torpor bout dur... more was 120.8 h and winter torpor bout duration correlated negatively with mean T a . Torpor bout duration did not differ between sexes, although female minimum T sk was significantly lower than males. The summer Heterothermy Index varied, and was also significantly affected by T a . Mean arousal time was correlated with sunset time and arousals occurred most frequently on significantly warmer evenings, which are likely associated with an increased probability of foraging success. We provide the first evidence that torpor is used flexibly throughout the year by M. tuberculata, demonstrating that roost choice and season impact torpor patterns. Our results add to the growing knowledge that even small changes in seasonal climate can have large effects on the energy balance of small mammals.
We used radio tracking and direct observation to determine the effect of roost closure on the roo... more We used radio tracking and direct observation to determine the effect of roost closure on the roosting and foraging behaviour of big brown bats {Eptesicus fuscus) in maternity colonies near Ottawa. Individuals were site loyal, but after eviction they moved short distances to new roosts where they tended to produce fewer offspring. The time spent on the first foraging flight, the maximum distance travelled, and the use of feeding areas did not change with exclusion. The results suggest that bats roost to take advantage of site-specific factors that may increase reproductive success.
In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoi... more In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoid interferences with reproduction. In forest-roosting bats, deep tree cavities buffer roost microclimate from abrupt temperature oscillations and facilitate thermoregulation. Forest bats also switch roosts frequently, so thermally suitable cavities may be limiting. We tested how barbastelle bats (Barbastella barbastellus), often roosting beneath flaking bark in snags, may thermoregulate successfully despite the unstable microclimate of their preferred cavities. We assessed thermoregulation patterns of bats roosting in trees in a beech forest of central Italy. Although all bats used torpor, females were more often normothermic. Cavities were poorly insulated, but social thermoregulation probably overcomes this problem. A model incorporating the presence of roost mates and group size explained thermoregulation patterns better than others based, respectively, on the location and structural ...
Migratory connectivity is the degree to which populations are linked in space and time across the... more Migratory connectivity is the degree to which populations are linked in space and time across the annual cycle. Low connectivity indicates mixing of populations while high connectivity indicates population separation in space or time. High migratory connectivity makes individual populations susceptible to local environmental conditions; therefore, evaluating migratory connectivity continuously across a species range is important for understanding differential population trends and revealing places and times contributing to these differences. The common nighthawk Chordeiles minor is a widespread, declining, long‐distance migratory bird. Variable population trends across the nighthawk breeding range suggest that knowledge of migratory connectivity is needed to direct conservation. We used GPS tags to track 52 individuals from 12 breeding populations. We estimated migratory connectivity as 0.29 (Mantel coefficient: 0 = no connectivity, 1 = full connectivity) between the breeding and wi...
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Papers by Mark Brigham