Proceedings. Biological sciences / The Royal Society, Jan 7, 2015
Phenotypic differences among individuals can arise during any stage of life. Although several dis... more Phenotypic differences among individuals can arise during any stage of life. Although several distinct processes underlying individual differences have been defined and studied (e.g. parental effects, senescence), we lack an explicit, unified perspective for understanding how these processes contribute separately and synergistically to observed variation in functional traits. We propose a conceptual framework based on a developmental view of life-history variation, linking each ontogenetic stage with the types of individual differences originating during that period. In our view, the salient differences among these types are encapsulated by three key criteria: timing of onset, when fitness consequences are realized, and potential for reversibility. To fill a critical gap in this framework, we formulate a new term to refer to individual differences generated during adulthood-reversible state effects. We define these as 'reversible changes in a functional trait resulting from life...
The Greenlandic and west-central Siberian breeding populations of Sanderlings Calidris alba are s... more The Greenlandic and west-central Siberian breeding populations of Sanderlings Calidris alba are separated by ca. 2000 km during the breeding season, but mix in Europe to some extent during migration. However, the number of Siberian Sanderlings that spend the nonbreeding season along the East Atlantic Flyway (extending from western Europe to South Africa), if any, is unknown. Although both populations are considered part of the nominate subspecies C. a. alba based on morphology, population structure in Sanderlings has yet to be described with molecular methods. We examined genetic differentiation at the mtDNA control region (CR) and seven microsatellite loci between Greenland- and Siberia-breeding Sanderlings in order to: (1) develop a diagnostic tool for assessing the breeding origin of Sanderlings along the East Atlantic Flyway, and (2) provide a comparison with the co-distributed and ecologically similar Red Knot, in which CR differentiation of geographically analogous populations (C. canutus islandica and C. c. canutus) has indicated isolation of lineages near the time of the last glacial maximum. By contrast, we found only weak differentiation between the Sanderling breeding populations at the CR, and no differentiation at microsatellite loci. These results suggest that the assignment of breeding origin of Sanderlings on Afro-European flyways will not be possible with simple and inexpensive genetic methods, and imply that Sanderlings and Red Knots have very different post-glacial phylogeographic histories.
Long-distance migration places severe constraints on the annual cycles of birds, as they balance ... more Long-distance migration places severe constraints on the annual cycles of birds, as they balance the energetic and scheduling requirements of breeding, moult, pre-migratory fuelling, and the journey itself. The most extreme migrations, traversing vast, inhospitable areas of the globe in protracted non-stop flights, may push birds to the limits of their capabilities, and would be expected to tolerate little variation in performance.
Flexibility in scheduling varies throughout an organism’s annual cycle, reflecting relative tempo... more Flexibility in scheduling varies throughout an organism’s annual cycle, reflecting relative temporal constraints and fitness consequences among life-history stages. Time-selection can act at different scales, either by limiting the range of alternative strategies in the population, or by increasing the precision of individual performance. We tracked individual bar-tailed godwits Limosa lapponica baueri for two full years (including direct observation during non-breeding seasons in New Zealand and geolocator tracking of round-trip migrations to Alaska) to present a full annual-cycle view of molt, breeding, and migration schedules. At both population and individual scales, temporal variation was greater in post-breeding than pre-breeding stages, and greater in molts than in movements, but schedules did not tighten across successive stages of migration toward the breeding grounds. In general, individual godwits were quite consistent in timing of events throughout the year, and repeatability of pre-breeding movements was particularly high (r = 0.82–0.92). However, we demonstrate that r values misrepresent absolute consistency by confounding inter- and intra-individual variation; the biological significance of r values can only be understood when these are considered separately. By doing so, we show that some stages have considerable tolerance for alternative strategies within the population, whereas scheduling of northbound migratory movements was similar for all individuals. How time-selection simultaneously shapes both individual and population variation is central to understanding and predicting adaptive phenological responses to environmental change.
In the annual cycle of migratory birds, temporal and energetic constraints can lead to carry-over... more In the annual cycle of migratory birds, temporal and energetic constraints can lead to carry-over effects, in which performance in one life history stage affects later stages. Bar-tailed godwits Limosa lapponica baueri, which achieve remarkably high pre-migratory fuel loads, undertake the longest non-stop migratory flights yet recorded, and breed during brief high-latitude summers, may be particularly vulnerable to persistent effects of disruptions to their rigidly-timed annual routines. Using three years of non-breeding data in New Zealand, we asked how arrival timing after a non-stop flight from Alaska (>11,000 km) affected an individual godwit’s performance in subsequent flight feather moult, contour feather moults, and migratory departure. Late arrival led to later wing moult, but godwits partially compensated for delayed moult initiation by increasing moult rate and decreasing the total duration of moult. Delays in arrival and wing moult up to 34–37 d had no apparent effect on an individual’s migratory departure or extent of breeding plumage at departure, both of which were extraordinarily consistent between years. Thus, ‘errors’ in timing early in the non-breeding season were essentially corrected in New Zealand prior to spring migration. Variation in migration timing also had no apparent effect on an individual’s likelihood of returning the following season. The bar-tailed godwits’ rigid maintenance of plumage and spring migration schedules, coupled with high annual survival, imply a surprising degree of flexibility to address unforeseen circumstances in the annual cycle.
The extreme long-distance migration of Alaska-breeding Bar-tailed Godwits (Limosa lapponica bauer... more The extreme long-distance migration of Alaska-breeding Bar-tailed Godwits (Limosa lapponica baueri) may present severe constraints on annual moult, and high individual variation in plumage and migration timing suggests that multiple strategies by sex and breeding region may exist. We used digital photography of free-living godwits to describe the timing and extent of prebasic and prebreeding contour feather moults in New Zealand, and used plumage of breeding birds in Alaska to infer the proportion of moults occurring in Alaska and Asia. These data demonstrated that: 1) godwits conducted overlapping prealternate and presupplemental moults; 2) prebasic and prebreeding moults were scheduled differently in relation to southbound and northbound migration, respectively; 3) northern and southern Alaska breeders of each sex were distinguishable by plumage differences throughout the nonbreeding season; and 4) males and northern breeders achieved more extensive breeding plumage by spending longer in prebreeding moult in New Zealand, rather than through faster moult rates or greater investment in moult during stopover in Asia. The existence of a ventral presupplemental moult implies that contemporary selection for red breeding plumage overrides older selection for barred alternate plumage. Our use of individual-based data revealed a continuum of annual moult strategies within the population, which may reflect individual differences in sex, size, migration distance, and/or breeding location. Even within the highly constrained annual cycle of extreme long-distance migrants, differential selection influences how individuals manage tradeoffs among nonbreeding activities such as moult, fuelling, and migration.
Capture myopathy is a complication of capture and handling in many species of birds and mammals. ... more Capture myopathy is a complication of capture and handling in many species of birds and mammals. Muscular necrosis leads to ataxia, paralysis, and pain, whereas metabolic disturbances can result in death. We conducted an opportunistic clinical trial on Bar-tailed Godwits (Limosa lapponica baueri) that developed capture myopathy after a cannon-net capture in New Zealand in October 2008. We assessed the beneficial effects of midazolam, a benzodiazepine with the effects of anxiolysis, muscle relaxation, and sedation, in the adjunctive treatment of capture myopathy. Physical and biochemical parameters were analyzed retrospectively for their potential as indicators for survival until release. Birds (n516) were treated with subcutaneous fluid therapy, a nonsteroidal anti-inflammatory (meloxicam), gavage feeding, and sling therapy twice daily. The treatment group (n58) was treated twice daily with intramuscular midazolam injections, 1.5 mg/kg. Surviving godwits were released over 1–9 days, with 6 of 8 treated birds (75%) surviving to release, compared with 3 of 8 controls (38%). Inability to counteract weight loss in captivity was the most significant problem for both groups. Lack of waterproofing and predation were contributing causes of death for at least two godwits after release. Birds treated with midazolam showed subjective benefits including improved tolerance of handling and sling therapy. Clinical parameters (change in body mass, packed cell volume [PCV], plasma creatine kinase [CK], aspartate aminotransferase [AST], total protein, and uric acid [UA] over time) were not statistically different between groups, although peak average values for CK, AST, and UA were lower in the treatment group. Decline in body mass (%), PCV, final plasma UA, and peak plasma CK were the most useful prognostic indicators. Midazolam shows potential as an ancillary treatment for capture myopathy in birds and is worthy of continued study and use.
Despite clear links between wind conditions and timing of migration at the population level, no s... more Despite clear links between wind conditions and timing of migration at the population level, no study has examined the contribution of winds to annual variation in the migration timing of individual birds. At a single non-breeding site in New Zealand, we closely monitored three years of departures of bar-tailed godwits (Limosa lapponica baueri), a long-distance migrant with remarkable annual consistency in individual migration schedules. Although individual godwits showed very little variation in departure date and generally experienced favorable departure conditions, most off-schedule departures were explained by maximizing initial wind assistance for the non-stop flight to Asia. Surprisingly, early departures attributable to wind were more common and of greater magnitude than wind-related departure delays, and prolonged weather-related departure lulls did not always result in late-departing individuals. Thus, our results show that knowledge of individual departure decisions with regard to wind can strongly influence interpretation of population patterns. Early departures associated with winds, previously only demonstrated theoretically, may reflect conservative timing and extent of premigratory fuelling, a possible adaptation for extreme long-distance migration in variable conditions.
Among scolopacid shorebirds, Bar-tailed Godwits (Limosa lapponica) have unusually high intra- and... more Among scolopacid shorebirds, Bar-tailed Godwits (Limosa lapponica) have unusually high intra- and intersexual differences in size and breeding plumage. Despite historical evidence for population structure among Alaska-breeding Bar-tailed Godwits (L. l. baueri), no thorough analysis, or comparison with the population’s nonbreeding distribution, has been undertaken. We used live captures, field photography, museum specimens, and individuals tracked from New Zealand to describe geographic variation in size and plumage within the Alaska breeding range. We found a north–south cline in body size in Alaska, in which the smallest individuals of each sex occurred at the highest latitudes. Extent of male breeding plumage (proportion of nonbreeding contour feathers replaced) also increased with latitude, but female breeding plumage was most extensive at mid-latitudes. This population structure was not maintained in the nonbreeding season: morphometrics of captured birds and timing of migratory departures indicated that individuals from a wide range of breeding latitudes occur in each region and site in New Zealand. Links among morphology, phenology, and breeding location suggest the possibility of distinct Alaska breeding populations that mix freely in the nonbreeding season, and also imply that the strongest selection for size occurs in the breeding season.
Despite clear benefits of optimal arrival time on breeding grounds, migration schedules may vary ... more Despite clear benefits of optimal arrival time on breeding grounds, migration schedules may vary with an individual’s innate quality, non-breeding habitat, or breeding destination. Here, we show that for the bar-tailed godwit (Limosa lapponica baueri), a shorebird that makes the longest known nonstop migratory flights of any bird, timing of migration for individuals from a non-breeding site in New Zealand was strongly correlated with their specific breeding latitudes in Alaska, USA, a 16,000–18,000 km journey away. Furthermore, this variation carried over even to the southbound return migration, six months later, with birds returning to New Zealand in approximately the same order in which they departed. These tightly scheduled movements on a global scale strongly suggest endogenously-controlled routines, with breeding site as the primary driver of temporal variation throughout the annual cycle.
We describe a method for tibia-mounted geolocator attachment successfully used on Bar-tailed Godw... more We describe a method for tibia-mounted geolocator attachment successfully used on Bar-tailed Godwits Limosa lapponica baueri in New Zealand. The return rate of 95% for instrumented godwits was higher than for other colour-banded individuals in the same study, and we observed no negative physical or behavioural effects of attachment. There was no loss of units, even after 24 months and two return migrations to Alaska. We believe this method is appropriate for a wide variety of migratory waders.
We studied Rock Sandpiper (Calidris ptilocnemis) breeding behavior and monitored reproductive suc... more We studied Rock Sandpiper (Calidris ptilocnemis) breeding behavior and monitored reproductive success from 1998 to 2005 on the Yukon-Kuskokwim River Delta, Alaska, USA. We banded 24 adults and monitored 45 nests. Annual return rate of adults ranged between 67 and 100%. Six pairs of Rock Sandpipers bred at our study site for ≥2 years, and among these we did not observe mate change (i.e., when both members of a pair returned and each mated with a new individual). Nests were typically initiated by mid-May and 53% of females laid second clutches if first clutches were lost through mid-June. Males regularly incubated clutches during the morning (0800–1259 hrs AKDT) and afternoon (1300–1759 hrs) and rarely during the evening (1800–2300 hrs), whereas female incubation was relatively consistent throughout the day. Apparent nest success (percent of known nests successfully hatching >1 chick) among first and second nests was 19 and 44%, respectively (n = 45). A minimum of 44% of hatching nests fledged at least one young. Males cared for young but half of females deserted mate and brood 1–7 days post-hatch. This first description of North American Rock Sandpiper breeding behavior from a color-marked population complements previous work on this species on the Chukotsky Peninsula, Russia.
Effective shorebird conservation requires a greater understanding of use and availability of high... more Effective shorebird conservation requires a greater understanding of use and availability of high-tide roosts in coastal non-breeding areas. In this paper, we explore 1) variation in use of roosts; 2) landscape and environmental correlates of roost use; and 3) responses to predators and humans at roosts, to evaluate roost availability for a wintering population of Dunlin Calidris alpina pacifica at Humboldt Bay, CA, USA. For four winters (2002–2005), Dunlin use of particular roosts was highly variable at the population and individual level, even at the most-used roosts. In any given day, week, or month, most Dunlin roosts were unused, and we continued to record new roosts even in the fourth year of study. Although roost use was influenced by landscape attributes, time of day, and environmental conditions, these variables left most variation in roost use unexplained. Dunlin departures from roosts were associated with the presence of avian predators, but not with human activity. Collectively, these observations revealed no strong evidence that roost availability was limited. This contrasts with findings of other studies, even after considering differences in methodology and spatial scale of analysis. We discuss implications for the interpretation of movement data, protection and/or creation of roosting habitat, and assessment of roost quality.
We repeatedly observed Dunlin Calidris alpina pacifica (n = 30) killed by collisions with a fence... more We repeatedly observed Dunlin Calidris alpina pacifica (n = 30) killed by collisions with a fence wire following raptor attacks at a single winter roost at Humboldt Bay, California, USA. If raptor-related collisions occurred at the observed rate over an entire winter, fatalities at the site represented approximately 4% of the local Dunlin population. The regularity of collisions may have promoted specialized behavior in individual avian predators (Peregrine Falcon Falco peregrinus) and scavengers (Western Gull Larus occidentalis) to exploit the situation. We are unaware of other reports of significant shorebird mortality resulting from the interaction of raptor attacks and a manmade object.
Among shorebirds, many individuals make migratory and short-distance movements in large flocks, s... more Among shorebirds, many individuals make migratory and short-distance movements in large flocks, suggesting that stable social groups may persist within populations for days to months. We examined high-tide associations among individual radio-marked Dunlin wintering at Humboldt Bay, California, to determine if flocks represented stable social groups. The rate of co-occurrence of two individuals in the same flock was generally low (mean = 15% of surveys), and 86% of pairs co-occurred no more than expected by chance. Associations were ephemeral, lasting 1.1 consecutive high tides on average. Variation in co-occurrence reflected individual fidelity to roosts, as well as population-wide differences in space use with precipitation and time of day. Dunlin flock composition was fluid, and individuals appeared to associate by chance according to shared attraction to common roosts. Our findings are consistent with predictions for a highly mobile, generally nonterritorial, long-distance migrant for which stable social associations have no clear benefit.
In coastal environs during the non-breeding season, many shorebirds (suborder Charadrii) congrega... more In coastal environs during the non-breeding season, many shorebirds (suborder Charadrii) congregate at roosts, long considered to be traditional sites where flocks of individuals coalesce when high tides inundate feeding areas. Humboldt Bay, California was surveyed (9.5 months at roughly 10-d intervals) to assess temporal variation in incidence (proportion of 28 surveys birds used a roost), proportional abundance, concentrations, and repeatability (of seasonal average proportional abundances) of shorebird use of diurnal, high-tide roosts. Two hundred and forty roosting locations were identified and observations were made of 30 species. Fourteen species accounted for over 99% of observations. Shorebirds occurred at most roosts infrequently (<20% of surveys) and only 4% of roosts had roosting birds present on more than 80% of occasions. Abundant species occurred at more roosts (20-141 roosts per species) compared with less common species. Even at the most-used roosts, abundances at the species level varied greatly. Repeatability of roost use among seasons was high. At Humboldt Bay, roost use formed a continuum from ephemeral locations used by a few birds to sites used consistently by large numbers of individuals.
Proceedings. Biological sciences / The Royal Society, Jan 7, 2015
Phenotypic differences among individuals can arise during any stage of life. Although several dis... more Phenotypic differences among individuals can arise during any stage of life. Although several distinct processes underlying individual differences have been defined and studied (e.g. parental effects, senescence), we lack an explicit, unified perspective for understanding how these processes contribute separately and synergistically to observed variation in functional traits. We propose a conceptual framework based on a developmental view of life-history variation, linking each ontogenetic stage with the types of individual differences originating during that period. In our view, the salient differences among these types are encapsulated by three key criteria: timing of onset, when fitness consequences are realized, and potential for reversibility. To fill a critical gap in this framework, we formulate a new term to refer to individual differences generated during adulthood-reversible state effects. We define these as 'reversible changes in a functional trait resulting from life...
The Greenlandic and west-central Siberian breeding populations of Sanderlings Calidris alba are s... more The Greenlandic and west-central Siberian breeding populations of Sanderlings Calidris alba are separated by ca. 2000 km during the breeding season, but mix in Europe to some extent during migration. However, the number of Siberian Sanderlings that spend the nonbreeding season along the East Atlantic Flyway (extending from western Europe to South Africa), if any, is unknown. Although both populations are considered part of the nominate subspecies C. a. alba based on morphology, population structure in Sanderlings has yet to be described with molecular methods. We examined genetic differentiation at the mtDNA control region (CR) and seven microsatellite loci between Greenland- and Siberia-breeding Sanderlings in order to: (1) develop a diagnostic tool for assessing the breeding origin of Sanderlings along the East Atlantic Flyway, and (2) provide a comparison with the co-distributed and ecologically similar Red Knot, in which CR differentiation of geographically analogous populations (C. canutus islandica and C. c. canutus) has indicated isolation of lineages near the time of the last glacial maximum. By contrast, we found only weak differentiation between the Sanderling breeding populations at the CR, and no differentiation at microsatellite loci. These results suggest that the assignment of breeding origin of Sanderlings on Afro-European flyways will not be possible with simple and inexpensive genetic methods, and imply that Sanderlings and Red Knots have very different post-glacial phylogeographic histories.
Long-distance migration places severe constraints on the annual cycles of birds, as they balance ... more Long-distance migration places severe constraints on the annual cycles of birds, as they balance the energetic and scheduling requirements of breeding, moult, pre-migratory fuelling, and the journey itself. The most extreme migrations, traversing vast, inhospitable areas of the globe in protracted non-stop flights, may push birds to the limits of their capabilities, and would be expected to tolerate little variation in performance.
Flexibility in scheduling varies throughout an organism’s annual cycle, reflecting relative tempo... more Flexibility in scheduling varies throughout an organism’s annual cycle, reflecting relative temporal constraints and fitness consequences among life-history stages. Time-selection can act at different scales, either by limiting the range of alternative strategies in the population, or by increasing the precision of individual performance. We tracked individual bar-tailed godwits Limosa lapponica baueri for two full years (including direct observation during non-breeding seasons in New Zealand and geolocator tracking of round-trip migrations to Alaska) to present a full annual-cycle view of molt, breeding, and migration schedules. At both population and individual scales, temporal variation was greater in post-breeding than pre-breeding stages, and greater in molts than in movements, but schedules did not tighten across successive stages of migration toward the breeding grounds. In general, individual godwits were quite consistent in timing of events throughout the year, and repeatability of pre-breeding movements was particularly high (r = 0.82–0.92). However, we demonstrate that r values misrepresent absolute consistency by confounding inter- and intra-individual variation; the biological significance of r values can only be understood when these are considered separately. By doing so, we show that some stages have considerable tolerance for alternative strategies within the population, whereas scheduling of northbound migratory movements was similar for all individuals. How time-selection simultaneously shapes both individual and population variation is central to understanding and predicting adaptive phenological responses to environmental change.
In the annual cycle of migratory birds, temporal and energetic constraints can lead to carry-over... more In the annual cycle of migratory birds, temporal and energetic constraints can lead to carry-over effects, in which performance in one life history stage affects later stages. Bar-tailed godwits Limosa lapponica baueri, which achieve remarkably high pre-migratory fuel loads, undertake the longest non-stop migratory flights yet recorded, and breed during brief high-latitude summers, may be particularly vulnerable to persistent effects of disruptions to their rigidly-timed annual routines. Using three years of non-breeding data in New Zealand, we asked how arrival timing after a non-stop flight from Alaska (>11,000 km) affected an individual godwit’s performance in subsequent flight feather moult, contour feather moults, and migratory departure. Late arrival led to later wing moult, but godwits partially compensated for delayed moult initiation by increasing moult rate and decreasing the total duration of moult. Delays in arrival and wing moult up to 34–37 d had no apparent effect on an individual’s migratory departure or extent of breeding plumage at departure, both of which were extraordinarily consistent between years. Thus, ‘errors’ in timing early in the non-breeding season were essentially corrected in New Zealand prior to spring migration. Variation in migration timing also had no apparent effect on an individual’s likelihood of returning the following season. The bar-tailed godwits’ rigid maintenance of plumage and spring migration schedules, coupled with high annual survival, imply a surprising degree of flexibility to address unforeseen circumstances in the annual cycle.
The extreme long-distance migration of Alaska-breeding Bar-tailed Godwits (Limosa lapponica bauer... more The extreme long-distance migration of Alaska-breeding Bar-tailed Godwits (Limosa lapponica baueri) may present severe constraints on annual moult, and high individual variation in plumage and migration timing suggests that multiple strategies by sex and breeding region may exist. We used digital photography of free-living godwits to describe the timing and extent of prebasic and prebreeding contour feather moults in New Zealand, and used plumage of breeding birds in Alaska to infer the proportion of moults occurring in Alaska and Asia. These data demonstrated that: 1) godwits conducted overlapping prealternate and presupplemental moults; 2) prebasic and prebreeding moults were scheduled differently in relation to southbound and northbound migration, respectively; 3) northern and southern Alaska breeders of each sex were distinguishable by plumage differences throughout the nonbreeding season; and 4) males and northern breeders achieved more extensive breeding plumage by spending longer in prebreeding moult in New Zealand, rather than through faster moult rates or greater investment in moult during stopover in Asia. The existence of a ventral presupplemental moult implies that contemporary selection for red breeding plumage overrides older selection for barred alternate plumage. Our use of individual-based data revealed a continuum of annual moult strategies within the population, which may reflect individual differences in sex, size, migration distance, and/or breeding location. Even within the highly constrained annual cycle of extreme long-distance migrants, differential selection influences how individuals manage tradeoffs among nonbreeding activities such as moult, fuelling, and migration.
Capture myopathy is a complication of capture and handling in many species of birds and mammals. ... more Capture myopathy is a complication of capture and handling in many species of birds and mammals. Muscular necrosis leads to ataxia, paralysis, and pain, whereas metabolic disturbances can result in death. We conducted an opportunistic clinical trial on Bar-tailed Godwits (Limosa lapponica baueri) that developed capture myopathy after a cannon-net capture in New Zealand in October 2008. We assessed the beneficial effects of midazolam, a benzodiazepine with the effects of anxiolysis, muscle relaxation, and sedation, in the adjunctive treatment of capture myopathy. Physical and biochemical parameters were analyzed retrospectively for their potential as indicators for survival until release. Birds (n516) were treated with subcutaneous fluid therapy, a nonsteroidal anti-inflammatory (meloxicam), gavage feeding, and sling therapy twice daily. The treatment group (n58) was treated twice daily with intramuscular midazolam injections, 1.5 mg/kg. Surviving godwits were released over 1–9 days, with 6 of 8 treated birds (75%) surviving to release, compared with 3 of 8 controls (38%). Inability to counteract weight loss in captivity was the most significant problem for both groups. Lack of waterproofing and predation were contributing causes of death for at least two godwits after release. Birds treated with midazolam showed subjective benefits including improved tolerance of handling and sling therapy. Clinical parameters (change in body mass, packed cell volume [PCV], plasma creatine kinase [CK], aspartate aminotransferase [AST], total protein, and uric acid [UA] over time) were not statistically different between groups, although peak average values for CK, AST, and UA were lower in the treatment group. Decline in body mass (%), PCV, final plasma UA, and peak plasma CK were the most useful prognostic indicators. Midazolam shows potential as an ancillary treatment for capture myopathy in birds and is worthy of continued study and use.
Despite clear links between wind conditions and timing of migration at the population level, no s... more Despite clear links between wind conditions and timing of migration at the population level, no study has examined the contribution of winds to annual variation in the migration timing of individual birds. At a single non-breeding site in New Zealand, we closely monitored three years of departures of bar-tailed godwits (Limosa lapponica baueri), a long-distance migrant with remarkable annual consistency in individual migration schedules. Although individual godwits showed very little variation in departure date and generally experienced favorable departure conditions, most off-schedule departures were explained by maximizing initial wind assistance for the non-stop flight to Asia. Surprisingly, early departures attributable to wind were more common and of greater magnitude than wind-related departure delays, and prolonged weather-related departure lulls did not always result in late-departing individuals. Thus, our results show that knowledge of individual departure decisions with regard to wind can strongly influence interpretation of population patterns. Early departures associated with winds, previously only demonstrated theoretically, may reflect conservative timing and extent of premigratory fuelling, a possible adaptation for extreme long-distance migration in variable conditions.
Among scolopacid shorebirds, Bar-tailed Godwits (Limosa lapponica) have unusually high intra- and... more Among scolopacid shorebirds, Bar-tailed Godwits (Limosa lapponica) have unusually high intra- and intersexual differences in size and breeding plumage. Despite historical evidence for population structure among Alaska-breeding Bar-tailed Godwits (L. l. baueri), no thorough analysis, or comparison with the population’s nonbreeding distribution, has been undertaken. We used live captures, field photography, museum specimens, and individuals tracked from New Zealand to describe geographic variation in size and plumage within the Alaska breeding range. We found a north–south cline in body size in Alaska, in which the smallest individuals of each sex occurred at the highest latitudes. Extent of male breeding plumage (proportion of nonbreeding contour feathers replaced) also increased with latitude, but female breeding plumage was most extensive at mid-latitudes. This population structure was not maintained in the nonbreeding season: morphometrics of captured birds and timing of migratory departures indicated that individuals from a wide range of breeding latitudes occur in each region and site in New Zealand. Links among morphology, phenology, and breeding location suggest the possibility of distinct Alaska breeding populations that mix freely in the nonbreeding season, and also imply that the strongest selection for size occurs in the breeding season.
Despite clear benefits of optimal arrival time on breeding grounds, migration schedules may vary ... more Despite clear benefits of optimal arrival time on breeding grounds, migration schedules may vary with an individual’s innate quality, non-breeding habitat, or breeding destination. Here, we show that for the bar-tailed godwit (Limosa lapponica baueri), a shorebird that makes the longest known nonstop migratory flights of any bird, timing of migration for individuals from a non-breeding site in New Zealand was strongly correlated with their specific breeding latitudes in Alaska, USA, a 16,000–18,000 km journey away. Furthermore, this variation carried over even to the southbound return migration, six months later, with birds returning to New Zealand in approximately the same order in which they departed. These tightly scheduled movements on a global scale strongly suggest endogenously-controlled routines, with breeding site as the primary driver of temporal variation throughout the annual cycle.
We describe a method for tibia-mounted geolocator attachment successfully used on Bar-tailed Godw... more We describe a method for tibia-mounted geolocator attachment successfully used on Bar-tailed Godwits Limosa lapponica baueri in New Zealand. The return rate of 95% for instrumented godwits was higher than for other colour-banded individuals in the same study, and we observed no negative physical or behavioural effects of attachment. There was no loss of units, even after 24 months and two return migrations to Alaska. We believe this method is appropriate for a wide variety of migratory waders.
We studied Rock Sandpiper (Calidris ptilocnemis) breeding behavior and monitored reproductive suc... more We studied Rock Sandpiper (Calidris ptilocnemis) breeding behavior and monitored reproductive success from 1998 to 2005 on the Yukon-Kuskokwim River Delta, Alaska, USA. We banded 24 adults and monitored 45 nests. Annual return rate of adults ranged between 67 and 100%. Six pairs of Rock Sandpipers bred at our study site for ≥2 years, and among these we did not observe mate change (i.e., when both members of a pair returned and each mated with a new individual). Nests were typically initiated by mid-May and 53% of females laid second clutches if first clutches were lost through mid-June. Males regularly incubated clutches during the morning (0800–1259 hrs AKDT) and afternoon (1300–1759 hrs) and rarely during the evening (1800–2300 hrs), whereas female incubation was relatively consistent throughout the day. Apparent nest success (percent of known nests successfully hatching >1 chick) among first and second nests was 19 and 44%, respectively (n = 45). A minimum of 44% of hatching nests fledged at least one young. Males cared for young but half of females deserted mate and brood 1–7 days post-hatch. This first description of North American Rock Sandpiper breeding behavior from a color-marked population complements previous work on this species on the Chukotsky Peninsula, Russia.
Effective shorebird conservation requires a greater understanding of use and availability of high... more Effective shorebird conservation requires a greater understanding of use and availability of high-tide roosts in coastal non-breeding areas. In this paper, we explore 1) variation in use of roosts; 2) landscape and environmental correlates of roost use; and 3) responses to predators and humans at roosts, to evaluate roost availability for a wintering population of Dunlin Calidris alpina pacifica at Humboldt Bay, CA, USA. For four winters (2002–2005), Dunlin use of particular roosts was highly variable at the population and individual level, even at the most-used roosts. In any given day, week, or month, most Dunlin roosts were unused, and we continued to record new roosts even in the fourth year of study. Although roost use was influenced by landscape attributes, time of day, and environmental conditions, these variables left most variation in roost use unexplained. Dunlin departures from roosts were associated with the presence of avian predators, but not with human activity. Collectively, these observations revealed no strong evidence that roost availability was limited. This contrasts with findings of other studies, even after considering differences in methodology and spatial scale of analysis. We discuss implications for the interpretation of movement data, protection and/or creation of roosting habitat, and assessment of roost quality.
We repeatedly observed Dunlin Calidris alpina pacifica (n = 30) killed by collisions with a fence... more We repeatedly observed Dunlin Calidris alpina pacifica (n = 30) killed by collisions with a fence wire following raptor attacks at a single winter roost at Humboldt Bay, California, USA. If raptor-related collisions occurred at the observed rate over an entire winter, fatalities at the site represented approximately 4% of the local Dunlin population. The regularity of collisions may have promoted specialized behavior in individual avian predators (Peregrine Falcon Falco peregrinus) and scavengers (Western Gull Larus occidentalis) to exploit the situation. We are unaware of other reports of significant shorebird mortality resulting from the interaction of raptor attacks and a manmade object.
Among shorebirds, many individuals make migratory and short-distance movements in large flocks, s... more Among shorebirds, many individuals make migratory and short-distance movements in large flocks, suggesting that stable social groups may persist within populations for days to months. We examined high-tide associations among individual radio-marked Dunlin wintering at Humboldt Bay, California, to determine if flocks represented stable social groups. The rate of co-occurrence of two individuals in the same flock was generally low (mean = 15% of surveys), and 86% of pairs co-occurred no more than expected by chance. Associations were ephemeral, lasting 1.1 consecutive high tides on average. Variation in co-occurrence reflected individual fidelity to roosts, as well as population-wide differences in space use with precipitation and time of day. Dunlin flock composition was fluid, and individuals appeared to associate by chance according to shared attraction to common roosts. Our findings are consistent with predictions for a highly mobile, generally nonterritorial, long-distance migrant for which stable social associations have no clear benefit.
In coastal environs during the non-breeding season, many shorebirds (suborder Charadrii) congrega... more In coastal environs during the non-breeding season, many shorebirds (suborder Charadrii) congregate at roosts, long considered to be traditional sites where flocks of individuals coalesce when high tides inundate feeding areas. Humboldt Bay, California was surveyed (9.5 months at roughly 10-d intervals) to assess temporal variation in incidence (proportion of 28 surveys birds used a roost), proportional abundance, concentrations, and repeatability (of seasonal average proportional abundances) of shorebird use of diurnal, high-tide roosts. Two hundred and forty roosting locations were identified and observations were made of 30 species. Fourteen species accounted for over 99% of observations. Shorebirds occurred at most roosts infrequently (<20% of surveys) and only 4% of roosts had roosting birds present on more than 80% of occasions. Abundant species occurred at more roosts (20-141 roosts per species) compared with less common species. Even at the most-used roosts, abundances at the species level varied greatly. Repeatability of roost use among seasons was high. At Humboldt Bay, roost use formed a continuum from ephemeral locations used by a few birds to sites used consistently by large numbers of individuals.
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Papers by Jesse Conklin
for assessing the breeding origin of Sanderlings along the East Atlantic Flyway, and (2) provide a comparison with the co-distributed and ecologically similar Red Knot, in which CR differentiation of geographically analogous populations (C. canutus islandica and C. c. canutus) has indicated isolation of lineages near the time of the last glacial maximum. By contrast, we found only weak differentiation between the Sanderling breeding populations at the CR, and no differentiation at microsatellite loci. These results suggest that the assignment of breeding origin of Sanderlings on Afro-European flyways will not be possible with simple and inexpensive genetic methods, and imply that Sanderlings and Red Knots have very different
post-glacial phylogeographic histories.
for assessing the breeding origin of Sanderlings along the East Atlantic Flyway, and (2) provide a comparison with the co-distributed and ecologically similar Red Knot, in which CR differentiation of geographically analogous populations (C. canutus islandica and C. c. canutus) has indicated isolation of lineages near the time of the last glacial maximum. By contrast, we found only weak differentiation between the Sanderling breeding populations at the CR, and no differentiation at microsatellite loci. These results suggest that the assignment of breeding origin of Sanderlings on Afro-European flyways will not be possible with simple and inexpensive genetic methods, and imply that Sanderlings and Red Knots have very different
post-glacial phylogeographic histories.