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Geographic locations of study sites where shorebird egg flotation data were collected between 1993 and 2006. A 5 Kuparuk Oilfield, Alaska, USA; B 5 Teshekpuk Lake, Alaska, USA; C, D 5 Prudhoe Bay, Alaska, USA; E 5 Barrow, Alaska, USA; F 5 Pt. Thomson, Alaska, USA; G 5 Arctic National Wildlife
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We modeled the relationship between egg flotation and age of a developing embryo for 24 species of shorebirds. For 21 species, we used regression analyses to estimate hatching date by modeling egg angle and float height, measured as continuous variables, against embryo age. For eggs early in incubation, we used linear regression analyses to predict...
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... present egg flotation data from 24 shorebird species collected at 17 study sites located throughout the northern hemisphere (Fig. 1). Latitude and longitude coordinates for each study site are given in an Appendix published online at 5 Liebezeitetal2007_Appendix.pdf 4 . Most sites (13 of 17) were located in arctic or subarctic tundra in habitats ranging from lowland marshes to drier uplands. The remaining sites were at temperate latitudes and consisted of rocky intertidal shorelines, prairie uplands, shallow alkaline wetlands, or mudflats. We determined the float characteristics of eggs by individually immersing them in water in a transparent, wide-mouthed container. We used lukewarm water from a thermos or water taken directly from ponds or lakes. We usually floated two or more eggs from each clutch, and we floated some clutches several times throughout the breeding season. Generally, observers used a protractor to measure the angle between the horizontal plane of the water and the longitudinal axis of the egg (hereafter ‘‘egg angle’’; typically measured to within 6 5 u ), although a few experienced observers estimated this angle visually. We also measured the vertical distance an egg floated above the surface of the water (hereafter ‘‘float height’’; typically measured to 6 1 mm) using a clear plastic ruler. For most species, egg angle and float height were measured as continuous data. However, for three species, observers classified egg flotation parameters into categories (Fig. 2). For eight species, egg angle measurements were collected as continuous data while float height measurements were collected as categorical data. We did not uniquely identify eggs or examine changes in flotation scores of individual eggs over time. To determine the relationship between egg flotation characteristics and embryo age, we used data from nests where the date of clutch completion or hatching was known. Nests were presumed to have hatched on the date when newly hatched chicks were observed either in or within a few meters of the nest, or within 24– 72 hr after star-cracked and pipped eggs were observed in the nest (exact number of hours based on shell-breaking and emergence times reported in Poole et al. [2003]). For nests with a known hatching date, we estimated embryo age at the time the eggs were floated by back- calculating from the date of hatching (labelled as ‘‘days until hatching’’ in all figures). For nests with a known clutch completion date only, we estimated the days until hatching using site-specific incubation durations if available, or more generic incubation durations provided in the literature (Poole et al. 2003). We determined clutch completion dates for nests discovered during laying by revisiting them daily until clutches were complete, or by assuming birds laid one egg per day until the standard clutch size for that species was reached (typically four eggs). We defined the first day of incubation as the date the final egg of the clutch was laid. When more than one egg per clutch was floated on a given visit, we used the average angle and height as the sample unit. We did not use egg angle data from nests with fewer than three eggs, as these nests could represent incomplete or partially depredated nests and thus bias our analyses. We discarded data from individual eggs within a clutch that had abnormal scores relative to the rest of the clutch ( , 1% of observations). In most cases, these eggs were either infertile or had a dead embryo inside. We developed species-specific equations to predict embryo development and thus antici- pate the day eggs would hatch. To do this, we first pooled data from different study populations for a given species; two study populations were pooled for three species, and between three and seven populations were pooled for nine species. The remaining 12 species had data from only one site (Appendix). Second, we pooled data across years (range: 2–13 years) for all species. For our analyses, we used float data from a single nest on a given day as our sample unit. Consequently, we did not restrict our data to a single observation per clutch per season. We accepted a low level of pseudoreplication because sample sizes of nests were sometimes small, and we wanted to explore general patterns in egg flotation across a large range of species. Continuous data. We analyzed the data for early (i.e., sinking eggs) and late (i.e., floating eggs) incubation separately. When individual eggs in the same clutch both sank and floated, we classified the nest as being in late incubation. As we were interested in predicting hatching date (a measure of embryo development, or age), our models are based on regressions of embryo development on float characteristics, i.e., we treated embryo age as the dependent variable and float characteristics as the independent variables. Although this method essentially requires rotating the axes by 90 u , the resulting regression parameters have standard errors describing variance in hatching date as opposed to flotation characteristics. More- over, this avoids under- or overestimating the rate of development for individual nests in a data set where development may progress differently among nests (as seen in aging studies using molt scores; Pimm 1976, Ginn and Melville 1983). We employed linear regression with logit- transformed egg angles to capture the relationship between embryo development and egg angle. We could not use logistic regression in these analyses because the relationship between variables was not sigmoidal when considering embryo age as the independent variable. Because of their pyriform profile, unincubated shorebird eggs lie at the bottom of the water container at a minimum angle of 20 u . Similarly, an egg can only rotate to a vertical position, or 90 u , as the embryo develops. Thus, 20 u and 90 u were the lowest and highest egg angles that could be measured during our study. To trans- form the egg angle measurements to logits, we first converted them to proportions (P) by assigning a value of 0 and 1 to 20 u and 90 u , respectively, and interpolating the values for intermediate angles. Eggs with observed angles of 20 u and 90 u were first adjusted to 21 u and 89 u to avoid proportional angles of exactly 0 and 1, which cannot be logit-transformed. Proportion- al angles were transformed to logits using the ...
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... For three nests with the lowest visitation frequency and unrecorded hatching dates, an egg flotation model was used to predict nest age. The model was based on repeated measurements of egg float height and angle in water from 11 nests with observed hatching dates (Liebezeit et al., 2007;Mabee et al., 2006; Table A1). ...
Birds nesting on riverine beaches are exposed to large temperature fluctuations, while changing water levels pose flooding risks. We used miniature temperature loggers ( i Buttons®) placed in nests and on the beach surface combined with time‐lapse photography to study incubation behaviour in the black skimmer ( Rynchops niger ) on the Manu River, Peru. Since the species exhibits sexual size dimorphism, we could identify partner switches in images and the contribution to incubation effort by each pair member. Results of the study documented that nest temperature was less affected by ambient temperature and fluctuated less than the surroundings. Despite shorter incubation bouts at midday, black skimmers maintained a close to constant presence at the nest by more frequent nest exchanges. In fact, while female black skimmers generally incubated more and for longer than males, pairs shared incubation most consistently during the hottest part of the day. Incubation probability decreased around dusk, a peak foraging time for the species and a time when beach temperature overlapped with nest temperature. A biparental incubation strategy across the diel cycle appears to allow black skimmers breeding at the Manu River to incubate in challenging thermal conditions, but further studies are needed to determine proximity to thermal limits.
... We found nests by rope-dragging suitable tundra areas. For each nest, we recorded its GPS coordinates and estimated the expected hatch date based on the stage of incubation as determined by egg flotation (Liebezeit et al., 2007). The next day, we captured one of the incubating parents by dropping a mist net over the nest, and during subsequent visits we captured its incubating mate using the same method. ...
... For nests that were found during laying (1-3 eggs), clutch initiation was determined by subtracting 1 day for each additional egg laid, assuming that one egg was laid per day. In nests that were found after clutch completion, we calculated clutch initiation date based on the flotation method that allows for the estimation of egg developmental stage (Liebezeit et al., 2007). For more details, see Krietsch et al. (2022). ...
All animals host a microbial community within and on their reproductive organs, known as the reproductive microbiome. In free‐living birds, studies on the sexual transmission of bacteria have typically focused on a few pathogens instead of the bacterial community as a whole, despite a potential link to reproductive function. Theory predicts higher sexual transmission of the reproductive microbiome in females via the males' ejaculates and higher rates of transmission in promiscuous systems.
We studied the cloacal microbiome of breeding individuals of a socially polyandrous, sex‐role‐reversed shorebird, the red phalarope (Phalaropus fulicarius). We expected (i) higher microbial diversity in females compared to males; (ii) low compositional differentiation between sexes; (iii) lower variation in composition between individuals (i.e. microbiome dispersion) in females than in males; (iv) convergence in composition as the breeding season progresses as a consequence of sexual transmission and/or shared habitat use; and (v) higher similarity in microbial composition between social pair members than between two random opposite‐sex individuals.
We found no or small between‐sex differences in cloacal microbiome diversity/richness and composition. Dispersion of predicted functional pathways was lower in females than in males. As predicted, microbiome dispersion decreased with sampling date relative to clutch initiation of the social pair. Microbiome composition was significantly more similar among social pair members than among two random opposite‐sex individuals. Pair membership explained 21.5% of the variation in taxonomic composition and 10.1% of functional profiles, whereas temporal and sex effects explained only 0.6%–1.6%. Consistent with evidence of functional convergence of reproductive microbiomes within pairs, some select taxa and predicted functional pathways were less variable between social pair members than between random opposite‐sex individuals.
As predicted if sexual transmission of the reproductive microbiome is high, sex differences in microbiome composition were weak in a socially polyandrous system with frequent copulations. Moreover, high within‐pair similarity in microbiome composition, particularly for a few taxa spanning the spectrum of the beneficial–pathogenic axis, demonstrates the link between mating behaviour and the reproductive microbiome. Our study is consistent with the hypothesis that sexual transmission plays an important role in driving reproductive microbiome ecology and evolution.
... Eggs are fragile and should be handled as little as possible. Where handling is necessary to determine laying date or similar (Liebezeit et al. 2007), personnel should handle only one egg at a time, carefully placing rather than dropping eggs onto any instruments or containers, and using cushioning or padding to minimise impact with hard surfaces (Figure 15.3). Small cracks and chips can be repaired successfully with glue or nail varnish (Gage and Duerr 2020), but care should be taken to minimise the amount of sealant spread over the surface of the eggs to avoid impeding airflow. ...
Over time, birds have been caught for food, husbandry, domestication, ornamentation, to carry messages, control pests and hunt food, as pets and status symbols, and for religious practices (Bub 1991). The diversity of their morphology, biology, and habitats means that a plethora of techniques has been developed for capturing, keeping, and collecting information about them. This chapter details general operating procedures (GOPs) for key contemporary avian- specific research methods. Methods with similar techniques and animal welfare considera-tions have been combined in the same GOP.
... Nest searching was conducted during egg laying and early incubation. The onset of incubation was estimated using the observed laying or hatching date (Brown et al., 2014), or using egg floatation if necessary (accurate to within ±4 days; Liebezeit et al., 2007). We also used light data patterns provided by geolocators to confirm the first nesting attempt and to identify onset of incubation for some individuals lacking nest monitoring data (n = 9). ...
Long-distance migrants are under strong selection to arrive on their breeding grounds at a time that maximizes fitness. Many arctic birds start nesting shortly after snow recedes from their breeding sites and timing of snowmelt can vary substantially over the breeding range of widespread species. We tested the hypothesis that migration schedules of individuals co-occurring at the same non-breeding areas are adapted to average local environmental conditions encountered at their specific and distant Arctic breeding locations. We predicted that timing of breeding site availability (measured here as the average snow-free date) should explain individual variation in departure time from shared non-breeding areas. We tested our prediction by tracking American Golden-Plovers (Pluvialis dominica) nesting across the North-American Arctic. These plovers use a non-breeding (wintering) area in South America and share a spring stopover area in the nearctic temperate grasslands, located >1,800 km away from their nesting locations. As plovers co-occur at the same non-breeding areas but use breeding sites segregated by latitude and longitude, we could disentangle the potential confounding effects of migration distance and timing of breeding site availability on individual migration schedule. As predicted, departure date of individuals stopping-over in sympatry was positively related to the average snow-free date at their respective breeding location, which was also related to individual onset of incubation. Departure date from the shared stopover area was not explained by the distance between the stopover and the breeding location, nor by the stopover duration of individuals. This strongly suggests that plover migration schedule is adapted to and driven by the timing of breeding site availability per se. The proximate mechanism underlying the variable migration schedule of individuals is unknown and may result from genetic differences or individual learning. Temperatures are currently changing at different speeds across the Arctic and this likely generates substantial heterogeneity in the strength of selection pressure on migratory schedule of arctic birds migrating sympatrically.
... We estimated nest initiation date (date first egg laid) based on the number of eggs if nests were found during egg-laying (assuming 1 egg laid per day for all taxa, although plovers may take 1.5 days, Colwell, 2006), or by back-calculating from known hatch date using standard incubation duration. If these two methods could not be used, we employed an egg-floatation technique to estimate nest initiation (Sandercock, 1998;Liebezeit et al., 2007;Brown et al., 2014). This technique relies on the fact that eggs lose mass as the embryos inside develop, causing them to sink initially and later float in water. ...
While increases in overall temperatures are widely reported in the Arctic, large inter-annual variation in spring weather, with extreme early and late conditions, is also occurring. Using data collected from three sites in Arctic Alaska, we explored how shorebird breeding density, nest initiation, nest synchrony, nest survival, and phenological mismatch varied between two exceptionally early (2015 and 2016) and late (2017 and 2018) springs. We assessed these differences in the context of long-term data from each site and whether species exhibited conservative or opportunistic reproductive strategies. Conservative shorebirds typically display nest-site fidelity and territoriality, consistent population densities, relatively even individual spacing, and monogamous mating systems with bi-parental incubation. In contrast, opportunistic shorebirds display the opposite traits, and a polygamous mating system with uniparental incubation. In this study, we evaluated 2,239 nests from 13 shorebird species, 2015–2018, and found that shorebirds of both strategies bred earlier and in higher numbers in early, warm springs relative to historic levels (based on 3,789 nests, 2005–2014); opposite trends were observed in late springs. In early springs, nests were initiated less synchronously than in late springs. Nest survival was unrelated to spring type, but was greater in earlier laid nests overall. Invertebrate food resources emerged earlier in early springs, resulting in a greater temporal asynchrony between invertebrate emergence and chick hatching in early than late springs. However, invertebrate abundance was quite variable among sites and years regardless of spring type. Overall, our results were generally consistent with predicted relationships between spring conditions and reproductive parameters. However, we detected differences among sites that could not be explained by other ecological factors (e.g., predators or alternative prey). Differences in shorebird community composition and other subtler methodological/ecological differences among sites highlight the difficulty of understanding the complex nature of these ecological systems and the importance of evaluating questions at multiple sites across multiple years. Our study demonstrates that shorebirds exhibit a high degree of behavioral flexibility in response to variable Arctic conditions, but whether this flexibility is enough to allow them to optimally track changing environmental conditions or if evolutionary adjustments will be necessary is unknown.
... Fieldwork was carried out on whimbrels at breeding grounds in the southern lowlands of Iceland (63.8 • N; 20.2 • W), between 2012 and 2018. Nests were searched for and upon finding, the incubation stage estimated through egg floatation (Liebezeit et al., 2007), and the laying date was back calculated from stage of incubation. Nests were monitored until hatching and for those that hatched, laying date was back calculated from the hatching date considering an incubation period of 25 days after the last egg laid (mean ± se: 24.8 ± 0.2 days, n = 24 nests found when laying, and hatch recorded). ...
The timing of annual events is key for organisms that exploit seasonal resources, as deviations from optimal timing might result in considerable fitness costs. Under strong time selection, individuals likely have fewer suitable strategies available than when selection is more relaxed, hence both consistency and flexibility might be advantageous depending on the life history or annual cycle stage. For migrants using both the arctic and the tropics during their annual cycle, the faster warming at higher latitudes than elsewhere in the range may lead to mismatches with local environmental conditions. Additionally, while individuals might already be limited in responding to changes at each stage, the potential degree of a given response will likely also be limited by responses at previous stages of the annual cycle. Contrary to other migratory waders breeding in Iceland, Icelandic whimbrels Numenius phaeopus islandicus have not changed arrival dates during the past 30 years, suggesting high individual consistency in spring arrival timing and a potential limitation in responding to a changing environment. After repeatedly tracking 12 individual Icelandic whimbrels at least twice throughout their annual cycle between 2012 and 2018, we investigated individual consistency of spring arrival date and other annual stages and migration strategy, and explored differences between sexes and seasons. Individuals were more consistent on timing of spring than autumn migration, and the most consistent stage was departure from the wintering sites. Timing of laying was the stage that varied the most, and no overall significant difference between sexes was observed, except on spring stopover duration. While lower consistency in laying dates might allow individuals to track the advancement of spring, consistency at departure from the wintering sites, stopover duration, and arrival into Iceland might limit the degree of advancement. Transgenerational changes in the migratory behavior of other wader species allows population level responses to a changing phenology, but seems unlikely for Icelandic whimbrels, given the stable dates of spring arrival in this population. Under continuing advancement of spring onset, it is thus important to acquire information on the timing of spring arrival of recruits and on the ontogeny of migration to understand how migratory schedules are defined and might influence responses of long-distance migrants to environmental change.
... The location of study sites and species are provided in Table 1. Where laying date was unknown, eggs were floated to estimate hatch date (and hence laying date) following Liebezeit et al. [39]. Clutch sizes (mean ± standard error [SE]; median) from our study (complete clutches only) were 3.70 ± 0.07 (4) eggs for the Masked Lapwing (411 eggs; n = 111), 1.95 ± 0.03 (2) for the Red-capped Plover (142; n = 73) and 2.73 ± 0.09 (3) for the Hooded Plover (71; n = 26). ...
Sex-biases in populations can have important implications for species’ social biology, population demography and mating systems. It has recently been suggested that in some shorebirds, sex-specific bias in survival of precocial young may occur. This may be driven by variation in the brood sex-ratio and/or the sexual size dimorphism of young birds, which may influence predator escape capacity. Understanding the survival of young birds remains a significant knowledge gap for many taxa, especially when young birds are mobile and cryptic. Our aims were to estimate the sex-ratio variation in three species of Australian resident shorebird, specifically to determine: (1) whether seasonal brood sex-ratio variation at hatching is occurring, (2) the extent of any sex-biased chick survival, (3) if sex specific dimorphism at hatching or during growth occurs; and, (4) whether escape capacity differs between the sexes. We radio-tracked 50 Masked Lapwing Vanellus miles, 42 Red-capped Plover Charadrius ruficapillus and 27 Hooded Plover Thinornis cucullatus chicks from individual broods, examined the likelihood of hatchlings being male or female based on the hatching date within the breeding season, and compared size at hatching, growth and mortality of chicks of different sexes. There was no sex-bias with the hatching date across the breeding season, nor were there differences in survival or growth rates between sexes for any of the three species studied. In one species, male hatchlings had longer tarsi than females, but this did not result in differential escape propensity or improved survival. In conclusion, the hatching date, survival and growth of chicks from three species of resident shorebird was not influenced by their sex.
... If a nest was found during laying, we estimated the start of incubation by assuming that the female laid one egg per day and started incubation when the clutch was complete (usually four, rarely three eggs). If nests were found with a full clutch, we estimated the start of incubation based on the median height and angle at which the eggs floated in water (as described in Liebezeit et al., 2007). ...
Theoretical models predict that parents feeding offspring should partially compensate for the reduced care of their partner. However, for incubating birds, the level of compensation may depend on how reduced care changes the risk of entire brood failure, for example due to clutch predation, and on individual variation in the timing of depletion of energy stores. Although biparental incubation dominates in non-passerines, short-term manipulations of care during incubation are scarce. Here, we describe the response of 25 semipalmated sandpipers (Calidris pusilla) to an unexpected ~12-h absence (experimental removal) of their partner in the middle of the 21-day incubation period. During the period when the removed partner would have taken over to start its regular ~12-h incubation bout, parents compensated partially for the absence of their partner's care (mean: 59%, 95%CI: 49–70%). However, individuals varied in their response from no to full compensation, independent of parental sex. In contrast to incubation in undisturbed nests or by uniparental species, nest attendance of compensating parents tended to be higher during the warmer part of the day. Whereas compensation was unrelated to before-experimental share of incubation, parents that left the nest from a further distance upon human approach (more aware of or more “responsive” to their environment) compensated more. The quality of incubation in the after-experimental period, i.e., after return of the partner, was lower than usual, but improved quickly over time. In seven nests where the removed parent never returned, the widowed partner attended the nest for 0–10 days (median: 4), which suggests that widowed semipalmated sandpipers can adjust their incubation behavior to that observed in uniparental incubators. To conclude, our results indicate that biparental incubators are willing to tolerate a missed or irregular incubation bout of their partner. We speculate that all individuals would compensate fully, but that some fail because they deplete their energy stores, while others may be less responsive to or initially unaware of the absence of their partner.
... This area, which encompasses 12,000 ha, stretches from 53.0672 • N, 5.4021 • E in the north to 52.8527 • N, 5.4127 • E in the south, and from 52.9715 • N, 5.6053 • E in the east to 52.8829 • N, 5.3607 • E in the west. In this area we located godwit nests and used the flotation method (Liebezeit et al., 2007) to determine lay dates. To reduce the chance of nest abandonment and increase the chance of capturing an adult, we caught breeding adults toward the end of their incubation period (24 ± 3.84 days after laying). ...
Variation in migratory behavior is the result of different individual strategies and fluctuations in individual performances. A first step toward understanding these differences in migratory behavior among individuals is, therefore, to assess the relative contributions of inter- and intra-individual differences to this variation. We did this using light-level geolocators deployed on the breeding grounds to follow continental black-tailed godwits (Limosa limosa limosa) throughout their south- and northward migrations over multiple years. Based on repeated tracks from 36 individuals, we found two general patterns in godwit migratory behavior: First, migratory timing in black-tailed godwits varies mostly because individual godwits migrate at different times of the year. Second, individuals also exhibit considerable variation in timing within their respective migratory windows. Although the absolute amount of inter-individual variation in timing decreased over the course of northward migration, individual godwits still arrived at their breeding grounds across a span of more than 5 weeks. These differences in migratory timing among individuals are larger than those currently observed in other migratory bird species and suggest that the selective forces that limit the variation in migratory timing in other species are relaxed or absent in godwits. Furthermore, we could not attribute these individual differences to the sex or wintering location of an individual. We suggest that different developmental trajectories enabled by developmental plasticity likely result in these generally consistent, life-long annual routines. To investigate this possibility and to gain an understanding of the different selection pressures that could be acting during migration and throughout a godwit's life, future studies should track juvenile godwits and other migratory birds from birth to adulthood while also manipulating their spatiotemporal environment during development.
