SHOREBIRD HABITAT USE AND NEST-SITE SELECTION IN THE PLAYA LAKES REGION

Abstract: Wetlands in the Playa Lakes Region (PLR) provide important habitats for wintering waterfowl, cranes, and both migrant and breeding shorebirds. Playa Lakes Region wetlands experience naturally fluctuating hydroperiods but are exposed to anthropogenic stresses, which are exacerbated during summer and may influence PLR wetland occupancy and selection by breeding shorebirds. We examined wetland-scale habitat use and nest-site selection of the 4 dominant shorebirds (American avocets [Recurvirostra americana], black-necked stilts [Himantopus mexicanus], killdeer [Charadrius vociferus], snowy plovers [C. alexandrinus]) nesting in playas, saline lakes, and in both created and riparian wetlands in the PLR of Texas, USA. All 4 species nested in saline lakes. Only avocets and killdeer nested in playas, and snowy plovers nested in riparian wetlands. No nests were found in created wetlands. Wetland habitat changed (P < 0.001) during the breeding season, while water habitats generally decreased. Used (i.e., shorebirds found nesting) wetlands had more (P < 0.05) mudflats than non-used (i.e., shorebirds not found nesting) wetlands, which had more (P < 0.05) dry habitats. Used and non-used wetlands had similar (P > 0.05) amounts of water habitats. Nests were located close to vegetation on bare dry ground and dry ground with vegetation. Because water is ephemeral in PLR wetlands, shorebirds must select—in a somewhat predictive manner upon arrival—wetlands with suitable nest-site and brood-rearing habitat. Although surface water is necessary for nesting, its presence is not adequate for delineating suitable PLR wetland habitat for breeding shorebirds. Our findings that created wetlands cannot compensate for regional wetland losses in habitat or function highlights the need for conservation of natural PLR wetlands     

Effect of capture frequency on the survival of Piping Plover chicks

Evaluating the possible effects of intensive research on species being studied and on the results of studies is important for both ethical and scientific reasons. We captured, banded, recaptured, and measured prefledged Piping Plover (Charadrius melodus) chicks during the 2010 breeding season at Lewis and Clark Lake on the Missouri River in South Dakota. We evaluated the potential for increased mortality related to frequent handling of chicks with an experiment that compared the survival of chicks handled a single time for banding (N = 48) to chicks handled repeatedly from hatch to fledge (N = 50). Estimates of daily survival rate (?) for chicks in the two treatments did not differ (?_{single‐capture} = 0.984 ± 0.006, ?_{multiple‐capture} = 0.985 ± 0.006). Similar to previous studies, we found little evidence of increased prefledge mortality associated with frequent handling of Piping Plover chicks. However, because the effects of frequent handling of shorebird chicks may vary among species and other factors such as habitat quality (e.g., food availability), we suggest that, where possible, researchers include experiments similar to ours to evaluate possible research impacts, especially when studying threatened and endangered species.     

Characterization of microsatellite loci isolated in Mountain Plover (Charadrius montanus)

Primers for 15 microsatellite loci were developed for Mountain Plover, a species whose distribution and abundance have been reduced drastically in the past 30 years. In a screen of 126 individuals collected from four breeding locales across the species’ range, levels of polymorphism ranged from two to 13 alleles per locus. No two loci were found to be linked, although one locus revealed significant departures from Hardy–Weinberg equilibrium. These microsatellite loci can be used in population genetic studies, ultimately aiding in management efforts for Mountain Plover. Additionally, these markers can potentially be used in studies investigating the mating system of Mountain Plover.     

Brood sex ratio in the Kentish plover

How and why do the mating opportunities of males and femalesdiffer in natural population of animals? Previously we showedthat females have higher mating opportunities than males inthe Kentish plover Charadrius alexandrinus. Both parents incubatethe eggs, and males provide more brood care than females; thusit is not obvious why the females find new mates sooner thanthe males. In this study we investigated whether the sex-biasedmating opportunities stem from biased offspring sex ratios.We determined the sex of newly hatched, precocial chicks usingCHD gene markers. Among fully sexed broods, 0.461 ± 0.024(SE) of chicks (454 chicks in 158 broods) were male, and thissex ratio was not significantly different from unity. The proportionof males at hatching decreased significantly over the breedingseason, which occurred consistently in all 3 years of the study.Large chicks were more likely to be males than females. Neitherparental age nor body size of male and female parents was relatedto brood sex ratio. We also sexed a number of chicks that werecaught after they left their nest (range of estimated ages 0–17days) and found that the proportion of males increased withbrood age. This relationship remained highly significant whencontrolling statistically for hatching date. As brood size decreaseddue to mortality after the chicks left their nest, these resultssuggest that the mortality of daughters was higher than thatof the sons shortly after hatching. Taken together, our resultsshow that the female-biased mating opportunities in the Kentishplover are not due to biased brood sex ratio at hatching but,at least in part, are due to female-biased chick mortality soonafter hatching.     

State uncertainty models and mark‐resight models for understanding non‐breeding site use by Piping Plovers

Conservation of beach‐nesting medium‐distance migrants has focused on breeding areas because protection of nests is more tractable than protection of non‐breeding habitat. As breeding ground management has encountered diminishing returns, interest in understanding threats in non‐breeding areas has increased. However, robust estimates of non‐breeding demographic rates and abundance are generally lacking, hindering the study of limiting factors. Estimating such rates is made more difficult by complex population dynamics at non‐breeding sites. In South Carolina, endangered Piping Plovers Charadrius melodus start arriving in July and some depart prior to December (the autumn‐only population) while others remain through at least March (the wintering population). State uncertainty capture‐mark‐recapture models provide a means for estimating vital rates for such co‐occurring populations. We estimated the proportion of the population entering the study area per survey (entry probability) and proportion remaining per survey (persistence rate) for both populations during autumn, and abundance of the wintering population, at four sites in South Carolina in 2006/7 and 2007/8, taking advantage of birds previously colour‐ringed on the breeding grounds. We made fairly precise estimates of entry and persistence rates with small sample sizes. Cumulative entry probability was ~50% by the end of July and reached 95% for both populations by October. Estimated stopover duration for birds in the autumn‐only population was 35 days in year 1 and 42 days in year 2. We estimated a wintering super‐population size of 71 ± 16 se birds in the first year and 75 ± 16 in the second. If ringing programmes on the breeding grounds continue, standardized resighting surveys in the non‐breeding period and mark‐recapture models can provide robust estimates of entry and persistence rates and abundance. Habitat protection intended to benefit non‐breeding Piping Plovers at our coastal sites should be in effect by late summer, as many birds are resident from July to the end of winter.     

Regional trends in coastal wintering waders in Britain

Regional trends in the populations of waders wintering largely on estuaries were analysed using data collected by the Wetland Bird Survey between the winters of 1969/70 and 1995/96 to assess whether trends seen at the national level were repeated across regions of Britain. Not all were. Over this period, the numbers of seven of the 12 species studied increased in south and southeast England, but remained static or declined in southwest England and south Wales. Possible explanations for this are proposed. Increases in the number of Curlews Numenius arquata in the north and northeast of Scotland occurred after 1981/82, when the species stopped being a legal quarry species. A rapid decline in Oystercatcher Haematopus ostralegus and Knot Calidris canutus numbers in east England after 1988/89 may be linked to a change in the Wash shell-fisheries. Warmer winters may be making it less essential for birds to winter in the milder west of Britain. In two pairs of regions, northeast and southeast Scotland, and in northwest England/north Wales and northeast England, waders showed similar long-term population changes. The long-term population trends of Oystercatchers in the different regions correlate to those of Ringed Plovers Charadrius hiaticula and Knot, while those of Ringed Plovers are very similar to those of Bar-tailed Godwits Limosa lapponica. In some regions of Britain, the population trends of some species varied a lot between sites, a factor that is an important consideration when determining the size and geographical position of regions for future regional indexing. The present separation of regions based on water catchments and geography has given a useful insight into population changes at a finer spatial scale but it could be improved further with added biological input.     

Using Nest Temperature to Estimate Nest Attendance of Piping Plovers

Abstract: Recent technological innovations allow remote monitoring of avian nest temperature that minimizes disturbance and expense without altering clutch sizes. However, the efficacy of such techniques has not been determined for ground-nesting birds. We compared the efficacy of 2 techniques, iButton® data loggers (Maxim/Dallas Semiconductor Corp., Sunnyvale, CA) and custom-built thermocouples, to measure nest temperature of piping plovers (Charadrius melodus) relative to nest attendance at Cape Cod National Seashore, Massachusetts, USA. Neither technique affected hatching success (U = 389.5, P = 0.874) or rates of predation of nests containing devices (P = 0.894). We estimated nest attendance successfully with thermocouples in nests as long as air and surface temperatures were <29° Cand 43° C, respectively. Although iButtons could not be used to determine duration of on-bouts and off-bouts of incubating piping plovers, they were effective at determining when nests were abandoned or predated. We recommend the use of thermocouples for studying nest attendance of ground-nesting birds, in general, and of threatened and endangered species, in particular, where disturbance should be minimized and altering clutch sizes is not feasible.     

Phylogeny and biogeography in the evolution of migration: shorebirds of the Charadrius complex

Aim We explore whether molecular phylogeny and biogeography can complement evolutionary ecology in developing a method to address a long-standing issue in the evolution of migration: have migrations between breeding and non-breeding grounds, which may be on different continents, evolved through origins in the breeding grounds with successive shifts of the non-breeding distribution or vice versa? Methods To accommodate the biology of migration, we treated breeding and non-breeding distributions as characters to be mapped onto a phylogeny derived from mitochondrial DNA sequence data and so examined the ancestral home issue as a study in the direction of character evolution. Results Our main findings from applying this approach to a subset of the Charadrius complex of shorebirds (Aves: Charadriinae) are that a case can be made for shifts of breeding distributions having occurred in the ancestries of C. alexandrinus and C. veredus as those species evolved their present migration patterns. Our results also argue for a southern hemisphere origin (specifically South America) for the Charadrius complex as a whole. A South American origin implies other shifts in breeding distributions having occurred in the evolution of the species C. semipalmatus and C. vociferus. On applying the methods we developed for dealing with phylogenetic uncertainty, these results are reinforced and the merit of testing them further is suggested. Conclusions By way of a new approach to the evolution of migration, our study adds to a consensus emerging from the evolutionary ecology of migrant birds, arguing that shifts of breeding distributions are commonly, though not necessarily exclusively, involved in the evolution of migration.     

The energetic implications of precocial development for three shorebird species breeding in a warm environment

We investigated the effect of body size, parental behaviour and timing of breeding on the chick growth and energetics of three precocial shorebird (Charadrii) species in a warm sub-tropical environment: the Kittlitz's Plover Charadrius pecuarius , Blacksmith Lapwing Vanellus armatus , and Crowned Lapwing V. coronatus . The three species exhibited slower growth, longer pre-fledging periods and lower energy expenditure during the pre-fledging period than Arctic and temperate zone relatives of similar size. It was found that relative growth rates of charadriid and scolopacid species increased by 1.77% per degree latitude. Blacksmith and Crowned Lapwings are of similar size (i.e. about 160 g), about four times the mass of Kittlitz's Plovers. Taking body mass into account, the resting metabolic rate and daily energy expenditure of the three study species were similar. The relative amounts of energy needed for chicks to grow from a hatchling to a fledgling were low for the three species studied. The relative amount of energy needed to complete growth in charadriid and scolopacid species increased by 2.54% per degree latitude. Because Crowned Lapwings exhibited faster growth than Blacksmith Lapwings but similar daily energy expenditure we suggest that Blacksmith Lapwings compensate for greater energy expenditure in colder weather by growing more slowly. We suggest that small growth rate coefficient, low resting metabolic rate and low daily energy expenditure are adaptations to lower food availability and milder ambient temperatures in sub-tropical breeding habitats compared to temperate or Arctic regions.