ArticlePublisher preview available

No effects of asynchrony between hatching and peak food availability on chick growth in Semipalmated Plovers (Charadrius semipalmatus) near Churchill, Manitoba

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

Birds rely on consistent patterns of food availability on their breeding grounds to successfully complete their breeding cycle. Due to ongoing warming of the sub-Arctic, there is potential for a mismatch between the peak in available invertebrate biomass and the peak in food demand for shorebird chicks. During the summers of 2010 and 2011, we investigated the relationship between temperature and benthic and terrestrial invertebrate biomass, measured using three sampling techniques in Churchill, Manitoba. We also investigated the relationship between timing of breeding of Semipalmated Plovers (Charadrius semipalmatus) and timing of peaks in invertebrate biomass. In 2011, chick growth rates were also measured to examine whether hatching in synchrony with the peak in invertebrate biomass during the brood rearing period affected growth rates. In 2010, emergent and core invertebrate biomass were negatively related to soil degree days, whereas in 2011, core biomass increased with soil degree days and pitfall biomass increased with air temperature. Total invertebrate biomass (summed over trap types) peaked from 25 to 31 days before the median chick hatch date in 2010 and 10 days after the median chick hatch date in 2011. In 2011 we did not detect any effects of asynchrony on the growth of Semipalmated Plover chicks. These results may indicate that food resources in their environment remain adequate throughout the breeding season, despite inter-annual fluctuations in the timing of invertebrate peaks.
This content is subject to copyright. Terms and conditions apply.
Vol.:(0123456789)
1 3
Polar Biology (2019) 42:593–601
https://doi.org/10.1007/s00300-019-02456-w
ORIGINAL PAPER
No eects ofasynchrony betweenhatching andpeak food availability
onchick growth inSemipalmated Plovers (Charadrius semipalmatus)
nearChurchill, Manitoba
C.AnneCorkery1· EricaNol1· LauraMckinnon2
Received: 26 March 2018 / Revised: 4 January 2019 / Accepted: 5 January 2019 / Published online: 22 January 2019
© Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
Birds rely on consistent patterns of food availability on their breeding grounds to successfully complete their breeding cycle.
Due to ongoing warming of the sub-Arctic, there is potential for a mismatch between the peak in available invertebrate
biomass and the peak in food demand for shorebird chicks. During the summers of 2010 and 2011, we investigated the rela-
tionship between temperature and benthic and terrestrial invertebrate biomass, measured using three sampling techniques in
Churchill, Manitoba. We also investigated the relationship between timing of breeding of Semipalmated Plovers (Charadrius
semipalmatus) and timing of peaks in invertebrate biomass. In 2011, chick growth rates were also measured to examine
whether hatching in synchrony with the peak in invertebrate biomass during the brood rearing period affected growth rates.
In 2010, emergent and core invertebrate biomass were negatively related to soil degree days, whereas in 2011, core biomass
increased with soil degree days and pitfall biomass increased with air temperature. Total invertebrate biomass (summed over
trap types) peaked from 25 to 31days before the median chick hatch date in 2010 and 10days after the median chick hatch
date in 2011. In 2011 we did not detect any effects of asynchrony on the growth of Semipalmated Plover chicks. These results
may indicate that food resources in their environment remain adequate throughout the breeding season, despite inter-annual
fluctuations in the timing of invertebrate peaks.
Keywords Charadrius semipalmatus· Invertebrates· Shorebird· Chick growth· Phenology· Weather
Introduction
Migratory species time their movements in part to take
advantage of seasonal flushes in food resources on their
breeding grounds (Johansson and Jonzen 2012). The phe-
nology of migration in many long-distance migrant birds
is primarily driven by day length, an environmental factor
that is not influenced by weather (Both and Visser 2005).
As climate change affects northern latitudes at a more accel-
erated pace than southern latitudes, differential changes in
climate may outpace the ability of populations to adapt to
climate-induced changes in the timing of resource peaks
on their breeding grounds (Both and Visser 2001; Stenseth
and Mysterud 2002; Senner 2012). A delayed migratory
response to changes in climate on the breeding grounds
could result in a later start to breeding, lower breeding suc-
cess, and a subsequent decline in population size (Both and
Visser 2001; Drever etal. 2012).
Climate change induced gaps between the timing of hatch
and peaks in food availability on the breeding grounds, here-
after “mismatch” (Stenseth and Mysterud 2002), has been
noted as one the of the possible mechanisms driving popu-
lation declines in insectivorous Arctic-nesting shorebird
populations (Tulp and Schekkerman 2008). In the Arctic,
short peaks in invertebrate abundance during mid-summer
(MacLean and Pitelka 1971; McKinnon etal. 2012; Bolduc
etal. 2013) are driven largely by temperature (Hodkinson
etal. 1998; Danks 2004). Short summer and weather-related
resource availability translates into a small window during
which there is adequate food available for reproduction and
the growth and survival of young. As such, birds breeding
* Laura Mckinnon
lmck@glendon.yorku.ca
1 Environmental andLife Sciences Graduate Program,
Trent University, 2140 East Bank Drive, Peterborough,
ONK9J7B8, Canada
2 Department ofMultidisciplinary Studies, York University
Glendon Campus, 2275 Bayview Avenue, Toronto,
ONM4N3M6, Canada
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... To measure the degree of a trophic mismatch, and to be able to make comparisons of mismatches among species and populations, it is necessary to view the advancement in timing of reproduction of the consumer relative to a yardstick which describes the phenology of its main food sources (Visser & Both, 2005). This yardstick most often is timing of the food peak, either expressed | 3 ZHEMCHUZHNIKOV Et al. in abundance (Corkery et al., 2019;Regular et al., 2014) or quality (Gauthier et al., 2013;Ross et al., 2017Ross et al., , 2018. Besides the timing of the food peak relative to the timing of the consumer's peak demand, a trophic mismatch can be defined relative to other parameters that describe food availability (Box S1). ...
... The timing of the food peak was suggested as a universal yardstick to describe fitness consequences of trophic mismatches between avian Rate of change in bird phenology (days per year) significant trends non-significant trends consumers and their prey (Visser & Both, 2005), although theoretical studies showed that to study fitness effects, it is important to consider the entire period during which food abundance sufficiently meets and overlaps with the food requirements of the offspring throughout the breeding season (Durant et al., 2005(Durant et al., , 2007. Several empirical studies indeed indicate that asynchrony with a food peak may not lead to fitness consequences when food is sufficiently abundant during the entire season (Corkery et al., 2019;Dunn et al., 2011;Reneerkens et al., 2016;Wesołowski & Rowiński, 2014). Vice versa, a good temporal match between offspring growth period and food peak might still result in negative fitness consequences when food availability during the entire season is low (Vatka et al., 2014). ...
Article
Full-text available
• Many organisms reproduce in seasonal environments, where selection on timing of reproduction is particularly strong as consumers need to synchronize reproduction with the peaked occurrence of their food. When a consumer species changes its phenology at a slower rate than its resources, this may induce a trophic mismatch, that is, offspring growing up after the peak in food availability, potentially leading to reductions in growth and survival. However, there is large variation in the degree of trophic mismatches as well as in its effects on reproductive output. • Here, we explore the potential causes for variation in the strength of trophic mismatches in published studies of birds. Specifically, we ask whether the changes in the degree of mismatch that have occurred over time can be explained by a bird's (a) breeding latitude, (b) migration distance, and/or (c) life‐history traits. • We found that none of these three factors explain changes in the degree of mismatch over time. Nevertheless, food phenology did advance faster at more northerly latitudes, while shifts in bird phenology did not show a trend with latitude. • We argue that the lack of support in our results is attributable to the large variation in the metrics used to describe timing of food availability. We propose a pathway to improve the quantification of trophic mismatches, guided by a more rigorous understanding of links between consumers and their resources.
... Those that have done so indicate large variation in effect size (Knudsen et al., 2011;. Recently, some studies have revealed mismatches that do not impact fitness (Corkery et al., 2019;Machín et al., 2018;Reneerkens et al., 2016) and in a recent review study, Zhemchuzhnikov et al. (2021) were unable to establish a clear link between the extent of a trophic mismatch and fitness impacts. The absence of a clear relationship between trophic mismatch and population dynamics may be influenced by the large variation in the effect sizes of trophic mismatches. ...
Article
Full-text available
In seasonal environments subject to climate change, organisms typically show phenological changes. As these changes are usually stronger in organisms at lower trophic levels than those at higher trophic levels, mismatches between consumers and their prey may occur during the consumers’ reproduction period. While in some species a trophic mismatch induced reductions in offspring growth, this is not always the case. This variation may be caused by relative strength of the mismatch, or by mitigating factors like increased temperature reducing energetic costs. We investigated the response of chick growth rate to arthropod abundance and temperature for six populations of ecologically similar shorebirds breeding in the Arctic and sub‐Arctic (four subspecies of Red Knot Calidris canutus, Great Knot C. tenuirostris and Surfbird C. virgata). In general, chicks experienced growth benefits (measured as a condition index) when hatching before the seasonal peak in arthropod abundance, and growth reductions when hatching after the peak. The moment in the season at which growth reductions occurred varied between populations, likely depending on whether food was limiting growth before or after the peak. Higher temperatures led to faster growth on average, but could only compensate for increasing trophic mismatch for the population experiencing the coldest conditions. We did not find changes in the timing of peaks in arthropod availability across the study years, possibly because our series of observation was relatively short; timing of hatching displayed no change over the years either. Our results suggest that a trend in trophic mismatches may not yet be evident; however, we show Arctic‐breeding shorebirds to be vulnerable to this phenomenon and vulnerability to depend on seasonal prey dynamics.
... www.nature.com/scientificreports/ in sampling chicks that leave nest sites within hours of hatching 24 , are highly mobile 25 , are difficult to relocate 26 , and often hide or remain motionless in the presence of a predator (or researcher) 27 . Instead, most studies have relied on growth rates of chicks when investigating the impacts of phenological mismatch 6,7,9,21,28,29 . However, the relationship between growth and survival of chicks is not necessarily straightforward; the assumption that slower growth leads to lower survival may not be true if undernourished chicks can simply grow more slowly over a longer period without compromising survival. ...
Article
Full-text available
Climate change in the Arctic is leading to earlier summers, creating a phenological mismatch between the hatching of insectivorous birds and the availability of their invertebrate prey. While phenological mismatch would presumably lower the survival of chicks, climate change is also leading to longer, warmer summers that may increase the annual productivity of birds by allowing adults to lay nests over a longer period of time, replace more nests that fail, and provide physiological relief to chicks (i.e., warmer temperatures that reduce thermoregulatory costs). However, there is little information on how these competing ecological processes will ultimately impact the demography of bird populations. In 2008 and 2009, we investigated the survival of chicks from initial and experimentally-induced replacement nests of arcticola Dunlin (Calidris alpina) breeding near Utqiaġvik, Alaska. We monitored survival of 66 broods from 41 initial and 25 replacement nests. Based on the average hatch date of each group, chick survival (up to age 15 days) from replacement nests (Ŝi = 0.10; 95% CI = 0.02–0.22) was substantially lower than initial nests (Ŝi = 0.67; 95% CI = 0.48–0.81). Daily survival rates were greater for older chicks, chicks from earlier-laid clutches, and during periods of greater invertebrate availability. As temperature was less important to daily survival rates of shorebird chicks than invertebrate availability, our results indicate that any physiological relief experienced by chicks will likely be overshadowed by the need for adequate food. Furthermore, the processes creating a phenological mismatch between hatching of shorebird young and invertebrate emergence ensures that warmer, longer breeding seasons will not translate into abundant food throughout the longer summers. Thus, despite having a greater opportunity to nest later (and potentially replace nests), young from these late-hatching broods will likely not have sufficient food to survive. Collectively, these results indicate that warmer, longer summers in the Arctic are unlikely to increase annual recruitment rates, and thus unable to compensate for low adult survival, which is typically limited by factors away from the Arctic-breeding grounds.
... However, it remains unclear whether this increased temporal asynchrony is harmful to young. McKinnon et al. (2013) and Corkery et al. (2019) both reported chicks growing sufficiently well even under depressed food conditions caused by phenological mismatch, perhaps due to lower thermoregulatory needs during the warmer springs. In contrast, Saalfeld et al. (2019) found that shorebirds experienced increased phenological mismatch with earlier snowmelt, and that, in general, chicks that hatched from nests initiated earlier experienced greater food availability and grew at faster rates than chicks from nests that hatched later. ...
Article
Full-text available
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.
... Some species have responded by advancing laying dates, whereas others have not, suggesting there are migratory constraints to an advancement (McKinnon et al. 2012, Liebezeit et al. 2014, Reneerkens et al. 2016 In Red Knots (Calidris canutus canutus) body size of juveniles is positively related to date of snow melt in the Arctic, suggesting that their body size at fledging is smaller following a mismatch in early springs, resulting in a lower subsequent survival (van Gils et al. 2016). In general, however, evidence for a phenological mismatch for shorebirds is rare, perhaps because arthropod abundance, more than plant growth, is strongly affected by weather conditions following snowmelt (McKinnon et al. 2012, Reneerkens et al. 2016, Leung et al. 2018, Corkery et al. 2019, Saalfeld et al. 2019). While only a few studies investigated the connection between proportion of juveniles and climatic conditions in the breeding grounds and none of these included onset of spring, most of these studies found a higher proportion of juveniles following warm breeding seasons (Schekkerman et al. 1998, Beale et al. 2006, Aharon-Rotman et al. 2015. ...
Article
Full-text available
Breeding output of geese, measured as the proportion of juveniles in autumn or winter flocks, is lower in years with a late onset of spring in some species, but higher in at least one other species. Here we argue that this is because the timing of spring affects different stages of the reproductive cycle differently in different species. Because the effects on 2 different stages are opposite, the combined effects can result in either a positive or a negative overall effect. These stages are the pre-laying, laying, and nesting phase on the one hand; and the hatchling, fledgling, and juvenile phase on the other hand. The first phase is predominantly positively affected by an early snowmelt, with higher breeding propensity, clutch size, and nest success. The second phase in contrast is negatively affected by early snowmelt because of a mismatch with a nutrient food peak, leading to slow gosling growth and reduced survival. We argue that recognition of this chain of events is crucial when one wants to predict goose productivity and eventually goose population dynamics. In a rapidly warming Arctic, the negative effects of a mismatch might become increasingly important.
... These changes could significantly influence populations of Arctic-breeding birds, the most diverse and vertebrate taxa of the circumpolar Arctic [2]. Northward shifts in vegetation communities have already influenced the availability of nesting habitat for sub-arctic breeding shorebirds [3], and advances in peak prey availability have created a mismatch with the phenology of chick hatch [4], and lower growth and chick survival in some [5,6] but not all cases [4,7,8]. While at large scales these changes have the potential to alter bird distribution, phenology, and demography, at smaller spatial scales the trophic interactions among predators and their prey may play a more dominant role in structuring communities [9,10]. ...
Article
Full-text available
The Arctic is undergoing rapid changes, with anthropogenic shifts in climate having important and well-documented impacts on habitat. Populations of predators and their prey are affected by changing climate and other anthropogenic factors, and these changing trophic interactions could have profound effects on breeding populations of Arctic birds. Variable abundance of lemmings (a primary prey of generalist Arctic predators) and increasing abundance of light geese (Lesser Snow and Ross' Geese; a secondary prey) could have negative consequences for numerous sympatric shorebirds (an incidental prey). Using 16 years of predator-prey observations and 13-years of shorebird nest survival data at a site near a goose colony we identify relationships among geese, lemmings, and their shared predators and then relate predator indices to shorebird risk of nest predation. During two years, we also placed time-lapse cameras and artificial shorebird nests at increasing distances from a goose colony to document spatial trends in predators and their effect on risk of predation. In the long-term data, yearly indices of light geese positively influenced indices of gulls and jaegers, and shorebird nest predation rate was negatively correlated with jaeger and fox indices. All three predator indices were highest near the goose colony and artificial nest predation probability was negatively correlated with distance from goose colony, but these effects were less apparent during the second year. Combined, these results highlight the variation in predator-mediated interactions between geese and shorebirds and outline one mechanism by which hyperabundant geese may be contributing to local or regional declines in Arctic-nesting shorebird populations.
Article
Over the last 60 years, Arctic goose populations have increased while many sympatric tundra nesting bird populations have declined. Hyperabundant geese have well-documented effects on tundra habitats, which can alter habitat use by sympatric bird species. These habitat changes may also alter invertebrate communities and abundances, with potentially important, but as of yet, undocumented effects on insectivorous birds such as shorebirds. Here, we determined the effects of goose-induced habitat alteration on invertebrate communities and relate the observed changes to shorebird diet. At sites and habitat types representing a gradient of goose influence, we identified goose-related changes in ground cover and linked these factors to variation in invertebrate communities. We then used DNA metabarcoding to characterize the diet of six shorebird species across sites and identify inter-site variation in abundance, biomass, and timing of emergence of dominant shorebird prey items. Invertebrate diversity and richness did not vary either among sites or habitat types. However, for prey items identified as part of the shorebird diet, we found significantly higher abundances and biomasses at a moderately goose-influenced site than at either low or high goose-influenced sites. Biomass of Tipulidae, the dominant prey taxon for shorebirds at the study sites, was 7.5 times higher at the moderately goose-influenced site compared to the site where goose influence was minor. We attribute this enhancement of prey biomass to both the fertilizing effect of goose fecal pellets and the moderate grazing pressure. Many studies have documented adverse effects of overabundant geese, but here we show that a moderate degree of goose grazing can lead to enhanced biomass of invertebrates, with the potential for improved shorebird foraging success and chick growth. These benefits, however, might be outweighed by negative effects of goose-induced habitat alteration and predation pressure.
Article
Full-text available
Aerial insectivores are highly mobile predators that feed on diverse prey items that have highly variable distributions. As such, investigating the diet, prey selection and prey availability of aerial insectivores can be challenging. In this study, we used an integrated DNA barcoding method to investigate the diet and food supply of Barn Swallows, an aerial insectivore whose North American population has declined over the past 40 yr. We tested the hypotheses that Barn Swallows are generalist insectivores when provisioning their young and select prey based on size. We predicted that the diets of nestlings would contain a range of insect taxa but would be biased towards large prey items and that the diet of nestlings would change as prey availability changed. We collected insects using Malaise traps at 10 breeding sites and identified specimens using standard DNA barcoding. The sequences from these insect specimens were used to create a custom reference database of prey species and their relative sizes for our study area. We identified insect prey items from nestling fecal samples by using high-throughput DNA sequencing and comparing the sequences to our custom reference database. Barn Swallows fed nestlings prey items from 130 families representing 13 orders but showed selection for larger prey items that were predominantly from 7 dipteran families. Nestling diet varied both within and between breeding seasons as well as between breeding sites. This dietary flexibility suggests that Barn Swallows are able to adjust their provisioning to changing prey availability on the breeding grounds when feeding their nestlings. Our study demonstrates the utility of custom reference databases for linking the abundance and size of insect prey in the habitat with prey consumed when employing molecular methods for dietary analysis.
Article
Full-text available
Climate change can cause mismatches between the breeding phenology and peak abundance of food resources of migratory species. Moreover, asynchronously changing climate regimes across their ranges may constrain the ability of migratory species to adapt to all the regimes they encounter. To understand the potential effect of asynchronous changes, I examined the influences of both large- and local-scale weather and climate on the timing of arrival of two disjunct breeding populations of Hudsonian Godwits (Limosa haemastica). I used arrival data from two study sites-Beluga River, Alaska, and Churchill, Manitoba-combined with 37 years of weather and climate data from both winter and stopover sites and the breeding grounds. The Alaskan population now arrives similar to 9 days earlier than it did in the early 1970s, and the Churchill population arrives >10 days later. A model-selection process using linear regression models suggested that these divergent trends result from different suites of environmental factors affecting the timing of migration for the two populations. The cues used by the Alaskan population have remained reliable indicators of the timing of the onset of spring on their breeding grounds, but this is not the case for the Churchill population. Conflicting warming regimes in midcontinental North America cause the Churchill population to arrive later to their breeding grounds and limit their ability to properly time their breeding efforts. These results suggest that ecological and phenological limitations, not just evolutionary constraints, are critical to determining how populations respond to climate change. Received 21 February 2012, accepted 12 July 2012.
Article
Full-text available
Extensive studies on invertebrates from Ny-Alesund, Spitsbergen, Svalbard and more limited data on aphids from Abisko, Sweden, produced the following main conclusions: (1) The population response to raised summer temperatures differed between the above and the below ground species, both in terms of speed and magnitude. (2) Similar animal communities responded differently to similar temperature manipulations on sites with different vegetation cover and composition. (3) For soil animals the between-year and between-site variations in population densities, were greater than the differences produced by the temperature manipulation experiments at any one site in any year. (4) Infrequent extreme climatic events strongly influence long-term trends in population density and community composition. (5) The population response of invertebrates to climate warming is greatest and most rapid at the coldest sites. (6) The spatial distribution of the above ground insect herbivores on their host plant is temperature limited. (7) The numerical abundance of flying predators/parasitoids of the above-ground herbivores is low. (8) The spatial distribution of some predators may be thermally restricted and less extensive than that of their prey. (9) Habitat temperature is the driving variable determining the flight activity patterns of insects. (10) Increased summer temperatures may alter or disrupt the seasonal patterns of insect emergence, particularly in species where the life cycle is cued into the seasonal rhythm. (11) The common species of arctic soil mites and Collembola are well adapted to survive enhanced summer temperatures, providing that moisture is not limited. (12) Water availability during the summer growing period is probably of greater significance than temperature in determining the survival and success of many arctic soil invertebrate groups. (13) Arctic soil microarthropod species are well adapted to survive and operate at subzero and low positive summer temperatures. (14) Freeze-thaw events represent critical points in the life history of the microarthropods. (15) Supercooling points are sometimes poor indicators of the capacity of arctic soil microarthopods to survive low temperatures. From these findings predictions are made as to how high arctic communities will respond to predicted changes in climate.
Article
Full-text available
Arthropods active on the surface of the tundra near Barrow, Alaska, were trapped throughout four summer seasons (1966-1969), using "sticky-board" traps. More than 95% of the arthropods (excluding Acarina and Collembola) captured were of the order Diptera. Adults of most species of Diptera emerged in the middle two weeks of July; the abundance of arthropods on the tundra surface was maximal at that time. Year-to-year variations in abundance of various arthropod taxa are related to prevailing weather conditions and to the cycle of tundra disturbance and recovery associated with the abundance of brown lemmings.
Article
Full-text available
Regional patterns of shorebird diets were examined by reviewing 75 papers reporting prey of 43 shorebird species throughout the western hemisphere. Collectively, shorebirds consumed a wide variety of invertebrate taxa, including 12 phyla, 22 classes, 72 orders, 238 families, and 404 genera of invertebrates. The most widely represented invertebrate classes were Insecta, Malacostraca, Gastropoda, Polychaeta, and Bivalvia. The ten most widely studied shorebird species exhibited considerable dietary breadth, consuming an average of 36 (range 23-65) families of invertebrates. Fifteen invertebrate families were common to the diets of seven or more of these ten species. For all shorebird species evaluated, there was little dietary overlap in invertebrate taxa between geographic regions, especially between tidal and inland areas. Diet similarities of species and guilds of shorebirds within regions and of coexisting species within studies were high. The flexible nature of food choice in shorebirds influences management approaches toward providing vital food resources for shorebirds during all seasons. Management efforts should focus on maintaining hydrologic regimes and ecosystem processes that promote the growth and maintenance of invertebrate populations in general; specific taxa need not be targeted. Successful maintenance of wetlands will ensure that naturally-occurring populations of invertebrates occur and are accessible to shorebirds.
Article
We examined diet of nonbreeding Semipalmated Plovers (Charadrius semipalmatus Bonaparte, 1825) in the Cumberland Island estuary, Georgia, USA, through fecal sample analysis. We also examined prey size selectivity by Semipalmated Plovers for the most common prey item found in the fecal samples, which are polychaetes in the family Nereidae (= Nereididae). We compared the size distribution of polychaetes in Semipalmated Plover fecal samples from salt marshes and mudflats with the size distribution of polychaetes sampled from the two habitats. Semipalmated Plovers foraging on mudflats had less variable diets than those foraging on salt marshes, although the mean number of prey per Semipalmated Plover fecal sample was similar between the two habitats. Size selectivity by Semipalmated Plovers of nereid (= nereidid) polychaetes varied as a function of habitat, with Semipalmated Plovers eating larger polychaetes in salt marshes than in mudflats, although in both habitats Semipalmated Plovers avoided extremely sma...
Article
This chapter gives results from some illustrative exploration of the performance of information-theoretic criteria for model selection and methods to quantify precision when there is model selection uncertainty. The methods given in Chapter 4 are illustrated and additional insights are provided based on simulation and real data. Section 5.2 utilizes a chain binomial survival model for some Monte Carlo evaluation of unconditional sampling variance estimation, confidence intervals, and model averaging. For this simulation the generating process is known and can be of relatively high dimension. The generating model and the models used for data analysis in this chain binomial simulation are easy to understand and have no nuisance parameters. We give some comparisons of AIC versus BIC selection and use achieved confidence interval coverage as an integrating metric to judge the success of various approaches to inference.
Article
Sexually dimorphic species generally are characterized by having one sex consistently larger, and often brighter, than the other. Semipalmated Plovers (Charadrius semipalmatus) exhibit a pattern of mixed dimorphism with females that are heavier and having longer wings than males, whereas males have longer toes and bills, and are more colorful than females. Although we found weak evidence that male and female plovers mate assortatively with respect to body size, this likely resulted from birds of certain phenotypes breeding at different times. The mixed pattern of dimorphism in Semipalmated Plovers has probably resulted from different selection pressures, ecological and sexual, operating on different characters.