Steve Oswald | Pennsylvania State University

Steve Oswald

Pennsylvania State University, Division of Science - Penn State Berks Campus, Faculty Member

Pennsylvania State University, Division of Science - Penn State Berks Campus, Faculty Member |

My research is on the ecology, comparative ecophysiology, evolution and conservation of seabirds. My reasearch areas are:
1) Thermal ecology of seabirds and waterbirds and how climate may directly affect their behavior, populations, and distributions.
2) The strength of evolutionary selection pressures on morphology and physiology of extant seabirds.
3) The ecology and conservation of inland breeding "seabirds" and waterbirds
4) Field instrumentation and analytical methods for studying colonial birds

I am always interested in collaborative proposals, consulting, and other research opportunities. Feel free to contact me.

Google Scholar: https://scholar.google.com/citations?user=PRLoG8kAAAAJ&hl=en&oi=sra

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Papers

A simple, band‐mounted device to measure behaviorally modified thermal microclimates experienced by birds

Journal of Field Ornithology, 2018

Birds encounter climate at the scale of microclimates that can vary rapidly in time and space and... more Birds encounter climate at the scale of microclimates that can vary rapidly in time and space and so understanding potential vulnerability and adaptations to those microclimates requires fine‐scale measurements that accurately track thermal exposures. However, few options exist for recording the microclimates actually experienced by birds (realized microclimates). We constructed and tested a simple, low‐cost, temperature logger for recording the realized microclimates of ground‐nesting birds. We developed attachment protocols for band‐mounting Thermochron iButtons on Ring‐billed Gull (Larus delawarensis) chicks. We tested these mounted, temperature‐logging devices on 20 chicks weighing > 200 g (device weight was 4 g), attaching devices for 48 h and observing behavior before and after attachment and removal. Devices recorded temperature immediately surrounding the leg at 2‐min intervals. Recorded temperatures were strong predictors of observed thermoregulatory behaviors (panting and sitting), outperforming predictions based on air temperatures measured by basic, static approaches. Through comparison with matched controls (chicks with just a band), we detected no adverse physiological effects of devices, no effects on social or feeding behavior, and only a short‐term decrease in inactivity immediately after device attachment (likely due to increased preening). By attaching iButtons to the legs of birds, we quantified realized thermal exposure, integrating air temperature, modes of environmental heat transfer, and bird behavior at microclimatic scales. Although not yet validated for broader use, our approach (including possible miniaturization) should be suitable to measure thermal exposure of adults, not just chicks, allowing collection of data concerning thermal exposures during flight under field conditions. At ~ $25 USD per device, our approach facilitates experimental protocols with robust sample sizes, even for relatively modest budgets.

Common Tern Sterna hirundo

Birds of North America (Cornell Lab of Ornithology), 2017

Since the first version of this account was published in 2002, important new information has been... more Since the first version of this account was published in 2002, important new information has been generated on the population genetics of Common Terns (see Systematics), migration patterns and overwintering areas (see Migration), chick growth (see Breeding), adult survival and breeding dispersal (see Demography). Much new information has been generated on the distribution of boreal populations in Canada away from large lakes and on other aspects of the ecology of inland populations (see Habitat, Breeding, and Demography). Declines in numbers breeding in the Great Lakes and the large lakes of Manitoba, combined with genetic evidence for asymmetric gene flow towards coastal populations and with the generally low reproductive success at inland colonies (see Systematics, Breeding, and Demography), have led to increased concern for the conservation status of many inland populations. The history of recent successes and failures in managing and restoring breeding colonies shows that North American Common Terns are heavily dependent on restored and artificial sites, and require continuing management (see Conservation). This revision also updates information on the numbers and trends in many regional and local populations, and on reproductive success at many breeding colonies throughout the southern part of the continental range (see Appendices).

From animal tracks to fine‐scale movement modes: a straightforward approach for identifying multiple spatial movement patterns

Methods in Ecology and Evolution, 2017

Thanks to developments in animal tracking technology, detailed data on the movement tracks of ind... more Thanks to developments in animal tracking technology, detailed data on the movement tracks of individual animals are now attainable for many species. However, straightforward methods to decompose individual tracks into high‐resolution, spatial modes are lacking but are essential to understand what an animal is doing.
We developed an analytical approach that combines separately validated methods into a straightforward tool for converting animal GPS tracks into short‐range movement modes. Our three‐step analytical process comprises: (i) decomposing data into separate movement segments using behavioural change point analysis; (ii) defining candidate movement modes and translating them into nonlinear or linear equations between net squared displacement (NSD) and time and (iii) fitting each candidate equation to NSD segments and determining the best‐fitting modes using Concordance Criteria, Akaike's Information Criteria and other fine‐scale segment characteristics. We illustrate our approach for three sub‐adults, male wild boar Sus scrofa tracked at 15‐min intervals over 4 months using GPS collars. We defined five candidate movement modes based on previously published studies of short‐term movements: encamped, ranging, round trips (complete and partial) and wandering.
Our approach successfully classified over 80% of the tracks into these movement modes lasting between 5 and 54 h and covering between 300 m to 20 km. Repeated analyses of GPS data resampled at different rates indicated that one positional fix every 3–4 h was sufficient for >70% classification success. Classified modes were consistent with published observations of wild boar movement, further validating our method.
The proposed approach advances the status quo by permitting classification into multiple movement modes (where these are adequately discernable from spatial fixes) facilitating analyses at high temporal and spatial resolutions, and is straightforward, largely objective, and without restrictive assumptions, necessary parameterizations or visual interpretation. Thus, it should capture the complexity and variability of tracked animal movement mode for a variety of taxa across a wide range of spatial and temporal scales.

Conservation implications of long-distance migration routes: Regional metapopulation structure, asymmetrical dispersal, and population declines

Biological Conservation, 2017

Understanding and conserving metapopulations of long-distance migrants is challenging since breed... more Understanding and conserving metapopulations of long-distance migrants is challenging since breeding population structure may not be delimited simply by geography, but also by migration or wintering distributions. We present the first study of the relative importance of breeding, migration and wintering distributions for regional metapopulation processes in breeding areas. Using a species for which life-history and demography are extensively studied (common terns Sterna hirundo), we explored population genetics across eastern North America to distinguish between these potential drivers of metapopulation structure, understand recent population declines in inland areas, and direct appropriate conservation efforts. We analyzed nuclear and mitochondrial DNA to determine changes in population structure and dispersal over prehistoric, historical and contemporary time at regional, sub-regional and local spatial scales. We found evidence for conservation-relevant, hierarchical metapopulation structure within breeding areas: at (i) local and sub-regional scales resulting from restricted dispersal distances, and (ii) between inland and coastal regions as a result of non-breeding distributions. Crucially, at regional scales (ii), asymmetrical dispersal rates from inland to coastal colonies have increased ten-fold since the 1960s, contributing to recent, largely-enigmatic inland population declines. Migrating inland common terns pass over coastal colonies but the reverse is not true. Thus, asymmetrical dispersal from inland to coastal areas provides the first demonstration that migration routes, not wintering distributions, are drivers of breeding population structure in the absence of physical barriers. Our results illustrate the conservation importance of this determination for long-distance migrants: definitive evidence connecting metapopulation demographics to regional population declines for common terns, previously only speculated at despite > 100 years of banding effort.

Energetic constraint of non‐monotonic mass change during offspring growth: a general hypothesis and application of a new tool

Journal of Animal Ecology, 2016

Post‐natal growth is an important life‐history trait and can be a sensitive indicator of ecologic... more Post‐natal growth is an important life‐history trait and can be a sensitive indicator of ecological stress. For over 50 years, monotonic (never‐decreasing) growth has been viewed as the predominant trajectory of post‐natal mass change in most animal species, notably among birds. However, prevailing analytical approaches and energetic constraints may limit detection of non‐monotonic (or multiphasic), determinate growth patterns, such as mass recession in birds (weight loss prior to fledging, preceded by overshooting adult mass), which is currently believed to be restricted to few taxa.
Energetic surplus and shortfall are widespread conditions that can directly influence the degree of mass overshooting and recession. Thus, we hypothesize that in many species, prevailing energetic constraints force mass change away from a fundamental non‐monotonic trajectory to instead follow a monotonic curve.
We observed highly non‐monotonic, mass change trajectories (overshooting adult mass by up to almost 20%) among common tern Sterna hirundo chicks, a well‐studied species long‐established as growing monotonically. We quantified the prevalence and magnitude of non‐monotonic mass change prior to fledging for 313 common tern chicks that successfully fledged from two discrete populations in multiple years. We used a new approach for analysing non‐monotonic curves to examine differences in mass change trajectories between populations under contrasting abiotic (freshwater vs. saltwater) and biotic stresses (low rates of food provisioning).
Some degree of mass recession occurred in 73% of all study chicks. Overshooting adult mass followed by extensive mass recession was most prevalent at our freshwater colony, being detected among 34–38% of chicks annually. Non‐monotonic trajectories were less marked in populations experiencing ecological stress and among lower quality individuals. Chicks that were provisioned at higher rates were more likely to both overshoot adult mass and experience subsequent mass recession.
Our results in common terns provide strong support for the hypothesis that non‐monotonic trajectories are the fundamental pattern of mass change but are constrained to be monotonic under energetic shortfall. This justifies future tests of the generality of this hypothesis across a broad range of taxa. We also demonstrate a recent analytical tool that prevents routine fitting of monotonic curves without prior investigation of non‐monotonic trends.

Premature feather loss among common tern chicks in Ontario: the return of an enigmatic developmental anomaly

PeerJ 4:e195, 2016

In July 2014, we observed premature feather loss (PFL) among non-sibling, common tern Sterna hir... more In July 2014, we observed premature feather loss (PFL) among non-sibling, common tern Sterna hirundo chicks between two and four weeks of age at Gull Island in northern Lake Ontario, Canada. Rarely observed in wild birds, to our knowledge PFL has not been recorded in terns since 1974, despite the subsequent banding of hundreds of thousands of tern chicks across North America alone. The prevalence, 5% of chicks (9/167), and extent of feather loss we report is more extreme than in previous reports for common terns but was not accompanied by other aberrant developmental or physical deformities. Complete feather loss from all body areas (wing, tail, head and body) occurred over a period of a few days but all affected chicks appeared vigorous and quickly began to grow replacement feathers. All but one chick (recovered dead and submitted for post-mortem) most likely fledged 10–20 days after normal fledging age. We found no evidence of feather dystrophy or concurrent developmental abnormalities unusual among affected chicks. Thus, the PFL we observed among common terns in 2014 was largely of unknown origin. There was striking temporal association between the onset of PFL and persistent strong southwesterly winds that caused extensive mixing of near-shore surface water with cool, deep lake waters. One hypothesis is that PFL may have been caused by unidentified pathogens or toxins welling up from these deep waters along the shoreline but current data are insufficient to test this. PFL was not observed among common terns at Gull Island in 2015, although we did observe similar feather loss in a herring gull Larus argentatus chick in that year. Comparison with sporadic records of PFL in other seabirds suggests that PFL may be a rare, but non-specific, response to a range of potential stressors. PFL is now known for gulls, penguins and terns.

FlexParamCurve v1.5-5 is now available

FlexParamCurve version 1.5-5 was released November 26, 2018, and is available from CRAN: https://... more FlexParamCurve version 1.5-5 was released November 26, 2018, and is available from CRAN: https://cran.r-project.org/web/packages/FlexParamCurve/index.html FlexParamCurve is a freely-available R package that provides model selection tools and 'selfStart' functions to fit parametric curves in 'nls', 'nlsList' and 'nlme' frameworks. This version has fixed all known bugs from v1.5-3

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FlexParamCurve v1.5-3: News and Known Bugs

9-30-2015 FlexParamCurve v1.5-3 is online but a revision is in progress Known bugs 1)The verbos... more 9-30-2015
FlexParamCurve v1.5-3 is online but a revision is in progress

Known bugs

1)The verbose output option is not correctly transitioning to model selection routines pn.mod.compare() and pn.modselect.step().

2) modpar(), pn.mod.compare() and pn.modselect.step() do not currently handle missing (NA) values. Please subset the data to remove them prior to function call:

e.g. mydataframe[!is.na(mydataframe),]

3) currently pn.mod.compare() and pn.modselect.step() overwrite existing output in the specified Envir argument and package environment, such that existing richardsR##.lis models not overrun will be evaluated in a current run. existing=F argument is not currently functioning. richardsR##.lis models MUST be manually removed from BOTH the working environment AND the FlexParamCurve environment prior to subsequent runs of these model selection tools (You can save existing data in a new environment prior to removal).
Use the following code between each different run:

#copy everything to envir "env1"
env1 <- as.environment(as.list(.GlobalEnv, all.names=TRUE))

#Remove richardsR##.lis from .GlobalEnv
rm(list = ls(pattern = "richardsR"))

#AND remove richardsR##.lis from FlexParamCurve env
rm(list = ls(pattern = "richardsR", envir=FlexParamCurve:::FPCEnv), envir=FlexParamCurve:::FPCEnv)

From the package NEWS file:

CHANGES IN FlexParamCurve 1.5-3:

(note FlexParamCurve 1.5-2 was not generally circulated thus changes detailed
are additions since 1.5-1)

* Change in default approach to fitting monotonic curves

Monotonic curves are exemplified by the logistic and Richards curve, and do not
incorporate a recessional part of the curve. In previous versions, FlexParamCurve
fixed recessional parameters to the values in the specified pn.options object (see
?modpar). However, if data used in modpar supported recessional parameters non-
intuitive recessional plots were generated using monotonic curve models (modno 12
or 32). The new approach implemented in v1.5-3 is to by default ignore recessional
parameters whenever modno 12 or 32 are optimized or plotted. To access the original
approach (for those who wish to optimize pre-recession parameters only but retain
fixed recession trajectories) set force.nonmonotonic = TRUE in modpar.

* Update of model selection routines (pn.mod.compare and pn.modselect.step)

The new default for pn.mod.compare is to proceed using variable models (those
with a shape parameter, M, for the pre-recessional part of the curve) for subsequent
model selection if neither of the initial models successfully converge. User preferences
can be selected using either forcemod = 3 or forcemod = 4; see ?pn.mod.compare. In both
selection routines the code has been adjusted to make forcemod work appropriately.

* Implementation of required package dependencies

The new dependency information required by CRAN has been incorporated.

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PREPRINT: Does contemporary premature feather loss among common tern chicks in Lake Ontario reflect persistent pollutants, enigmatic diseases or novel pathogens?

PeerJ Preprints, Jun 2015

We observed premature feather loss (PFL) among common terns Sterna hirundo at a small colony in n... more We observed premature feather loss (PFL) among common terns Sterna hirundo at a small colony in northern Lake Ontario, Canada in July 2014. This condition is characterized by affected chicks losing all their wing, tail, head and body feathers several weeks after hatching. Rarely observed in wild birds, to our knowledge PFL in terns has not been recorded since 1974 (despite the banding of tens of thousands of tern chicks across North America since then). In July 2014, we observed PFL in chicks at between 2 and 4 weeks of age. The extent of feather loss was more extreme than in previous reports but was not accompanied by other aberrant developmental or physical deformities. Complete feather loss occurred over a period of a few days but all affected chicks quickly began to grow replacement feathers and all but one most likely fledged 10-20 days after normal fledging age. Feather samples, both shed feathers and re-growing live feathers, were collected from both affected chicks and normal individuals. One subsequently dead PFL chick was collected. Samples are awaiting further analysis. There was striking temporal association between the onset of PFL and persistent strong southwesterly winds that caused extensive mixing of near-shore, surface water with cool, deep lake waters. To our current knowledge it seems most probable that the PFL we observed in 2014 was caused by pathogens (viruses, bacteria, algal toxins) welling up from these deep waters along the shoreline but a direct link has not yet been made. The re-emergence of PFL in common terns may indicate acute health risks for birds and other wildlife in the Lake Ontario region and may also have potential for human health risks. [NOT PEER-REVIEWED]

Non-breeding season movements of six North American Roseate Terns Sterna dougallii tracked with geolocators

Seabird, Dec 2014

Little is known of the endangered and declining western North Atlantic population of the Roseate ... more Little is known of the endangered and declining western North Atlantic population of the Roseate Tern Sterna dougallii outside the breeding season, when most mortality probably occurs. We used geolocators to track Roseate Terns in 2007 and 2009 and retrieved six units with useful data. In the post-breeding period in July–August, all six birds staged around Cape Cod, close to the breeding site. They started southward migration from 28 August to 14 September and flew directly across the western North Atlantic Ocean to staging areas around Puerto Rico and the Dominican Republic. We identified five major areas and four minor areas in the West Indies and along the north and east coasts of South America where birds stopped over for 2–24 d during southward and northward migrations. Birds arrived at (Northern Hemisphere) wintering areas from Guyana/Suriname on the north coast of South America to eastern Brazil between 3 October and 2 November. They left wintering areas from 7–23 April and arrived back at the breeding area from 5–30 May. Although this study is based on data for only six birds, it identifies several stopover and wintering areas that should receive priority for future studies and potential conservation measures. Geolocators did not impair Roseate Terns’ ability to raise young in the year the devices were attached, but lower than expected rates of return suggest that the geolocators reduced survival, and most of the birds that returned had lost body-mass and did not breed in the year of return.