Smith JAM, Hafner S., Niles L. (In press) The impact of past management practices on tidal marsh resilience to sea level rise in the Delaware Estuary. Ocean and Coastal Management.


Defining appropriate management and conservation strategies to maximize tidal marsh resilience to sea level rise requires a clear understanding of the causes of marsh degradation. While sea level rise is a well-known threat to tidal marshes, current and past management practices on marshes can also greatly influence present-day marsh condition, resilience and future persistence. Using point-intercept analysis of maps and imagery, we assessed the past and current landcover and elevation of Delaware Estuary tidal marshes in New Jersey, USA. We estimated the historic extent of tidal marsh impoundment for agriculture and determined current marsh vegetation composition and elevation in areas that were and were not historically impounded. We estimate that more than half of all tidal marsh in the 36,539 ha study area had been historically impounded. A small fraction of this area remains impounded at present (7.6%). While tidal flow has since returned to formerly diked areas, marsh recovery has been incomplete. Overall 21.6% (4048.8 ha) of formerly impounded marsh has not revegetated, becoming open water after impoundment breaches. Marsh loss as a result of impoundment is also responsible for the loss of 2.3 km of adjacent shoreline beaches. Conversely, only 0.5% of marsh that was never impounded has converted to open water since 1931. This difference is likely due to dramatic elevation deficits caused by impoundment. Marsh elevation of current and formerly impounded areas (derived from LiDAR and validated with RTK GPS) is significantly lower than the elevation of marsh areas that were never impounded. Supporting this finding, the frequency of high marsh vegetation (an indicator of higher elevation) in vegetated formerly impounded areas is half that of areas that were never impounded. Marsh edge erosion and creek expansion have added an additional estimated 3,836 ha to the amount of tidal marsh loss since 1931. Marsh transgression inland into forest and agricultural areas has resulted in estimated gains in marsh area of 2,815 ha, offsetting a considerable proportion of losses. Given our results, we recommend the following management actions to maximize tidal marsh persistence in the Delaware Estuary: (1) Beneficial use of sediment to offset marsh elevation deficits resulting from historic impoundment, (2) Strategic land protection to maximize the potential for inland marsh migration, (3) Tidal flow restoration to remaining impounded areas in combination with the beneficial use of sediment to address elevation deficits. Determining the impacts to tidal marshes from past management practices makes it possible parse the relative contribution of relative sea level rise and site-level management, resulting in more targeted conservation strategies.

Smith JAM and Niles L. (2016) Are salt marsh pools suitable sites for restoration? Wetland Science and Practice. 33(4):101-109. PDF


The signs and causes of marsh degradation must be correctly identified in order to plan restoration actions that (1) do no harm to functioning ecosystems, (2) produce lasting results, and (3) use scarce restoration dollars effectively. There are many ways to productively use dredged material to conserve, manage and restore tidal wetlands. The broad acceptance of dredged sediment use for tidal marsh conservation is an important step forward in the management of marshes. However, sediment must be used in a way that does not adversely impact systems that are currently functioning well, such as unaltered marshes with dynamic pool systems.

Martin Bulla et al. (2016) Unexpected diversity in socially synchronized rhythms of shorebirds. Nature. 540:109-113. PDF


The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators. Individuals can temporally segregate their daily activities (e.g. prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (e.g. group foraging, communal defence, pairs reproducing or caring for offspring. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood. Here, we address this in the context of biparental care, a particularly sensitive phase of social synchronization where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally-incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1 – 19 hours, while period length – the time in which a parent’s probability to incubate cycles once between its highest and lowest value – varied from 6 – 43 hours. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or actively protect their nest against predators. Rhythms entrainable to the 24-h light-dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

Burger J, Niles LJ, Dey AD, Dillingham T, Gates AS, Smith J (2015) An experiment to examine how Red Knots Calidris canutus rufa and other shorebirds respond to oyster culture at Reed’s Beach, Delaware Bay, New Jersey Wader Study. 122(2). PDF


We examined how Red Knots Calidris canutus and other shorebirds responded to experimental oyster racks at Reed’s Beach, New Jersey, USA. Our goal was to investigate ways that human activities (e.g. oyster culture) and migrant shorebirds can co-exist without negatively impacting each other. The expansion of oyster culture just offshore from beaches where shorebirds feed on Horseshoe Crabu Limulus polyphems eggs could have positive benefits or negative effects on shorebird foraging. In collaboration with a local oysterman, oyster racks were constructed 25 m offshore from Reed’s Beach South, one of the primary shorebird foraging sites, and regular surveys were carried out throughout the Delaware Bay shorebird stopover period in May 2013.

We found that oyster racks (whether the beach had racks or was a reference site), tidal stage, people, and interactions amongst these variables, significantly affected shorebird numbers. Specifically, (1) oyster racks and tidal stage (alone and as interactions) had the greatest effect on presence and abundance of shorebirds and gulls, except for Red Knots, (2) Red Knots were most affected by people, followed by tide, (3) more shorebirds were present at high tide than at other tide times, (4) numbers were highest on the beach near the oyster racks, largely reflecting those of Semipalmated Sandpipers Calidris pusilla, (5) fewer shorebirds of any species were present when workers were present, compared to when beach-users were present, and (6) virtually no Red Knots and Ruddy Turnstones Arenaria interpres were present when workers or beach-users were present on the beach next to the oyster racks. The number of shorebirds feeding was highest when no people were present, intermediate when beach-users were present, and lowest when workers were present. These preliminary results suggest that Red Knots are more sensitive to oyster culture activities than other shorebird species. Therefore we suggest that regulators and managers should incorporate this sensitivity in their management and rule-making.

Schweitzer DF, Garris JR, McBride AE, Smith JAM (2014) The current status of forest Macrolepidoptera in northern New Jersey forests: evidence for the decline of understory specialists. Journal of Insect Conservation. 18(4): 561-571. PDF

Supplementary material — Appendix A: Species documentation; Appendix B: Tree feeding species; Appendix C: Understory feeding species; Appendix D: Litter feeding species; Appendix E: Operational taxonomic units that are possibly two species; Appendix F: Excluded guilds


We compared most taxa of the forest Macrolepidoptera fauna of the northwestern corner of New Jersey documented from the late 1800s through the 1970s with that documented in 2003-2013.  Over 95% of documented species whose caterpillars feed on trees (n=307) and forest litter (n=27) were found.  Among understory specialists, all eight specialists on ferns, which deer generally avoid, were found, as were all 12 specialists or oligophages on browse-tolerant lowbush blueberries.  In contrast, only 11 of 20 specialists on non-ericaceous shrubs and 16 of 25 specialists on forest forbs were found, despite the bias of targeted sampling for most undetected forb feeders. Non-detections of understory species are highly consistent with deer impacts and most of those we did not find were still being found in the 1970s or 1980s.  Most of  the 13 undetected tree-feeders have last known collection dates in the 1950s or 1960s locally, and seven have reportedly declined more widely to the east,  However, detection success for tree feeders was at least 90% of all families.

Smith JAM (2013) The role of Phragmites australis in mediating inland salt marsh migration in a mid-Atlantic estuary. PLoS ONE 8(5): e65091 Link to article.  


Many sea level rise adaptation plans emphasize the protection of adjacent uplands to allow for inland salt marsh migration, but little empirical information exists on this process. Using aerial photos from 1930 and 2006 of Delaware Estuary coastal habitats in New Jersey, I documented the rate of coastal forest retreat and the rate of inland salt marsh migration across 101.1 km of undeveloped salt marsh and forest ecotone. Over this time, the amount of forest edge at this ecotone nearly doubled. In addition, the average amount of forest retreat was 141.2 m while the amount of salt marsh inland migration was 41.9 m. Variation in forest retreat within the study area was influenced by variation in slope. The lag between the amount of forest retreat and salt marsh migration is accounted for by the presence of Phragmites australis which occupies the forest and salt marsh ecotone. Phragmites expands from this edge into forest dieback areas, and the ability of salt marsh to move inland and displace Phragmites is likely influenced by salinity at both an estuary-wide scale and at the scale of local subwatersheds. Inland movement of salt marsh is lowest at lower salinity areas further away from the mouth of the estuary and closer to local heads of tide. These results allow for better prediction of salt marsh migration in estuarine landscapes and provide guidance for adaptation planners seeking to prioritize those places with the highest likelihood of inland salt marsh migration in the near-term.

Renfrew RB, Kim D, Perlut N, Smith JAM, Fox J, Marra PP (2013) 9(8):1008-1019. Phenological matching across hemispheres in a long-distance migratory bird. Diversity and DistributionsPDF  


In the Northern Hemisphere, bird migration from the tropic to the temperate zone in spring is thought to proceed at a rate determined in large part by local phenology. In contrast, little is understood about where birds go or the factors that determine why they move or where they stop during the post-breeding period.Location Study sites were in Oregon, Nebraska and Vermont, and location data we collected extend south to Argentina. We deployed light-level geolocators on individual Bobolinks from three populations across the breeding range and compare their southbound movement phenology to austral greening as indicated by the Normalized Difference Vegetation Index. Bobolinks from all breeding populations synchronously arrived and remained for up to several weeks in two sequential, small non-breeding areas that were separated by thousands of kilometres, before staging for pre-alternate moult. Similar to the migration patterns of birds to northern breeding areas, movements into the Southern Hemisphere corresponded to increasing primary productivity.Main conclusions Our findings suggest that the Bobolink’s southbound migration is broadly constrained by resource availability, and its non-breeding distribution has been shaped by the seasonal phenology of grasslands in both time and space. This is the first documentation of individual birds from across a continental breeding range exhibiting phenological matching during their post-breeding southward migration. Known conservation threats overlap temporally and spatially with large concentrations of Bobolinks, and should be closely examined. We emphasize the need to consider how individuals move and interact with their environment throughout their annual cycle and over hemispheric scales.

Larson KW, Smith JAM, Merker SA, Reitsma LR (2013) Plasticity in the Swainson’s Thrush (Catharus ustulatus) First Pre-basic Molt. North American Bird Bander. 38(1):28-30. PDF

Smith JAM, Reitsma LR, Marra PP (2011) Influence of moisture and food supply on the movement dynamics of a nonbreeding migratory bird in a seasonal landscape. The Auk. 128(1):43-52. PDF Article summary @ Smithsonian Migratory Bird Center  



We radiotracked Northern Waterthrushes (Parkesia noveboracensis) in four habitats in Puerto Rico during two winters (i.e., January–April) in 2003 and 2004 to determine the ecological determinants of diurnal space use and overwinter site persistence in this species. The majority of birds (69%) were sedentary and used a contiguous area within a single habitat over the winter period. A smaller percentage (31%) initially used a contiguous area within a single habitat but then permanently moved from that area to another disjunct location (mean = 418 m). Most of these movements were out of the two habitats (dry forest and Black Mangrove) that became the driest from January to mid-March and into wetter mangrove areas. The primary determinants of movement probability were moisture and food availability on each bird’s home range. Foraging areas of birds that eventually moved were drier and had lower food availability than areas used by site-persistent individuals. The sites that these itinerant birds moved to were wetter and had higher food availability, which suggests that individuals moved in response to changing resources. Our results (1) indicate that habitats used by this species differ in suitability and (2) support previous findings that turnover rates within a habitat could serve as an indicator of habitat quality. The ability to predict behavioral responses of individuals to habitat conditions that vary across space and time is essential for understanding individual and population responses to habitat loss and the effects of a changing climate in the New World tropics.

Smith JAM, Reitsma LR,Marra PP (2011) Multiple space use strategies and their divergent consequences in a nonbreeding migratory songbird. The Auk. 128(1):53-60. PDF Article summary@ Smithsonian Migratory Bird Center  



We investigated the relationships among space-use patterns, home-range attributes, and individual characteristics to determine the consequences of different space-use strategies for the overwinter physical condition of Northern Waterthrushes (Parkesia noveboracensis). We have elsewhere demonstrated that heterogeneity in food availability drives the movement decisions of site-persistent and itinerant individuals during the nonbreeding period. Here, we show that intraspecific competition played an important role in determining where individuals initially and eventually settled. Territoriality, characterized by aggression, sitepersistence, and exclusive home ranges, was more often found in males. Territorial birds gained mass over the winter, whereas birds that made midseason home-range shifts or that had home ranges with high intraspecific overlap tended to lose mass over the winter. The benefits associated with territoriality may be the result of maintaining higher-quality territories that were both wetter and had higher food availability than less exclusive home ranges. Our results suggest that despotism in the form of territoriality drives patterns of habitat occupancy, and in this system, high-quality habitat appears to be limiting for the Northern Waterthrush. This may have long-term consequences for the success of individual birds, because continued destruction of naturally limited habitats such as coastal mangroves, and predictions of a drying climate on wintering areas, have the potential to severely affect populations.

Smith JAM, Reitsma LR, Marra PP (2010) Moisture as a determinant of habitat quality for a nonbreeding neotropical migratory songbird. Ecology. 91:2874-2882. PDF Article summary@ Smithsonian Migratory Bird Center Listed as one of the Nature Conservancy’s Top 100 publications between 2001-2010.  



Identifying the determinants of habitat quality for a species is essential for understanding how populations are limited and regulated. Spatiotemporal variation in moisture and its influence on food availability may drive patterns of habitat occupancy and demographic outcomes. Nonbreeding migratory birds in the neotropics occupy a range of habitat types that vary with respect to moisture. Using carbon isotopes and a satellite-derived measure of habitat moisture, we identified a moisture gradient across home ranges of radiotracked Northern Waterthrush (Seiurus noveboracensis). We used this gradient to classify habitat types and to examine whether habitat moisture correlates with overwinter mass change and spring departure schedules of Northern Waterthrush over the late-winter dry season in the tropics. The two independent indicators of moisture revealed similar gradients that were directly proportional to body mass change as the dry season progressed. Birds occupying drier habitats declined in body mass over the study period, while those occupying wetter habitats increased in body mass. Regardless of habitat, birds lost an average of 7.6% of their mass at night, and mass recovery during the day trended lower in dry compared with wet habitats.This suggests that daily incremental shortfalls in mass recovery can lead to considerable season-long declines in body mass. These patterns resulted in consequences for the premigratory period, with birds occupying drier habitats having a delayed rate of fat deposition compared with those in wet habitats. Taken together with the finding that males, which are significantly larger than females, are also in better condition than females regardless of habitat suggests that high-quality habitats may be limited and that there may be competition for them. The habitat-linked variation in performance we observed suggests that habitat limitation could impact individual and population-level processes both during and in subsequent periods of the annual cycle. The linkage between moisture and habitat quality for a migratory bird indicates that the availability of high-quality habitats is dynamic due to variation in precipitation among seasons and years. Understanding this link is critical for ascertaining the impact of future climate change, particularly in the Caribbean basin, where a much drier future is predicted.

Smith JAM, Reitsma LR, Rockwood LR, Marra PP (2008) Roosting behavior of a neotropical  migrant songbird, the northern waterthrush, during the non-breeding season. Journal of Avian Biology.  39:460-465. PDF  Article summary@ Smithsonian Migratory Bird Center


Several species of Nearctic-Neotropical migratory songbirds appear to form roosting aggregations while on their wintering grounds but little is understood about the ecology of this behavior. We studied roosting behavior and patterns of roost habitat selection in the northern waterthrush Seiurus noveboracensis, during three winter years (2002-2004) in Puerto Rico using radio telemetry. Overall, red mangrove was selected for roosting disproportionately to its availability. Regardless of diurnal habitat used, 87% (n=86) of northern waterthrush selected dense stands of coastal red mangrove for roost sites. Individuals traveled up to 2 km to access roost sites in this habitat on a daily basis. The majority (8 of 14) of individuals roosted alone, while others roosted in loose aggregations near communal roosts of gray kingbirds Tyrannus dominicensis. Patterns of roost site selection did not vary by sex. Individuals showing aggressive response to playback during the day, however, selected roost sites significantly closer to the coast. Several additional migratory and resident bird species also used red mangrove for night-time roosting habitat. Red mangrove may be a critical nocturnal roosting habitat for bird populations that live in proximity to coastal areas in the Neotropics. The benefits of nocturnal roosting behavior as well as why individuals appear to select red mangrove remain poorly understood.


Niles L J, Smith JAM, Daly DF, Dillingham T. Shadel W, Dey A, Danihel MS, Hafner S, Wheeler D (2013) Restoration of horseshoe crab and migratory shorebird habitat on five Delaware Bay beaches damaged by Superstorm Sandy. PDF

Anderson MG, Smith JAM, Wilson BD (2011) Benthic habitats of the Delaware Bay. Report submitted to the National Fish and Wildlife Foundation by the Nature Conservancy. PDF

Smith JAM and Katkowski M (2011) Delaware Bay salt marsh condition assessment. In Delaware River Basin Priority Conservation Areas and Recommended Conservation Strategies. Report submitted to the National Fish and Wildlife Foundation by the Nature Conservancy.

Smith JAM and Kapatulik N (2011) Population estimation for Northeastern Beach Tiger Beetles at Monomoy NWR (2006-2010) and recommendations for modifying surveys to monitor larger beetle populations. Report submitted to USFWS New England Field Office.

writing on the web

I’m a regular contributor to the Nature Conservancy’s Cool Green Science blog.  See my posts here .  

I also have written a series of “bird of the month” posts at the Smithsonian Migratory Bird Center:

Ruby-throated Hummingbird: Flower Specialist.  Bird of the Month, Smithsonian Migratory Bird Center. November 2009.

Canada Goose: Good for the Goose.  Bird of the Month, Smithsonian Migratory Bird Center. September 2009.

Willet: Conservation Success Story.  Bird of the Month, Smithsonian Migratory Bird Center. August 2009.

Sedge Wren: A Mousy Mite.  Bird of the Month, Smithsonian Migratory Bird Center. July 2009.

Rock Pigeon: Noble in its Proper Place.  Bird of the Month, Smithsonian Migratory Bird Center. June 2008.

Northern Waterthrush: Swamp Thing.  Bird of the Month, Smithsonian Migratory Bird Center. June 2007.