No abstract

Weekly counts of western Atlantic red knots (Calidris canutus rufa) at their Delaware Bay migration stopover site have suggested a major decline since the 1980s. We estimated red knot spring passage population size in the New Jersey Coast‐Delaware Bay region (DENJ; 2004 and 2006) and Virginia (VA; 2006 and 2007), USA, by correcting weekly aerial counts for mean daily residence probability between counts in a Monte‐Carlo simulation. We used daily telemetry relocations in mark‐resight models to estimate mean daily residence probability. Average daily residence probability was approximately 1.0 in mid‐May, 0.96–0.97 in the week of 22 May, and 0.64–0.77 after May 28 in DENJ in 2004 and 2006 and in VA in 2006. Average daily residency was approximately 0.88 in VA in 2007 from 22 May to 5 June. No birds moved from VA to DENJ in 2006 and only 2 birds (5.5%) moved in 2007. Stopover population sizes (±SE) in DENJ were 17,108 ± 1,322 in 2004 and 19,555 ± 831 in 2006, and in VA were 7,224 ± 389 in 2006 and 8,332 ± 718 in 2007, significantly greater than peak aerial counts. Years with similar peak counts had different residence probabilities; hence, adjustments for turnover should be used in the future to assess annual population changes. Our results suggest that VA can support a significant portion of this red knot subspecies during migration in at least some years. Managing red knots for recovery should entail improving our understanding of the use of other Atlantic Coast sites and protecting key coastal habitat from disturbance and development.

Abstract-Automatic land cover classification maps were developed from Airborne Hyperspectral Scanner (HyMAP) imagery acquired May 8, 2000 over Smith Island, VA, a barrier island in the Virginia Coast Reserve. Both unsupervised and supervised classification approaches were used to create these products to evaluate relative merits and to develop models that would be useful to natural resource managers at higher spatial resolution than has been available previously. Ground surveys made by us in late October and early December 2000 and again in May, August, and October 2001 and May 2002 provided ground truth data for 20 land cover types. Locations of pure land cover types recorded with global positioning system (GPS) data from these surveys were used to extract spectral end-members for training and testing supervised land cover classification models. Unsupervised exploratory models were also developed using spatial-spectral windows and projection pursuit (PP), a class of algorithms suitable for extracting multimodal views of the data. PP projections were clustered by ISODATA to produce an unsupervised classification. Supervised models, which relied on the GPS data, used only spectral inputs because for some categories in particular areas, labeled data consisted of isolated single-pixel waypoints. Both approaches to the classification problem produced consistent results for some categories such as Spartina alterniflora, although there were differences for other categories. Initial models for supervised classification based on 112 HyMAP spectra, labeled in ground surveys, obtained reasonably consistent results for many of the dominant categories, with a few exceptions. For an invasive plant species, Phragmites australis, a particular concern of natural resource managers, this approach initially had an excessively high false-alarm rate. Increasing the number of spectral training samples by an order of magnitude and making concomitant improvements to the georectification led to dramatic improvements in this and other categories. The unsupervised spatial-spectral approach also found a cluster closely associated with Phragmites patches near the thicket boundary, but this approach did not identify the exposed are compared against HyMAP image spectra at model-predicted pixels and at validated GPS waypoints.Index Terms-Barrier islands, hyperspectral, in situ spectrometry, invasive plant species, land cover classification, neural networks, principle component analysis, projection pursuit, supervised classification, unsupervised classification.

For most shorebird species, our understanding of the basic limiting factors and when or where they operate during the annual cycle is currently inadequate to either understand ongoing declines or effectively allocate conservation resources for recovery. Whimbrels (Numenius phaeopus) exhibit delayed recruitment and have low fecundity, and populations with such life-history traits are often vulnerable to increases in adult mortality. We tracked 33 adult Whimbrels with satellite transmitters for 12,802 bird-days to investigate patterns in survival and recorded 16 probable and 5 confirmed mortalities. We used Cox’s proportional hazards model to estimate daily hazard rates by season and a Kaplan-Meier product limit estimator to estimate monthly survival. Daily hazard rates varied by season and were 5 times higher during migratory periods (fall and spring migration) compared to stationary periods (winter and breeding). Estimated annualized survivorship was 0.54 ± 0.21 (SE) and on the lower end of the range of 0.8–0.9 believed to be required to maintain a stable population. More than half of the mortality recorded during the study occurred during the fall hunting season and within the last remaining area throughout the Western Hemisphere where significant legal and illegal hunting occurs. One-third of mortality occurred during spring migration either within terminal staging sites or as birds made final movements to breeding grounds. Survival during the migratory periods may have been influenced by the use of transmitters.

Numbers of Western Atlantic Red Knots (Calidris canutus rufa (A. Wilson, 1813)) have declined since 1980, with a sustained downward trend observed after 1998. Because the reproductive output of a closely related Eurasian subspecies (Calidris canutus islandica (L., 1767)) is known to be low when lemming numbers are low, and because lemming cycles in Fennoscandia were recently interrupted, we investigated the relationship between the rodent cycle in arctic Canada and numbers of C. c. rufa migrating through the United States. Shooting records from Cape Cod in the 1800s and Red Knot counts on the Delaware Bay from 1986 to 1998 cycled with 4-year periods. Annual peaks in numbers of Red Knots stopping in the Delaware Bay in 1986–1998 occurred 2 years after arctic rodent peaks more often than expected at random. The results suggest that the reproductive output of C. c. rufa was linked to the rodent cycle before the Red Knot decline. There is no evidence that such a link existed after 1998. These findings are consistent with the hypothesis that an interruption of the rodent cycle in Red Knot habitat could have been a driver in the recent Red Knot decline. Field studies in the Arctic are needed to further investigate this hypothesis.