Lawrence J. Niles

Rapid population decline in red knots: fitness consequences of decreased refuelling rates and late arrival in Delaware Bay

Most populations of migrant shorebirds around the world are in serious decline, suggesting that vital condition–dependent rates such as fecundity and annual survival are being affected globally. A striking example is the red knot (Calidris canutus rufa) population wintering in Tierra del Fuego, which undertakes marathon 30 000 km hemispheric migrations annually. In spring, migrant birds forage voraciously on horseshoe crab eggs in Delaware Bay in the eastern USA before departing to breed in Arctic polar deserts. From 1997 to 2002 an increasing proportion of knots failed to reach threshold departure masses of 180–200 g, possibly because of later arrival in the Bay and food shortage from concurrent over–harvesting of crabs. Reduced nutrient storage, especially in late–arriving birds, possibly combined with reduced sizes of intestine and liver during refuelling, had severe fitness consequences for adult survival and recruitment of young in 2000–2002. From 1997 to 2002 known survivors in Delaware Bay were heavier at initial capture than birds never seen again, annual survival of adults decreased by 37% between May 2000 and May 2001, and the number of second–year birds in wintering flocks declined by 47%. Population size in Tierra del Fuego declined alarmingly from 51 000 to 27 000 in 2000–2002, seriously threatening the viability of this subspecies. Demographic modelling predicts imminent endangerment and an increased risk of extinction of the subspecies without urgent risk–averse management.

Abundance and distribution of migrant shorebirds in Delaware Bay

Northbound migrant shorebirds (Charadridae and Scolopacidae) were surveyed weekly by air on Delaware Bay beaches on the Atlantic coast of North America in May-June 1986 through 1992. The single day peak count occurred between 26-30 May when an average of more than 216,000 birds was counted. The most abundant species were Semipalmated Sandpiper (Calidris pusilla), Ruddy Turnstone (Arenaria interpres), Red Knot (Calidris canutus) and Sanderling (Calidris alba). Our surveys documented high hemispheric counts for each of these species, and established Delaware Bay as the most important spring stopover in the eastern U.S. for these shorebirds. Counts of Sanderlings and Semipalmated Sandpipers declined significantly over the seven years; no trends for other species were detected. Differences among species in distribution along bay beaches were attributable partly to habitat factors. We suggest that a thorough understanding of shorebird abundance and habitat use in Delaware Bay is necessary to develop a conservation strategy for regulatory protection and conservation of migrant shorebirds using this area.

Is the occurrence of avian influenza virus in Charadriiformes species and location dependent

Birds in the order Charadriiformes were sampled at multiple sites in the eastern half of the continental USA, as well as at Argentina, Chile, and Bermuda, during 1999–2005, and tested for avian influenza virus (AIV). Of more than 9,400 birds sampled, AIV virus was isolated from 290 birds. Although Ruddy Turnstones (Arenaria interpres) comprised just 25% of birds sampled, they accounted for 87% of isolates. Only eight AIV isolations were made from birds at four locations outside of the Delaware Bay, USA, region; six of these were from gulls (Laridae). At Delaware Bay, AIV isolations were predominated by hemagglutinin (HA) subtype H10, but subtype diversity varied each year. These results suggest that AIV infection among shorebirds (Scolopacidae) may be localized, species specific, and highly variable in relation to AIV subtype diversity.

Importance of beach, mudflat and marsh habitats to migrant shorebirds on Delaware Bay

Shorebirds migrate over long distances from breeding to wintering grounds, stopping at a few bays and estuaries to refuel. Most information on migration of shorebirds concentrates on population dynamics and foraging behavior on intertidal habitats. We studied the behavior of shorebirds on mudflats, beaches and marshes on Delaware Bay to understand how they use different habitats. Dense flocks of shorebirds concentrated on a tidal mudflat, but shorebirds used all the habitats, including several marshes. The overall percent of shorebirds feeding ranged from 34% (open beach), and 59-63% (tidal and nontidal marshes), to 80% (tidal mudflat). Variations in the percentage of shorebirds engaged in feeding, resting and other behaviors depended on location, date, time, tide and species. ,4 higher percentage of shorebirds fed during the middle of migration, in early to mid-morning, and during low and rising tides than at other times. Some shorebirds fed on the marshes and mudflats during all tidal states, but none fed on beaches at high tide (beaches were too narrow). Within each habitat, the highest percentage of shorebirds engaged in foraging during low tide (marshes) or rising tides (mudflats and beaches). Using the percentage of shorebirds engaged &foraging as an indication of foraging value for each habitat type within the landscape, we concluded that a mosaic of habitat types ranging from mudflats to high marshes is essential to sustain the high populations of shorebirds that use Delaware Bay during spring migration. Copyright

Ecotourism and birds in coastal New Jersey: contrasting responses of birds, tourists, and managers

People of diverse cultures appreciate and observe wildlife. With the increase in the importance of economic, social, and aesthetic, values of wildlife comes the responsibility for wise management and use of these resources to ensure biodiversity and the continued wellbeing of the populations. We describe several ways in which ecotourists affect the behaviour, reproductive success, and population levels, of breeding and migratory birds in New Jersey — a heavily industrialized, coastal US state with a dense human population. We use several case-studies to illustrate the effects of ecotourists on birds: heronries, breeding Least Terns ( Sterna antillarum ), foraging Piping Plovers ( Charadrius melodus ) during the breeding season, migrant shorebirds and gulls at Caven Point and Delaware Bay, and migrant hawks at Cape May.

DECLINES IN WINTERING POPULATIONS OF RED KNOTS IN SOUTHERN SOUTH AMERICA

Abstract Surveys of the North American race of the Red Knot (Calidris canutus rufa) on its main wintering areas on the coasts of Patagonia and Tierra del Fuego (Argentina and Chile) showed a dramatic decline in the wintering population: totals in 2003 were about 30 000 compared to 67 500 in the mid-1980s. Numbers at the principal wintering site, Bahia Lomas, fell by approximately 50%, from 45 300 in 2000 to 22 000–25 000 in 2002–2003. Numbers at peripheral sites on the coast of Patagonia declined dramatically, decreasing 98% compared to numbers in the mid-1980s. The results showed that declines at core sites did not result from birds moving to other places within the known wintering (or other) areas, but reflected a general population decline, with most birds now restricted to key sites in Tierra del Fuego. This phenomenon may explain why long-term declines noted elsewhere have only recently become apparent at key wintering areas. Possible reasons for the declines are discussed. Banding studies in Delaware Bay have shown that in recent years an increasing proportion of Red Knots is unable to gain sufficient weight for migration to the breeding grounds. This is likely due to reductions in their main food resource, eggs of the horseshoe crab Limulus polyphemus. The resulting increase in mortality could account for the magnitude and severity of the declines we observed. Disminuciones en las Poblaciones Invernantes de Calidris canutus rufa en el Sur de Sur América Resumen. Censos de la raza norteamericana de Calidris canutus (rufa) en sus áreas de invernada principales en las costas de la Patagonia y Tierra del Fuego (Argentina y Chile) mostraron una disminución dramática en la población invernante. Los totales en 2003 fueron aproximadamente 30 000, comparados con 67 500 a mediados de los años 80. Los números en el sitio principal de invernada (Bahía Lomas) decayeron en aproximadamente un 50%, de 45 300 en 2000 a 22 000–25 000 en 2002–2003. Los números en sitios periféricos en la costa de Patagonia declinaron dramáticamente, en un 98% en comparación con los números de mediados de los ochenta. Los resultados mostraron que las disminuciones en los sitios núcleo no fueron el resultado de que las aves se movieran a otros sitios dentro del rango invernal conocido, o a otras áreas. En cambio, reflejaron una disminución general de la población; la mayoría de las aves están ahora restringidas a sitios claves en Tierra del Fuego. Este fenómeno podría explicar por qué las disminuciones poblacionales de largo plazo detectadas en otros lugares sólo se han hecho aparentes ahora en las áreas claves de invernada. Se discuten las posibles causas de las disminuciones. Estudios de anillamiento en la bahía de Delaware han mostrado que en años recientes una mayor proporción de las aves es incapaz de incrementar su peso hasta los niveles necesarios para la migración hacia las áreas de invernada. Esto probablemente es debido a reducciones en su principal recurso alimenticio, los huevos de Limulus polyphemus. El incremento en mortalidad resultante podría explicar la magnitud y la severidad de las disminuciones poblacionales que observamos.

Effects of Horseshoe Crab Harvest in Delaware Bay on Red Knots: Are Harvest Restrictions Working?

Each May, red knots (Calidris canutus rufa) congregate in Delaware Bay during their northward migration to feed on horseshoe crab eggs (Limulus polyphemus) and refuel for breeding in the Arctic. During the 1990s, the Delaware Bay harvest of horseshoe crabs for bait increased 10-fold, leading to a more than 90% decline in the availability of their eggs for knots. The proportion of knots achieving weights of more than 180 grams by 26–28 May, their main departure period, dropped from 0.6–0.8 to 0.14–0.4 over 1997–2007. During the same period, the red knot population stopping in Delaware Bay declined by more than 75%, in part because the annual survival rate of adult knots wintering in Tierra del Fuego declined. Despite restrictions, the 2007 horseshoe crab harvest was still greater than the 1990 harvest, and no recovery of knots was detectable. We propose an adaptive management strategy with recovery goals and annual monitoring that, if adopted, will both allow red knot and horseshoe crab populations to recover and permit a sustainable harvest of horseshoe crabs.

The effect of human activities on migrant shorebirds: successful adaptive management

SUMMARY The effect of human disturbance on migrant birds is a conservation issue of international importance, as is determining if disruption has long-term population effects. Disruptions can occur during migration, wintering, breeding and foraging. Thousands of shorebirds migrate through Delaware Bay (Atlantic Coast of North America) in a four-week period each spring; this is the largest concentration of shorebirds in the continental USA. Ecotourists come to see them, creating the potential for disruption. Data available on shorebird/human interactions at a migratory stopover over a 20-year period were used to describe the interactions of shorebirds and people from 19822002 and examine trends in human disruptions and shorebird behaviour during this time. The rate of disruptions caused by people increased during the 1980s, declined slightly by the early 1990s, and declined sharply by 2002. The decline in human activity along the beach was directly related to the conservation efforts of the New Jersey Endangered and Nongame Species Program, New Jersey Audubon, and others interested in preserving the shorebirds. In the 1980s, birdwatchers concentrated on the beaches on which it was easy to walk and which had the highest shorebird counts, because there were no restrictions on human behaviour. During this time, the average disturbance duration was over 10min, regardless of the type of intruder, and shorebirds were often disruptedforover40minhr −1 .Eventhoughthenumber of disruptions declined over the study period, the percentage of shorebirds that flew away (and did not return within 10min) did not change during the 1980s, and increased in 2002. The average time that shorebirds were disrupted per hour by people declined during this period (mainly because there were fewer people on the beaches). The Endangered and Nongame Species Program placed signs on shorebird foraging beaches, restricted access, built viewing platforms to contain ecotourists, and eventually patrolled key beaches and issued summonses for infractions. These activities were so effective that only one bird watcher disturbed the birds in 2002. Education was also vital to encouraging local residents not to walk or fish along these beaches during the spring migratory stopover, and to keep their dogs on a leash. These data support the importance of actions on the part of state agencies and conservation organizations to limit disruptions to foraging shorebirds during critical migratory stopovers, a problem faced by shorebirds in many temperate regions of the world.

Prevalence of antibodies to type A influenza virus in wild avian species using two serologic assays

Serologic testing to detect antibodies to avian influenza (AI) virus has been an underused tool for the study of these viruses in wild bird populations, which traditionally has relied on virus isolation and reverse transcriptase-polymerase chain reaction (RT-PCR). In a preliminary study, a recently developed commercial blocking enzyme-linked immunosorbent assay (bELISA) had sensitivity and specificity estimates of 82% and 100%, respectively, for detection of antibodies to AI virus in multiple wild bird species after experimental infection. To further evaluate the efficacy of this commercial bELISA and the agar gel immunodiffusion (AGID) test for AI virus antibody detection in wild birds, we tested 2,249 serum samples collected from 62 wild bird species, representing 10 taxonomic orders. Overall, the bELISA detected 25.4% positive samples, whereas the AGID test detected 14.8%. At the species level, the bELISA detected as many or more positive serum samples than the AGID in all 62 avian species. The majority of positive samples, detected by both assays, were from species that use aquatic habitats, with the highest prevalence from species in the orders Anseriformes and Charadriiformes. Conversely, antibodies to AI virus were rarely detected in the terrestrial species. The serologic data yielded by both assays are consistent with the known epidemiology of AI virus in wild birds and published reports of host range based on virus isolation and RT-PCR. The results of this research are also consistent with the aforementioned study, which evaluated the performance of the bELISA and AGID test on experimental samples. Collectively, the data from these two studies indicate that the bELISA is a more sensitive serologic assay than the AGID test for detecting prior exposure to AI virus in wild birds. Based on these results, the bELISA is a reliable species-independent assay with potentially valuable applications for wild bird AI surveillance.

Habitat Choice, Disturbance, and Management of Foraging Shorebirds and Gulls at a Migratory Stopover

Abstract Habitat choice and interactions of foraging shorebirds and gulls were studied at a migratory stopover in Delaware Bay, New Jersey. Foraging, vigilance, aggressive behavior, and habitat choice of shorebirds were affected by the presence of gulls. There were significant differences in the time each species devoted to actively feeding; knots spent significantly less time foraging than did the other species. Birds congregated in the habitats where their foraging rates were the highest. When turnstones and laughing gulls fed in larger conspecific flocks, they had higher foraging times. Red knots were most aggressive toward laughing gulls, turnstones were most aggressive toward herring gulls, sanderlings were most aggressive toward turnstones, and semipalmated sandpipers were most aggressive toward knots. There were significant differences in habitat use: 1) Gulls and turnstones were more abundant along the tide line, 2) turnstones were more abundant on the upper beach, 3) semipalmated sandpipers and turnstones were more abundant on sandbars, 4) only gulls fed on the beach mud, and 5) laughing gulls and semipalmated sandpipers were more common along creeks than were the other species. Within 5 minutes of a human disturbance, gulls returned to predisturbance levels, while the shorebirds did not. Shorebirds responded most strongly to the presence of dogs than to other disturbances and did not return to beaches following a disturbance by a dog. These observations suggest that there may be some competition for foraging space among foraging species, especially between the shorebirds and the larger gulls, that human disturbance affects shore-birds more strongly than gulls, and that shorebirds and gulls use the habitats differently. The data can be used to manage human disturbance and to protect habitats where the shorebirds have the highest foraging rates, but the least exposure to gulls.