David P. Craig

Colonial Waterbird Predation on Juvenile Salmonids Tagged with Passive Integrated Transponders in the Columbia River Estuary: Vulnerability of Different Salmonid Species, Stocks, and Rearing Types

Abstract Passive integrated transponder (PIT) tags implanted in Columbia River basin juvenile salmonids Oncorhyncus spp. were recovered from breeding colonies of Caspian terns Sterna caspia and double-crested cormorants Phalacrocorax auritus on Rice Island, a dredge spoil island in the Columbia River estuary. Tags were recovered to assess the relative vulnerability of different salmonid species, stocks, and rearing types to avian predators. We detected 50,221 PIT tags at the two bird colonies, mostly from juvenile chinook salmon O. tshawytscha and steelhead O. mykiss raised in hatcheries; 72% of the total tags were from the tern colony and 28% from the cormorant colony. Tagged steelhead smolts were more vulnerable to predation by both bird species than were yearling chinook salmon. More than 15% of PIT tags from steelhead smolts that were available in the estuary in 1998 were detected at the bird colonies compared with 2% of PIT tags from yearling chinook salmon. The greater vulnerability of steelhead may...

Colony Size and Diet Composition of Piscivorous Waterbirds on the Lower Columbia River: Implications for Losses of Juvenile Salmonids to Avian Predation

Abstract We investigated colony size and diet composition of piscivorous waterbirds (gulls, terns, and cormorants) nesting on the lower Columbia River from the mouth (river km 0) to the head of McNary Pool (river km 553) in 1997 and 1998. The study was prompted by concern that avian predation might constitute a significant source of mortality to juvenile salmonids Oncorhynchus spp. during out-migration. The diet of California gulls Larus californicus and ring-billed gulls L. delawarensis nesting in colonies above The Dalles Dam (river km 308) included few fish and very few juvenile salmonids. The sole exception was a small colony of California gulls in which salmonids accounted for 15% (by mass) of the diet. Juvenile salmonids were, however, an important component of the diet of colonial waterbirds nesting in the Columbia River estuary. On Rice Island (river km 34), salmonids accounted for 74% (by mass) of the diet of Caspian terns Sterna caspia, 46% for double-crested cormorants Phalacrocorax auritus, an...

Lasting recognition of threatening people by wild American crows

While many domestic and laboratory animals recognize familiar humans, such ability in wild animals is only anecdotally known. Here we demonstrate experimentally that a cognitively advanced, social bird, the American crow, Corvus brachyrhynchos, quickly and accurately learns to recognize the face of a dangerous person and continues to do so for at least 2.7 years. We exposed wild crows to a novel ‘dangerous face’ by wearing a unique face mask as we trapped, banded and released 7–15 birds at five sites near Seattle, WA, U.S.A. After trapping, crows consistently used harsh vocalizations to scold and mob people of different sizes, ages, genders and walking gaits who wore the dangerous mask, even when they were in crowds. In contrast, prior to trapping, few crows scolded people who wore the dangerous mask. Furthermore, after trapping, few crows scolded trappers who wore no mask or who wore a mask that had not been worn during trapping. In a fully crossed, balanced experiment in which each site had a unique trapping (dangerous) mask and five neutral masks, crows scolded and mobbed a mask more when it was the dangerous mask at that site than when it was a neutral mask at another site. When simultaneously presented with a person in the dangerous mask and a person in the neutral mask, crows typically ignored the neutral mask and followed and scolded the person wearing the dangerous mask. Risky, aggressive scolding by crows was sensitive to variable costs across study sites; aggression was less where people persecuted crows most. We suggest that conditioned and observational learning of specific threats may allow local bird behaviours to include aversions to individual people.

Effects of colony relocation on diet and productivity of Caspian terns

We investigated the efficacy of management to reduce the impact of Caspian tern (Sterna caspia) predation on survival of juvenile salmonids (Oncorhynchus spp.) in the Columbia River estuary. Resource managers sought to relocate approximately 9,000 pairs of terns nesting on Rice Island (river km 34) to East Sand Island (river km 8), where terns were expected to prey on fewer juvenile salmonids. Efforts to attract terns to nest on East Sand Island included creation of nesting habitat, use of social attraction techniques, and predator control, with concurrent efforts to discourage terns from nesting on Rice Island. This approach was successful in completely relocating the tern colony from Rice Island to East Sand Island by the third breeding season. Juvenile salmonids decreased and marine forage fishes (i.e., herring, sardine, anchovy, smelt, surfperch, Pacific sand lance) increased in the diet of Caspian terns nesting on East Sand Island, compared with terns nesting on Rice Island. During 1999 and 2000, the diet of terns nesting on Rice Island consisted of 77% and 90% juvenile salmonids, respectively, while during 1999, 2000, and 2001, the diet of terns nesting on East Sand Island consisted of 46%, 47%, and 33% juvenile salmonids, respectively. Nesting success of Caspian terns was consistently and substantially higher on East Sand Island than on Rice Island. These results indicate that relocating the Caspian tern colony was an effective management action for reducing predation on juvenile salmonids without harm to the population of breeding terns, at least in the short term. The success of this management approach largely was a consequence of the nesting and foraging ecology of Caspian terns: the species shifts breeding colony sites frequently in response to changing habitats, and the species is a generalist forager, preying on the most available forage fish near the colony.

Habitat Relationships Among Grasshoppers (Orthoptera:Acrididae) at the Western Limit of the Great Plains in Colorado

Abstract We measured grasshopper densities on 66 shortgrass, mixed grass, tallgrass and hayfield plots on Boulder, Colorado, open space in 1995–1996. Grasshoppers as a group, and most species individually, were more abundant on relatively sparse short and mixed grass plots than on lusher hayfields and tallgrass plots—a result consistent with the hypothesis that most species require warm and sunny open ground for survival and reproduction. Bandwinged grasshoppers (Oedipodinae) were particularly associated with open ground in shortgrass vegetation, whereas spur-throated grasshoppers (Melanoplinae) were most abundant in mixed grass plots with a high percentage of forb vs. graminoid cover. Slant-faced grasshoppers (Gomphocerinae) were the most uniformly distributed among habitats, but were generally associated with plots including relatively high proportions of grass vs. forb cover. While 20 of the 25 most common grasshopper species on Boulder open space occurred in all four grassland types, each habitat was dominated by a distinctive set of species. However, numerically dominant grasshoppers on short, mixed and tallgrass plots only loosely resembled groups of dominant species in the same habitats elsewhere on the Great Plains. While most Great Plains grasshoppers are widely distributed, they are apparently numerically responsive to combinations of environmental conditions expressed at local scales. Common species of grasshoppers on Boulder open space in 1995–1996 were the same as those collected in the region in the 1950s. Our results suggest these protected grasslands, although invaded by alien vegetation and fragmented by suburbanization, are still effectively conserving this particular insect group.

REDISTRIBUTION AND GROWTH OF THE CASPIAN TERN POPULATION IN THE PACIFIC COAST REGION OF NORTH AMERICA, 1981–2000

Abstract We examined nesting distribution and demography of the Pacific Coast population of Caspian Terns (Sterna caspia) using breeding records and band recoveries spanning two decades since the first population assessment. Since 1980, population size has more than doubled to about 12 900 pairs, yet the proportion of the population nesting at inland (18%) versus coastal sites (82%) has remained constant. Although the breeding range of the Pacific Coast population has expanded northward into Alaska and farther south in Mexico, there was no net latitudinal shift in the distribution of breeding pairs or new colonies. The distribution of breeding birds among areas changed dramatically, however, with 69% of breeding terns now nesting in Oregon (primarily in the Columbia River estuary) versus 4% during the late 1970s. During the past 20 years, there has continued to be a greater proportion of Caspian Terns breeding at anthropogenic sites compared to natural sites. Estimated annual survival rates for hatch-year and after-third-year birds during 1981– 1998 were greater than during 1955–1980, consistent with the higher rate of population increase in recent decades. Fecundity required to maintain a stable population (λ = 1) was estimated at 0.32–0.74 fledglings pair−1, depending on band recovery probabilities for subadults. Caspian Terns readily moved among breeding sites and rapidly colonized new areas; however, a greater concentration of breeding Caspian Terns among fewer colonies in response to anthropogenic factors is an important conservation concern for this species. Redistribución y Crecimiento de la Población de Sterna caspia en la Región de la Costa Pacífica de América del Norte entre 1981 y 2000 Resumen. Se examinó la distribución de anidamientos y la demografía de la población de Sterna caspia en la costa del Pacífico usando registros reproductivos y anillos recobrados de aves marcadas durante dos décadas desde la primera evaluación poblacional. Desde 1980 el tamaño poblacional se duplicó a 12 900 parejas, aunque la proporción de la población anidando en la zona interior (18%) versus la zona costera (82%) permaneció constante. A pesar de que el rango reproductivo de la población costera del Pacífico se expandió hacia el norte llegando a Alaska y hacia el sur hasta México, no hubo un cambio latitudinal neto en la distribución de parejas reproductivas o de nuevas colonias. Sin embargo, la distribución de aves reproductivas entre las áreas cambió dramáticamente, con un 69% de los individuos reproductivos de Sterna caspia anidando ahora en Oregón (principalmente en el estuario del Río Columbia) comparado con un 4% a fines de la década del 70. Durante los últimos 20 años continuó habiendo una mayor proporción de individuos de Sterna caspia anidando en sitios con actividad antropogénica en comparación con áreas naturales. Las tasas de supervivencia anual para aves con menos de un año y aves con más de tres años fueron mayores durante 1981–1998 que durante 1955–1980, lo que es consistente con una mayor tasa de crecimiento poblacional en décadas recientes. La fecundidad requerida para mantener estable la población (λ = 1) se estimó en 0.32–0.74 volantones producidos por pareja, dependiendo de la probabilidad de recuperación de anillos en aves subadultas. Sterna caspia es capaz de moverse entre sitios reproductivos y coloniza nuevas áreas rápidamente. No obstante, una mayor concentración de individuos reproductivos de Sterna caspia en unas pocas colonias, como respuesta a factores antropogénicos, es una importante preocupación para la conservación de esta especie.

Digiscoping Vouchers for Diet Studies in Bill-load Holding Birds

Abstract We conducted an observer-based diet study of Caspian Terns (Sterna caspia) incorporating digiscoping to collect digital photographic vouchers of fish. Observer-based diet studies pose several problems, ranging from differential experience and abilities of observers to the lack of vouchers for confirming identification. One solution to these problems is to recover fish either directly from birds (i.e., trapping, shooting) or ones dropped on the colony. This may not, however, be desirable or achieve adequate sample sizes. Some species are difficult to capture or methods may cause significant disturbance and/or nest abandonment. To overcome these problems, we used a relatively inexpensive new photographic technique known as digiscoping. By holding a high-resolution point-and-shoot digital camera up to the eyepiece of a spotting scope or pair of binoculars, we could take digital photographic vouchers of fish as terns brought them into the colony. During the study, we made 16,423 observations, identifying 92% of the fish to the family (3%), genus (15%), or species (74%) level. We supported these observations with over 2,500 digital photograph vouchers. Vouchers confirmed identification of all fish taxa and allowed for later identification, by us or qualified fisheries biologists, of several species unidentifiable in the field. The ability to have independent experts confirm observations and identify previously unidentifiable observations greatly expanded our understanding of the range of fish taken by Caspian Terns.

Avian Predation on Juvenile Salmonids in the Lower Columbia River: 1997 Annual Report.

The authors initiated a field study in 1997 to assess the impacts of fish-eating colonial waterbirds (i.e., terns, cormorants, and gulls) on the survival of juvenile salmonids in the lower Columbia River. Here the authors present results from the 1998 breeding season, the second field season of work on this project. The research objectives in 1998 were to: (1) determine the location, size, nesting chronology, nesting success, and population trajectories of breeding colonies of fish-eating birds in the lower Columbia River; (2) determine diet composition of fish-eating birds, including taxonomic composition and energy content of various prey types; (3) estimate forage fish consumption rates, with special emphasis on juvenile salmonids, by breeding adults and their young; (4) determine the relative vulnerabilit2048 different groups of juvenile salmonids to bird predation; (5) identify foraging range, foraging strategies, and habitat utilization by piscivorous waterbirds; and (6) test the feasibility of various alternative methods for managing avian predation on juvenile salmonids and develop recommendations to reduce avian predation, if warranted by the results.

The development and lateralization of prey delivery in a bill load-holding bird

Laterality or the preferential use of one or the other side of the body is associated with differential brain activity and increased specialization of brain function. Right or left biases are widespread among vertebrates and have been documented among some birds. Bill load holding or the delivery of whole prey in a birds beak is common among terns (Charadriiformes) and many other birds. We recorded more than 2000 Caspian tern, Hydroprogne caspia, chick-feeding events for analysis of lateralization of prey within the bills of adult birds, size and shape of prey items delivered to chicks in relation to chick age, and the development of prey-handling skills among chicks. No initial lateralization of prey head position was found as adults flew into the colony, but head position of successful feeds was found to be significantly lateralized with a bias to the right side. Adults switched prey orientation significantly more often from left to right than from right to left without dropping the prey item, suggesting an adult bias. Adults appeared to adjust the length but not the shape of prey delivered according to chick age. Ability of chicks to manipulate prey items increased with age. Lateralization was most obvious in the first week of a terns life, and adults modified their delivery behaviour to respond to these changes. Bill load-holding birds are excellent subjects to study lateralization of feeding behaviour in the wild and they may allow integration of lateralization with developmental changes.

Migratory Connectivity of North American Caspian Tern (Hydroprogne caspia) Populations

Abstract. Migratory connectivity of Caspian Terns (Hydroprogne caspia) was investigated using individuals marked in North America between 1922 and 2015. The results support recent genetic work describing three breeding regions (Pacific, Great Lakes, and Central Canada). Further, our results show strong migratory connectivity of Pacific breeders to wintering regions in central and western Mexico, and connectivity of Great Lakes breeders to wintering regions in the Gulf of Mexico and Caribbean. This integrated picture of demographic connectivity throughout North America should help in planning more effective management of the species.