Cape May Research Articles

Bird–habitat relationships in jack pine boreal forests

We made counts of 42 bird species at 217 points in 44 jack pine Pinus banksiana stands in the boreal region of north-central Saskatchewan, Canada because of concerns about the impact of forestry on avian biodiversity. Using multivariate analyses we describe the main patterns of bird species abundance and composition in relation to local habitat variables. According to canonical correspondence analysis (CCA), 17 of 43 explanatory variables accounted for significant variation in the bird species matrix: stand age, tamarack Larix laricina canopy cover, percentage shrub Alnus glutinosa, canopy closure (6–30%), percentage herbs, maximum canopy height, percentage shrub Alnus viridis, percentage moss, percentage shrub Betula nana, minimum and mean shrub height, percentage litter, white birch Betula papyrifera canopy cover, white spruce Picea glauca canopy cover, mean canopy height, canopy closure (71–100%), and zero shrub canopy closure. Habitat and stand identity (clustering of sites within stands) explained 55.5% of the total variation; 16.3% was unique to habitat alone (29.4% of the total variance explained — TVE) and 17.2% (31.0% TVE) was shared with stand identity. Stand identity accounted for 22.0% (39.6% TVE) of the variation. Neotropical migrants associated with “overmature” mixed-wood stands included Cape May Dendroica tigrina, bay-breasted D. castanea and Tennessee Vermivora peregrina warblers. Conversely, orange-crowned V. celata, palm D. palmarum, and Nashville V. ruficapilla warblers were found in young stands. The presence of several Neotropical migrants was associated with mixed-wood attributes (ovenbird Seiurus aurocapillus with aspen, red-eyed vireo Vireo olivaceus with shrub alder, and Swainson’s thrush Catharus ustulatus with canopy white birch). Jack pine stands older than commercial rotation age must be maintained in a managed landscape because their bird communities differ from younger stands. Because of the limited avian diversity in pure jack pine stands, sufficient mixed-wood stands must be regenerated to sustain populations of characteristic bird species. We recommend that jack pine mixed-woods be managed using shelterwood or selective cuts, and that rotation age of some stands be increased. Without the extensive fires necessary for regeneration, cutting patterns at the landscape level should approximate natural disturbance patches both in size and frequency of disturbance.

Revising the convergence hypothesis of avian use of honeydew: evidence from Dominican subtropical dry forest

A honeydew‐producing scale insect (family Margarodidae, tribe Xylococcini, genus Stigmacoccus) was found associated with the tree Bursera simaruba in subtropical dry forests at elevations of 100–400 m on the south side of the Sierra de Bahoruco, Pedernales Province, Dominican Republic. At two study sites, 91% of Bursera trees supported locally dense populations of Margarodidae. Fifteen species of birds were observed foraging on the honeydew, but most observations were of the winter resident Cape May warbler (Dendroica tigrina) and black‐throated blue warbler (D. caerulescens), and the permanent resident bananaquit (Coereba flaveola) and black‐crowned palm tanager (Phaenicophilus palmarum). The Cape May warbler actively defended the honeydew resource but frequency of use of honeydew was influenced by the close presence of flowering agave and scale insect density. Data suggest that honeydew may be a critical component of the diet of this species especially during the late winter dry‐season. Hymenopteran insects also were observed feeding on honeydew, but rates of consumption did not approach that of avian species. The occurrence of this phenomenon in Dominican dry forest is discussed in light of the convergence hypothesis of bird use and defense of homopteran honeydew in which it is proposed that birds are able to maintain relationships with scale insects in moist, warm temperate forests because it is in these climates where ant abundance is low. We suggest that our observation of a well‐developed bird–homopteran system in classic subtropical dry forest supports the proposed mechanism of reduced competition with ants allowing bird use of honeydew, but we suggest that a broader array of especially insular habitats which may be relatively depauperate in terms of ants also can be expected to support bird–homopteran systems.

Patterns of Knemidokoptes jamaicensis (Acari: Knemidokoptidae) infestations among eight new avian hosts in the Dominican Republic.

The ectoparasitic mite Knemidokoptes jamaicensis Turk burrows into the cornified epithelium of the legs and feet of Passeriform birds and has been reported from 12 species of North American birds. Here we establish new host and distribution records for K. jamaicensis from eight species of birds from three habitats in the Dominican Republic. These species include Hispaniolan pewee (Contopus hispaniolensis Bryant), northern mockingbird (Mimus polyglottos L.), Cape May warbler (Dendoica tigrina Gmelin), prairie warbler (Dendroica discolor Vieillot), palm warbler (Dendroica palmarum Gmelin), green-tailed warbler (Microligea palustris Cory), black-crowned palm tanager (Phaenicophilus palmarum L.), and Greater Antillean bullfinch (Loxigilla violacea L.). Rates of infestation were as great as 18.2% but varied between species and habitats. Mites were far more common in the dry desert thorn scrub than they were in higher elevation and more moist habitats, despite the fact that many of the affected species had distributions that spanned multiple habitat types. Results suggest that the abundance of scaley-leg mites is controlled by the abundance of suitable host species and by specific ecological conditions that promote transmission.

ALGAE AS WATER QUALITY INDICATORS FOR A DYSTROPHIC POND

The physico‐chemical, bacteriological, and algal composition of R.U.Bi.S. Pond were studied since March 1999. The pond, located in Cape May County, NJ, is a dystrophic body of water, with high sediment:water ratio and organic matter content creating anoxic conditions during fall and early winter. Water quality indicators based on periphytic algae and water quality indices that are specific to R.U.Bi.S. Pond are being developed. Such indicators could be used for similar bodies of water and for the restorability of this dystrophic ecosystem integrity. Two sampling sites were studied. Samples were collected weekly, using a periphytometer, for seasonal analysis of succession. Samples for water chemistry, bacteriology, and periphytic algae were collected bi‐monthly. The predominant algal species found during summer ‘99 were Phormidium, Oscillatoria, Chlorella, and Eunotia. During fall ‘99, the predominant species were Oscillatoria and Phormidium. In winter, the community was dominated by Chlorella and Chlamydomonas. Species present year‐round were Nitzschia, Oedogonium, Eunotia, and Navicula. Data analysis indicated variations among the two sampling sites, with total cell counts and species diversity higher at the northern site. Algal cell counts, chlorphyll a concentrations, species diversity, and D.O. levels were greatest during summer. Biomass, hardness, HPCs and total organic carbon peaked during the fall. Nutrients, pH, and coliforms remained constant during the study period. The predominant algae found were pollution‐tolerant genera, categorizing the pond as highly dystrophic. Species diversity indices indicated that water quality decreased during the fall/winter months, with the southern site being more environmentally stressed than the northern site.

Influence of Ambient Flow around the Horseshoe Crab Limulus polyphemus on the Distribution and Orientation of Selected Epizoans

Cumulatively scored distributions of the slipper shell gastropodCrepidula sp., the sand-building polychaete wormSabellaria vulgaris, the calcareous meandering tubed polychaeteFilograna implexa, the barnacleSemibalanaus balanoides, and the lacy bryozoanSchizoporella sp. were mapped on a cm-square gridded silhouette of the prosoma, opisthosoma, and movable spines, and telson of the horseshoe crabLimulus polyphemus stranded on Reeds Beach, Cape May County, New Jersey in the Delaware Bay. Statistically tested and contoured epizoan frequencies for 81 males and 59 females revealed that slipper shells and agglutinated worm tubes are concentrated near the movable spines on the opisthosoma, but rare on recessed chilarial or opercular pleurites, the prosoma, and telson. Barnacles are disproportionately concentrated in entapophyseal pits on the opisthosoma and in the longitudinal furrows flanking the cardiac lobe of the prosoma. Bryozoans are concentrated near movable marginal spines of the opisthosoma, but also found on all areas of the prosoma, opisthosoma, and hinge area in between, as well as the telson. Different morphologic sites for their respective modal concentrations may result from competitive exclusion of bryozoans by barnacles. Genal angles have lower statistically predicted frequencies of bryozoans, barnacles, and sand worm tubes. Apertural openings of calcareous tubes are predominantly posteriorly oriented whereas the anterior magin of slipper shells are randomly oriented on the opisthosoma. Eschewing differential mortality, nonrandom distributions indicate possible: rugophilic (groove-seeking) larval settlement behavior for barnacles that preferred the recessed hinge area, longitudinal grooves, and pits; rheophilic (current-seeking) larval settlement behavior for the gastropods and tube-building polychaetes that filter feed in the eddies generated near the movable spines of the downcurrent-sloping opisthosoma; and geotactic (gravity-influenced) larval settlement or post-settlement migration to the vaulted crest (cardiac lobe). Deficiencies of protruding epizoic skeletons on the genal angles and anterior margin of the host may be due to removal by abrasion as the horseshoe crab plowed through sediment or shearing of the epizoans from the carapace substratum in strong currents or waves.

Offshore-onshore correlation of upper Pleistocene strata, New Jersey Coastal Plain to continental shelf and slope

High-resolution seismic reflection profiles (,1‐5 m resolution), including Geopulsee, Uniboome, minisparker, small air gun, and water gun sources, are used to trace the d 18 O stage 5 portion of the outcropping Cape May Formation across the shelf to the continental slope. The d 18 O stage 5/6 boundary identified at Ocean Drilling Project (ODP) Site 903 on the continental slope anchors the onshore-offshore seismic correlations. Above the d 18 O stage 5 sequence, there are distinguishable lowstand systems tracts (LST), transgressive systems tracts (TST) and highstand systems tracts (HST) that correlate with d 18 O stages 4 through 1. Atlantic Margin Coring Project (AMCOR) holes 6009, 6010, 6011, 6020, and 6021C provide age and paleoenvironmental indicators that agree with these correlations. The sub-arctic paleoenvironmental indicators in sequences of d 18 O stage 3 agree with the cooler temperatures and lower sea-level highstands of that time. Thicker d 18 O stage 3 and 4 sequences are preserved in the Paleo-Hudson River incised valley across the shelf. The expanded ice sheets during stage d 18 O 3 compared to d 18 O stages 1 and 5 probably increased sediment discharge in the Hudson River drainage system. q 2000 Elsevier Science B.V.

Rotated Bitmaps, a New Twist on an Old Idea

This paper describes some developments related to using bitmaps (64-bit integers using one bit for each square of the chessboard). In late 1994, after the ACM computer-chess event in Cape May, New Jersey, I decided to embark on a complete replacement

BRACKISH GROUNDWATER DESALINATION: A COMMUNITY'S SOLUTION TO WATER SUPPLY AND AQUIFER PROTECTION1

ABSTRACTThe City of Cape May, New Jersey, draws its primary water supply from the Cohansey Aquifer, a unit serving residential, community, and industrial users throughout the Coastal Plain. By the year 2000, projected population growth will impose a peak water demand beyond available supplies. In addition, regional over‐pumping threatens the Cohansey with saltwater intrusion, placing the city wells at risk by 1998. In the early‐to mid 1990s, three broad categories of water‐supply alternatives were evaluated by regional, state, and federal agencies — additional pumping from the Cohansey, conjunctive use of the Cohansey with other aquifers, and desalination of brackish groundwater. An approach was adopted in 1996 which derives up to 2 MGD from desalination of brackish groundwater, with the remaining peak demand satisfied by short‐term pumpage from existing wells in the Cohansey. The first of two wells has been completed, yielding 1.4 MGD of brackish groundwater. Similar performance from the second well will exceed the design goal. When the initial system comes on line during the summer of 1998, New Jersey will have its first public water supply derived from desalinated groundwater. The use of desalinated groundwater balances competing demands for water resources in the southern Cape Region of New Jersey, allowing continued economic growth while reducing human impacts on a threatened aquifer.

Latitudinal gradients in benthic community composition in Western Atlantic estuaries

Summary AimThe community composition of benthic macroinvertebrates from 295 estuarine sites was examined in order to either confirm or challenge established boundaries of zoogeographical provinces. We also investigated the postulate that, while local distributions were determined by natural habitat characteristics such as salinity, sediment type and depth, distributions on a large geographical scale would be correlated with temperature. LocationThe Atlantic coast of the United States (on a latitudinal gradient from 42° to 25°N). MethodsUsing the descriptive techniques of cluster analysis and nonmetric multi‐dimensional scaling, we determined the similarities in benthic community composition between sites within 1° latitudinal bands and compared the biotic ordinations to natural habitat characteristics such as salinity, sediment type and depth. We then evaluated the overall community composition within each 1° latitudinal band and established whether or not similarities existed between adjacent 1° latitudinal bands. In this manner, we were able to confirm that a latitudinal gradient existed in estuarine benthic community composition along the western Atlantic coast. This latitudinal gradient was demarcated by biogeographical boundaries at (1) Biscayne Bay, Florida, (2) the southern end of the Indian River Lagoon, Florida, (3) St John's River, Florida, (4) Cape Island, South Carolina, (5) the mouth of the Cape Fear River, North Carolina and (6) Cape Cod, Massachusetts, with a subprovince boundary just north of Cape May at Wildwood, New Jersey. ResultsThe major divisions approximated widely recognized biogeographical boundaries. Average summer water temperatures correlated better than sediment type, depth, or salinity with the latitudinal groupings of sites determined by cluster analysis. ConclusionsBased on this relationship, we speculate on the potential impacts of current global climate change scenarios on the distribution of benthic macroinvertebrates along the western Atlantic coast.

Land subsidence due to groundwater withdrawal: potential damage of subsidence and sea level rise in southern New Jersey, USA

Land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region. Groundwater withdrawal results in fluid pressure change in the layers. The pressure change in the layers induces both elastic and inelastic land compaction. The elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent. Groundwater response to barometric pressure change is used to estimate the elastic compaction in this study. The storativity, specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal. The discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern New Jersey. The estimated subsidence is about 2–3 cm near the location of monitoring wells in Atlantic, Camden, Cumberland and Cape May Counties over the past 20 years. If the current trend of water-level drop continues, the average subsidence in southern New Jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years. The rise of global sea level is about 2 mm/year on average. Because of the very gentle slope in southern NJ, the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period. This combination will also accelerate the coastal flooding frequency and the erosion rate of the New Jersey coastal plain, and pose a serious threat to the coastal economy.

Grenville age of basement rocks in Cape May NJ well: new evidence for Laurentian crust in u.s. Atlantic Coastal Plain basement Chesapeake terrane

The Chesapeake terrane of the U.S. mid-Atlantic Coastal Plain basement is bounded on the northwest by the Salisbury positive gravity and magnetic anomaly and extends to the southeast as far as the Atlantic coast. It underlies the Coastal Plain of Virginia, Maryland, Delaware and southern New Jersey. Rubidium/ Strontium dating of the Chesapeake terrane basement yields an age of 1.025±0.036 Ga. This age is typical of Grenville province rocks of the Middle to Late Proterozoic Laurentian continent. The basement lithologies are similar to some exposed Grenville-age rocks of the Appalachians. The TiO 2 and Zr/P 2O 5 composition of the metagabbro from the Chesapeake terrane basement is overlapped by those of the Proterozoic mafic dikes in the New Jersey Highlands. These new findings support the interpretation that Laurentian basement extends southeast as far as the continental shelf in the U.S. mid-Atlantic region. The subcrop of Laurentian crust under the mid-Atlantic Coastal Plain implies unroofing by erosion of the younger Carolina (Avalon) supracrustal terrane. Dextral-transpression fault duplexes may have caused excessive uplift in the Salisbury Embayment area during the Alleghanian orogeny. This extra uplift in the Salisbury area may have caused the subsequent greater subsidence of the Coastal Plain basement in the embayment. © 1999 Elsevier Science Ltd. All rights reserved.

Bird Communities in Riparian Buffer Strips of Industrial Forests

Retention of riparian buffers is a common management practice used to protect streams from the effects of upslope forest harvest. We compared bird use of riparian buffers along main stem rivers, tributary streams, and reference riparian zones having intact, upslope forests. Community composition differed considerably between buffers and references, and also between main stems and tributaries. Density of the more common species (those detected >20 times) was significantly higher along main stems than along tributaries. Four species (bay-breasted warbler, black-throated green warbler, blue jay, Cape May warbler) were more abundant along main stems than along tributaries; no species was more abundant along tributaries. The overall density of less common species was significantly higher in buffer strips than in reference sites, but four of the more common species (bay-breasted, blackburnian, black-throated green, and Cape May warblers) were more abundant in reference sites than in buffer strips. We did not detect differences in species diversity or richness among the different site types, but edge-species were significantly more common in buffer strips than in reference sites. Interior-species, in contrast, were significantly more common in reference sites.

Massive Swarm Migrations of Dragonflies (Odonata) in Eastern North America

We describe massive autumn migrations of dragonflies (Odonata) which occurred at Chicago, Illinois (14 September 1978), Cape May, New Jersey (11 September 1992), and Crescent Beach, Florida (3–5 September 1993). Estimated numbers of migrant dragonflies involved in these flights were approximately 1.2 million, >400,000, and 200,000, respectively. We also document other recent observations of large swarm migrations of dragonflies in eastern North America, review previous reports of this phenomenon, and compare these events to the flights at Chicago, Cape May and Crescent Beach. Records of large dragonfly migrations show several distinct patterns: (1) all reports fell between late July and mid-October, with a peak in September; (2) most of the large flights occurred along topographic leading lines such as coastlines and lakeshores; (3) massive swarm migrations generally followed the passage of synoptic-scale cold fronts; and (4) the common green darner (Anax junius) was the principal species involved in the majority of these flights. Striking parallels between the patterns of seasonal timing, geographical distribution, and meteorological context of dragonfly migrations and those of birds suggest that similar causal factors are involved.

Efficacy of an oral vaccinia-rabies glycoprotein recombinant vaccine in controlling epidemic raccoon rabies in New Jersey.

A field trial to evaluate the efficacy of an oral vaccinia-rabies glycoprotein recombinant virus vaccine in controlling epidemic raccoon (Procyon lotor) rabies was conducted by distributing 180,816 doses (10(8.2)TCID50/ml) of vaccine in wax ampules within fish-meal polymer baits at a rate of 64 doses/km2/treatment throughout a 552 km2 area, forming an 18 km wide band across the northern Cape May Peninsula of New Jersey (USA). Vaccination treatments were conducted in the spring and fall between May 1992 and October 1994 from a helicopter along ecotones and from motor vehicles along roads. Vaccine-laden baits were removed by animals from tracking stations within 3 wk and 61% of the identifiable tracks were those of raccoons. Tetracycline incorporated in the baits as a biomarker was detected in 155 (73%) of the vaccination area raccoons following the fall 1993 and spring 1994 vaccinations. Eleven (61%) of the raccoons sampled in the same time period seroconverted (> or = 0.5 IU) in response to rabies virus glycoprotein. A raccoon diagnosed with rabies from the northern border of the vaccination area on 30 April 1993 provided the first evidence that the barrier was being challenged by the rabies epidemic. The prevalence of rabies in raccoons from the vaccination area for the first year (10%, n = 96) and second year (8%, n = 61) of challenge was reduced more than six-fold by vaccination compared to unvaccinated raccoons from northern adjacent surveillance areas during the corresponding first (65%, n = 189) and second years (53%, n = 43). Vaccination also effectively reduced by three-fold the rate at which the epidemic moved through the raccoon population (15 km/yr). The breach of the vaccination area resulted in a resumption of the high rate (43 km/yr) of epidemic movement and a significant nine-fold increase in rabies prevalence (77%, n = 47). The maximum linear movement (12.9 km) among five ear-tagged rabid raccoons in the study area was significantly greater than that of 19 normal radio-collared raccoons (2.58 km) in the area. These large movements of rabid raccoons, together with relocation of nuisance raccoons, spillover of raccoon rabies in skunks (Mephitis mephitis) and other species, insufficient funding and a decision to discontinue the program in 1994 (which could have resulted in insufficient population immunity among raccoons in the vaccination area) may have contributed to the eventual breach of the barrier.

Absence of Cold Acclimation Response in Gray Treefrogs, Hyla chrysoscelis and Hyla versicolor

The gray treefrog complex consists of two morphologically similar species, Hyla chrysoscelis and Hyla versicolor. These sibling species can be differentiated by genome size in the laboratory and by mating call in the field. Hyla chrysoscelis is diploid (2n = 24) with a mating call pulse rate of 36 pulses per second or higher, while H. versicolor is tetraploid (2n = 48) with a mating call pulse rate at or below 25 pulses per second depending upon temperature (Zweifel, 1970; Ralin and Selander, 1979). The overall distribution of the two species extends from northern Florida to southern Maine in the east and from central Texas to southern Manitoba in the west (Conant and Collins, 1991). Although the distribution of each species has not been accurately delineated, H. versicolor (the tetraploid species) occurs more frequently in the northern region of this range while H. chrysoscelis occurs primarily in the southern region (Ralin and Selander, 1979). Compensation of metabolic rate in response to lower temperatures (cold acclimation) allows organisms to survive and function under adverse thermal conditions (Rome et al., 1992). For example, Rieck et al. (1960) demonstrated that Rana pipiens held at 5 C had metabolic rates two times greater upon exposure to 10 C than specimens held at 25 C. Such a response allows for greater physiological efficiency at lower temperatures and improved cold tolerance. Previous research provided evidence that H. chrysoscelis (the diploid species) does not have the ability to acclimate to cold temperature (Blem et al., 1986). However, Bailey and Thye (1975), showed that polyploidy enabled gene duplication as well as gene divergence in function. In their study, tetraploid salmonid fish showed a modification in isoenzyme regulation for lactate dehydrogenase (LDH). As with amphibians (Enig et al., 1976; Tsugawa, 1976), a relationship appears to exist between acclimation ability and LDH concentrations in the killifish Fundulus heteroclitus (Crawford and Powers, 1989). The purpose of the current study was to determine if polyploidy imparts a similar physiological advantage to H. versicolor with respect to its thermal acclimation ability. Calling male H. versicolor and H. chrysoscelis were collected between 15 and 31 May 1994 from Hunterdon and Cape May Counties, New Jersey, respectively. The body masses of the frogs ranged from 5.6-10.2 g for H. versicolor (mean = 8.0 g, SE = 0.45, N = 10) and 6.0-7.8 g for H. chrysoscelis (mean = 6.9 g, SE = 0.21, N = 12). Species identification was verified by analyzing recordings of the mating calls (Zweifel, 1970). The two species were held in separate aquaria at a constant temperature (21 C) and fed live crickets 2 to 3 times a week until experimentation in November and December, 1994. Individual frogs were identified by dorsal blotches and/or thigh spots, body mass and snout to urostyle length. Metabolic rates were measured as the amount of

Temporal Trends in Metal Levels in Eggs of the Endangered Roseate Tern (Sterna dougallii) in New York

Female birds sequester certain organic and inorganic compounds in their eggs which have been widely used as a bioindicator for examining the body burdens of contaminants and therefore the temporal and spatial trends of the contaminants in the environment. The same analyses can also reflect the status or vulnerability of the indicator species. Extensive bridge de-leading activities in the New York Bight (Cape May to Montauk) in the early 1990s coincided with a long-term study of the endangered roseate tern (Sterna dougallii) on Long Island, New York, affording the opportunity to test the utility of such fish-eating species as bioindicators of lead contamination, as well as the potential impact on the bird population itself. In this paper we test the null hypothesis that there were no temporal trends between 1989 and 1994 in metal levels in eggs of roseate terns nesting at Cedar Beach, Long Island, where the birds have been declining since the late 1980s. We report levels and trends for cadmium, chromium, manganese, mercury, and selenium as well as lead in abandoned eggs collected each year. There were significant interyear differences for all metals, with 1990 to 1992 generally having higher levels than 1989 and 1994. The yearly differences were particularly prominent for lead, where the 10-fold increase may have been partially due to the increased removal of leaded paint from bridges in the early 1990s, leading to increased lead in the aquatic environment. Cadmium and chromium are also released during de-leading. The causes for the higher levels in the other metals in the early 1990s are unclear. Metal levels in roseate tern eggs are several times higher than the median reported for most birds, and the possible impact on the population requires study.

Spruce budworm outbreaks and the incidence of vagrancy in eastern North American wood-warblers

The Tennessee (Vermivora peregrina), Cape May (Dendroica tigrina), Bay-breasted (D. castanea), and Canada (Wilsonia canadensis) warblers and the Ovenbird (Seiurus aurocapillus) appear to show positive numerical responses to outbreaks of the spruce budworm (Choristoneura fumiferana); the Magnolia (D. magnolia), Black-throated Green (D. virens), and Blackburnian (D. fusca) warblers may occur in lower numbers during outbreaks because of increased competition with these budworm specialists. Thus, we predicted that the number of fall vagrant Tennessee, Cape May, and Bay-breasted warblers and Ovenbirds occurring in California are highly positively associated with budworm population density, positively intercorrelated, and negatively associated with numbers of Magnolia, Black-throated Green, and Blackburnian warblers. A 23-year (1972-1994) data set of budworm population densities and vagrant warbler occurrences in California showed that (i) budworm population density was an excellent predictor (explaining about 50% of the variance) of numbers of occurrences of the Cape May, Bay-breasted, and Canada warblers; (ii) all warbler species tended to co-occur, with numbers of Cape May and Bay-breasted warblers especially highly intercorrelated; and (iii) Magnolia Warbler numbers were negatively associated with those of budworm specialists, but Black-throated Green and Blackburnian warblers showed no association.

Cape May Warbler (Setophaga tigrina)

Cape May Warbler (Setophaga tigrina)

Cape May Warbler (Setophaga tigrina)

Cape May Warbler (Setophaga tigrina)

The Influence of Weather, Geography, and Habitat on Migrating Raptors on Cape May Peninsula

For many shorebirds and passerines, stopovers in areas of concentrated resources increase survival during migration. For raptors, physical factors have generally been considered to be the chief influence on migratory behavior, and few studies have collected quantitative data on the use of resting and foraging habitat during migration. Our object was to survey three different habitats along a 30-km section of the Cape May peninsula. We measured abundance, flight altitude, and flight direction of eight species of migrating raptors to evaluate the influence of habitat and physical factors, including wind speed, wind direction, and location, on migratory behavior. Physical factors such as wind speed and direction were weakly related to bird density and altitude. Although interactions among physical factors were significant, they were not consistent with predictions based on bird mass or wing-aspect ratio. Habitat type was significantly associated with most species' altitude and density. Birds generally occurred in higher densities and at lower altitudes above habitats similar to those used in breeding or wintering seasons. We suggest that the strong habitat association is due to the need for suitable foraging sites. Many migratory raptors are able to prey upon migratory birds, insects, and fish that also concentrate at the end of the Cape May peninsula or in waters offshore. Most of the raptors observed in Cape May are immature and inexperienced, and the concentration of similarly immature and inexperienced prey may prove to be a critical factor in successful migration along the Atlantic Coast.