James L. Hayward

Eggshell Taphonomy at Modern Gull Colonies and a Dinosaur Clutch Site

Abstract Eggshell taphonomy often is acknowledged to be worthy of investigation, but few studies have examined factors influencing eggshell preservation. In this study eggshell weathering, fragmentation, dispersal, orientation, and predation were characterized in field and laboratory studies. Modern gull eggshell fragment dispersal and orientation patterns were compared with analogous patterns at a non-avian dinosaur egg clutch site. Among other findings: (1) hatched and depredated gull eggshells protected by an exclosure, but exposed to two years of colony weathering, fragmented relatively slowly, suggesting that colony resident activity is responsible for the relatively rapid disappearance of eggshell on the colony surface; (2) depredated eggshells could be distinguished from hatched eggshells due, in part, to differences in fracture patterns; (3) both gull and non-avian dinosaur eggshell fragments were most abundant close to nest centers, whereas this was not true for bones and mollusc shells in gull territories; (4) both gull and non-avian dinosaur eggshell fragments within nest areas were oriented concave up more commonly than concave down, in contrast to transported eggshell fragments; (5) chicken eggs experimentally placed in a gull colony were more likely to be taken by egg predators in areas of short or sparse vegetation than in areas of tall vegetation; and (6) the extent of fracturing was greater in fresh than in hollow chicken eggshells following compression beneath simulated sediment loads. Eggshell weathering, fragmentation, orientation, and dispersion patterns should be characterized during the excavation of fossilized eggs and nest sites.

Foraging-Related Activity of Bald Eagles at a Washington Seabird Colony and Seal Rookery

Abstract From 1980 to 1998, Washingtons Bald Eagle (Haliaeetus leucocephalus) population increased at an annual rate of 10%. Over the same time period, foraging activity of Bald Eagles at marine bird breeding colonies also increased. From 1993 to 2008, we observed foraging-related behavior of Bald Eagles on Violet Point, Protection Island. This island hosts more than 70% of the breeding seabirds in Washingtons inner seaways and serves as an important rookery for harbor seals (Phoca vitulina). We found that (1) eagles landed more frequently in seal haul-out (beach) areas than in gull-nesting (non-beach) areas of Violet Point, and that subadult eagles were more likely to land in gull-nesting areas than were adult eagles; (2) the presence of eagles on the beach was positively related to the presence of harbor seals on the beach; (3) a greater-than-expected number of adult eagles as compared with subadult eagles preyed on gull chicks; (4) subadult and adult eagles that attempted prey capture were equally successful at snatching gull chicks from the gull colony; (5) eagles were more likely to prey on gull eggs in tall grass than on gull eggs in sparse vegetation. Prey remains beneath one eagle nest on the island did not accurately reflect the range and relative frequencies of observed eagle predation events. Although seal afterbirths and dead pups constitute a major component of the diet of Bald Eagles on the island, the effect of eagles on live seals is probably negligible. In contrast, direct predation and indirect effects of eagle activity on Glaucous-winged Gull (Larus glaucescens) reproductive success may be substantial and may have been partly responsible for a 44% decrease in the number of gull nests in the colony from 1993–2008.

Taphonomic Effects of pH and Temperature on Extant Avian Dinosaur Eggshell

Abstract Avian and non-avian dinosaur eggshell contains clues that are helpful in the reconstruction of ancient habitats and behaviors. Fossilized eggshell often shows signs of corrosion attributed to acid dissolution of the calcium carbonate, but this process has never been quantified in controlled experiments. In work reported here, extant avian dinosaur eggshell fragments were placed in buffered solutions of varying pH and temperature for varying periods of time. Changes in the appearance, mass, surface area, and thickness were described and compared with naturally weathered eggshell. Treatment resulted in corrosion and pitting of the outer surface and corrosion of the mammillary structure of the inner surface. Fragment mass, surface area, and thickness generally decreased in response to decreased pH and to increased temperature and exposure time. A classification scheme for eggshell corrosion is proposed.

Eggshell taphonomy: environmental effects on fragment orientation

Dinosaur eggshell is abundant in the fossil record but only during the last several decades has this reproductive product been considered more than a novelty. Recent work has provided evidence that both whole eggs and fragmented eggshell represent a rich source of information related to paleoecology and dinosaur reproductive biology. In this paper, we report the effects of environmental variables on modern eggshell fragment orientation. Non-transported eggshell fragments at hatching and predation sites favoured concave-up over concave-down orientations. Trampled fragments and fragments transported by wind and water favoured concave-down over concave-up orientations. Although differences in orientation between non-transported and transported eggshell fragments were usually obvious and significant under the chosen experimental conditions, paleontologists are cautioned to interpret the taphonomy at fossil eggshell sites with care and within their sedimentological context.

Experiments on the taphonomy of amniote eggs in marine environments

Experiments to identify taphonomic variables influencing the fossilization of eggs and eggshells in marine environments were carried out using chicken eggs as models. We examined: (1) the recruitment of eggs into the sea by wave and tidal action; (2) the transport of eggshell fragments by simulated turbidity currents; (3) the capacities of whole eggs to withstand hyperbaric pressures: and (4) the fates of eggs placed on and beneath the benthic surface. Eggs placed along a beach during rising tides were quickly recruited into the sea. Once in the water, fresh eggs rolled along the benthic surface to deeper sites, whereas partially dehydrated eggs floated away from shore. Eggshell fragments transported by simulated turbidity currents settled toward the bottom of the resultant turbidites, with the number and size of fragments decreasing as a function of increasing distance from the source. Fresh eggs lowered in the ocean to a depth of 626 m did not fracture. Most eggs placed at or just beneath the benthic surface in a shallow bay remained unbroken for at least 44 days and became infested with epibionts. Paleontologists interested in fossil eggs should not overlook paleomarine sediments as one likely source of these important trace fossils.

PREDICTING DYNAMICS OF AGGREGATE LOAFING BEHAVIOR IN GLAUCOUS-WINGED GULLS (LARUS GLAUCESCENS) AT A WASHINGTON COLONY

Abstract Seabirds move throughout the day in changing, patchy environments as they engage in various behaviors. We studied the diurnal abundance dynamics of Glaucous-winged Gulls (Larus glaucescens) in a habitat patch dedicated to loafing in the Strait of Juan de Fuca, Washington. We constructed three differential equation models as alternative hypotheses and then used model selection techniques to choose the one that most accurately described the system. We validated the model on an independent data set, made a priori model predictions, and conducted a field test of the predictions. Clear dynamic patterns emerged in the abundance of loafing gulls, even though individuals moved in and out of the loafing area more or less continuously throughout the day. Temporal patterns in aggregate loafing behavior are predicted by three environmental factors: day of the year, height of the tide, and solar elevation. This result is important for several reasons: (1) it reduces the aggregate behavior of complicated vertebrates to a simple mathematical equation, (2) it gives an example of a field system in which animal abundances are determined largely by low dimensional exogenous forces, and (3) it provides an example of accurate quantitative prediction of animal numbers in the field. From the point of view of conservation biology and resource management, the result is important because of the pervasive need to explain and predict numbers of organisms in time and space.

Egg cannibalism in a gull colony increases with sea surface temperature

ABSTRACT Cannibalism occurs regularly across a broad range of taxa with a variety of ecological and evolutionary consequences. Rises in sea surface temperature (SST) have been linked to increased cannibalism in some species, including polar bears (Ursus maritimus), Peruvian anchovy (Engraulis ringens), and Peruvian hake (Merluccius gayi peruanus), and might be expected in birds that depend on marine food webs for sustenance. Increased SSTs are associated with lowered ocean thermoclines and weakened upwellings. These changes, in turn, lead to decreased productivity in surface water and movement of surviving forage fish to deeper water, thereby food-stressing surface feeders such as gulls, diminishing energy intake and lengthening foraging bouts. While controlling for a suite of other environmental factors, we tested whether egg cannibalism and hatching success were independent of rises in local SST at a colony of Glaucous-winged Gulls (Larus glaucescens) and Glaucous-winged × Western Gull (L. glaucescens × occidentalis) hybrids during 2006–2011 on Protection Island, Washington, USA. Cannibalism increased and hatching success decreased with rises in SST. It is unclear if rises in SST impact overall population trends. Gulls are multiyear breeders; if they experience reproductive failure during one or several El Niño-Southern Oscillation–related events, they typically have other opportunities to breed. With rising SSTs associated with climate change, however, increasing levels of cannibalism could lead to declining populations in the absence of compensatory adaptive modifications or range shifts.

Socially Induced Synchronization of Every-Other-Day Egg Laying in a Seabird Colony

ABSTRACT. Spontaneous oscillator synchrony has been documented in a wide variety of electrical, mechanical, chemical, and biological systems, including the menstrual cycles of women and estrous cycles of Norway Rats (Rattus norvegicus). In temperate regions, many colonial birds breed seasonally in a time window set by photoperiod; some studies have suggested that heightened social stimulation in denser colonies can lead to a tightened annual reproductive pulse. It has been unknown, however, whether the analog of menstrual synchrony occurs in birds—that is, whether avian ovulation cycles can synchronize on a daily timescale within the annual breeding pulse. We report every-other-day clutch-initiation and egg-laying synchrony in a breeding colony of Glaucous-winged Gulls (Larus glaucescens) and show that the level of synchrony declined with decreasing colony density. We also pose a mathematical model based on the hypothesis that preovulatory luteinizing hormone surges synchronize through social stimulation. Model predictions are consistent with observations. Finally, we suggest a procedure for identifying synchronous egg laying in other colonies and species.

Modeling territory attendance and preening behavior in a seabird colony as functions of environmental conditions

In previous studies we developed a general compartmental methodology for modeling animal behavior and applied the methodology to marine birds and mammals. In this study we used the methodology to construct a system of two differential equations to model the dynamics of territory attendance and preening in a gull colony on Protection Island, Strait of Juan de Fuca, Washington. We found that colony occupancy was driven primarily by abiotic environmental conditions, including tide height, time of day, solar elevation, and wind speed over open water. For birds in the colony, preening behavior was driven to some extent by abiotic environmental conditions (including time of day, solar elevation, humidity, and wind speed on the colony), but apparently was driven primarily by local and/or biotic effects not included in the model. In terms of R 2 values, the model explained 65% and 37% of the variability in colony occupancy and preening data, respectively, as a function of these six abiotic environmental factors.

BALD EAGLE ACTIVITY AT A GULL COLONY AND SEAL ROOKERY ON PROTECTION ISLAND, WASHINGTON

foraging Dietary preferences of bald eagles (Haliaeetus leucocephalus) reflect local prey availability in many parts of the United States; depending on time and place, eagles prey upon fish, marine birds, gull eggs, and sea otter (Enhydra lutris) pups and they scavenge cow, sheep, deer, salmon, and seal carcasses (Murie 1940; Servheen