Geology topics

Michael T. Shultz

Publications and source records attributed to Michael T. Shultz.

4 recordsLinked to original sources

USGS2007

Seabirds as indicators of marine food supplies: Cairns revisited

In his seminal paper about using seabirds as indicators of marine food supplies, Cairns (1987, Biol Oceanogr 5:261–271) predicted that (1) parameters of seabird biology and behavior would vary in curvilinear fashion with changes in food supply, (2) the threshold of prey density over which birds responded would be different for each parameter, and (3) different seabird species would respond differently to variation in food availability depending on foraging behavior and ability to adjust time budgets. We tested these predictions using data collected at colonies of common murre Uria aalge and black-legged kittiwake Rissa tridactyla in Cook Inlet, Alaska. (1) Of 22 seabird responses fitted with linear and non-linear functions, 16 responses exhibited significant curvilinear shapes, and Akaike’s information criterion (AIC) analysis indicated that curvilinear functions provided the best-fitting model for 12 of those. (2) However, there were few differences among parameters in their threshold to prey density, presumably because most responses ultimately depend upon a single threshold for prey acquisition at sea. (3) There were similarities and some differences in how species responded to variability in prey density. Both murres and kittiwakes minimized variability (CV < 15%) in their own body condition and growth of chicks in the face of high annual variability (CV = 69%) in local prey density. Whereas kittiwake breeding success (CV = 63%, r 2 = 0.89) reflected prey variability, murre breeding success did not (CV = 29%, r 2 < 0.00). It appears that murres were able to buffer breeding success by reallocating discretionary ‘loafing’ time to foraging effort in response (r 2 = 0.64) to declining prey density. Kittiwakes had little or no discretionary time, so fledging success was a more direct function of local prey density. Implications of these results for using ‘seabirds as indicators’ are discussed.

Marine Ecology Progress Series↗

USGS2006

Assessing the nutritional stress hypothesis: Relative influence of diet quantity and quality on seabird productivity

Food availability comprises a complex interaction of factors that integrates abundance, taxonomic composition, accessibility, and quality of the prey base. The relationship between food availability and reproductive performance can be assessed via the nutritional stress (NSH) and junk-food (JFH) hypotheses. With respect to reproductive success, NSH posits that a deficiency in any of the aforementioned metrics can have a deleterious effect on a population via poor reproductive success. JFH, a component of NSH, posits specifically that it is a decline in the quality of food (i.e. energy density and lipid content) that leads to poor reproductive success. We assessed each in relation to reproductive success in a piscivorous seabird, the black-legged kittiwake Rissa tridactyla . We measured productivity, taxonomic composition, frequency, size, and quality of meals delivered to nestlings from 1996 to 1999 at 6 colonies in Alaska, USA, 3 each in Prince William Sound and Lower Cook Inlet. Productivity varied widely among colony-years. Pacific herring Clupea pallasi , sand lance Ammodytes hexapterus , and capelin Mallotus villosus comprised ca. 80% of the diet among colony-years, and each was characterized by relatively high energy density. Diet quality for kittiwakes in this region therefore remained uniformly high during this study. Meal delivery rate and meal size were quite variable among colony-years, however, and best explained the variability in productivity. Parent kittiwakes appeared to select prey that were energy dense and that maximized the biomass provisioned to broods. While these results fail to support JFH, they do provide substantial support for NSH.

Marine Ecology Progress Series↗

USGS2003

Protocols for long-term monitoring of seabird ecology in the Gulf of Alaska

Seabird populations will need to be monitored for many years to assess both recovery and ecological conditions affecting recovery. Detailed studies of individual seabird colonies and marine ecosystems in the Gulf of Alaska have been conducted by the U.S. Geological Survey and U.S. Fish and Wildlife Service under the auspices of damage assessment and restoration programs of the Trustee Council. Much has been learned about factors influencing seabird populations and their capacity to recover from the spill in the Gulf of Alaska. As the restoration program moves toward long-term monitoring of populations, however, protocols and long-term monitoring strategies that focus on key parameters of interest and that are inexpensive, practical, and applicable over a large geographic area need to be developed.

Alaska↗

USGS1999

Biological effects of the 1997/98 ENSO in Cook Inlet, Alaska

We have been conducting detailed studies of the biology of seabirds in relation to oceanography and forage fish ecology in lower Cook Inlet, Alaska, since 1995. This fortuitously allowed us to document biological effects of the 1997/98 ENSO in this region. Anomalously warm sea surface temperatures (SSTs) were observed in the Gulf of Alaska (GOA) beginning in June of 1997, but not in Cook Inlet until September, 1997. Warm temperature anomalies at the surface and at depth persisted until May of 1998, when temperatures returned to average in the GOA and Cook Inlet. Thus, temperature anomalies occurred outside the core window of productivity (June–August) for forage fish and seabirds in both 1997 and 1998. Abundance or production of phytoplankton, zooplankton, fish, and seabirds in lower Cook Inlet varied among years, and overall appeared to be depressed in 1998. We observed a few biological anomalies that might be attributed to ENSO effects: (1) a significant die-off of Common Murres occurred in March–May of 1998, (2) murres and Black-legged Kittiwakes were physiologically stressed during the 1998 breeding season, (3) murres failed to reproduce at one colony in 1998, (4) kittiwake breeding success was lower than usual at colonies in 1998, and (5) phenology of breeding was later in 1998 for both murres and kittiwakes. We presume that seabird die-offs, reduced productivity and delayed phenology were linked to a reduction or delay in food availability, but the mechanism by which anomalously warm water temperatures in winter reduce forage fish availability during the summer breeding season for seabirds is not known.

Alaska↗