In Chapter 1, I present a population model of the MR breeding colony, based on studies of population growth and reproductive success, and supplemented with previously collected data from the National Audubon Society Seabird Restoration Program (Project Puffin), with whom I collaborated. I also describe chick diet (supplemented with Project Puffin data) and draw connections between diet and reproductive success. I found that reproductive success was too low to account for the observed population growth rate, and conclude that the colony is a sink population supported by substantial immigration. Because annual fledging success was positively associated with prey quality, I suggest that substandard chick diet may contribute to the sink population dynamic via diet-driven depressed fledging success.

In Chapter 2, I report on the foraging behavior of chick-rearing Razorbills fitted with bird-borne data-loggers at MR in 2008-2009. I describe diving behavior including depth, duration, and profile shape of dives, as well as diel patterns. Diving activity was restricted to daylight hours, and dives were shallowest and most frequent in the evening. Though generally similar to diving behavior reported at four European and Canadian colonies, Razorbills at MR performed three times as many dives per day as at the Gannet Islands, Labrador, and the mean dive depth was greater than three of four previous studies. Deeper and more frequent dives may indicate higher foraging effort and lower prey availability. Reproductive success would suffer if parents cannot buffer chicks against the effects of low prey availability through increased foraging effort or other behavioral modifications.

Together, the pieces of our research indicate that prey availability may be negatively affecting reproduction and population growth at MR. Rapid colony growth cannot be explained by local reproductive success, and is likely the result of substantial immigration from other colonies. Chick diet is varied and includes multiple high-quality forage fish species, yet chicks also consume poor-quality prey (larval fish and euphausiids) that may signal periods of very poor prey availability. Frequency and depth of dives made by chick-provisioning adults are also suggestive of parents allocating extra effort to foraging, relative to other colonies.

In recent decades urbanization and the human population on the Galápagos islands has increased rapidly, affecting wildlife in unknown ways. During 2005 and 2006, we sampled birds along a 4-km transect extending northeast of the city of Puerto Ayora, Santa Cruz Island. This allowed us to collect data on the potential impacts of rapidly growing urban center on passerine bird diversity and abundance. We also documented movement patterns of the medium ground finch (Geospiza fortis), the most abundant species on the transect, with a mark/recapture protocol. Although Darwin's finches have been an influencial model for the last 150 years, little is known about their movements on larger islands.

Avian species diversity did not vary significantly along a transect from a periurban area into more remote habitat. Avian abundance, however, was inversely correlated with distance from the urban center. This latter finding is consistent with a well-documented trend in urban ecology, in which periurban areas show higher abundance as compared to adjacent, less developed regions. We also found recapture/re-sight rates for G. fortis within years were 7% and 11% in 2005 and 2006, respectively. The mean distance traveled by individual birds between recaptures or re-sightings was 430.4 m. The majority of movements were less than 500 m from the location of previous sighting. There was no relationship between the distance moved and the time between captures or re-sightings; birds were equally likely to move large distances over short intervals (days) as over longer intervals (years). There was no significant difference in movement distances between males and females. These data document the movement of G. fortis on a larger island. Further studies of gene flow among populations may provide further insight into the genetic and evolutionary consequences of movement patterns documented here.