The song thrush (Turdus philomelos) was introduced to New Zealand from Britain during the mid 19th century and has become one of the most common terrestrial bird species in New Zealand. In this study, I surveyed a range of life-history traits in New Zealand song thrushes for comparison with traits of British thrushes. Clutch size, egg size and nest size have decreased, while the nestling period is shorter and the incubation period longer. This combination of changes suggests birds are investing less energy into each reproductive bout. Birds also appear unable to raise large broods, as nestling starvation is common in New Zealand, which suggests that food is limiting. I experimentally tested the ability of song thrushes to incubate enlarged clutches and broods, but productivity was not higher for enlarged broods and natural 3- and 4-egg clutches produced similar numbers of fledglings. Thus reduced clutch size may be an adaptation to the local environment. Differences in female incubation behaviour, with 3- and 4-egg clutches receiving higher levels of incubation and more visits per hour than 5-egg clutches, also suggest New Zealand thrushes have difficulty coping with clutches as large as those in Britain. The decrease in clutch size between New Zealand and Britain is in the direction and magnitude expected based on the change in latitude, which supports the hypothesis that factors affecting foraging time and food availability, such as daylength, temperature and rainfall, may be selecting for smaller clutches. Egg size was also found to have decreased in New Zealand, though this may be the result of smaller adult size. Hatchling mass was related to egg volume, but I found no effect of egg volume or clutch size on hatching success. However, nests containing more pointed eggs (i.e., abnormally-shaped eggs), had lower survival and hatching/fledgling success. Data from the national nest record database and my study both suggest that differences in song thrush productivity are the result of differential survival of nestlings. Nestling mortality due to starvation was common at Kowhai Bush, but rare in Britain, so either adult condition or food availability may be lowering reproductive success in New Zealand. High rates of nest failure (>65%) could also affect clutch size, but the strong directional selection imposed by food limitation during the nestling period suggests that increases in food supply would result in increased reproductive success even with the same levels of nest failure. When comparing clutch size throughout New Zealand, I found a significant, positive relationship with rainfall, which further suggests that food limitation may be the main factor driving changes in life-history traits of song thrushes in New Zealand.

Birds are a major pest in vineyards both in New Zealand and overseas. There is a need for new behavioural research on birds' foraging habits and feeding preferences in vineyards, as much of the literature to date is anecdotal. Research on cues to birds' feeding will provide a basis on which new deterrent and control strategies can be devised. Spatial-and temporal bird damage in a small vineyard block was mapped to find if damage was correlated with grape maturity and environmental factors. Vineyard and field observations of bird behaviour using video technology combined with preference experiments aimed to establish the relative roles of grape sugar concentration and colour in avian selection. Proximity of vineyards to bird roosts affects damage levels, regardless of differing maturity between locations. The rate of damage tends to increase exponentially once grape maturity has passed a threshold of 13 °Brix. Bunches positioned closest to the ground receive more damage if blackbirds or song thrushes are the predominant pests. Both sugar concentration and grape colour were found to affect birds' feeding preference, but the importance of the two factors varied between years. Black and green grape varieties were differentially preferred by blackbirds (Turdus merula) and song thrushes (Turdus philomelos) while silvereyes (Zosterops lateralis) appeared to have no strong colour preference. It was apparent that there were other, not assessed, grape factors that also affect selection. In small unprotected vineyards that are adjacent to bird roosts the entire grape crop can be taken by bird pests. Besides removing the roosts, which can be beneficial shelterbelts in regions exposed to high winds, growers currently may have no alternative other than to use exclusion netting to keep crops intact. The differential preferences between bird species for variety characteristics suggest that any new deterrents and other strategies to deflect birds from grape crops may need to be species-specific.