Referente Disciplinar:

The weight increase recorded during a 4 h sampling interval is not the actual amount of food ingested during the interval, because nestlings lose weight through respiration, evaporation and defecation. The aim of the statistical analysis was to find a

regression equation that would correct for inherent weight loss and determine corrected meal sizes delivered overnight. The regression equation was also used to estimate the amount of food accepted by the nestling overnight, based on daily

weights. Data analysis was performed using SPSS Statistical Package for Windows.

For each year, the positive mass increases recorded during each night were summated (SUM), following Ricklefs (1984). The maximum mass increase recorded in 2000 was 75 g. A minimum meal was defined as 10 % of this maximum meal to maintain an acceptable level of error (Phillips and Hamer 2000). Subsequently, therefore, an increase of 8 g was used to define a meal received during a 4 h interval, in 2000, 2001 and 2002. Analysis then focused on the weight loss experienced by nestlings before and after feeding. Unfed individuals were used to define inherent weight loss over time. Multiple Analysis of Covariance was used to determine how inherent weight loss was influenced by other factors, such as initial weight (PWEIGHT), burrow of origin (BURROW) and the size of an individual (BSINDEX), which reflects age. Rates of weight loss were considered as both linear and proportional functions of time (g.h-1 and log10 (PWEIGHT/final weight) h-1). All of these factors, converted to a log

methodology and analysis employed in this study matched that used in other studies (Ricklefs 1984a, Ricklefs et al. 1985, Hamer and Hill 1993, Bolton 1995, Hamer and Hill 1997).

It is important to correct for nestling size when determining the regression of weight loss on nestling weight, especially in species that breed asynchronously.

Hence, nestling size was introduced as a composite body size index as a covariate into the regression (Phillips and Hamer 2000). Z-scores of measured parameters such as head length, beak length and tarsus length were used. The analysis used in this study differs slightly from Phillips and Hamer (2000), since values for each of the

parameters were log-transformed and a mean calculated. The mean for each parameter was then deducted from individual measurements for that parameter and divided by the standard deviation, giving the z-score for that individual. The z-scores were then summated for each individual. In contrast Phillips and Hamer (2000) log- transformed the summed z-scores rather than the original skeletal measurements.

Regression equations were developed to calculate weight loss between the initial and final weights determined each night, loss that occurred prior to feeding and after the consumption of food. The total amount of food delivered overnight (corrected meal size) to a nestling could then be calculated by correcting SUMs for inherent weight loss (CSUM). CSUMs were graphed to determine the amount of food needed to maintain a steady weight over a 24 h period (Hamer and Hill 1997). The resultant regression equation was later used to calculate the total amount of food delivered overnight throughout the nestling period, using daily morning weights. For Little Shearwaters the overnight food consumed by the nestling throughout ontogeny in

2000 and 2002 was used to comment on adult behaviour in years of different quality, along with the percentage of nestlings fed, based on 12 h weight differences and the average morning and afternoon weights recorded for the cohort over time.

Frequent weighing of Wedge-tailed Shearwater nestlings occurred over four consecutive nights on Lancelin Island from 11 to 15 March 2001 and on Rottnest Island from 16 to 20 April 2002. Nestlings were weighed at 4 h intervals at 17:30, 21:30, 01:30, 05:30 and 09:30 h WST. Previous studies suggest that the meal sizes and delivery rates in this species were not adversely affected by human handling of adults and nestlings (Baduini 2002).

The frequent weighing data were analysed as detailed in Chapter 4, however a larger meal size was defined for a larger species. The weight differences (uncorrected meal sizes) calculated over the 4 h intervals revealed that, for the Wedge-tailed Shearwater, ten percent of the maximum uncorrected meal size was 15 g. Consequently, 15 g was subsequently used to define a meal over a 4 h interval. In both years, the body size index derived from skeletal measurements of Wedge-tailed Shearwaters did not emerge as a significant factor for either fed or unfed nestlings. Nonetheless, body size index was incorporated in the analysis, using z-scores, to allow comparison with other studies which have found it to be an important factor (Phillips and Hamer 2000).

At Lancelin Island, Wedge-tailed Shearwater nestlings were weighed twice daily from 24 January to 03 May 2001, at 09:30 h and 17:30 h WST. The birds were visited at 09:30 h WST rather than sunrise (as was the case with the Little Shearwater), because of the need to swim to a moored dinghy and drive it to the island. Sampling did not

occur on the following days: 20-23 January, 20 February to 01 March, 10 March, 25- 31 March, 01-03 April, and 19-24 April 2001.

In 2001, the total overnight food consumed by the nestlings throughout ontogeny was estimated from morning weights, using the regression equation derived from frequent weighing. This resulted in a real time sequence, which displayed the total food consumed by nestlings from 24 January until the whole colony fledged by May.