PARENT SESSION
Poster Session 28: Avian Ecology
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Assessing the condition of song sparrow nestlings using stable isotopes.

Kempster, Bethany^*,1, Zanette, Liana¹, Longstaffe, Fredrick¹, ¹ University of Western Ontario, London, Ontario, Canada

ABSTRACT- Mounting evidence is showing that the amount and quality of food received by songbird nestlings is the ultimate factor determining their growth and development. Nutritional stress at this stage can have both short-term effects and long term (i.e. carry-over) effects where the current condition of an adult can be traced to its prior rearing condition. Thus, poor nutrition at the nestling stage may carry-over to adulthood leading to impaired reproductive success and/or survival. It is possible then that by measuring nestling condition, future success can be predicted. Currently, fluctuating asymmetry, morphometrics, feather fault bars, and blood analyses are used to measure nestling condition. None of these methods, however, have been proven to be reliable or consistent. Stable isotope analysis has been proposed as a measure of nutritional stress, but has never been tested in a passerine species. To test this, I manipulated the food provided to hand-reared song sparrows Melospiza melodia. The control birds were provided with unlimited food, while the food-stressed birds were given 65% of what was fed to the control birds, mimicking a level of stress comparable to that experienced by wild nestlings. The birds were sacrificed after 23 to 26 days post-hatch. The control birds fledged significantly earlier and had faster growth rates. At the end of the experiment, the control birds weighed significantly more, had larger predicted adult weights, higher fat scores, and higher condition indices, but their right tarsi and right 6th primary feathers were not significantly larger. The control birds had significantly lower glucose concentrations and larger hematocrits. There were no significant differences in the number of fault bars in either the rectrices and remiges between the two treatments. There were no significant differences between the ¹⁵N or ¹³C ratios in the feathers and blood of the two treatments. Blood analyses and some morphometric measurements, therefore, were positive indicators of nutritional stress, while fault bar analyses and stable isotopes showed no difference. I conclude that moderate nutritional stress is not enough to cause stable isotope enrichment, which may only occur under stress approaching prolonged starvation.

Key words: nutritional stress, stable isotopes, Melospiza melodia, stress measures