Research Methods:

• Adult male Abert’s Towhees, Melozone aberti, were caught during January 2011 using a mist net and playback of conspecific song. We determined sex and age by behavior (singing and territorial aggression only in males), skull pneumatization, and morphology (developed CP only in adult males, incubation patch only in adult females). Birds were transferred to ASU animal care maintained at 23°C (± 1°C) with a short light cycle (9 L: 15D; lights on at 06:00). Birds were individually housed in 76 x 46 x 46 cm cages. After a one-week acclimation period in captivity, we increased the photoperiod to 14 L to induce reproductive development. To measure the average daily ad libitum food consumption of each individual over two weeks, we provided a pre-weighed amount of food shortly after the lights went on and weighed the remaining food (including spillage on the cage bottom) 24 hours later. To minimize spillage, we partially covered food dishes with tape, allowing only a small opening to access food.
• Following the two week ad libitum food consumption period, we randomly assigned birds to one of three groups: (1) ad libitum food, (2) restricted food availability for four weeks or (3) two weeks of food restriction followed by two weeks of ad libitum food. Experimental birds received 70% of their individual average ad libitum food consumption. We weighed all birds daily immediately prior to dispensing the daily food ration. If a bird’s mass decreased below its 85% target mass, this bird was immediately fed the difference between its current mass and its target mass.
• From each bird, we collected a blood sample to quantify plasma testosterone immediately prior to (1) the switch to food restriction (defined as day 0), (2) the switch back to ad libitum food (day 14), and (3) the end of the study (day 28). Immediately following blood collection, we measured wing chord (± 0.5 mm) and CP width (± 0.1 mm) using digital calipers. Body mass (± 0.5 g) was measured using a pesola spring balance. To quantify fat stores, we visually inspected the amount of furcular fat by assigning a score of 0 – 5 (a score of 0 representing no fat, 5 representing bulging fat deposits, Helms & Drury, 1960 Bird Banding, 31, 1-40). We also estimated the size of the pectoral muscles on a scale ranging from 0 – 3 (0 representing concave pectoral muscles and a prominent keel, 3 representing convex pectoral muscles that protruded above the keel, Salvante et al. (2007, J. Exp. Biol. 210, 1325-1334).
• To investigate the effect of food availability on the central control of reproduction and testicular development, on day 29 we collected the brain and testes of each bird. Methods follow Small et al. (2008, Brain, Behav. Evol. 71, 127-142). We quantified hypothalamic GnRH, GnIH, and NPY, as well as the average diameter of seminiferous tubules. We quantified plasma testosterone concentration using a commercial competitive enzyme-linked immunoassay, according to the manufacturer’s instructions (Enzo Life Sciences, Farmingdale, NY, USA).