lipids during this period. Lower lipid stores in females can be explained by an increase in ovarian size during the breeding season. Predators Northern cricket frogs are preyed upon by a number of species, including birds, fish, and other frogs. To escape predators, they are capable of leaping up to 3 feet in a single jump and are excellent swimmers. It has been found that not only temperature, but hydration also has an effect on how far these frogs can jump. Being hydrated at a higher temperature is thought to allow them to jump farther and higher. Physiology Sun compass orientation Many animals can navigate using the sun as a compass in combination with an internal clock providing a sense of time, which is known as sun compass orientation. Other orientation cues used by cricket frogs include the moon and stars. Acris crepitans and A. gryllus, both cricket frogs, have been observed to show similar orienting mechanisms, namely the Y-axis concept. The Y-axis is a reference axis established by land and water. Frogs require information about shore position, direct view of a celestial cue, and sense of time in order for the successful use of Y-axis type of orientation during the day. Sex determination Numerous environmental factors have been associated with sex determination in amphibians, including temperature, pH, and presence of foreign chemicals that affect the gonads. A study observing Northern cricket frogs in environments contaminated with organochlorides concluded that sites contaminated with point polychlorinated biphenyl (PCB) and polychlorinated dibenzofuran (PCDF) were significantly related to sex-ratio reversal: contaminated sites had more males compared to control ponds, suggesting that organochlorines can influence cricket frog sexual differentiation. For example, the same study had shown that in certain parts of Illinois that are more industrialized and had organochlorine peptides there was a larger proportion of intersex frogs. In the case of Illinois, this was in the northeast. However, more environmentally friendly regions, like southern Illinois, had a more diverse frog population. Immunology vs. reproduction Metabolic resources are allocated to different physiological systems. The amount of allocation may vary with changing external conditions and thus internal demands. Much research has been conducted to demonstrate the balance of resources between immunity and reproduction, including that of Acris crepitans. Male northern cricket frogs were collected at the peak of the breeding season and injected with sheep blood cells to elicit an immune response. Researchers found that