Tropical vs. Temperate Life History Life History = Timing, duration, and magnitude of events in an organism’s life time. Most of what we know about birds comes from temperate zone. Why? –Note: More studies on RWBB’s than studies on all tropical species combined –Side Note: Sometimes classifying tropical vs. temperate is tough. Are migratory tanagers, vireos, warblers temperate or tropical? What is more important, where they breed or where they spend most of the year? Or perhaps where they evolved? –For our purposes, we will be talking about breeding residents in the tropics

What is special about the tropics? High Diversity: example, Panama—size of S. Carolina, has 900 bird species, more than all of N. America. –Diversity of Ecological Interactions –Increased Specialization Weird colors, behaviors, plumage? (percentage-wise, these ideas are a myth!) –Bright colors may be numerically more common in the tropics, but as a percentage of species relatively rare. Bright colors is a tropical myth. Most tropical birds are dull. A larger percentage of temperate breeding birds have bright colors. –Ant following, male/female song duetting, lekking (not unique to tropics, but more common there), these are all behaviors that are more or less unique or well- developed in the tropics, but actually rare percentage-wise—so again a myth. These behaviors actual ARE relatively well-studied. The vast majority of other more “normal” tropical species are completely unstudied. – – Even Day length/stable climate/little seasonality –Migration may be limited, or altitudinal rather than latitudinal –How do you time breeding if day length cues are weak or non-existant? –How do you time breeding or other life history events (such as molt) if seasonal differences are negligible?

Temperate zone bias: examples Myth: EPCs are the norm and high in Passerines –But LOW in tropics: Why? Less synchrony in breeding (the pair next door may not be breeding when you are, so you may not be ready to mate with them) Low density populations (pair next door might not be that close—species diversity is high, but density of any one species is low) tropical male Passerines have small testes (not producing a lot of extra sperm to share) Low EPC rate, means low associated behaviors, at least in few species studied (males and females not sneaking around, and males not particularly protective of females) Myth: High T in males is necessary for territory defense –But T is almost always low in tropical birds and many defend territories year round: Why? Perhaps the high T in temperate birds drives EPCs rather than territory defense? Perhaps there is another hormonal mechanism maintaining aggression because it is detrimental to maintain high plasma T year-round Convergent behavior among males and females in the tropics: again, other hormonal mechanism for territory defense Parental care –Altricial versus precocial young—tropical birds do more parental care. Get birds out of nest early because nests are dangerous, and then stay with them as they grow up. Dad takes one chick, mom takes the other. T conflicts with male ability to care.

Myth: Territory boundaries unstable year to year –Temperate source of myth: Males compete with each other annually –Tropics: Long-term stable territory boundaries—5 years or more with same mate No need to maintain high territoriality if you know your neighbors for 5 years or more. The boundaries are established. Cooperative male-female defense of real estate

Timing of Breeding Food availability –insects and fruit availability can vary across year in tropics –Experiments—manipulate food availability Day length? –Day length only differs by 12 minutes in the tropics, but can birds sense this? Probably. –Experiments—manipulate day length artificially with tropical birds in captivity Predation –Linked to food availability for other animals Time your breeding when predators have other food available Competition? –Avoid competition with other species or conspecifics Genetics? –Is it fixed under genetic control? No environmental cue.

Other tropical life history Nest predation: 80% for tropical birds vs % for temperate. Why? Survival Rates: 70% for tropical birds, 50% for temperate. – > 11 years on territory for some tropical Passerines. – < 5 years for temperate Passerines Clutch Size: 2 for tropical Passerines, 4+ for temperate. Why? –Temperate: Long days, burst of food, low predation of juvies— produce a large clutch Less investment per offspring. Survival of adults is not guaranteed because of harsh envis—just get a lot of offspring out there. –Tropical: Shorter days, no seasonal burst of food, high predation of juvies—produce a small high quality clutch, and save energy for re-nesting if clutch is eaten Get off spring out of nest and take care of them for longer—greater investment in each offspring to ensure they make it to adulthood where they can survive for a long time