Presentation on theme: "Where to live? BIOL 3100. Least Terns have specific breeding requirements – namely, open, sandy beaches."— Presentation transcript:
Where to live? BIOL 3100
Least Terns have specific breeding requirements – namely, open, sandy beaches
By understanding the species’ habitat requirements, we can create new beaches or cordon off parts of beaches. The result: increased nesting success.
How do animals figure out where a “good” place to breed is?
Black-throated blue warblers are small neotropical/nearctic migrants that breed across northeastern US and eastern Canada Generally nest low in shrubs Lots of previous work has demonstrated that survival and reproductive success is higher is correlated with vegetation structure and nest-site characteristics. Birds (and other animals) select nest sites that maximize fitness
Question: Can social information about nest site-quality trump information gained from an individual examining vegetation structure? Test: 1)Establish 3 research sites: 60 year old forest. Younger forests are preferred nesting sites 2)Made sure no birds were present at any of the sites 3)Used 3 expermiental treatments 1)Playback of male song 2)Playbacks of recordings of fledglings begging for food 3)Silence 4)Check for evidence of birds prospecting for nest sites late in the season 5)Year following treatments – search for presence of birds at each site 6)Tested if post-breeding singing was correlated with breeding success.
More birds prospected the experimental sites during the treatment year More males settled in the experimental treatment sites in the subsequent spring More females settled in experimental treatment sites the subsequent spring
In the control site, birds acted as expected, only settling in areas with high-shrub cover (young forests) However, in response to the experimental treatments, birds also settled in low and medium shrub cover areas! It seems to make sense that birds would respond to public information, i.e., that begging calls would indicate the area is a good one to settle in, but why is just song also highly effective?
Turns out that males that successfully fledge offspring are much more likely to continue singing post- breeding, thus song rates can also indicate that the area is a high-quality spot to breed in.
When to stay and when to go?
When a honey bee colony gets too large, the colony will split in two. The old queen will eventually leave with half her worker force, fly off in a swarm, and leave the old hive and remaining workers to a daughter queen. Question: How do they find and decide upon a new place to live? In this picture, half a colony huddles in a swarm on a tree branch waiting for scouts to bring back information on new nest sites
Over several days, scout workers search for chambers in the ground, cliffs, or hollow trees. When sites with a 30-60L capacity are discovered, the bees return and perform a dance back at the swarm, communicating information about the location of a potential new home. Other workers may be sufficiently stimulated to fly out and see the spot themselves. If it is also attractive to them, they will dance upon their return and send still more workers out to the area. Typically, only make a few trips out to a spot and dance for shorter periods each time before giving up. So, for a site to be attractive enough to build up a population of advertisers, it must have a recruitment rate that exceeds the drop-out rate.
Eventually, many (or all) of the recruiters will be advertising the same location, leading to tons scouts going to the same location. When bees encounter several dozen others coming from the same site, they begin piping, initiating dispersal to the new site
Are there costs to dispersal?
Lots of variation in amount of movement exhibited by ruffed grouse
Some birds spent months in the same location (A), while others moved around substantially). Alas, being in a new, unfamiliar location boosted the risk of being killed by a hawk or mammal at least threefold. So, why disperse?
One possibility is avoidance of inbreeding depression. Many taxa exhibit similar patterns with differences in dispersal distances between males and females (e.g., in most birds females generally disperse further than males)
There are clear costs to inbreeding. In oldfield mice, inbred mice survival is about half that of outbred mice. Even if they survive, reproduction is much lower in inbred motheers.
-Another potential reason for male dispersal in mammals: avoiding getting beaten up. -When new mature males move into a pride, subadults are evicted or disperse on their own -Advantage to females being sedentary: familiarity with hunting grounds, assistance from their mothers -Advantage to males dispersing: mating with non-relatives
Sometimes you really want to get away…. Migration involves breeding site selection, stopover site selection, and non-breeding site selection
How did migration evolve in the first place?
Migratory decisions can be condition- dependent. a)Birds with low fat reserves head west and fly overland toward Mexico. b)Birds with high energy reserves fly straight across the Gulf of Mexico
If flying over water is risky, why fly non-stop hours from Nova Scotia to Venezuela? Faster, few predators, also wait for west-to-east winds to begin the journey But, upon their return, blackpolls fly up across land. Why?
Why do Swainson’s Thrushes cross North America to migrate south rather than follow the coast – a much faster, safer trip?