Learned or evolved behavior?

[bristow]

Each year when salmon swim upstream to spawn, bears and other predators gather to eat them. Also during the annual wildebeest migration, crocodiles gather to feast on the wildebeest as they cross the Mara River in great numbers. There are other examples of where animals gather to hunt at a particular annual event.

 

Is the information that wildebeest will be crossing the river at a particular time of the year learnt by young crocodiles from older ones, or is it a genetically programmed behavior whereby day length, temperature etc triggers the behavior of the crocodiles? It is easier to imagine that this behavior might be learned in bears, but not so easy to imagine it in crocodiles, though perhaps I am being ‘mammal-centric’.

 

[arc]

We salmon fished when I was a kid on the Columbia River between Oregon and Washington state. I have always understood that the salmon find their exact spawning grounds they hatched from by their powerful sense of smell. I would bet, but do not know for sure, that these predators are forewarned by the changes in the air that they can smell. Bears and crocodiles are already known for their great olfactory ability, I think this is the likely signal and receptor for them to gather and feast.

 

If these annual events continue for thousands of years, I would think group behavior would help reinforce both the predators and prey's responses to the events. But this just my personal opinion, I am not an authority in these matters.

[LastHit]

With paticular reference to your croc example im going to say that the behaviour is instinctive. I suggest this because reptiles are born precotial, and do not require parental care, as such most of their behaviour is instinctive.

[arc]

With paticular reference to your croc example im going to say that the behaviour is instinctive. I suggest this because reptiles are born precotial, and do not require parental care, as such most of their behaviour is instinctive.

 

I think it is not so clean cut. Even we humans with our lower sense of smell can distinguish the change of seasons. That smell of the coming fall season here in the forested NW U.S. is so locked into my memory I can imagine it now. These biological mechanisms that trip the behavior to migrate in the case of wildebeest or to gather to feast on them as in the case of the crocodiles is likely seasonal change in regards to temperature and humidity and not a trigger, for example, from a particular length of daylight that would seem more an instinctual response.

 

http://en.wikipedia.org/wiki/Wildebeest

Wildebeest are famous for their annual long-distance migration, seemingly timed to coincide with the annual pattern of rainfall and grass growth. The timing of their migrations in both the rainy and dry seasons can vary considerably (by months) from year to year. At the end of the rainy season (May or June in East Africa), wildebeest migrate to dry-season areas in response to a lack of surface (drinking) water. When the rainy season begins again (months later), animals quickly move back to their wet-season ranges. Factors suspected to affect migration include food abundance, surface water availability, predators and phosphorus content in grasses. Phosphorus is a crucial element for all life forms, particularly for lactating female bovids. As a result during the rainy season, wildebeest select grazing areas that contain particularly high phosphorus levels. One study found, in addition to phosphorus, wildebeest select ranges containing grass with relatively high nitrogen content. Large-scale wildebeest migration is quite likely a consequence of decisions being made by individuals at multiple spatial scales, involving a balance of food abundance, food quality, local density of other wildebeest, social interactions, surface water, perceived predation risk, and culturally (or possibly genetically) learned routes and ranges.

 

though not decisive, in the wildebeests case it is a behavior with a wide timing variable (by months), that would complicate a crocodiles response if it were a instinctively derived behavior in them.

 

I do not believe the behavior of either the wildebeest to migrate or the crocodiles to gather to feast is incumbent of an instinctual trigger. Both animal groups have life spans that overlap considerable enough in generations that there is always a majority of "past experienced" adults over the younger "first timer" participants. This would be what in itself programs instinctual behavior. This could be tested in the case of wildebeests with a small isolated group that were fenced in for several generations and then set loose.

 

My guess is they would have enough instinct to reestablish in time the migratory behavior that is reinforce by learned group behavior. The period of time it takes to reestablish the behavior is proportional to the isolation period. Simply being the more generational separation from the migratory behavior the longer it would take to reestablish. And of coarse with enough time the instinctual behavior would be lost.

Edited July 28, 2013 by arc

[Bill Angel]

With paticular reference to your croc example im going to say that the behaviour is instinctive. I suggest this because reptiles are born precotial, and do not require parental care, as such most of their behaviour is instinctive.

Birds exhibit similar precotial behavior. Ducklings will be swimming and feeding on their own within 24 hours of hatching.

[arc]

Birds exhibit similar precotial behavior. Ducklings will be swimming and feeding on their own within 24 hours of hatching.

And as a multi-generational group that gathered several times a year at chronologically indeterminate periods based on the indiscriminate behavior of a separate species, the ducks behavior would be considered; A - Instinctive or B - Learned group behavior based on reinforcing environmental signals.