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Food hoarding: Memory and social conditions - an evolutionary approach

Lundborg, Ken LU (2003)
Abstract (Swedish)
Popular Abstract in Swedish

Spridningshamstring är en form av matlagring som används av många djur för att t.ex. överleva en lång svår vinter då det finns mycket lite mat i naturen. I Sverige är talltitan en av de i särklass främsta spridningshamstrarna och den brukar lagra tiotusentals frön inför varje vinter. Ett flertal andra mesfåglar, nötskrikor och nötkråkor har samma vanor. Det som skiljer spridningshamstring från andra typer av hamstring är att maten lagras i små, spridda gömmor. I varje gömma lägger fågeln bara ett eller ett par frön, och eftersom det rör sig om så stora mängder gissar man att fåglarna måste ha ett mycket bra minne för att komma ihåg alla gömmorna. Detta minne – det rumsliga minnet – är hos... (More)
Popular Abstract in Swedish

Spridningshamstring är en form av matlagring som används av många djur för att t.ex. överleva en lång svår vinter då det finns mycket lite mat i naturen. I Sverige är talltitan en av de i särklass främsta spridningshamstrarna och den brukar lagra tiotusentals frön inför varje vinter. Ett flertal andra mesfåglar, nötskrikor och nötkråkor har samma vanor. Det som skiljer spridningshamstring från andra typer av hamstring är att maten lagras i små, spridda gömmor. I varje gömma lägger fågeln bara ett eller ett par frön, och eftersom det rör sig om så stora mängder gissar man att fåglarna måste ha ett mycket bra minne för att komma ihåg alla gömmorna. Detta minne – det rumsliga minnet – är hos däggdjur associerat med ett område i hjärnan kallat hippocampus, och man antar att detta område har en liknande funktion hos fåglar. Det har länge diskuterats om huruvida graden av hamstring hos fåglar hänger ihop med en stor hippocampus. Genom att mäta volymen på hippocampus hos flera hamstrande och icke-hamstrande arter, och genom att jämföra resultaten med tidigare forskningsresultat har vi kommit fram till att så ligger det antagligen inte till. Skillnader i hippocampus-storlek går inte att skylla enbart på hamstring. En faktor som påverkar hamstring är fåglarnas sociala omgivning, speciellt för fåglar som talltitorna eftersom dessa delar sitt revir med andra talltitor året runt. Vi har kommit fram till att under hamstringssäsongen och vintern har dominansrangen – den sociala statusen – betydelse för hur en fågel ska lägga upp sin hamtringsstrategi. Dominanta fåglar behöver inte hamstra lika mycket som mindre dominanta fåglar, eftersom de förstnämnda kan stjäla mat från sina revirgrannar i större utsträckning. Men om vintern ser ut att bli svår kommer skillnaderna mellan de olika dominansrangerna att jämnas ut. Det måste också vara svårare att hitta andra revirgrannars mat än sin egen, annars skulle dominanta fåglar strunta helt i att hamstra egen mat. För att komma fram till detta konstruerade vi först en matematisk modell som förutsåg hur fåglarna skulle bete sig, och verifierade sedan förutsägelserna genom försök med talltitor i både voljärer och i fält. (Less)
Abstract
Food hoarding is a widespread behavior among a large number of animals, and it exists in several different varieties, all of them used by the animals as a method of having a steady supply of food during periods of low food abundance such as the winter. This thesis concentrates mainly on two aspects of scatter food hoarding behavior, using small birds as study and model animals. Scatter hoarding is common in many bird species, and it means that the hoarding animal stores only one or just a few food items in each of its caches. These caches can be very numerous and spread out over a large area, making them hard to defend but also hard to find. It is generally believed that birds use spatial memory as an aid in recovering scatter-hoarded... (More)
Food hoarding is a widespread behavior among a large number of animals, and it exists in several different varieties, all of them used by the animals as a method of having a steady supply of food during periods of low food abundance such as the winter. This thesis concentrates mainly on two aspects of scatter food hoarding behavior, using small birds as study and model animals. Scatter hoarding is common in many bird species, and it means that the hoarding animal stores only one or just a few food items in each of its caches. These caches can be very numerous and spread out over a large area, making them hard to defend but also hard to find. It is generally believed that birds use spatial memory as an aid in recovering scatter-hoarded food. Lately, many studies have been made, trying to find out whether the degree of hoarding in birds is correlated with the volume of the hippocampus – a region of the avian brain thought to play an important role for spatial memory. This thesis concludes that a correlation between hippocampal size and degree of food hoarding probably not exists, and that food hoarding alone cannot be the cause of different hippocampus size in the studied species. Some food hoarding bird species share their territories with conspecifics during the hoarding season and the following winter, and this creates a social environment that affects food hoarding decisions. Social dominance in a winter flock is studied theoretically and predicted to affect food storing strategies of both dominant birds and subordinate ones. Subordinate birds are predicted to always store more than dominant birds, but this difference should even out if winter conditions become predictably worse, with the dominant bird increasing its hoarding effort. If better winter conditions are expected, dominants should instead spend more time pilfering from subordinates. And, if no selfish recovery advantage for hoarders exists, dominants should refrain from hoarding entirely. The theoretical predictions were tested in two field studies and we found that subordinate birds always stored more than dominants, that both ranks stored more food when winter conditions got worse, and that the differences between the ranks became smaller during bad conditions. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof. Lucas, Jeff, Purdue University, Indiana
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Djurekologi, Animal ecology, Corvidae, Paridae, dominance rank, memory, food hoarding, foraging, hippocampus, birds, behavioural ecology
pages
67 pages
publisher
Ken Lundborg, Dept for Theoretical Ecology, Ekologihuset, Sölvegatan 37, s-223 62 Lund,
defense location
Ekologihuset
defense date
2003-01-16 10:15
ISBN
91-7105-199-6
language
English
LU publication?
yes
id
138d7f3b-93e9-4368-9dcd-76f4f1c349a1 (old id 466559)
date added to LUP
2007-09-05 10:37:16
date last changed
2016-09-19 08:45:04
@phdthesis{138d7f3b-93e9-4368-9dcd-76f4f1c349a1,
  abstract     = {Food hoarding is a widespread behavior among a large number of animals, and it exists in several different varieties, all of them used by the animals as a method of having a steady supply of food during periods of low food abundance such as the winter. This thesis concentrates mainly on two aspects of scatter food hoarding behavior, using small birds as study and model animals. Scatter hoarding is common in many bird species, and it means that the hoarding animal stores only one or just a few food items in each of its caches. These caches can be very numerous and spread out over a large area, making them hard to defend but also hard to find. It is generally believed that birds use spatial memory as an aid in recovering scatter-hoarded food. Lately, many studies have been made, trying to find out whether the degree of hoarding in birds is correlated with the volume of the hippocampus – a region of the avian brain thought to play an important role for spatial memory. This thesis concludes that a correlation between hippocampal size and degree of food hoarding probably not exists, and that food hoarding alone cannot be the cause of different hippocampus size in the studied species. Some food hoarding bird species share their territories with conspecifics during the hoarding season and the following winter, and this creates a social environment that affects food hoarding decisions. Social dominance in a winter flock is studied theoretically and predicted to affect food storing strategies of both dominant birds and subordinate ones. Subordinate birds are predicted to always store more than dominant birds, but this difference should even out if winter conditions become predictably worse, with the dominant bird increasing its hoarding effort. If better winter conditions are expected, dominants should instead spend more time pilfering from subordinates. And, if no selfish recovery advantage for hoarders exists, dominants should refrain from hoarding entirely. The theoretical predictions were tested in two field studies and we found that subordinate birds always stored more than dominants, that both ranks stored more food when winter conditions got worse, and that the differences between the ranks became smaller during bad conditions.},
  author       = {Lundborg, Ken},
  isbn         = {91-7105-199-6},
  keyword      = {Djurekologi,Animal ecology,Corvidae,Paridae,dominance rank,memory,food hoarding,foraging,hippocampus,birds,behavioural ecology},
  language     = {eng},
  pages        = {67},
  publisher    = {Ken Lundborg, Dept for Theoretical Ecology, Ekologihuset, Sölvegatan 37, s-223 62 Lund,},
  school       = {Lund University},
  title        = {Food hoarding: Memory and social conditions - an evolutionary approach},
  year         = {2003},
}