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Does anyone have any solid information about how often birds (e.g. cormorants, mergansers, gulls etc) steal fish from any sort of fish trap? Fish traps include, but are not limited to, fyke nets, pound nets, gill nets etc. I'm not looking for info on birds getting caught in the traps, rather any cases where the birds actually take the fish in the trap.

Ideally I'm looking for published articles, but grey literature or any reports are useful.

If you can think of anything more or less suitable, please let me know.

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  • $\begingroup$ taken that fish and fishtraps are under water it is unlikely that birds can open a trap under water. $\endgroup$ Sep 25, 2023 at 15:37
  • $\begingroup$ @trondhansen Cormorants and mergansers at least do their hunting under water normally. These are not necessarily closed traps that need to be "opened"; I'm not familiar with all of them but a gill net for example is a net where the fish swims partway through and then gets stuck past the gills, so that they cannot move forward (body too big) nor backward (gills caught). There's a half of a fish sticking out either side. $\endgroup$
    – Bryan Krause
    Sep 25, 2023 at 21:48
  • $\begingroup$ @BryanKrause i was unaware that a fishing net can be seen as a trap,but atleast i now know the definition of a trap.maybe this question can be narrowed down by focusing on just a few types of traps.birds do take fish from nets every single day and many birds get trapped in the nets and drown. $\endgroup$ Sep 26, 2023 at 3:53
  • $\begingroup$ @trondhansen OP specifically listed the sort of instruments they are considering. $\endgroup$
    – Bryan Krause
    Sep 26, 2023 at 4:19
  • $\begingroup$ @trondhansen, Could you provide any reasearch or reports about birds taking fish from nets? Especially if you have info on the amount of fish taken and what species of birds took it. $\endgroup$
    – JuhaniH
    Sep 26, 2023 at 5:19

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Since kleptoparasitism, that is, stealing food from other entities that have procured that food earlier for themselves, is a widespread strategy in animals, it is no surprise that birds also engage in this kind of behavior (up to 856 accounts of some sort of interspecific thievery). Food stealing skills is even related to parental quality in Sterna dougallii. Honest parents had lower productivity. Additionally, in parrot-owner behavioral problems dynamics, stealing human food got a 2.34 in a 5-point Likert scale where 5 = always.

On top of that, theoretical ecology tells us that behavioral dynamics are characterized by a cooperation/conflict tension where a behavior such as theft may thrive (while also depending on many other factors, e.g.: larger thieves tended to get the highest payoff, and bear in mind size is but one factor). So I think a bird will maximize stealing if the opportunity is present to it and whether it's physically capable of doing it.

In Larus argentatus, head turns, approaches, and angular body position were three behavioral markers identified in an ethogram to measure attention to anthropogenic food-based contexts. I think this article is the one that is key to your question, considering how difficult it is to find statistics for how often thievery from anthropogenic sources happens. It is key, because combined with theoretical ecology, and the amount of bird intelligence research nowadays, it shows intuitively that birds will probably steal from human fish traps 1) if they have knowledge about it, and 2) as much as they can.

Anecdotally, birds, (both known and unknown to me) have also stolen from me several times in varied environments (many of them could be considered "traps" or at least "food containers that require a certain degree of skill to operate or get to"), but not fish traps.


References

Anne Tygesen & Björn Forkman (2023) The Parrot–Owner Relationship and Problem Behaviors in Parrots, Anthrozoös, DOI: 10.1080/08927936.2023.2238434

David A. Shealer, Jeffrey A. Spendelow, Jeff S. Hatfield, Ian C. T. Nisbet, The adaptive significance of stealing in a marine bird and its relationship to parental quality, Behavioral Ecology, Volume 16, Issue 2, Mar./Apr. 2005, Pages 371–376, https://doi.org/10.1093/beheco/ari008

Feist F, Graham P. An ethogram identifies behavioural markers of attention to humans in European herring gulls (Larus argentatus). Biol Open. 2023 Jun 15;12(6):bio060016. doi: 10.1242/bio.060016. Epub 2023 Jun 13. PMID: 37309817; PMCID: PMC10281265.

Hadjichrysanthou C, Broom M, Rychtář J. Models of kleptoparasitism on networks: the effect of population structure on food stealing behaviour. J Math Biol. 2018 May;76(6):1465-1488. doi: 10.1007/s00285-017-1177-7. Epub 2017 Sep 18. PMID: 28921258; PMCID: PMC5840298.

Morand-Ferron J, Sol D. and Lefebvre L (2007) Food stealing in birds: brain or brawn? Animal Behaviour, 74, 6, 1725-1734. https://doi.org/10.1016/j.anbehav.2007.04.031

Phillips JA, Peacock SJ, Bateman A, Bartlett M, Lewis MA, Krkošek M. An asymmetric producer-scrounger game: body size and the social foraging behavior of coho salmon. Theor Ecol. 2018;11(4):417-431. doi: 10.1007/s12080-018-0375-2. Epub 2018 May 1. PMID: 30931016; PMCID: PMC6405016.

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  • $\begingroup$ Thanks, I'll look into the references you provided $\endgroup$
    – JuhaniH
    Oct 9, 2023 at 12:58

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