From south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Wed May 21 09:43:07 2003 Received: from www.plaidworks.com (localhost [127.0.0.1]) by plaidworks.com (8.12.9/8.12.9) with ESMTP id h4LGeQa9005211 for <[[email protected]]>; Wed, 21 May 2003 09:40:27 -0700 (PDT) Received: from sccrmhc01.attbi.com (sccrmhc01.attbi.com [204.127.202.61]) by plaidworks.com (8.12.9/8.12.9) with ESMTP id h4LGd9fF005164 for <[[email protected]]>; Wed, 21 May 2003 09:39:09 -0700 (PDT) Received: from computer.attbi.com (12-234-255-153.client.attbi.com[12.234.255.153]) by attbi.com (sccrmhc01) with SMTP id <2003052116390600100s5r4ue>; Wed, 21 May 2003 16:39:07 +0000 Message-Id: <[[email protected]].> X-Sender: [[email protected]]. X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Wed, 21 May 2003 09:42:08 -0700 To: "Tom Grey" <[[email protected]]>, [[email protected]] From: Alvaro Jaramillo <[[email protected]]> Subject: Re: [SBB] Stanford HOOR drama In-Reply-To: <[[email protected]]> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Cc: X-BeenThere: [[email protected]] X-Mailman-Version: 2.1.2+ Precedence: list List-Id: South Bay Birding List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Errors-To: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] At 08:34 AM 5/21/2003 -0700, Tom Grey wrote: >At Frenchman's Meadow, Stanford, this morning between about 7 and 7.30 I >happened to catch an all-out attack by a Scrub Jay on the new HOODED ORIOLE >nest. The female and especially the adult male oriole attacked the jay with >loud calling and pecking each time it entered the nest, apparently driving >it off a couple of times within a second or so of its entry. A second male >and eventually a second female oriole joined in the defense -- possibly >second summer offspring accompanying the adults? or would another adult >pair join in cooperative nest defense? The jay returned to the attack after >being driven away twice, and I saw it finally stay within the nest for >several seconds -- the oriole energies seemed to flag -- and then fly away >with one egg in its bill. Afterwards the two orioles flew back and forth >between the two neighboring fan palms in the meadow, and I saw fragments of >a second nest in the second (southerly) palm. Tom and South Bay Birders Jays are pretty good nest predators, a fact that many people don't realize until they see it. Wrens are pretty sneaky, and good at attacking nests as well. Orioles make obvious but relatively difficult nests to attack, the fact that they dangle makes it harder for a predator, particularly a large one, to get in there and get the eggs. Its part of the hanging nest strategy. It is most useful against mammalian attack though, birds still have access as you saw. A strategy used by orioles is to attack avian nest predators, and make it difficult for them to try and reach the hanging nest, and harder for them to get enough time to successfully grab an egg or young. Basically an oriole does not have a hope of winning a fight with a jay, but if they pester it enough as it tries to have access to the nest, it may just go off and try to find easier food. This strategy is even more successful if other orioles join in and help in the fight against the jay. Most likely what you saw was another pair of orioles, that breed adjacent to the ones you have been following who were drawn in by alarm calls. In certain situations, partially due to the density of breeding orioles and the density of predators this strategy could select for colonial living, several oriole pairs nesting in the same tree or in adjacent trees. This does happen and it has been studied in Orange Orioles of the Yucatan, and Orchard Orioles in the mid-west. There is evidence (not well studied) that other small orioles have a tendency to breed close to each other, not in a colony but just in proximity to the next pair. I bet that this goes on in Hooded Orioles, particularly farther south where they are more common. So territoriality is relaxed as a trade-off for nest defence. This is taken to an extreme in a group of blackbirds related to orioles, the caciques and oropendolas of the American Tropics. Most of these species are always colonial. Coloniality occurs primarily to increase nest defence against mammalian predators such as monkeys and squirrels, but it works very well for avian predators such as hawks and toucans. Getting back to the orioles it seems that its the smaller species which show a tendency towards coloniality or joint nest defence. regards Al Alvaro Jaramillo Biologist San Francisco Bay Bird Observatory P.O. Box 247 Alviso, CA 95002 (408)-946-6548 http://www.sfbbo.org/ [[email protected]] _______________________________________________ Do not post admin requests to the list. They will be ignored. south-bay-birds mailing list ([[email protected]]) Help/Unsubscribe/Update your Subscription: http://www.plaidworks.com/mailman/options/south-bay-birds/south-bay-birds-archive%40plaidworks.com This email sent to [[email protected]]