[TN-Bird] Re: LA WT, B&W warbler arrive Costa Rica
- From: Scott Somershoe <ssomershoe@xxxxxxxxx>
- To: "littlezz@xxxxxxxxx" <littlezz@xxxxxxxxx>
- Date: Mon, 19 Aug 2013 09:17:33 -0500
What is interesting is that most Neotropical migrants are still arriving
basically on time every year, but as Bill said, there are some early birds
most years. For example, we in TN had many very early birds and a few
earliest ever dates in 2012, while in 2013, migration was pretty much on
par with essentially no early records. That said, some folks will argue
that migration is earlier than it was 40 years ago, but it isn't by much,
if it is at all for Neotropical migrant birds. Birds wintering in the
tropics still primarily use photoperiod to time migration and thus have no
idea what weather conditions and food resources are like in North America.
However, temperate migrants that winter in the southern United States are
arriving earlier and nesting noticeably earlier now than 30 or 40 years
ago, i.e. tree swallows. I'd think that temperate migrants are much more
likely to respond to local weather cues and resource availability and head
north earlier, or overwinter further north with suitable conditions (i.e.
Orange-crowned warbler, blue-headed vireo, etc. wintering in TN). This
isn't really any different from the St James Bay population of Canada Geese
that used to winter in the southeast in the 10's of thousands and are now
in much smaller numbers (or nonexistent) or with wintering waterfowl
staying further north with the warmer temperatures and open water. Why fly
a lot further than you need to and put yourself at significant risk
migrating when you can stay further north with adequate food resources?
In Europe, the Pied Flycatcher (nest box user) has shifted spring arrival
earlier in some parts of their range and nest 10+ days earlier than they
used to and time their breeding with peak insect outbreaks. Those
populations are stable. Populations in other parts of their breeding range
have not responded to earlier insect emergence and the birds arrive without
making arrival earlier, thus nesting is mistimed and those populations are
declining significantly due to poor nesting success.
The big question/concern in my mind is about Neotropical migrant birds
getting further and further mistimed from peak insect emergence in the
future and how that affects nesting success and long term population
declines. If peak insect emergence gets earlier and earlier and the birds
arrive at the same time every year...... We need genetically modified
migrants! :)
Interesting Monday morning migration discussion.
Cheers,
Scott Somershoe
On Mon, Aug 19, 2013 at 7:43 AM, Bill Pulliam <littlezz@xxxxxxxxx> wrote:
> What interests me is actually how much the timing of migration does NOT
> respond dramatically to the year-to-year variability in weather. Dates of
> first/last frosts, leaf out, and flowering of most plants vary widely
> between years, ranging by 4 weeks or more. Meanwhile the timing of bird
> migration for the most part stays consistent within about a week. Sure
> there are occasional very early or very late individuals, but the arrivals
> and departure of the bulk of the population are pretty consistent within
> about a 7 day spread for most species in the large majority of years. This
> tells me that migration timing is mostly controlled by genetics and day
> length, with weather patterns, food crops, etc. only adding a modest push
> or pull.
>
> Bill Pulliam
> Hohenwald TN
>
> On Aug 18, 2013, at 8:50 PM, Dev Joslin wrote:
>
>
> Tommie,
>
> We've heard a lot about your unusual weather there. But these arrival
> dates for these two species are not unusual for here. Louisiana
> waterthrush and Black and White warblers are always the first to
> arrive. Most of the other migrants don't normally arrive until late Sept.
> or October. I'll try to report if anything appears unusual here.
>
> Dev Joslin
>
> ------------------------------
> From: Bananaquit1@xxxxxxxxxxx
> To: devjoslin@xxxxxxxxxxx
> Subject: Re: [TN-Bird] LA WT, B&W warbler arrive Costa Rica
> Date: Sun, 18 Aug 2013 20:52:32 -0400
>
> Dev, I am not surprised to hear that warblers are leaving here. I just
> have not seen caterpillars here this season for birds to eat. Butterflies
> have been largely absent here until just this month. We had such cold
> weather in April and May. I believe it killed a lot of larvae and many
> insects locally.
> In past years, have you seen warbler return this early?
> You live in a very beautiful area.
> Tommie Rogers
> Chattanooga
>
>
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