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Hi Fred, David and all,
As Nancy and Don have mentioned already, food availability, or the lack there of, is not the main trigger for normal migration in the fall for passerines and hummingbirds. The vast majority of birds head south long, long before their food sources are no longer available.
Why birds such as this solitary hummingbird show up at unusual times or in unusual places past the normal migration date can be attributed to many causes. Everything from a weather related event to genetic predisposition, illness, injury, insufficient food during nest rearing, etc.
There are advantages for a bird species to have variability built into its behaviour of course. While most individuals follow the historical migration path and timing, some small numbers don't. There are risks and advantages. In spring the 'early bird' gets the best breeding areas but a late freeze could spell its death. In fall, a new overwintering area means the dangers of migration are removed but again, too much cold or not enough food to carry the bird through winter is deadly.
The Mourning Dove has moved north into Nova Scotia in the last century. It was certainly aided by bird feeders and by inefficiencies in corn harvesting and loading practices in its establishment originally. Would it survive now in some parts of the province even without feeders? Fifty years ago probably not but now it probably would.
As the climate continues to warm new species will continue to colonize Nova Scotia, even without human help. A good case study elsewhere in the country is the American Robin which is now exploiting areas of northern Canada in which it has never been seen before.
To address Fred's question, there is more than food to be considered. I think if one looks at the case of Baltimore Orioles trying to overwinter in Nova Scotia for instance, you'll find that in spite of supplemental feeding the majority do not make it through the winter. Some do but one would need a method of tracking these survivors over the subsequent year to determine if they were successful breeders, whether they attempted to overwinter in the following year and whether this was a genetic trait passed along to their young. An interesting experiment indeed.
Cheers,
Lance
Lance Laviolette
Glen Robertson, Ontario
-----Original Message-----
From: naturens-owner@chebucto.ns.ca [mailto:naturens-owner@chebucto.ns.ca] On Behalf Of Frederick W. Schueler
Sent: October-19-18 7:28 AM
To: naturens@chebucto.ns.ca
Subject: Re: [NatureNS] Hummingbird
On 19/10/2018 6:55 AM, Don MacNeill wrote:
> It appears that migration is triggered by things other than the
> abundance of food. I see recommendations that hummingbird feeders be
> kept up until freezing. It also might help to finally fatten up those
> needing it for migration.
> On 10/19/2018 7:28 AM, nancy dowd wrote:
>> I don’t feel that feeders delay HBs and other birds from migrating.
>> Other cues, such as day length and many we don’t fully understand,
>> seem to send the majority on their way at roughly the same time each
>> fall. There are always stragglers like this Hummingbird who is
>> benefitting from Marg’s high-energy feeder at this late date. But I
>> doubt feeders are what postponed its departure in the first place.
* it's a really interesting question how one would study this much-discussed quandary. With the question of whether populations of Cardinals and Gray Squirrels are sustained by feeders, you could temporarily flood some feederless area with feeders, and see if these areas are colonized and then abandoned when feeding is ended, but with these autumnal stragglers it's hard to see how you could assess if they do better or worse in migration (or not-migrating as some of the Orioles seem to do), than they would have if they hadn't been subsidized -- and then what the selective impact of these individual better-or-worse outcomes would be on the overall departure dates of subsequent generations of the population.
fred.
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on the Smiths Falls Limestone Plain 44.87156° N 75.70095° W
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