Hawk Population Trends

[Scully]

Mark, that is a very misleading statement...only in the last 40 years have we seen an explosion in the number of martin colonies in the U. S. , beginning with the introduction of the Trio houses in the early 1960's. Prior to that, hawks and martins DID exist together, on a level playing field, with not nearly the concentrated levels of martins that are now seen.
Consequently, we are now seeing an explosion of hawk attacks on purple martin colonies.

Your failure to acknowledge the fact that the dynamic has changed only shows what we on this forum already know..........you are an unapologetic advocate of hawks. This forum is for the growth and welfare of purple martins.............hawks are a detriment to purple martins...........maybe your views would find a more receptive audience on the Hawk Forum.

Perhaps we might equally well ask ourselves if our large colonies are a detriment to purple martins, predisposing them as they do to predation by hawks and owls.

In my area the average martin colony size is something in the area of three pairs occupying one or two twelve-room houses. Sparrows especially certainly play a role in limiting colony size by the simple mechanism of plugging house cavities with their nests. Starlings are not nearly as numerous in local martin housing (the old style 6x6 cavity is less than ideal for starlings apparently) but must kill local martins each year and destroy many more martin nests.

I do believe though that the large numbers of Cooper's and Sharp-shinned Hawks overwintering here in the city and especially passing through in migration until the end of April must have a powerful effect on limiting colony size. We have forty pairs here at school, but we are set in a relatively open location. Most colonies around here are sitting ducks.

Yet... we still have martins ...and Cooper's and sharpies.

I have lived here for going on twenty years now, and all three of these species have been common sights in this city for at least that long.

Me, I would say I like Purple Martins and Cooper's and Sharp-shinned Hawks about equally well, and don't much care about what sort of silly labels I might get stuck with by a few folks here.

What I do worry about is how some folks might feel like leaving when their posts are ridiculed with such things as "LMAO"

Mike Scully

[litedave]

Man's destruction of natural habitat have encouraged these birds to begin encroaching on suburbia. I have seen many more hawks and owls this year then before. It worries me as to how this will effect my Martin population.
Hawks got to make a living, too.

[starling shooter]

From my seat it is lots of easy food in surburia, hence they are adapting. They have little to no fear of people. I was BBQing about 5 years ago, a Coopers was sitting on a tree limb about 25 yards away. Sat there the whole time staking out some robins/grackles as I was going about my business.

Some animals are flourishing, others are not. Quail, jackrabbits, spotted skunks, barn owls are waning or have crashed dramatically. Racoons, WTDeer, armadillos are explodging or have exploded. Just saw a piece put out by MDC on raccoons. In one single picture in a city, there were 26 coons at a Pizza Hut dumpster. My old neighobor, who lived through the depression, said they went coon hunting in the winter every single night. He said one coon hide was worth one month's salary, you could see a lanten (other coon hunters) whereever you looked. As I posted earlier, times have changed. I generallize but folks just don't garden, raise animals for food or hunt small game anymore for food.

[Brad-AL]

I saw hawk predation on my colony in my first year, when I had 4 pair. I also have had predation every year since and had over 100 pair last year. The size of a colony is not the determining factor in whether or not that colony will experience hawk predation, the proximity of the closest accipter hawk nest is.

[geezer]

The fire ants have decimated almost all ground nesting bird populations such as quail.

I live near East Fork Creek in the creek bottom. There are fire ant hills every five or ten feet in the areas surrounding my property. Ground nesting birds don't stand a chance. Fire ants are carnivores, and they don't discriminate.

I spend at least $100 per year in a futile attempt to keep them under control on my property. They are as much a disaster for native wildlife as sparrows and starlings.

geezer

[Scully]

The size of a colony is not the determining factor in whether or not that colony will experience hawk predation, the proximity of the closest accipter hawk nest is.

Consider my case, 40 pairs. In a good year, over a three week period in end of May/beginning of June we can reasonably expect to fledge as many as 160 nearly helpless young martins (in a Supercolony that figure can increase to more than 400!). More than fifty fledglings each week fluttering clumsily around our gourdsets under entirely artificial conditions, concentrated there as a result of my my actions.

Add to that the allure of the constant comings and goings of more than eighty resident martins into our small area for at least two months before that and I'm amazed that we have gotten away with this thing as long as we have.

Most wild things are creatures of habit, including hawks. Compare the draw of our 150+ fluttering youngsters to the 11 or 12 produced by an average three-pair colony during that same time period.

Do North American songbirds succeed in raising their helpless young even in the presence of Accipiters? Certainly, I believe estimates run along the lines of about 300 million songbirds still returning across the Gulf each Spring, most of these songbirds nesting in scattered pairs or clusters, as most martins still do out West.

The bottom line is this; martins and Accipiters have been co-existing on this Continent for a very long time, and while martins and songbirds both may be declining, in no case are Accipiters thought to be a major cause of that decline.

Mike Scully

[Brad-AL]

Actually over 500 nestlings fledged from my site last year. My first year 16 birds fledged from my colony. Some of them, both years were taken by hawks. Fledglings are weaker fliers than adults, certainly less aware of the maneuvers it takes to outrun one. Fledglings are going to be taken by predation whether at a colony, or at a roost. That's just the way it is. At a large colony the adults have a better chance of surviving a hawk attack mainly because there are more eyes watching for a hawk attack. My first year I lost 2 out of the 8 adult birds at my site to hawks. I rarely see one lost now. Too many birds to spot the oncoming attack.

[Scully]

I got to wondering just how many young martins a pair of Cooper's might potentially take during a season, so I consulted Cornell Ornithology Lab's "Birds of North America Online", a subscriber site and pretty much the horse's mouth when it comes to bird research....
http://bna.birds.cornell.edu/bna

With regards to Purple Martins, the original supercolony might have been in Minnesota...

Colonies: >100 nests are noteworthy, and the largest reported colony had about 300 pairs nesting under boulders and in rock crevices on islands in Minnesota up to 1930

That reference came from Roberts, 1930: "Roberts, T. S. 1932. The birds of Minnesota. Vol. 2. Univ. of Minnesota Press, Minneapolis." Anyone know where that site was? it'd be interesting to study it today.

So plainly, martins CAN nest naturally in large concentrations in open situations. Although in the 1930's Cooper's were shot regularly so I dunno how much they were a factor at that time.

Pertaining to Cooper's...

Nest site selection is apparently a function of: (1) proximity to hunting areas with dense prey populations; (2) availability of prey in nearby area during the fledgling dependency period; (3) historic nesting success...

So lets say the worst happens and a pair of Cooper's move in just down the street. For food requirements...

For a nest in New York, an average of 66 medium-sized (e.g., American Robin) prey items required to raise a young bird to age 6 wk

Given an average clutch size of four eggs, in a perfect Cooper's world where all four survived to fledging we're looking at 264 birds over that six weeks after hatching.

The two adults together would need around 136 grams of food per day or about 2.6 martin sized birds/day between them, or 109 birds just for the adults over that same six weeks.

Sooo.... two adults plus four young; 373 medium sized songbirds over six weeks, or about 62 birds per week during that time.

During the month before hatching when both adult Cooper's were present they'd need about another 78 medium-sized birds to maintain themselves, or about 18 birds per week.

Sooo again.... a need of 18 martin-sized birds per week increasing to around 62 per week during breeding season.

Thats a LOT of birds, no wonder breeding Cooper's might turn their attention to a martin colony, they must be desperate for prey (Actually, I believe its rare for Cooper's to succeed in bringing off four young, prey being the limiting factor). Steve K has posted instances of where a large martin colony was just hammered and eventually closed down by a pair of Coopers.

With martin success its all about numbers. If they fledge four on average that makes six martins where before there were two, enough to overcome the enormous annual mortality that martins endure (better than fifty percent annually for the whole). If just one in four fledglings are lost, that makes five martins where before they were two, and long-term survival of the population becomes an iffy prospect.

Knock that down to two surviving fledglings per nest, so that you have only four martins where before there were two, and the population declines, annual mortality being greater than the reproductive rate.

So you can have actively breeding martins presumably returning year after year, and still be losing the martin population battle. This is what happened to us in 2006, when in that record-dry year our fledging success dropped off to around two fledges per nest.

The fact that we still filled all our gourds the next year in 2007 was a sort of false prosperity, as many as one-third of our local sites active in 2006 shut down in 2007. We must have been just drawing from the local colonies is all, our particular show being the biggest game in town for martins around here. The total number of returning martins nesting in the area declined in 2007, as one would predict based upon the dismal 2006 fledge rates.

No way we would have known that by just looking at our colony.

In that context, Cooper's don't HAVE to be catching the adult martins to decimate local martin populations over the long-term, just them taking enough of the fledglings will do that. Not that you'd notice anything was wrong by looking at the biggest colony around.

(Geeze! A long post, hope I didn't bore anyone... )

Mike Scully

[Guest]

What bothers me the most about hawk predation is the effect it has on my martins.......they have been reduced to sneaking out at first light, then circling overhead the WHOLE day, before diving into the houses at dusk to roost. What a life. None of the activity that makes landlords out of all of us........no social activity whatsoever. I'm starting to wonder if my colony is doomed to fail this year......I don't see how they could possibly successfully nest this season.

But of course, hawks aren't a detriment to purple martins.........must be something else.

Gary Berger

[KathyF]

Gary, how many martins do you have? I checked your profile and couldn't tell.

[Scully]

I got to wondering if Cooper's are breeding around Houston yet. I know there are no reports in San Antonio, although at least one pair has nested for years on Camp Bullis military base just north of town.

Turns out Coopers are apparently in the process of arriving as breeders in the Houston area. This from 2006....
http://www.texasbirds.org/2006_summer/2 ... er_UTC.pdf

Cooper's Hawk Accipiter cooperii After only a handful of summer records in the past few decades, this summer experienced a relative explosion. Two young were seen with adults from 7 Jul+ along Houston’s Buffalo Bayou, Harris where birds had been heard cackling earlier in the year (Joe Kennedy).

This represents the first modern breeding record for the Upper Texas Coast. Other Cooper’s included birds believed to be adult males 3 Jun at Cullinan Park, Fort Bend and 6 Jun soaring near Briar Forest Dr and the West Sam Houston Parkway, Harris (both Don Verser), 11 Jun at Terry Hershey Park, Fort Bend (Bernd Gravenstein), an adult 27 Jun at Angleton, Brazoria (David Heinicke), an immature seen 9 Jul along Mason
Creek north of Buffalo Bayou, Harris (Al Schultz), one seen 21 Jul at Russ Pitman Park in Bellaire, Harris (Don Verser), and an adult 29 Jul at Brazos Bend SP, Fort Bend (Johnnie Greene).

I could find no data on line for 2007.

I expect Cooper's will arrive as breeding birds in San Antonio before many years have passed. The effect on our purple martins remains to be seen. It is of some comfort that there are still many martin colonies elsewhere in the US where Cooper's have been breeding for years.

Mike Scully[/quote]

[Guest]

Just saw a piece put out by MDC on raccoons. In one single picture in a city, there were 26 coons at a Pizza Hut dumpster. My old neighobor, who lived through the depression, said they went coon hunting in the winter every single night. He said one coon hide was worth one month's salary

I remember back in the late 70's early 80's, we would take our deer hides to town and sale them for 1.00or so and now you cant give them away! A good coon pelt would get 7-10.00, now 2.00 is the most.

Chuck

[starling shooter]

Guess those Tx coons don't put on much of a winter coat. MO coon hides in the 70s averaged in the 20s and at least one year was in the 30s! I knew a guy with a local legendary dog who got 16 in one night. That was back when hog farmers were farmers and had hogs outside (also a thing of the past). The feeders were used as much by the coons as the hogs. That was $480 in hides in 1970's money. You could feed a dog pretty easy. This year I think they sold for 7-10, knew of one fellow wtih one big hide that brought 25.

[litedave]

We use to get 2.50 for a squirrel hide back in the sixties when I was a young boy. Me and my brothers would hunt down in creek bottoms in Texas and get a bunch. Pretty good eating, too if you cook in low and slow in a sauce picante.
This has been a very informative forum. It is interesting that there are so many of us that have similar challenges in this thing we do. Hawk problems are just part of it. Accipeters are beautiful creatures in there on right. I just wish they would be beautiful somewhere else.
David

[Guest]

I certainly have noticed more hawks around, and I think that will ultimately be helpful in keeping the number of rodents down, but what about starlings and sparrows? I have noticed hawk attacks on doves in my area, but have not witnessed a hawk attack on a starling or sparrow. Have any of you noticed hawks targeting the large groups of starlings that are so common in some areas (mine for instance)? While there is no way hawks preying on martins is a good thing for martins, I wonder if the increased presence of predators in suburban areas may create some pressure on some of the invasive, non-native species, perhaps providing a balance, if not a benefit. Or perhaps, hawks do not target sparrows or starlings for some reason.

[KathyF]

Nerdman,
according to Scully's report here:
http://www.purplemartin.org/forum/viewtopic.php?t=10202

their prey is 95% starlings.

[Guest]

That is encouraging. I missed that thread, thank you for pointing it out. It sure seems like starlings would be a pretty easy target for raptors, I suppose the starlings are so prolific that they aren't slowed too terribly though.