Bill,

Your question is one I've asked myself many times. We had a discussion
of this quite a long time ago on tweeters. Here is what Erica Dunn
sent me over a decade ago in response to my querying her. I've copied
it in at the end of this message. It's hard to believe that anything
has changed since then. Sorry for the length, but it makes
sufficiently interesting reading that I think all tweeters readers
might benefit from it. I suggest cutting and pasting it into a Word
document and reformatting it for easiest reading!

I also recently wrote a few words about this in the Slater Museum blog
(http://slatermuseum.blogspot.com/) under "feeding birds."

Dennis


On Sep 23, 2009, at 12:00 PM, tweeters-
request at mailman2.u.washington.edu wrote:

> Date: Tue, 22 Sep 2009 13:07:19 -0700
> From: "William R. Andersen" <ander at u.washington.edu>
> Subject: [Tweeters] Is bird feeding good or bad?
> To: "tweeters at u.washington.edu" <tweeters at u.washington.edu>
> Message-ID:
> <1D2DEC060AF9A54BBF97D9F4D5075388A69739CF at ads-mbx-02.exchange.washington.edu
> >
>
> Content-Type: text/plain; charset="us-ascii"
>
> Friends: Is there a consensus on the question of whether it is good
> or bad practice to feed birds during seasons when natural food is
> plentiful? Some tell me that while this feeding may be pleasurable
> for us, it is bad for the birds as it blunts development of their
> food hunting skills. On the other hand, some argue that this
> feeding is good because many birds die for lack of nourishment and
> the more we feed them the more birds we'll have.
>
> Bill Andersen
> Seattle
> ander at u.washington.edu

-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net

PROS AND CONS OF FEEDING BIRDS



From: "Dunn,Erica [NCR]" <DunnE at msm1s6.sid.ncr.doe.ca>

To: "'Dennis Paulson'" <dpaulson at ups.edu>

Subject: RE: Inquiry about birds an use of bird feeders over use of
wild food

Date: Wed, 18 Sep 96 11:28:00 PDT

---

Dennis: Here is a copy of what I sent to "Natasha", in case you are
interested. As far as I am aware, my papers on predation and window
kills at feeders (1993 & 1994) are the only ones of their type.
Brittingham and Temple have a paper on disease at feeders that is not
listed below, but which might be cited in one of their papers that
is. They found that tray feeders were more associated with spread of
disease than other types. Overall, I agree that bird feeding is more
for people than it is for birds, and that research is urgently needed
on its effects. However, as far as I can tell with present data,
there is no need to tell people they should quit altogether.

----------

Dear Ms. Urbistondo:



I have written an article on whether feeders are good/bad for

birds, which I append below. (It's a bit out of date, but the

ideas and references may prove useful. However, it deals

primarily with effects of feeders on bird population size.



I am not aware of any work on influence of feeders on seed

dispersal. Presumably the question is whether or not feeders

cause reductions in natural seed-dispersal functions of birds(??)

My guess (more educated than most, but still a guess) is that

there would be little such effect. Most evidence suggests that

birds use feeders only as top-ups, as storage for a rainy day,

and as emergency food--but not as a primary food supply (see

references below). The one paper I know of that looks at

nutritional consequences of relying on feeders is that by Cowie

and Hinsley (see below), which showed that feeder food is not

great for nestlings. They also showed, however, that the birds

were only feeding nestlings with feeder food because of an odd

combination of circumstances. (Late spring prevented normal

dispersal from suburban to wilder breeding areas, so birds bred

in suburbia--where natural foods were scarce. Thus, these pairs

would have done very poorly even if feeders had not been

present.)



There are numerous papers in the literature on food choice, which

suggest that birds are quite sensitive to constituents of the

foods they eat (protein, fat, secondary compounds, sugar type and

levels, etc.). Birds evidently change or vary diet readily to

meet nutritional needs. This literature implies that birds will

not rely on bird feeders if the foods provided in them are

incomplete (which they are). As an example, Project FeederWatch

has found that Black-capped Chickadees, Mourning Doves and House

Finches are significantly more likely to choose sunflower seeds

(over millet or milo) in northern (colder areas) than in southern

regions. This suggests to me that there is a greater need for

fat in the colder areas--but where fat content of seeds is less

important (in the south), birds shift their preferences to other

foods.



Here are a few references (besides ones in the appended article)

which may prove helpful:

Brittingham, M.C., and S.A. Temple. 1989. Patterns of feeder use

by Wisconsin birds: a survey of WSO members. Passenger Pigeon

51:321-324.

Brittingham, M.C., and S.A. Temple. 1992a. Does winter bird

feeding promote dependency? J. Field Ornithol. 63:190-194.

Brittingham, M.C., and S.A. Temple. 1992b. Use of winter bird

feeders by Black-capped Chickadees. J. Wildl. Manage. 56:103-110.

Cowie, R.J., and S.A. Hinsley. 1987. Breeding success of blue

tits and great tits in suburban gardens. Ardea 75:81-90.

Jansson, C., J. Ekman and A. von Bromssen. 1981. Winter mortality

and food supply in tits Parus spp. Oikos 37:313-322.

Wilson, W.H., Jr. 1994. The distribution of wintering birds in

central Maine: the interactive effects of landscape and bird

feeders. J. Field Ornithol. 65:512-519.



[Article printed in 'Bird Observer' Vol. 20(6): 308-314, 1992]



IS WINTER BIRD FEEDING GOOD FOR BIRDS?



Erica H. Dunn, 159 Sapsucker Woods Rd., Ithaca, NY 14850

(Current address: Canadian Wildlife Service, National

Wildlife Research Centre, 100 Gamelin Blvd., Hull, Quebec,

Canada K1A 0H3)



Every person who feeds birds on a regular basis wonders

occasionally about possible negative effects. Might birds become

dependent on feeders and lose their natural foraging skills? Do

feeders lure birds to areas where predation and disease are more

likely? Alternatively, bird feeding might be too much of a good

thing. Some authors have suggested that species like Blue Jays

and Brown-headed Cowbirds benefit so much from bird feeding that

their nest-robbing and nest-parasitic habits are putting

increased pressure on other, less common species.

Despite the incredible food bonanza provided to birds by the

estimated 50 million North Americans who purchase bird food

annually, remarkably little research has been carried out on its

impacts (Shaw and Mangun 1984, Filion et al. 1985). One of the

best North American studies was done by Margaret Brittingham,

then a graduate student at the University of Wisconsin

(Brittingham and Temple 1988). She followed Black-capped

Chickadees wintering in woodlots with similar characteristics

except for differing availability of feeders.

Chickadee flocks without feeder access had lower over-winter

survival than did chickadees with supplemental food. However,

the effect was seen only in winters with prolonged, severe cold

snaps. This suggests that feeding in areas with a milder winter

climate would have no effect. Moreover, the density of breeding

birds did not differ between Brittingham's study areas. If the

"extra" birds that survived because of bird feeding bred at all,

it must have been through dispersal to other, perhaps less

suitable areas. Overall, then, the impact of bird feeding on

chickadees remains obscure.

Other studies, too, have generated equivocal results (van

Balen 1980, Desrochers et al. 1988, Kallender 1981, Orell 1989.

Each research project takes intensive effort over a period of

years, so data will not accumulate quickly. And even when we

have solid, clear results, any effect of bird feeding that is

documented might apply only to the species studied or to a

particular geographic location.

We can get around the limitations of single-species studies

by looking at continent-wide population trends in feeder birds.

If feeder species have increased or decreased as a group in

directions that differ from trends in other bird populations, we

would have strong suggestive evidence that feeders play a role.

I recently carried out this very analysis.

For a definition of a "feeder species", I turned to Project

FeederWatch (a cooperative survey of North American bird

feeders). Any bird that was reported by at least 25% of

FeederWatchers within its winter range during a winter was

considered to be a feeder bird. I then mined the U.S. Fish &

Wildlife Service's Breeding Bird Survey (BBS) for information on

population trends during the period 1966-1989. The BBS consists

of over 2000 road-side counts of birds conducted annually during

the breeding season, and has been running since 1966. BBS is not

infallible, but is the best source of data we have on continent-

wide trends in bird populations over the past 25 years.

If nothing in particular is happening to bird populations,

we expect about 50% of species to have increasing trends and 50%

to be declining, simply by chance. It is quite rare for a

population trend to show no change at all. Of the 48 feeder

species in my analysis, 40% were increasing and 56% declined over

the past 25 years, according to BBS (Table 1). These figures did

not differ in a statistical sense from the 50:50 ratio expected

by chance. But when the analysis was restricted to the most

wide-spread species, those visiting at least 50% of feeders in a

region, the results showed that significantly more feeder species

declined than increased (70% vs. 31%, respectively). When I

considered only population changes that were so large or

persistent over the 25-year period that the trends could be

considered biologically important (as opposed to chance events),

I got the same results. Only among the most widespread species

was there a difference from the 50:50 ratio. Of the 13

widespread species with important population changes, 21%

increased while 77% declined.

All the feeder species with significant population trends

are listed in Table 2. It is apparent that the more woodland-

dependent birds such as nuthatches, woodpeckers and chickadees

are on the increase side of the ledger, while the declines

include more open-country and suburban species. Moreover, most

of the "pest" species are among the decliners, including nest-

robbers (Blue Jay, grackle, magpie) and nest-site competitors

(House Sparrow, European Starling). One of the more serious

pests in terms of its impact on other species is the Brown-headed

Cowbird. This bird is not included in the table, because its

declining trend was not significant in statistical terms.

If we assume that the population changes shown in Table 2

were a result of winter bird feeding, we might conclude that

feeding is a bad thing. But when we put the data in a broader

context, this seems less a concern. Compilations of Breeding Bird

Survey data for all species show that 92% of grassland-nesting

birds have declined since 1966, along with 62% of scrub-nesters

(S. Droege, U.S.F.W.S. unpubl.). Many of the declining species

in Table 2--grackle, sparrows, thrashers--are members of these

groups that are decreasing across the board, whether or not the

constituent species visit feeders.

Further evidence that bird feeding does not cause excess

mortality came from a special inquiry undertaken by Project

FeederWatch. Participants recorded any deaths observed in their

yards over one winter, providing details on causes and

surrounding circumstances. The aim was to discover whether

feeding exposed birds to unusual danger from window collisions,

disease and predation.

Window strikes accounted for more deaths near feeders than

any other factor (close to half of the 2000+ deaths reported). A

full analysis of this data set (to be published in the Journal of

Field Ornithology [see Dunn and Tessaglia 1994]) suggested that

between 1 and 10 birds might be killed annually by striking

windows at every building in North America. As high as this

number sounds, it probably represents less than a percent or two

of all birds alive each fall.

Predation came a fairly close second in the Project

FeederWatch study, causing about one-third of reported deaths.

Sharp-shinned and Cooper's Hawks were the culprits in about 51%

of kills witnessed, and cats in 29%. Bird-eating hawks make

about 1-3 prey captures daily (Palmer 1988), but most

FeederWatchers who witnessed predation at all saw only one or two

cases over the whole winter. [See Dunn 1993] The conclusion was

that the majority of hawks use feeders opportunistically, and not

as a primary food source. In one European study, bird-eating

hawks were estimated to kill about 10% of all finches passing

through a particular migratory stopover site in autumn (Lindstrom

1989). Compared to this level of risk, bird feeders are

positively safe havens!

Relatively few of the deaths observed in the FeederWatch

study were attributed to disease. Most of these were probably

the results of salmonella infection, in which birds appear

lethargic, fluff up their feathers and have difficulty breathing

for a few days prior to death (Terres 1981). Passed through the

faeces, the disease can spread readily through contaminated bird

seed. It is seen most often in flocking species when they are

stressed by severe weather or food shortages.

Summing up all the sources of mortality reported in this

FeederWatch study, it was found that only one bird death was

reported over the winter for every two feeder sites. There is no

doubt, of course, that many dead birds were not found or

reported. Nonetheless, natural mortality rates in songbirds of

35-50% annually would lead us to predict at least 4-5 bird deaths

over a winter at each FeederWatch home, based on the average

number of birds present at those feeders and assuming that

mortality is spread evenly through the year. Actual figures were

a tenth of that prediction. Even if under-reporting was a severe

problem, therefore, it appears that feeders do not draw birds

into an environment that is far more dangerous than the one they

face in the wild.

These analyses suggest that bird feeding has not had blanket

effects on populations of all feeder species. More subtle

effects may exist, perhaps varying among species (positive for

some, negative for others). It will take detailed studies on

individual species, however, to demonstrate such effects. In the

meantime, you can continue to feed birds with a clear conscience.

All current evidence suggests you are not unduly upsetting

natural ecological systems.



REFERENCES CITED



Brittingham, M.C., and S.A. Temple. 1988. Impacts of supplemental

feeding on survival rates of Black-capped Chickadees.

Ecology 69: 581-589.

Desrochers, A., S.J. Hannon, and K.E. Nordin. 1988. Winter

survival and territory acquisition in a northern population

of Black-capped Chickadees. Auk 105: 727-736.

Dunn, E.H. 1993. Bird mortality from striking residential windows

in winter. J. Field Ornithol. 64(3): 302-309.

Dunn, E.H., and D.L. Tessaglia. 1994. Predation of birds at

feeders in winter. J. Field Ornithol. 65(1): 8-16.

Filion, F.L., A. Jacquemot, and R. Reid. 1985. The importance of

wildlife to Canadians: An executive overview of the

recreational economic significance of wildlife. Can. Wildl.

Serv., Environment Canada, Cat. No. CW66-76/1985E.

Kallendar, H. 1981. The effects of the provision of food in

winter on a population of the Great Tit Parus major and the

Blue Tit Parus caeruleus. Ornis. Scand. 12: 244-248.

Lindstrom, A. 1989. Finch flock size and risk of hawk predation

at a migratory stopover site. Auk 106: 225-232.

Orell, M. 1989. Population fluctuations and survival of Great

Tits Parus major dependent on food supplied by man in

winter. Ibis 131: 112-127.

Palmer, R.S. (Ed.) 1988. Handbook of North American Birds, Vol.

4: Diurnal Raptors (Part I). Yale University Press, New

Haven.

Shaw, W.W., and W.R. Mangun. 1984. Nonconsumptive use of wildlife

in the United States. U.S.F.& W.S., Resource Publ. 154: 20

pp.

Terres, J.K. 1981. Diseases of birds--how and why some birds die.

Amer. Birds 35: 255-260.

van Balen, J.H. 1980. Population fluctuations of the Great Tit

and feeding conditions in winter. Ardea 68: 143-164.





Table 1. Population trends of feeder species in the period 1966-1989,

according to the Breeding Bird Survey. (Data from S. Droege,

U.S.F.W.S.

unpubl.).



Percent of Number of % Species % Species

Feeders Visited Species Increasing Decreasing



> 25 % 48 40

56



> 50 % 29 31

70







Table 2. Feeder species with statistically significant population
changes,

1966-1989. (Data from S. Droege, U.S.F.W.S. unpubl.).



Percent of Increasing Decreasing

Feeders Visited Populations Populations



> 75 % Black-capped Chickadee Blue Jay





European Starling



American Goldfinch



House Sparrow



50-75 % Hairy Woodpecker Northern Flicker

White-breasted Nuthatch Northern
Mockingbird



Rufous-sided Towhee



Song Sparrow



Common Grackle



Pine Grosbeak



25-50 % Scrub Jay Black-
billed Magpie

Red-breasted Nuthatch Brown Thrasher

Varied Thrush

White-crowned Sparrow
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