Agriculture, Ecosystems and Environment 78 2000 261–272
Benefits of rotational grazing and dense nesting cover for island-nesting waterfowl in southern Quebec
Stéphane Lapointe
a,1
, Jean-François Giroux
a,∗
, Luc Bélanger
b
, Bernard Filion
c
a
Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec, Canada H3C 3P8
b
Environment Canada, Canadian Wildlife Service, 1141 route de l’Église, C.P. 10100, Ste-Foy, Québec, Canada G1V 4H5
c
Ducks Unlimited Canada, 710 rue Bouvier, suite 260, Québec, Canada G2J 1A7 Received 7 July 1998; received in revised form 9 August 1999; accepted 29 September 1999
Abstract
Intensification of agricultural practices is an important factor responsible for the decline of duck populations throughout North America. More than 200 islands covering a total of 5000 ha are found in the St. Lawrence river between Montreal
and Trois-Rivieres in southern Quebec. The value of these islands as duck nesting habitat, however, is often limited by cattle grazing. The effects of two types of habitat improvements, rotational grazing and establishment of dense nesting cover
DNC, on island-nesting waterfowl was studied from 1992 to 1994. Four treatments were compared: idle fields with no vegetation improvement but exclusion of cattle, improved pastures with seeding of forage plants for cattle, DNC fields with
improved cover for ducks and exclusion of cattle and unimproved pastures used after the duck nesting season. Before habitat improvements, grazing by cattle reduced dry mass of green vegetation by 53 relative to ungrazed plots. No difference
was found in the biomass of live green and dead residual vegetation among the islands’ sections before treatments. Nest density and the number of expected nests based on the area covered by each habitat were also similar among sections before
treatment. Gadwall Anas strepera L., mallard Anas platyrhynchos L., and pintail Anas acuta L. were the most abundant species nesting on the islands and this was not affected by treatments. Two years after habitat improvements, the number
of duck nests increased. Idle fields and 2-year old DNC had greater visual obstruction, more residual vegetation and more litter. Densities of 2.8 and 7.0 nests ha
− 1
with 69 and 82 Mayfield nest success were recorded in the idle and DNC fields, respectively. Nest success was low in improved pasture where a large proportion of nests were trampled 33 or depredated
28. Fencing permitted growth of emergent vegetation which enabled over-water nesting by ducks. These results indicate that with appropriate management, coexistence of cattle and nesting waterfowl is possible on islands of the St. Lawrence river.
©2000 Elsevier Science B.V. All rights reserved.
Keywords: Ducks; Nesting density; Nesting success; Rotational grazing; DNC; Quebec
∗
Corresponding author. Tel.: +1-514-987-3000 ext. 3353; fax: +1-514-987-4647.
E-mail address: giroux.jean-francoisuqam.ca J.-F. Giroux.
1
Present address: Pharmascience inc, 6111 Royalmount Avenue, suite 100, Montr´eal, Qu´ebec, Canada H4P 2T4.
1. Introduction
Expansion of farming and changes to more intensive agricultural practices are among the most important
factors responsible for the decline of duck populations throughout North America Sugden and Beyersber-
0167-880900 – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 9 9 0 0 1 3 2 - 2
262 S. Lapointe et al. Agriculture, Ecosystems and Environment 78 2000 261–272
gen, 1984. Ducks now have to nest in the remaining small and fragmented habitats where predation is often
higher than in contiguous habitats Clark and Nudds, 1991; Pasitschniak-Arts and Messier, 1995. Even
though dabbling duck populations have less declined in eastern than in western North America, biologists
are concerned with the rate at which wetlands and their surroundings are being converted into farmlands and
industrial lands Anonymous, 1986. They are there- fore seeking ways to overcome loss of natural habi-
tats. Island construction is one of the most productive techniques because ducks can nest at higher densities
and with better success attributed to lower mammalian predation Giroux, 1981; Duebbert, 1982. However,
island construction is expensive and could be inappro- priate where duck populations are low Lokemoen,
1984; Bélanger and Tremblay, 1989. Managing ex- isting islands may therefore be a more cost-efficient
strategy Lokemoen and Woodward, 1992.
In Quebec, the most productive areas for nest- ing dabbling ducks are located on islands of the St.
Lawrence river. More than 200 islands ranging in size from 0.1 to 2000 ha and representing nearly
5000 ha of land are found between Montreal and Trois-Rivieres. However, the value of these islands
for ground-nesting birds is often limited by cattle grazing Bélanger and Lehoux, 1995; Bélanger and
Picard, 1999. This reduces the screening effect of vegetative cover, which can lower nest density and
success Lokemoen et al., 1990; Gilbert et al., 1996; Kruse and Bowen, 1996. Grazing can also affect
residual vegetation, an important component of nest- ing cover for early nesting ducks Duebbert, 1969;
Kirsh, 1969; Kirsh et al., 1978. It may provide ideal temperature and humidity for better egg hatchability
Francis, 1968; Duebbert, 1969. In addition, graz- ing and trampling of shoreline vegetation decrease
over-water nesting Krapu et al., 1979; Kirby et al., 1992. Finally, trampling of eggs by cattle directly
affects nest success Jensen et al., 1990.
Studies have shown that it is possible to reduce the adverse effects of cattle with rotational grazing
systems Gjersing, 1975; Barker et al., 1990. Pas- tures are divided into smaller range units and cattle
are periodically moved among these units Kie et al., 1994. Rotation of cattle throughout the growing sea-
son maintains plants at a vegetative stage that pro- vides the most digestible forage Conrad and Martz,
1985. Thus, higher stocking rates are possible and calf weight gain per hectare is better than with contin-
uous grazing Barker et al., 1990. Furthermore, this leaves more undisturbed cover for nesting waterfowl
because less area is required for cattle.
The establishment of dense nesting cover DNC has also been proposed to enhance duck productivity
because it generally supports higher nest densities and success Duebbert and Kantrud, 1974; Klett
et al., 1988; but see McKinnon and Duncan, 1999 for different results. Improved nesting cover is easy
and less expensive to establish and can be sown on islands where cover is inadequate Lokemoen, 1984;
Willms and Crawford, 1989. Several years, however, may be needed before cover becomes adequate for
nesting Livezey, 1981.
The effectiveness of rotational grazing systems and cover improvements on nesting waterfowl has been
generally demonstrated in the mid continent of North America. This area is characterized by productive wet-
lands called prairie potholes that support large num- bers of breeding ducks Bellrose, 1979. On the other
hand, little is known about the effects of these tech- niques in eastern North America where wetlands are
often located along rivers or coastal shores and where breeding populations of ducks are less numerous than
in the mid continent. Moreover, growing conditions are different between the dryer prairie region and east-
ern North America and this could affect the estab- lishment of seeded vegetation. The objective of this
study was therefore to evaluate the effectiveness of ro- tational grazing systems and cover improvements to
enhance nesting habitat for waterfowl in eastern North America. More specifically, the aims were to com-
pare different grassland management practices on 1 quality of nesting cover, 2 nest density of dabbling
ducks and 3 their nesting success on islands of the St. Lawrence river in southern Quebec.
2. Material and methods
